Phylum annelida
 

[SIZE=3][B]Phylum Annelida[/B][/SIZE]

[SIZE=3][B][FONT=Times New Roman]Characteristics[/FONT][/B]
[FONT=Times New Roman]Annelids were the first animals to evolve a complete coelom (an internal body cavity lined with epithelial tissue). They are segmented and have most comlete body systems. [/FONT][/SIZE]
[SIZE=3][B][FONT=Times New Roman]Classification[/FONT][/B]
[FONT=Times New Roman]Members of the class Polychaeta are marine worms. Members of the class Oligocheata are earthworms. Members of the class Hirudinea are parasitic worms. [/FONT][/SIZE]
[SIZE=3][B][FONT=Times New Roman]Movement[/FONT][/B]
[FONT=Times New Roman]Annelids have various muscle groups and simple appendages. They use setae and parapodia for movement. [/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Feeding & Digestion[/B][/FONT]
[FONT=Times New Roman]Marine worms are filter feeders or scavengers. Earthworms squeeze organic material out of the earth. The digestive systems for all three classes are well-developed and use division of labor. [/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Circulation[/B][/FONT]
[FONT=Times New Roman]Annelids are the first to have a closed system of blood vessels -- making pumping more efficient. [/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Excretion[/B][/FONT]
[FONT=Times New Roman]Annelids have one pair of nephridia per segment for excretion. [/FONT][/SIZE]
[SIZE=3][B][FONT=Times New Roman]Respiration[/FONT][/B]
[FONT=Times New Roman]Respiration occurs through diffusion. [/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Nervous System[/B][/FONT]
[FONT=Times New Roman]Members of this phylum have a simple brain located in the anterior end with ganglia in every segment. They can sense light, moisture, and chemicals. [/FONT][/SIZE]
[SIZE=3][B][FONT=Times New Roman]Reproduction[/FONT][/B]
[FONT=Times New Roman]Since annelids are hermaphroditic, sexual reproduction occurs through the exchange of sperm packets. [/FONT]
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[FONT=Times New Roman][SIZE=3]Segmented worms are placed in the phylum [I]Annelida[/I], which consists of over 12,000 species of segmented worms grouped into three classes. The three classes comprise freshwater worms and [/SIZE][/FONT][URL="http://www.allaboutworms.com/category/segmented-worms/earthworms/"][FONT=Times New Roman][SIZE=3][COLOR=#000099]earthworms[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3], [/SIZE][/FONT][URL="http://www.allaboutworms.com/category/marine-worms/"][FONT=Times New Roman][SIZE=3][COLOR=#000099]marine worms[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3], and [/SIZE][/FONT][URL="http://www.allaboutworms.com/leeches-medical-friend-or-deadly-predator"][FONT=Times New Roman][SIZE=3][COLOR=#000099]leeches[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3]. Annelids have the unique ability to inhabit a variety of unusual places such as inside of other spineless or invertebrate animals (such as sponges) and they even live in cylinders or tubes that are actually produced by their own systems and discharged around their bodies. The Feather Duster Worm, for example, secretes a spacious leather-like tube while the Calcareous Tube Worm secretes a hard calcium carbonate tube. Annelids also live in other protected environments such as sand, muddy areas and rock chasms.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Annelid bodies are characterized by segments. Each segment contains a compartment of the coelom or body cavity, with its internal organs, and a part of the body wall. The body wall consists of tough muscles and short rigid hairs collectively called “setae.” These tough muscles are used for swimming from place to place and for crawling while the setae help to keep the annelid inside its cylinder or they help to grip dirt, sand and soil.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]You can’t tell by looking at them, but Annelids do have a circulatory system, a digestive system and a nervous system. The blood of an annelid can be either red or green in color or no color at all - it depends on the species. The digestive system or gut can be found on the underside of annelids and it extends down the middle from the mouth to the head. Waste is released through openings or ducts throughout the body cavity. The nervous system is made up of sense organs including tentacles and taste buds as well as eyes and statocysts (organ of balance). Non-aquatic annelids do not have a respiratory system as respiration takes place through the body wall and some aquatic annelids do have gills for breathing.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]So how do annelids reproduce? This can be a little confusing. Depending on the species, annelids can reproduce asexually or sexually. Asexual reproduction takes place through a method called fission. During fission, the rear end of the body splits from the rest of the body to form a new annelid. Earthworms do not have the ability to reproduce this way, but they do have the ability to regenerate their posterior segments. Sexual reproduction takes place by species that are hermaphroditic (some earthworms and many leeches) or species that have separate females and males. During sexual reproduction, fluids are transferred from the male pore to the female ovipore. Annelids tend to mate when conditions are moist or following a rain, meaning they may mate quite frequently throughout the year.[/SIZE][/FONT]

[CENTER][IMG]http://www.emc.maricopa.edu/faculty/farabee/BIOBK/annelidbody.gif[/IMG][/CENTER]

Phylum annelida
 

Phylum annelida

All about phylum Annelida a ppt presentation

[URL="http://faculty.evansville.edu/de3/b10802/PPoint/Annelida/sld001.htm"]Click here[/URL]

This link is about the metamerism and reproduction in Annelids.

[URL="http://new.scribd.com/doc/6710224/9-Metamerism-Repd"]Check this[/URL]

regards

coelom
 

[FONT=Times New Roman][SIZE=3][COLOR=black]The [B]coelom[/B] is a fluid filled cavity formed within the [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Mesoderm"][FONT=Times New Roman][SIZE=3][COLOR=black]mesoderm[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black]. Coeloms developed in [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Triploblast"][FONT=Times New Roman][SIZE=3][COLOR=black]triploblasts[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black] but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size. Coeloms are only ever present in [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Triploblast"][FONT=Times New Roman][SIZE=3][COLOR=black]triploblastic[/COLOR][/SIZE][/FONT][/URL][SIZE=3][FONT=Times New Roman][COLOR=black] animals, though coelom is sometimes (incorrectly) used to refer to any developed digestive tract.[/COLOR][/FONT][/SIZE]
[FONT=Times New Roman][SIZE=3][COLOR=black]Functionally, a coelom can absorb shock or provide a [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Hydrostatic_skeleton"][FONT=Times New Roman][SIZE=3][COLOR=black]hydrostatic skeleton[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black]. It also allows organs to grow independently of the body wall. This can be seen in the digestive tract of earthworms and other [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Annelid"][FONT=Times New Roman][SIZE=3][COLOR=black]annelids[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black], which is suspended within the body in a [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Mesentery"][FONT=Times New Roman][SIZE=3][COLOR=black]mesentery[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black] derived from a mesoderm-lined coelom. In [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Mammals"][FONT=Times New Roman][SIZE=3][COLOR=black]mammals[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black], the coelom forms the [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Peritoneal"][FONT=Times New Roman][SIZE=3][COLOR=black]peritoneal[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black], [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Pleural"][FONT=Times New Roman][SIZE=3][COLOR=black]pleural[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black], and [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Pericardial_sinus"][FONT=Times New Roman][SIZE=3][COLOR=black]pericardial[/COLOR][/SIZE][/FONT][/URL][SIZE=3][FONT=Times New Roman][COLOR=black] cavities.[/COLOR][/FONT][/SIZE]
[FONT=Times New Roman][SIZE=3][COLOR=black]In the past, zoologists grouped animals based on characters related to the coelom. The presence or absence of a coelom and the way in which it was formed was believed to be important in understanding the [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Phylogenetic"][FONT=Times New Roman][SIZE=3][COLOR=black]phylogenetic[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black] relationships of animal [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Phylum"][FONT=Times New Roman][SIZE=3][COLOR=black]phyla[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black]. However, recent molecular phylogenies have suggested this characteristics is not as informative as previously believed. Indeed, the coelom may have arisen twice, once in [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Protostome"][FONT=Times New Roman][SIZE=3][COLOR=black]protostomes[/COLOR][/SIZE][/FONT][/URL][FONT=Times New Roman][SIZE=3][COLOR=black] and once among the [/COLOR][/SIZE][/FONT][URL="http://en.wikipedia.org/wiki/Deuterostome"][FONT=Times New Roman][SIZE=3][COLOR=black]deuterostomes[/COLOR][/SIZE][/FONT][/URL][SIZE=3][FONT=Times New Roman][COLOR=black].[/COLOR][/FONT][/SIZE]





[CENTER][IMG]http://kvhs.nbed.nb.ca/gallant/biology/coelom.jpg[/IMG][/CENTER]



[CENTER][IMG]http://www.nhc.ed.ac.uk/images/collections/invertebrates/intros/LgCoelom.jpg[/IMG][/CENTER]








[CENTER][IMG]http://universe-review.ca/I10-82-coelom.jpg[/IMG][/CENTER]

Annelids
 

[B][COLOR=black][FONT=Verdana]Which are the morphological features that differentiate the beings of the phylum Annelida from nematodes and platyhelminthes?[/FONT][/COLOR][/B]
[COLOR=black][FONT=Verdana]Platyhelminthes are worms with flat bodies (flatworms), [/FONT][/COLOR][U][COLOR=#009900][FONT=Verdana]nematodes[/FONT][/COLOR][/U][COLOR=black][FONT=Verdana] are worms with cylindrical but not segmented bodies (roundworms). Annelids are cylindrical worms with segmented bodies (they are metameric).[/FONT][/COLOR]

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[B]What is the main evolutionary novelty presented by annelids?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]The main evolutionary novelty presented by the beings of the phylum Annelida is the coelom, the internal body cavity totally covered by mesoderm, a feature also present in arthropods, molluscs, echinoderms and chordates. Platyhelminthes are acoelomate and nematodes are pseudocoelomate (their internal cavity is partially covered by mesoderm). [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Another important evolutionary novelty of the annelids is the closed circulatory system.

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[B]What is the morphological characteristic that evolutionarily approximates the beings of the phylum Annelida to arthropods?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]The metameric feature, i.e., the body segmentation in metameres, approximates annelids to arthropods since these animals are segmented beings too. (Bristles present in oligochaete and polychaete annelids are also covered with chitin, the same substance of the arthropod exoskeleton.)[/FONT][/COLOR]
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[B]How does digestion in beings of the phylum Annelida work and which type of digestive system do they have?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Digestion in beings of the phylum Annelida is extracellular. These animals have a complete digestive system, with mouth and anus.
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[B]Which are the characteristics and organs of [/B][/FONT][/COLOR][B][U][COLOR=#009900][FONT=Verdana]the digestive system[/FONT][/COLOR][/U][/B][B][COLOR=black][FONT=Verdana] of earthworms related to the type of diet of these animals?[/FONT][/COLOR][/B]
[COLOR=black][FONT=Verdana]Earthworms[/FONT][/COLOR][COLOR=black][FONT=Verdana] eat decomposing organic material and small organisms ingested together with soil particles. The digestive tubes of earthworms have special structures, like a muscular wall and a gizzard, that triturate the food and scratch it against the ingested soil particles. Since annelid digestion is exclusively extracellular earthworms also present in the posterior part of their digestive system structures like the cecum and the typhlosole that have the function of increasing the absorption surface of the intestine.[/FONT][/COLOR]

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[B]The vascular lesions caused by leeches upon the blood vessels of their host cause blood naturally to coagulate. How does the leech solve this problem since it could be expected that the ingested blood would coagulate inside its body?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Ingested blood does not coagulate inside the leech (Hirudo medicinalis) because in its saliva there is a potent anticoagulant substance, a protein called hirudin.[/FONT][/COLOR]
[COLOR=black][FONT=Verdana]In the past leeches were largely used as medical treatment. Nowadays hirudotherapy is being used in patients with extensive and chronic inflammation of the skin, in prevention against tissue necrosis after some surgeries and in several others fields of Medicine.[/FONT][/COLOR]
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[B]How is the respiratory system of beings of the phylum Annelida characterized?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Respiration in annelids can be cutaneous or branchial. Cutaneous respiration occurs due to the rich vascularity under the epidermis. The gills, present in aquatic annelids, are located in the parapodia (false claws) that have an extensive capillary net.
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[B]What is meant when it is said that beings of the phylum Annelida are vascular beings? From which other phyla of the animal kingdom does this feature differentiate them?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]The classification of these beings as vascular beings means that they have a circulatory system, with vessels that distribute substances throughout the body.[/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Poriferans, cnidarians and flatworms do not have a circulatory system. In nematodes there is circulation of gases and nutrients through the pseudocoelom fluid.[/FONT][/COLOR]

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[B]How are the circulatory systems of animals classified?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]A [/FONT][/COLOR][U][COLOR=#009900][FONT=Verdana]circulatory system[/FONT][/COLOR][/U][COLOR=black][FONT=Verdana] is classified as open or closed. In open circulatory systems blood gets out of vessels and flows also to large cavities that perfuse the tissues to be irrigated. In closed circulatory systems blood circulates only within blood vessels and through the heart.
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[B]What is the type of circulatory system present in annelids?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]In beings of the phylum Annelida the circulatory system is closed, i.e., blood circulation takes place only within specialized vessels.[/FONT][/COLOR]

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[B]Is there a respiratory pigment in the annelid blood?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]The blood in beings of the phylum Annelida contains the respiratory pigment hemoglobin (the same found in chordates) and other pigments too. [/FONT][/COLOR]

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[B]How can the presence, localization and function of muscular tissue in beings of the phylum Annelida be explained?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]In these beings there are a longitudinal muscular layer under the epidermis and, internally juxtaposed and perpendicular to it, another circular (radial to the axis) muscular layer. The circular muscle layer has the function of elongating the body while the longitudinal shortens it. By alternating actions both promote movement.[/FONT][/COLOR]

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[B]How can the excretory system of annelids be described?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]In each segment (metamere) of the being a pair of complete excretory structures called metanephridium exists. The metanephridium has an extremity, the nephrostoma, which collects residuals from the coelom, filtering them and causing reabsorption along its extension (similar to human nephron tubules). The material to be excreted goes out through a pore, the nephridiopore, which opens in the body surface.
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[B]How is the nervous system characterized in beings of the phylum Annelida? How can one compare cephalization in annelids to cephalization in nematodes and platyhelminthes?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Annelids have a nervous system made of two ventral chords and one relatively big nervous cell concentration in its anterior portion resembling a primitive brain.[/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Nematodes[/FONT][/COLOR][COLOR=black][FONT=Verdana] have an anterior neural ring connected to two neural chords, a ventral and a dorsal one, while in planarias (platyhelminthes) there are only two small anterior “cerebral” ganglia from which neural chords split. Cephalization in annelids thus is more outstanding than in nematodes or in flatworms.

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[B]What is the clitellum of earthtworms and where it is located?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]The clitellum is a special region of the annelid constituted by rings (metameres) with reproductive function. It can be found in the anterior portion of the animal and it is characterized by a lighter color in comparison to the normal color of the other segments. [/FONT][/COLOR]

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[B]Concerning the occurrence of separated sexes how are the beings of the phylum Annelida classified?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]These beings may be dioecious (the majority of polychaetes) or hermaphrodite monoecious (oligochaetes and hirudineans). [/FONT][/COLOR]

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[B]Is the embryonic development in earthworms direct or indirect?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]In earthworms there is no larval stage, so the embryonic development is direct. [/FONT][/COLOR]

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[B]What is the name of the larval stage of polychaetes?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Among the annelid classes only polychaetes present a larval stage. Their larva is called trocophore.[/FONT][/COLOR]

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[B]What is the ecological role of earthworms?[/B] [/FONT][/COLOR]
[COLOR=black][FONT=Verdana]Earthworms[/FONT][/COLOR][COLOR=black][FONT=Verdana] have an important ecological role as they eat decomposing organic material. They also dig tunnels in the subsoil allowing the entrance of gases and nutrients that are useful for plant roots and other living beings. So they act as decomposers and as fertilizers too.[/FONT][/COLOR]

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[B]Into which classes is the phylum Annelida divided?[/B] [/FONT][/COLOR]
[FONT=Verdana]The phylum is divided into three classes: oligochaetes (for example, [/FONT][COLOR=black][FONT=Verdana]earthworms[/FONT][/COLOR][FONT=Verdana]), hirudineans (e.g., leeches) and polychaetes (these are mostly marine aquatic with parapodia, like nereis).

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Annelida
 

[SIZE=3][FONT=Times New Roman][B]Excretion.[/B][/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman]The basic units of the annelid excretory system are either protonephridia, which have tubules (solenocytes) that end blindly within cells, contain flagella (whiplike projections), and are joined to a common duct that drains to the outside; or metanephridia, which are funnel-shaped structures containing cilia (short, hairlike processes) that open to the outside.[/FONT][/SIZE]
[FONT=Times New Roman][SIZE=3]Ammonia is the chief nitrogen-containing end product of protein metabolism in aquatic annelids; earthworms, adapted to living in the soil, excrete more of another nitrogen-containing compound, urea, probably as part of a mechanism to control salt and water balance in the worm. The [/SIZE][/FONT][URL="http://www.britannica.com/EBchecked/topic/530649/sea-mouse"][FONT=Times New Roman][SIZE=3][COLOR=#0000ff]sea mouse[/COLOR][/SIZE][/FONT][/URL][SIZE=3][FONT=Times New Roman] [I]Aphrodita[/I], a polychaete, excretes 80 percent of its nitrogen as ammonia, which is also the primary nitrogenous excretory product in leeches (smaller amounts of urea also are excreted). Part of the ammonia excreted by leeches may come from bacteria in part of the leech’s excretory system (nephridial capsules). The ability of leeches to withstand high concentrations of ammonia is believed to result from a protective effect provided by high levels of calcium in their cells.[/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman]Three aspects of nephridial function in annelids correspond to those of the vertebrate kidney—filtration, resorption, and secretion. Coelomic fluid filters through solenocytes. The ciliated funnels of metanephridia retain minute particles and those of moderate size. In oligochaetes, whose coelomic fluid contains proteins, particles are actively absorbed in the ciliated region of the tubule. The tubules of earthworms also resorb inorganic ions such as sodium and calcium and can selectively eliminate excretory products from both the coelomic fluid and the bloodstream.[/FONT][/SIZE]

[CENTER][IMG]http://www.cbu.edu/%7Eseisen/LcEx02Fa2008EssayAnswers_files/image008.jpg[/IMG]


[IMG]http://cas.bellarmine.edu/tietjen/Laboratories/Bio%20Pix%204%20U/nephron.gif[/IMG]





[SIZE=3][FONT=Times New Roman][IMG]http://trc.ucdavis.edu/biosci10v/bis10v/week9/nephridium.gif[/IMG][/FONT][/SIZE]
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phylum mollusca
 

[B]Phylum mollusca[/B]

"[B]Mollusk[/B]" sounds like it ought to be the name of some prehistoric animal, but it isn’t. Mollusks are a huge division of animals without back bones, and they range from snails to clams, and oysters to octopuses. They differ in size from almost in visible in creatures to giant squids 15 meters long! They may live in the tropics or in the arctic, in deep seas or on land! But even though there are more than 60,000 different species of mollusks, they have certain characteristics in common. All mollusks have soft, slimy, boneless bodies which are covered with big folds of flesh called "mantles." In many mollusks, this mantle is covered with a hard shell, such as that of the oyster, while others have no protecting shell at all. Almost all mollusks have a kind of "foot," which is an extension of the mantle and which helps them move about. It may help them swim or walk, burrow in the mud, or tunnel through wood, depending on the species. There are five groups of mollusks, and the members of three of them are very well known to everybody.
The first of these common groups is called "[B]Gastropoda[/B]," which means "stomach feet." Among the gastropods are snails, slugs, and periwinkles, all of which have one large "foot" on their stomachs. All gastropods have a head on which are eyes and feelers, and many of them carry single spiral shells on their backs. The second common group of mollusks is the [B]bivalve [/B]group. In this group you will find oysters, clams, mussels, scallops, and many others. All bivalves have shapeless bodies protected by double, hinged shells. All of them are water creatures. The last common group of mollusks is called the "[B]Cephalopoda[/B]," which means "head-footed." The members of this group have many arms, or tentacles, surrounding their mouths. This group includes the octopus, cuttlefish, squid, nautilus, and others. They are the aristocrats of the mollusk world, with a nervous system that raises them far above other mollusks. All mollusks lay eggs, but some lay only a few and others, many. In some the young hatch out as larvae; in others, they are tiny reproductions of their parents.

[CENTER][IMG]http://www.allthesea.com/img/sea-shell-mollusk-01.gif[/IMG][/CENTER]

Phylum mollusca
 

[B]Phylum mollusca[/B]

[B]link to ppt presentation[/B]

[B][URL="http://faculty.evansville.edu/de3/b10802/PPoint/Mollusca/sld001.htm"]check this[/URL][/B]

[B]this is a link to another comprehensive presentation about phylum mollusca[/B]

[B][URL="http://www.scribd.com/doc/6710182/12-Mollusca-Foot-and-Shell"]click here.[/URL][/B]

[B]regards[/B]

Phylum mollusca
 

[LEFT]Phylum Mollusca[/LEFT]

[B][SIZE=4]Torsion (gastropod)[/SIZE][/B][SIZE=5]
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Torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the [URL="http://dic.academic.ru/dic.nsf/enwiki/42022"][U][COLOR=#0000ff]visceral mass[/COLOR][/U][/URL], [URL="http://dic.academic.ru/dic.nsf/enwiki/707185"][U][COLOR=#0000ff]mantle[/COLOR][/U][/URL] and [URL="http://dic.academic.ru/dic.nsf/enwiki/5206372"][U][COLOR=#0000ff]shell[/COLOR][/U][/URL] 180˚ with respect to the head and foot of the gastropod. This brings the mantle cavity and anus to an anterior position above the head.
In some groups of gastropods there is a degree of secondary detorsion or rotation towards the original position, this may be only partial detorsion or full detorsion (see Opisthobranchia.)
There are two different developmental stages which cause torsion. The first stage is caused by the development of the asymmetrical velar/foot muscle which has one end attached to the left side of the shell and the other end has fibres attached to the left side of the foot and head. At a certain point in larval development this muscle contracts, causing an anticlockwise rotation of the visceral mass and mantle of roughly 90˚. This process is very rapid taking from a few minutes to a few hours. After this transformation the second stage of torsion development is achieved by differential [URL="http://dic.academic.ru/dic.nsf/enwiki/63346"][U][COLOR=#0000ff]tissue[/COLOR][/U][/URL] growth of the left hand side of the organism compared to the right hand side. This second stage is a much slower stage and rotates the visceral mass and mantle a further 90˚. Detorsion is brought about by reversal of the above phases.
During torsion the visceral mass remains almost unchanged anatomically, there are however other important changes to other internal parts of the gastropod. Before torsion the gastropod has an euthyneural nervous system, where the two visceral nerves run [URL="http://dic.academic.ru/dic.nsf/enwiki/354119"][U][COLOR=#0000ff]parallel[/COLOR][/U][/URL] down the body. Torsion results in a streptoneural nervous system, where the visceral nerves cross over in a figure of eight fashion. As a result the parietal ganglions end up at different heights. Because of differences between the left and right hand sides if the body, there are different evolutionary pressures on left and right hand side organs and as a result in some species there are considerable differences. Some examples of this are: in the ctenidia (equivalent to lungs or gills) in some species, one side may be reduced or absent; or in some hermaphrodite species the right hand [URL="http://dic.academic.ru/dic.nsf/enwiki/1081312"][U][COLOR=#0000ff]renal system[/COLOR][/U][/URL] has been transformed into part of the reproductive system.

[B]Evolutionary roles[/B]

The original advantage torsion gave gastropods is unclear. It is further complicated by the fact that torsion brought with it a number of problems. A particular problem gastropods had to overcome come was the location where wastes were [URL="http://dic.academic.ru/dic.nsf/enwiki/158727"][U][COLOR=#0000ff]excreted[/COLOR][/U][/URL] – above the head which can potentially lead to fouling of the mouth and sense organs. Nevertheless, the diversity and success of the gastropods suggests torsion is very advantageous indeed.
One role which is seems a likely candidate for the original purpose is that of defence against predators in adult gastropods. By moving the mantle cavity over the head, the gastropod can retract its [URL="http://dic.academic.ru/dic.nsf/enwiki/464710"][U][COLOR=#0000ff]vulnerable[/COLOR][/U][/URL] head into its shell. Some gastropods close the entrance to their shell with a tough [URL="http://dic.academic.ru/dic.nsf/enwiki/1920182"][U][COLOR=#0000ff]operculum[/COLOR][/U][/URL] which is attached to their foot. In evolutionary terms the appearance of an operculum occurred shortly after that of torsion, a possible link with the role of torsion, though there is not sufficient evidence either for or against this theory.
There are many other advantages torsion provided gastropods. For aquatic gastropods the anterior positioning may be useful for preventing sediment getting into the mantle cavity, which is more likely with a posterior positioning due to sediment being stirred up by the motion of the gastropod. In [URL="http://dic.academic.ru/dic.nsf/enwiki/2937683"][U][COLOR=#0000ff]terrestrial[/COLOR][/U][/URL] species, ventilation is better with anterior positioning. This is due to the back and forth motion of the shell during movement which would tend to block the mantle opening against the foot if it was in a posterior position. Another possible advantage for aquatic species is the osphradium (olfactory sense organs) are moved to an anterior position and are able to sample the water the gastropod is moving into to rather than from, this may help the gastropod locate food or avoid predators.
Evolution of an asymmetrical conispiral shell allowed gastropods to grow larger but resulted in an unbalanced shell. Torsion allows repositioning of the shell, bringing the centre of gravity back to the middle of the gastropod’s body and so helps prevent the animal or shell from falling over.
Whatever the original role of torsion, it is clear that further adaptations linked to torsion provide modern gastropods with many advantages.


[CENTER][IMG]http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/gastropo/Diagrams/tort.gif[/IMG][/CENTER]





[CENTER][IMG]http://www.bumblebee.org/invertebrates/images/Torsion.gif[/IMG][/CENTER]
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Economic importance of Molluscs
 

[B]Economic importance of Molluscs.[/B]
Molluscs are indirectly harmful to man but most of them are beneficial. Molluscs are of great important in various ways. There are some benefits of molluscs:

1. The harmful molluscs ate slugs and shipworms. Slugs are injurious in gardens and cultivations. They not only eat leaves but also destroy plants by cutting up their roots and stems. Teredo, a shipworm damages wooden parts of ship.

2. Many mollusks are great source of food for man in many parts of world. Large quantity of calms, oysters and mussels are eaten in Fareast, Europe and America. Oysters are regarded as delicacy.

3. Shell of fresh water mussels is used in button industry.

4. The shell of oyster are mixed with tar for making roads in America.

5. Shells in certain parts of world are also used for making ornaments.

6. Some oysters also make valuable pearls e.g. the pearl oyster.

7. Some pearls are used for making jewellery.

8. Some [COLOR=black][URL="http://www.blurtit.com/q631046.html"][COLOR=black]animals[/COLOR][/URL][/COLOR] including in this phyla are use to eat in some countries,mussels.


9.Some of the shelled barnacles get attached to the ships and cause problems for shipping industry.

Biology site
 

[B]Biology Questions and Answers is a website that discusses all branches and subjects of Biology. You can learn anything about Biology here! [/B]
[B]This site was specially written and organized to make Biology learning easier. More than 1800 questions and answers are available to help you study Biology in the easiest way possible. [/B]

[COLOR=black][B]The content is divided into all Biology branches: [/B][/COLOR][URL="http://www.biology-questions-and-answers.com/biochemistry-review.html"][B][COLOR=darkred]biochemistry[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/cell-biology-review.html"][B][COLOR=darkred]cell biology[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/microbiology-review.html"][B][COLOR=darkred]microbiology[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/zoology-review.html"][B][COLOR=darkred]zoology[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/physiology-review.html"][B][COLOR=darkred]physiology[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/embryology-review.html"][B][COLOR=darkred]embryology[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/plants.html"][B][COLOR=darkred]botany[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/genetics.html"][B][COLOR=darkred]genetics[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/evolution.html"][B][COLOR=darkred]evolution[/COLOR][/B][/URL][B][COLOR=darkred], [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/the-environment.html"][B][COLOR=darkred]ecology[/COLOR][/B][/URL][B][COLOR=darkred] and [/COLOR][/B][URL="http://www.biology-questions-and-answers.com/disease.html"][B][COLOR=darkred]diseases[/COLOR][/B][/URL][COLOR=black][B]. Each of these branches are then subdivided into specific subjects.[/B][/COLOR]

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[B]Regards[/B]

Phylum Arthropoda
 

[B]Phylum Arthropoda[/B]

Arthropods are multicellular, triploblastic, bilaterally symmetrical, metamerically segmented, schizocoelous, protostomous invertebrate metazoans.

Cephalization of some anterior segments of the arthropods from the head is present.
Externally the body is covered with a thick tough, non living, chitinous and protective cuticle, forming the exoskeleton. Exoskeleton is non-living and cannot grow. Appendages are segmental, paired, lateral and jointed and variously modified as [URL="http://www.blurtit.com/q641804.html/l"][U][COLOR=#0000ff]jaws[/COLOR][/U][/URL], gills and legs etc.
Arthropods are triploblastic animals have true coelom.

Arthropods possess separate striated muscles. More than one pair of jaw is present.
Circulatory system is open, capillaries are absent and arteries open into irregular spaces called sinuses. Malpigian tubules or coelomoducts are the excretory organs that excrete ammonia, urates, amines or guanine. Nervous system is of anneidian type. Compound eye with [URL="http://www.blurtit.com/q641804.html/l"][U][COLOR=#0000ff]mosaic[/COLOR][/U][/URL] vision is well developed. Cilia and flagella are entirely absent.

Sexes are usually separate (dioecious), but a few are hermaphrodite. Sexual dimorphism is usually evident. Parthenogenesis is common in some groups. Gonads and their ducts usually paired. Fertilization is internal and development include complete, incomplete or no metamorphosis. Parental care often well marked.



[B][COLOR=darkred]these are two links of PPt presentation about Arthropods[/COLOR][/B]

[B][URL="http://www.cbu.edu/~seisen/Arthropoda/sld001.htm"]Click here[/URL][/B]

and

[B][URL="http://faculty.evansville.edu/de3/b10802/PPoint/Arthropoda/sld001.htm"]check this[/URL][/B]

regards

Arthropoda
 

[B]Phylum Arthropoda[/B]

The following is the link to detailed article on mouth parts of insects on Wikipedia

[B][URL="http://wapedia.mobi/en/Insect_mouthparts"]check this link[/URL][/B]

The link mentioned below is a comprehensive presentation on mouthparts of insects with fully labelled diagrams.

[B][URL="http://www.scribd.com/doc/6710206/10-Insect-Mouth-Parts"]click here [/URL][/B]

[B]regards[/B]

metamorphosis
 

[B]Phylum Arthropoda[/B]
[B]Insect Metamorphosis[/B]

[SIZE=5][SIZE=4]Introduction[/SIZE] [/SIZE][SIZE=5]

[/SIZE]Metamorphosis refers to a major change of form or structure during development.
[SIZE=5][SIZE=4]Insect Metamorphosis [/SIZE][/SIZE][SIZE=5]

[/SIZE]One of the most dramatic forms of metamorphosis is the change from the immature insect into the adult form. Most of the major insect orders have a typical life cycle which consists of an egg, which hatches into a larva which feeds, moults and grows larger, pupates, then emerges as an adult insect that looks very different from the larva. These insects are often called 'Holometabolous', meaning they undergo a complete ([I]Holo[/I] = total) change ([I]metabolous[/I] = metamorphosis or change). Those which have immature stages similar in shape to the adult minus the wings are called 'Hemimetabolous', meaning they undergo partial or incomplete ([I]Hemi[/I] = part) change.

[SIZE=5][SIZE=4]Holometabolous (complete metamophosis) [/SIZE][/SIZE][SIZE=5]

[/SIZE]Typical holometabolous insect groups are the Coleoptera (Beetles), Lepidoptera (moths, butterflies and skippers), Hymenoptera (sawflies, wasps, ants and bees) and Diptera (flies). All these groups have a life cycle where the egg hatches into a larva (eg a caterpillar, grub, maggot) which goes through an inactive, pupa stage (eg wrapped up like a cocoon) before emerging as an adult (eg a butterfly, beetle, wasp).

[SIZE=5][SIZE=4]Hemimetabolous (incomplete metamorphosis) [/SIZE][/SIZE][SIZE=5]

[/SIZE]Typical hemimetabolous insects are the Hemiptera (Scales, Aphids, Whitefly, Cicadas, Leafhoppers and True Bugs), Orthoptera (Grasshoppers and Crickets), Mantodea (Praying Mantids), Blattodea (Cockroaches), Dermaptera (Earwigs) and Odonata (Dragonflies and Damselflies). These groups go through gradual changes as they turn into adults. Immature forms of these insects are called nymphs and these gradually increase in size and change form. As the insect grows, it sheds its skin (called moulting). After each moult, the nymph looks a bit different or a bit bigger. After a final moult, the full adult form emerges.

[SIZE=5][SIZE=4]A successful strategy [/SIZE][/SIZE][SIZE=5]

[/SIZE]Metamorphosis is one of the key elements that explains why insects are so successful. Many insects have immature stages with completely different habitats from the adults. This means that insects can often exploit valuable food resources while still being able to disperse into new habitats as winged adults. The potential for adaptation and evolution is greatly enhanced by metamorphosis.

[SIZE=5][SIZE=4]Growth and maturity [/SIZE][/SIZE][SIZE=5]

[/SIZE]There is an important feature to note regarding metamorphosis. Insects are not able to mate and reproduce until they undergo their final moult or emerge from a pupa as a winged adult. Wings do not appear until the final moult (the one exception to this is the Ephemeroptera, or Mayflies). When you see an insect with wings, it is fully grown. This means that small flies do not become larger flies, they are as big as they will get.

[SIZE=5][SIZE=4]Caterpillars, Grubs and Maggots - Holometabolous Larvae [/SIZE][/SIZE][SIZE=5]

[/SIZE]Holometabolous larvae are larvae that pupate before emerging as adult insects, and include many of the most familiar insects.
Holometabolous larva in general are little more than tubular, efficient eating machines. They do not have to lay eggs, or find a mate. Apart from eating, they are mainly concerned with avoiding being eaten themselves. This means that they may have good camouflage, or hide in shelters or holes, or they may taste dreadful to any prospective predators.
The major insect orders have larvae with different common names. For instance, moths, butterflies and skippers have larvae which are usually called caterpillars. Fly larvae are nearly always called maggots. Beetle larvae are often referred to as grubs.

[SIZE=4]Caterpillars[/SIZE]

Moth, butterfly and skipper (Lepidoptera) caterpillars have pairs of prolegs on their abdomen in addition to the three pairs of jointed walking legs on the thorax. Prolegs differ from the usual insect legs in that they are not jointed. Each proleg has a set of tiny hooks, which are arranged in rings or series around the tip of the proleg. These are called crochets, and only occur in the insect order Lepidoptera. Although there are some caterpillar-like larvae from other insect orders, such as sawfly larvae (Order Hymenoptera, Suborder Symphyta) and leaf beetle larvae (Order Coleoptera, Family Chrysomelidae), they can be distinguished from lepidopteran larvae by the absence of prolegs with crochets. Lepidopteran larvae have chewing mouthparts, and the majority of species are adapted to eating plant material

[SIZE=4]Maggots[/SIZE]

Fly larvae (Diptera) lack any segmented legs on the thorax, and are often highly specialised for living in wet environments. Very few are adapted to dry conditions. Quite a few species are internal parasites of other animals, where legs would be of no use. Unlike the larvae of Lepidoptera there is no one character that can be used to separate fly maggots from other large orders such as the Hymenoptera (Wasps, Bees, Ants, and Sawflies), as the immature stages of many species in these orders also lack segmented legs. Fly maggots live on a huge range of foods - from human flesh through to kelp on the seashore

[SIZE=4]Grubs[/SIZE]

Beetle larvae (Coleoptera) are highly diverse in their shapes. The majority live in concealed habitats, such as underground, or inside trees. There are many aquatic species, and a few which resemble caterpillars and feed openly on leaves. Many retain segmented legs, although weevil grubs nearly always lack legs. Most legless beetle grubs have robust chewing mouthparts and can be distinguished from fly maggots, which often have modified mouth 'hooks'.
The larvae of sawflies, wasps, bees and ants (Hymenoptera) are diverse in form. Many sawfly larvae are similar to lepidopteran caterpillars, and feed externally on plant material. The social Hymenoptera, which includes some wasps, some bees, and all ants have larvae with very few external features, as they do not have to forage for food. In these species food is brought to them by the adult nest mates. The parasitic Hymenoptera are similar in that they spend their larval period inside hosts or well-stocked nests. They do not need camouflage or legs in these habitats

[SIZE=5][SIZE=4]Nymphs, hoppers and mudeyes - Hemimetabolous insects[/SIZE][/SIZE][SIZE=5]

[/SIZE]Hemimetabolous insects do not have a pupal stage. The general appearance of the immature stages is somewhat similar to that of adults, although there may be some dramatic differences in lifestyle. Only adult insects are able to reproduce, and only adult insects have functional wings (in those species that have wings).
The immature stages of these insects are generally called nymphs rather than larvae. Some have common names such as 'hoppers' (immature grasshoppers, Order Orthoptera), 'crawlers' (immature scale insects, Order Hemiptera) and 'mudeyes' (immature dragonflies, Order Odonata).
Examples of hemimetabolous insects include cockroaches (Order Blattodea), crickets and grasshoppers (Order Orthoptera), stick insects (Order Phasmatodea), praying mantids (Order Mantodea), termites (Order Isoptera), dragonflies and damselflies (Order Odonata), earwigs (Order Dermaptera), sucking bugs (Order Hemiptera), wood and book lice (Order Psocoptera), and parasitic lice (Order Phithaptera).
The feeding habits of hemimetabolous insects commonly mirror that of the adults, but often with a significant twist. Dragonfly nymphs are aquatic predators, but the adults are active flying insects, which hunt other flying insects. Stick insect nymphs can resemble ants, while later stage nymphs blend with the food plants. All stages of stick insects feed on plant material. The final moult between mature nymph and adult is usually accompanied by changes in colour, and in shape of the body, but there is never the dramatic difference between larvae and adult as observed in holometabolous insects.



[CENTER][IMG]http://www.umd.umich.edu/eic/aquatic_insecta/complete_metamorphosis.jpg[/IMG][/CENTER]

[CENTER][IMG]http://www.insectennet.be/incompmetamorph.JPEG[/IMG][/CENTER]

[CENTER][IMG]http://www.naturegrid.org.uk/biodiversity/invert/graphics/meta,comp.jpg[/IMG][/CENTER]

Insect
 

[B]Phylum Arthropoda[/B]


[SIZE=3][B]The importance of insects[/B]

[/SIZE]Insects represent animals commonly found in different types of the environment. They adapted to extremely harsh living conditions by developing modified, and often quite complicated mouth-parts. This helps them use all kinds of available food. It is therefore not surprising, that these widespread and numerous animals significantly affect the environment in which they live. Insects are also of great importance for the economy. Some of them are our allies whereas others are grimly fought enemies.
One of the most important roles insects play in the natural word is the pollination of flower plants . Over millions of years, the evolution of flower plants and the related insects proceeded in parallel. As a result, various tools for collecting and transporting pollen have been developed, such as ventral brushes, pollen-baskets on legs or tufts of hair on other parts of the body. Some species, for instance, have unusually long tongues which help them reach the bottom of elongated flower tubes in search of nectar. Some insects pollinate flowers blooming in the daytime while others prefer flowers that open at twilight. The most important pollinators of flower plants are hymenopterans, especially wild bees, as well as lepidopterans, dipterans and coleopterans.
Numerous insect species compete for food with man, causing considerable damage to crops or consuming wild plants which are also utilized by people. The chrysomelid beetles (Chrysomelidae) feed on green plant tissue. This leads to a significant decrease in the size of yield where the beetles occur in large numbers.The most famous representative of this family is the Colorado beetle (Leptinotarsa decemlineata). Other species commonly found in the Park include the red poplar leaf-beetle (Chrysomela populi), which feeds on poplars, willows and aspen, as well as one of the spotted leaf beetles, Chrysomela viginitipunctata.
Insects which exercise the greatest influence on tree stands are the bark beetles (Ipidae). These miniature beetles can cause the withering of large forest areas already weakened by air pollution or severe weather conditions such as long-lasting drought. Bark beetles live mainly in wood and under the bark, the traces of boring of which are characteristic of individual species. Most changes in the spruce stands of the Wigry National Park have for years been caused by the eight-dentated bark beetle (Ips typographus).
Tree stands are destroyed also by some Hymenoptera species. The mass occurrence of phytophagus hymenopterans (Symphyta) such as the pine web-spinning sawfly (Acantholyda posticalis) or the pine sawfly (Diprion pini), can severely damage the assimilation organs in trees (caterpillars feed on needles) and significantly decrease their immunity to possible attacks of other insects (e.g. one of buprestid beetles, Phaenops cyanes) or fungi, presenting as they do a considerable danger to entire tree stands.
A small group of insects feeds on the blood of warm-blooded animals. This way of acquiring food is characteristic of certain dipterans such as keds (Melophagus), fowl flies (Ornithomyia), horse flies (Tabanus) and deer flies (Chrysopus), as well as various bugs (e.g. bed bug). Blood-sucking dipterans may transmit many diseases. Horse flies and deer flies may carry rabbit fever and plague germs by sucking the blood of farm animals.
In spite of their arduousness as well as negative impact on the environment of man, insects play an important role in the natural world. Many species of predatory and parasitic insects significantly reduce the number of organisms which are harmful to the human economy . These insects regulate and maintain the biocoenotic balance and ensure in this way a proper functioning of the natural environment. This insect group includes, among others, all carabid species (Carabus). The larvae of most ladybird species (Coccinellidae) (e.g. two-spot lady-bird) play a similar role in nature by devouring enormous amounts of aphids, scale insects and other tiny insects. Some species of the rove beetles family (Staphylinidae) penetrate the corridors of bark beetles in search of their larvae. A similar behaviour is typical of some representatives of the chequered beetle family (Cleridae), including the ant beetle (Thanasismus formicarius) inhabiting the park.
Another group of insects which plays a crucial role in different types of forest environment is ants (Formicidae). Large mound ants belonging to the Formica genus act as "orderlies" by regulating the number of other insects. In the case of the mass appearance of Lepidoptera or Diptera caterpillars feeding on plants, ants switch to these species thereby significantly reducing their number. By building their nests, ants improve the quality of the soil. Numerous chambers and corridors in the underground part of the nest have a beneficial impact on the air and water regime in the soil.
Insects actively accelerate the circulation of the organic matter in the environment. The larvae of many Diptera species (e.g. bluebottle flies Caliphora and flesh-flies Sarcophaga) feed on dead plants and animals as well as on animal dung. This significant contribution leads to a faster decomposition. Carrion is a source of nourishment for numerous beetle species (e.g. burying beetles (Necrophorus) and carrion beetles Silpha). Because eggs are deposited in the carrion, the larvae feed on the animal remains. The dor beetles (Geotrupes) remove immense quantities of dung from the environment . They build deep burrows ending with chambers under an accumulation of dung where females deposit their eggs. The beetles then fill the chambers with lumps of dung providing food reserves for the developing larvae

crustaceans
 

[B]Phylum Arthropoda[/B]

[B][SIZE=3]General features » Importance to humans[/SIZE][/B]

The crustaceans of most obvious importance to humans are the larger species, chiefly decapods. Fisheries in many parts of the world capture shrimps, prawns, [URL="http://www.cssforum.com.pk/EBchecked/topic/560255/spiny-lobster"][COLOR=black]spiny lobsters[/COLOR][/URL][COLOR=black],[/COLOR] and the king crab (Paralithodes) of the northern Pacific and its southern counterpart, the centolla, found off the coast of Chile. Many species of true crabs—such as the blue crab, [URL="http://www.cssforum.com.pk/EBchecked/topic/173742/Dungeness-crab"][COLOR=black]Dungeness crab[/COLOR][/URL][COLOR=black], and[/COLOR] the stone crab, all [COLOR=black]in [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/418612/North-America"][COLOR=black]North America[/COLOR][/URL][COLOR=black], and the [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/179135/edible-crab"][COLOR=black]edible crab[/COLOR][/URL] of Europe—are valuable sources of food. The most highly prized decapod is probably the true lobster (Homarus species), although overfishing since the early 20th century has greatly diminished the catches of both the North American and the European species. Freshwater crustaceans include crayfish and some river prawns and river crabs. Many species have only local market value. It is probable that no crustaceans are poisonous unless they have been feeding on the leaves or fruits of [URL="http://www.cssforum.com.pk/EBchecked/topic/719998/poisonous-plant"][COLOR=black]poisonous plants[/COLOR][/URL][COLOR=black].[/COLOR]

Another crustacean, the [COLOR=black]large [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/506065/rock-barnacle"][COLOR=black]acorn shell[/COLOR][/URL][COLOR=black] (Balanus psittacus), a barnacle (order Cirripedia) measuring up to 27 centimetres (11 inches) in length, is regarded as a delicacy in [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/555844/South-America"][COLOR=black]South America[/COLOR][/URL][COLOR=black], and a [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/562754/stalked-barnacle"][COLOR=black]stalked barnacle[/COLOR][/URL][COLOR=black] (Mitella pollicipes) is eaten in parts of France and Spain. In Japan, barnacles[/COLOR] are allowed to settle and grow on bamboo stakes, later to be scraped off and crushed for use as fertilizer.
Copepods and krill are important [COLOR=black]components of most marine [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/212738/food-web"][COLOR=black]food webs[/COLOR][/URL][COLOR=black]. Planktonic (i.e., drifting) copepods, such as Calanus, and members of the order Euphausiacea (euphausiids), or krill, may be present in such great numbers that they discolour large areas of the open sea, thus indicating to fishermen where shoals of herring and mackerel are likely to be found.[/COLOR]
[COLOR=black]The water flea (Daphnia magna) and the [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/79674/brine-shrimp"][COLOR=black]brine shrimp[/COLOR][/URL][COLOR=black] ([/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/36787/Artemia-salina"][I][COLOR=black]Artemia salina[/COLOR][/I][/URL][COLOR=black]) are used as fish food in aquariums and fish ponds, and the larvae of the latter are widely used as food for the larvae of larger crustaceans reared in[/COLOR] captivity. Ostracods, of which numerous fossil and subfossil species are known, are important to geologists and oil prospectors.
[COLOR=black]Much damage may be done to [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/437980/paddy"][COLOR=black]rice paddies[/COLOR][/URL][COLOR=black] by burrowing crabs of various species and by the mud-eating, shrimplike Thalassina of Malaya. By undermining paddy embankments, they allow water to drain away, thus exposing the roots of the plants to the sun; if near the coast, [/COLOR][URL="http://www.cssforum.com.pk/EBchecked/topic/531121/seawater"][COLOR=black]salt water[/COLOR][/URL][COLOR=black] may thus be allowed to seep into the paddies. Tadpole shrimps (Triops) are often numerous in rice fields, where they stir up the fine silt in search of food, killing many of the plants. Land crabs and crayfish may damage tomato and cotton crops.[/COLOR]


Reference:Britannica

Respiration in insects
 

[COLOR=black]Respiration in Insects[/COLOR]

All insects are aerobic organisms -- they must obtain oxygen (O2) from their environment in order to survive. They use the same metabolic reactions as other animals (glycolysis, Kreb's cycle, and the electron transport system) to convert nutrients (e.g. sugars) into the chemical bond energy of ATP. During the final step of this process, oxygen atoms react with hydrogen ions to produce water, releasing energy that is captured in a phosphate bond of ATP.

The respiratory system is responsible for delivering sufficient oxygen to all cells of the body and for removing carbon dioxide (CO2) that is produced as a waste product of cellular respiration. The respiratory system of insects (and many other arthropods) is separate from the circulatory system. It is a complex network of tubes (called a [B]tracheal system[/B]) that delivers oxygen-containing air to every cell of the body.
Air enters the insect's body through valve-like openings in the exoskeleton. These openings (called [URL="http://www.cssforum.com.pk/l 1"][COLOR=#0000ff]spiracles[/COLOR][/URL]) are located laterally along the thorax and abdomen of most insects -- usually one pair of spiracles per body segment. Air flow is regulated by small muscles that operate one or two flap-like valves within each spiracle -- contracting to close the spiracle, or relaxing to open it.

After passing through a spiracle, air enters a longitudinal [URL="http://www.cssforum.com.pk/l 1"][COLOR=#0000ff]tracheal trunk[/COLOR][/URL], eventually diffusing throughout a complex, branching network of [URL="http://www.cssforum.com.pk/l 1"][COLOR=#0000ff]tracheal tubes[/COLOR][/URL] that subdivides into smaller and smaller diameters and reaches every part of the body. At the end of each tracheal branch, a special cell (the [B]tracheole[/B]) provides a thin, moist interface for the exchange of gasses between atmospheric air and a living cell. Oxygen in the tracheal tube first dissolves in the liquid of the tracheole and then diffuses into the cytoplasm of an adjacent cell. At the same time, carbon dioxide, produced as a waste product of cellular respiration, diffuses out of the cell and, eventually, out of the body through the tracheal system.

Each tracheal tube develops as an invagination of the ectoderm during embryonic development. To prevent its collapse under pressure, a thin, reinforcing "wire" of cuticle (the [URL="http://www.cssforum.com.pk/l 1"][COLOR=#0000ff]taenidia[/COLOR][/URL]) winds spirally through the membranous wall. This design (similar in structure to a heater hose on an automobile or an exhaust duct on a clothes dryer) gives tracheal tubes the ability to flex and stretch without developing kinks that might restrict air flow.

The absence of taenidia in certain parts of the tracheal system allows the formation of collapsible [URL="http://www.cssforum.com.pk/l 1"][COLOR=#0000ff]air sacs[/COLOR][/URL], balloon-like structures that may store a reserve of air. In dry terrestrial environments, this temporary air supply allows an insect to conserve water by closing its spiracles during periods of high evaporative stress. Aquatic insects consume the stored air while under water or use it to regulate buoyancy. During a molt, air sacs fill and enlarge as the insect breaks free of the old exoskeleton and expands a new one. Between molts, the air sacs provide room for new growth -- shrinking in volume as they are compressed by expansion of internal organs.

Small insects rely almost exclusively on passive diffusion and physical activity for the movement of gasses within the tracheal system. However, larger insects may require active [B]ventilation[/B] of the tracheal system (especially when active or under heat stress). They accomplish this by opening some spiracles and closing others while using abdominal muscles to alternately expand and contract body volume. Although these pulsating movements flush air from one end of the body to the other through the longitudinal tracheal trunks, diffusion is still important for distributing oxygen to individual cells through the network of smaller tracheal tubes. In fact, the rate of gas diffusion is regarded as one of the main limiting factors (along with weight of the exoskeleton) that prevents real insects from growing as large as the ones we see in horror movies!

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Arthropoda appendages
 

[B]Arthropoda appendages[/B]

Arthropods are unusual among invertebrates; they lack locomotory cilia, even as larvae. The problem that a rigid external covering imposes on movement has been solved by having the exoskeleton divided into plates over the body and through a series of cylinders around the appendages. At the junction, or joints, between the plates and cylinders the exoskeleton is thin and flexible because it lacks the exocuticle and because it is folded. The folds provide additional surface area as the joints are bent. The arthropod’s exoskeleton is therefore somewhat analogous to the armour encasing a medieval knight.
Most arthropods move by means of their segmental appendages, and the exoskeleton and the muscles, which attach to the inside of the skeleton, act together as a lever system, as is also true in vertebrates. The external skeleton of arthropods is a highly efficient system for small animals. The exoskeleton provides a large surface area for the attachment of muscles and, in addition to functioning in support and movement, also provides protection from the external environment. The cylindrical design resists bending, and only a relatively small amount of skeletal material need be invested in thickness to prevent buckling. The external skeleton imposes limits on the maximum size of an arthropod, especially in those that live on land. The largest arthropods live in the sea, where they gain considerable support from the buoyance of seawater. On land, an excessive amount of skeleton would be required to support a large bulk and, in addition, the new soft skeleton might collapse following a molt.
Appendages of arthropods have been adapted for all types of locomotion—walking, pushing, running, swimming, and burrowing. In most arthropods the legs move alternately on the two sides of the body; i.e., when one leg is in a power stroke, its mate on the opposite side of the body is in the recovery stroke (the same is true of mammals when walking). The legs in front or back are a little ahead or behind in the movement sequence. Because of the lateral position of the legs, the body of an arthropod tends to hang between them. Leg interference and trunk wobble tend to be problems in an animal with a long trunk and many legs, such as a millipede or centipede. Most arthropods have evolved more compact bodies and a smaller number of legs. The number of pairs of legs used in walking is not more than seven (crustacean pill bugs), four or five (shrimps and crabs), four (arachnids), and three (insects). This reduces the problem of mechanical interference. When a [URL="http://www.cssforum.com.pk/EBchecked/topic/232788/ghost-crab"][U][COLOR=#0000ff]ghost crab[/COLOR][/U][/URL], for example, is running rapidly across a beach or dune, only the second, third, and fourth pairs of the five pairs of legs (counting the claws) are employed. Leg interference is further reduced in most arthropods by varying limb length and placement. For example, in Scutigera, the centipede commonly seen in houses, the legs increase in length from front to back and thus pass over or under one another in stepping. The tendency for the trunk to wobble has been reduced in some centipedes by having overlapping dorsal plates and in millipedes by having pairs of segments fused to form double segments. Many arthropods are capable of walking on vertical surfaces. Some simply grip minute surface irregularities with the claws at the end of the legs. Others, such as certain spiders and flies, have an array of specialized gripping hairs at the ends of the legs.
Insect wings are not segmental appendages as are the legs. The paired wings arise as lateral folds of the integument, one pair above each of the last two pairs of legs. Each wing thus consists of an upper and lower sheet of exoskeleton closely applied to each other. The two skeletal sheets are separated at various places, forming tubular supporting veins. Unlike the wings of an airplane, the wings of insects are flat plates, and lift is obtained by changing the angle at which the front margin of the wing meets the oncoming air stream. The evolution of flight is one of several adaptations that have enabled insects to become the most diverse and populous group of terrestrial animals.
A burrowing habit has evolved in some insects, such as [URL="http://www.cssforum.com.pk/EBchecked/topic/388077/mole-cricket"][U][COLOR=#0000ff]mole crickets[/COLOR][/U][/URL] and ants, but the largest burrowers are crustaceans. Mole crabs and box crabs are rapid burrowers in soft marine sands, and various species of [URL="http://www.cssforum.com.pk/EBchecked/topic/362964/mantis-shrimp"][U][COLOR=#0000ff]mantis shrimps[/COLOR][/U][/URL], [URL="http://www.cssforum.com.pk/EBchecked/topic/232813/ghost-shrimp"][U][COLOR=#0000ff]mud shrimps[/COLOR][/U][/URL], and snapping shrimps create elaborate burrows below the bottom surface. Crustaceans also include the largest number of arthropod tube dwellers, surpassed only by certain [URL="http://www.cssforum.com.pk/EBchecked/topic/468364/polychaete"][U][COLOR=#0000ff]marine worms[/COLOR][/U][/URL] (polychaetes). Most of the tube-dwelling crustaceans are amphipods. Their tubes are usually composed of sand or mud particles secreted together and attached to bottom objects; there are, however, some amphipods that carry their tubes with them like a portable house.

[COLOR=darkred][B]Reference:Britannica.[/B][/COLOR]
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Phylum Echinodermata
 

[B]Phylum Echinodermata[/B]


[SIZE=4][LEFT][B]Introduction[/B][/LEFT]


[/SIZE][LEFT]Echinoderms form a well-defined and highly-derived clade of metazoans. They have attracted much attention due to their extensive fossil record, ecological importance in the marine realm, intriguing adult morphology, unusual biomechanical properties, and experimentally manipulable embryos. The approximately 7,000 species of extant echinoderms fall into five well-defined clades: Crinoidea (sea lilies and feather stars), Ophiuroidea (basket stars and brittle stars), Asteroidea (starfishes), Echinoidea (sea urchins, sand dollars, and sea biscuits), and Holothuroidea (sea cucumbers). The phylogenetic position of the Concentricycloidea (sea daisies; 2 species), remains controversial (Baker et al. 1986; Smith 1988b; Pearse and Pearse 1994; Mooi et al. 1997).
Approximately 13,000 echinoderm species are known from the fossil record. All Mesozoic and Cenozoic forms clearly fall into the five extant clades, but the Paleozoic record contains numerous distinct and often bizarre forms that have been placed into approximately 15 additional classes. Phylogenetic relationships, and in some cases status as monophyletic groups, remains unclear for the extinct classes. Unquestionable echinoderms first appear in the fossil record during the mid-Cambrian. Arkarua, a possible echinoderm, has been described from the Vendian (latest Proterozoic) (Gehling 1987).
[/LEFT]


[B][SIZE=4][LEFT][B]Characteristics[/B][/LEFT]


[/SIZE][LEFT][B]Synapomorphies of the Echinodermata[/B][/LEFT]


[/B][LEFT]Echinoderms are among the most distinctive of all animal phyla. Inclusion in the phylum is readily diagnosable on basis of the four synapomorphies below. Most of these features are present, or can be inferred, even in the earliest fossils. Together, these synapomorphies define much of what makes the functional biology of echinoderms distinctive from that of other metazoans.
[B]Calcitic skeleton composed of many ossicles. [/B]

The biomineral matrix of echinoderm skeletons is composed of calcium carbonate and several proteins. The calcite is deposited as numerous tiny crystals, but all of them lie on the same crystal axis within an ossicle. For this reason, ossicles are birefringent under polarizing light. Ossicles are not solid, but have a sponge-like microstructure called stereom that is unique to the phylum. Embryologically, echinoderm ossicles are a true endoskeleton, since they are produced by mesenchymal cells and are usually covered by epidermis. Functionally, however, the majority of ossicles act more like an exoskeleton, lying just under the epidermis and enclosing most other tissues in a flexible but tough covering.

[B]Water vascular system. [/B]

The water vascular system performs many important functions in echinoderms, including locomotion, respiration, and feeding; in addition, most sensory neurons are located at the termini of podia (tubefeet) which are part of this organ system. The water vascular system may have evolved from simple tentacular systems similar to those in other deuterostome phyla, such as the tentacles of pterobranch hemichordates. However, there are many derived features of the water vascular system in echinoderms, including: an embryological origin from left mesocoel, podia arranged along branches (ambulacra), and a central circumesophageal ring.

[B]Mutable collagenous tissue. [/B]

The ossicles of echinoderms are connected by ligaments composed predominantly of collagen. The material properties of this connective tissue are mutable on short timescales, under neuronal control. Ligaments are normally "locked" (rigid), but can be temporarily "unlocked" (loosened). This provides some interesting mechanical advantages, including the ability to maintain a variety of postures with no muscular effort. In holothuroids, which contain only microscopic ossicles, the entire body wall contains mutable collagenous tissue.

[B]Pentaradial body organization in adults. [/B]

The adults of all extant echinoderms are radially symmetrical. A superficial bilateral organization has evolved twice, in irregular echinoids and holothuroids, but is based on an underlying five-fold organization of skeleton and most organ systems, and is clearly secondary. Higher order radial symmetry (e.g., seven-fold or nine-fold) has evolved on several occasions, and is also clearly a secondary modification. The evolutionary origins of five-fold symmetry remain obscure. Some early Paleozoic echinoderms are not radially symmetrical (e.g., carpoids and helicoplacoids), while a possible echinoderm from the Vendian (Arkarua) has five-fold radial body organization.
[/LEFT]


[B][LEFT][B]Plesiomorphies and other features[/B]
[B]Marine habit.[/B]
[/LEFT]
[/B][LEFT]
All extant echinoderms live in the ocean, and there is no fossil evidence of any exception to this. Within the marine realm, echinoderms occupy nearly all habitats, where they often constitute a major proportion of the biomass.

[B]Pelago-benthic life cycle. [/B]
With rare exception, echinoderms are gonochoric (separate sexes) with no overt sexual dimorphism. Fertilization is almost always external. Ancestrally (and still, typically), the life cycle is complex, with a free-living larva that is planktotrophic (grazes on unicellular algae). Larvae are plesiomorphically bilaterally symmetrical, have a recurved gut and transparent ectoderm, and feed by upstream particle capture using the ciliated band. Metamorphosis is typically radical and occurs during settlement onto the benthos.

[/LEFT]


[B][LEFT][B]Coelomate[/B].[/LEFT]
[/B][LEFT]
Echinoderms form their coeloms as outpocketings from the archenteron (embryonic gut), a process called enterocoely. In most species, the coeloms are trimerous, and initially bilaterally symmetrical. The fates of the various coelomic compartments vary among echinoderms, but some features seem broadly similar and may reflect a common evolutionary origin deep within the phylum: left mesocoel gives rise to most or all of the water vascular system, and one or both somatocoels form the lining of the body cavity.

[/LEFT]


[B][LEFT][B]Deuterostome[/B].[/LEFT]
[/B][LEFT]
Like some related phyla, the blastopore (site where gastrulation begins) in echinoderm embryos becomes the larval anus; the larval mouth is a secondary opening. In some extant forms, the larval mouth is preserved as the adult mouth, while in others the entire digestive system is re-plumbed during metamorphosis and a new mouth and anus form.

[B]Simple hemal/excretory system. [/B]
The hemal and excretory systems of echinoderms are linked into what Nielsen (1996) calls the "axial complex". This organ system shows similarities, and may be homologous, to those of other deuterostome phyla. In echinoderms, it is composed of: a thickened vessel (the "heart") lacking an endothelium and surrounded by a pericardium; a region where ultrafiltration occurs via podocytes; a closed circulatory system; and an opening to the external environment called the madreporite.

[B]Decentralized nervous system. [/B]
The arrangment of the central nervous sytem of echinoderms is quite different from that in other deuterostomes. Radial nerves run under each of the ambulacra, and contain the cell bodies of almost all motor neurons and interneurons. A central nerve ring surrounds the gut, and is composed primarily of fiber tracks connecting the radial nerves. No known echinoderm contains anything that could be called a brain, although ganglia are present along the radial nerves in some echinoderms. Unlike most bilaterian phyla, echinoderms lack any trace of cephalization, and have no specialized sense organs. Sensory neurons are located primarily within the ectoderm of podia, and send axons to the radial nerves.
[/LEFT]

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Phylum Echinodermata
 

Phylum Echinodermata

The following link is about Echinodermata,characters,classes,water vascular system.

[URL="http://faculty.evansville.edu/de3/b10802/PPoint/Echinodermata/11-Echinodermata.PPT"]Click Here[/URL]

Another link to ppt presentation about Echinodermata.

[URL="http://cfcc.edu/rogers/courses/msc174/Lectures/Phylum%20Echinodermata.ppt"]Check this [/URL]

regards

Phylum Echinodermata
 

Phylum Echinodermata

[B][SIZE=4]Importance »[/SIZE][/B][SIZE=5]
[/SIZE][URL="http://www.britannica.com/EBchecked/topic/31082/aquatic-ecosystem"][B][SIZE=4][COLOR=black]Role in nature[/COLOR][/SIZE][/B][/URL][SIZE=4]
[/SIZE]Echinoderms are efficient scavengers of decaying matter on the seafloor, and they prey upon a variety of small organisms, thereby helping to regulate their numbers. When present in large numbers, sea urchins can devastate sea-grass beds in the tropics, adversely affecting the organisms dwelling within. Sea urchins that burrow into rocks and along a shore can accelerate the erosion of shorelines. Other tropical species of sea urchins, however, control the growth of seaweeds in coral reefs, thereby permitting the corals to flourish. Removal of the sea urchins results in the overgrowth of seaweeds and the devastation of the coral reef habitat. Echinoderms can alter the structure of seafloor sediments in a variety of ways. Many sea cucumbers feed by swallowing large quantities of sediment, extracting organic matter as the sediment passes through the intestine, and ejecting the remainder. Large populations of sea cucumbers in an area can turn over vast quantities of surface sediments and can greatly alter the physical and chemical composition of the sediments. Burrowing starfish, sand dollars, and [URL="http://www.britannica.com/EBchecked/topic/258504/heart-urchin"][U][COLOR=#0000ff]heart urchins[/COLOR][/U][/URL] disturb surface and subsurface sediments, sometimes to depths of 30 centimetres or more. In addition, echinoderms produce vast numbers of larvae that provide food for other planktonic organisms.

[B][SIZE=4]Relation to human life[/SIZE][/B][SIZE=4]
[/SIZE]Some of the larger species of tropical sea cucumbers, known commercially as trepang or [URL="http://www.britannica.com/EBchecked/topic/57879/beche-de-mer"][U][COLOR=#0000ff]bêche-de-mer[/COLOR][/U][/URL], are dried and used in soups, particularly in Asia. Raw or cooked mature [URL="http://www.britannica.com/EBchecked/topic/498606/reproductive-system"][U][COLOR=#0000ff]sex organs[/COLOR][/U][/URL], or [URL="http://www.britannica.com/EBchecked/topic/238252/gonad"][U][COLOR=#0000ff]gonads[/COLOR][/U][/URL], of sea urchins are regarded as a delicacy in some parts of the world, including parts of Europe, the [URL="http://www.britannica.com/EBchecked/topic/372688/Mediterranean-region"][U][COLOR=#0000ff]Mediterranean region[/COLOR][/U][/URL], Japan, and Chile. Some tropical holothurians produce a toxin, known as [URL="http://www.britannica.com/EBchecked/topic/269649/holothurin"][U][COLOR=#0000ff]holothurin[/COLOR][/U][/URL], which is lethal to many kinds of animals; Pacific islanders kill fish by poisoning waters with holothurian body tissues that release the toxin. Holothurin does not appear to harm human beings; in fact, the toxin has been found to reduce the rate of growth of certain types of tumours and thus may have medical significance. The eggs and spermatozoa of echinoderms, particularly those of sea urchins and starfishes, are easily obtained and have been used to conduct research in developmental biology. Indeed, echinoids have been collected in such large numbers that they have become rare or have disappeared altogether from the vicinity of several marine biologic laboratories.
Starfishes that prey upon commercially usable mollusks, such as oysters, have caused extensive destruction of oyster beds. Sea urchins along the California coast have interfered with the regrowth of commercial species of seaweed by eating the young plants before they could become firmly established. The crown-of-thorns starfish, which feeds on living polyps of reef corals, has caused extensive short-term damage to coral reefs in some parts of the Pacific and Indian oceans.


[COLOR=darkolivegreen][B]Reference:Britannica[/B][/COLOR]

Phylum Echinodermata
 

[B]Phylum Echinodermata[/B]

[B]Water Vascular System.[/B]

Enchinodermata are phylum of marine animals found in the ocean at all depths. The echonodermata has six classes which are Asteroidea example starfish, Concentricycloipea example sea daises, Crinoidea example feather stars, Echonoidea example sea urchin, Holuthuroidea example sea cucumbers and Ophiuroidea example brittle stars. The phylum is containing approximately six thousands species and constitute the group of deuterostome invertebrates. Enchinodermata are characterizes by a unique vascular system.

The vascular system can be defined as a hydraulically controlled system consisting of a circumoral ring around the esophagus with connecting radial canals each leading to an ambulacrum. "The vascular system can be closed or opened. Crinoids have an open vascular system. The water vascular system is used by echinoderm such as sea stars and sea urchins. They may be evolved from tentacular system similar to those of deuterostone phyla such as tentacle pterebranch hemichordates". However, there are different kinds of derived features of the vascular system, these include an embryological origin from left mesocoel, podia arranged along branches (ambulacra), and a central curcumesophagel ring .

The characteristics of vascular system do differ according to class. Crinoid has madreporite with multiple pores and madreporite may be replaced by minute scattered openings called hydropores. It has no polian vesicles, tube feet suckers and ampullae on podia. "Podia penetration is between plate and podia spacing is stumble . In asteroid madreporite of vascular system has aboral" . Some asteroid have tube feet sucker whereas others do not have. Podia penetration is between plates. It has ampullae on podia.

In Ophiuroid, madreporite of vascular system has oral. It has a polian vesicles Ophiuroid does not tube feet sucker. Podia penetrations are found between plates. Podia spacing is paired. It does not have ampullae on podia. In Echinoid madreporite has aboral. It has polian vesicles, tube feet sucker may be present or absent. "Podia penetration is paired through plates. Podia spacing is stagger. It has ampullae on podia. In Holothuroid madreporite are internal" . It has polian vesicles. Tube feet sucker a may be present or absent. Podia penetration between suckers may be present or absent. Podia penetrations are found between plates. Podia spacing is stagger. It has ampullae on podia .


Vascular systems network canals to create hydrostatic pressure, to help the starfish to move. Water enters through sieve plate or madreporite on aboral surface into a short stone canal. Stone canal connects to a circular canal around the mouth called the ring canal. "Five radial canals carry water to hundreds of paired tube feet. Bulb-like sacs or ampulla’s on the upper end of each tube foot contract and form suction to help move, attach or open bivalves’ mollusk shells and create suction to pull valves apart slightly" . Starfish exerts its stomach through its mouth and inserts into prey. Stomach secretes enzymes to partially digest bivalve then stomach withdrawn and digestion completed inside the starfish .

"The vascular systems perform different functions in echinoderm; these include locomotion, respiration, and feeding" . Most of the sensory neurons are located at the podia which are also part of this organ. Most oxygen enters starfish through diffusion into the tube feet. "This water vascular system can be used as a source of oxygen for respiration" . Many sea cucumbers also have a complex respiratory tree. The surface of many echinoderms is perforated by extensions of the body wall. Through these thin membranes of the body wall respiration can take place.

The vascular systems are very essential to echonodermata. They are responsible for digestion, locomotion and respiration. Even though echonodermata do differ with some characteristics but they all have vascular system. The vascular system is either open or close.

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Phylum Echinodermata
 

[B]Phylum Echinodermata[/B]

[B]Echinodermal Larvae[/B]

The echinoderms include the familiar sea stars, brittle stars, and sea urchins, as well as the more enigmatic sea cucumbers and crinoids. All species are marine, and most live in benthic habitats. Many of the animals have a planktonic larval stage, some of which may live in the plankton for months before settling as adults. Echinoid larvae are among the smaller [URL="http://www.cssforum.com.pk/plintroduction/plintroduction.htm/lsize"][B][U][COLOR=#0000ff]meroplankton[/COLOR][/U][/B][/URL], approximately 0.01-0.03 mm in length, and are relatively rare to find in the plankton.

[B]Asteroids[/B]
Sea stars, or asteroids, develop through several larval stages, including this [B]brachiolaria[/B] larva of the ochre seastar, [I]Pisaster ochraceous[/I]. The larva uses its ciliated arms to sweep food into its mouth as it glides through the water column. The arms can also be used to supplement the larva's cilia-drive locomotion. Each arm has a glandular tip, with which the larva attaches itself to the substratum as it settles. The animal is then able to metamorphose into the familiar five-armed adult form.
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[B][U]Ophiuroids[/U][/B]

The brittle stars, or ophioroids, have a distinctive larval form known as the [B]ophiopluteus[/B]. Like all echinoderm larvae, the ophiopluteus uses ciliated bands to feed on particles suspended in the water column. Brittle star larvae may be found in the plankton throughout the year in this region, and are thought to spend several weeks in the plankton before settling as juveniles.
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[B][U]Echinoids[/U][/B]
The [B]echinopluteus[/B] larva (1 mm wide) of the green sea urchin uses its extensive ciliated band for swimming and suspension feeding. As the larva develops, it will add arms, changing from the four-armed animal shown here to a six and then eight-armed individual. The body form changes dramatically with metamorphosis. Many of the larval structures used during planktonic life are lost, to be replaced by appendages adapted to the adult's benthic lifestyle.
.



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Young sand dollars have a pluteus larva as well. This larva captures food along a ciliated band that loops around the larval arms. Food is then transfered by cilia to the mouth. The body shape slows the natural tendency of the larva to sink, enabling it to stay in the food-rich upper layers of the coastal ocean. Echinoids have separate sexes and reproduce by free spawning gametes into open water.




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[B][U]Holothurians[/U][/B]
[SIZE=3][SIZE=2]Sea cucumbers, such as this larva of [I]Parastichopus californicus[/I], begin life as a feeding planktonic larvae in the early summer. They swim in a gliding motion, using a ciliated band, similarly to other echinoderm larva. The larvae feed in the plankton for one to two months, after which they settle subtidally, in areas with high current flow.[/SIZE] [/SIZE]
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Phylum Echinodermata
 

[B]Phylum Echinodermata[/B]


[B]Gallery of echinodermal larvae with their description.[/B]

[B][URL="http://www.microscopy-uk.org.uk/mag/artjul00/echino.html"]check this[/URL][/B]

[B]regards[/B]

Chordates
 

[CENTER][B][SIZE=3]Chordates[/SIZE][/B][/CENTER]
[B]Phylum Chordata[/B]

[SIZE=4][SIZE=2]Although not the largest phylum, Chordata contains the most familiar species, including humans. All chordates have several things in common that occur at some stage of development. They have pharyngeal slits, which are openings that connect the inside of the throat to the outside of the neck. These are often used as gills. Their main feature, what they are named after, is the notochord, which is a rod that supports the nerve cord. The nerve cord is also present in all species. This is a bundle of nerve fibers which connect the brain with the muscles and organs, and is through which messages from the brain are sent. A tail is also present, which extends past the anal opening. In most species these features disappear with age. For example, the pharyngeal slits are only present in the human fetus. There are approx 44 000 species in 3 subphylums: [/SIZE]

[B]1. Cephalochordata[/B]

This is a small, very unusual subphylum of creatures commonly called lancelets or amphioxus. These animals are fish-like in appearance, but are invertebrates with a notochord, and a nerve cord right above it. They lack bones, a brain, eyes, and most other organs associated with the brain. There are 25 species, and they do not seem to be placed in any class. However, some experts do not call this a subphylum and they place it in a class of the same name:
Cephalochordata (lancelets)

2[B]. Tunicata (Urochordata)[/B]

This is a large subphylum of unusual invertebrates that do not look like anything much more than a strange underwater worm or mushroom. They start off life as tadpole-like larvae with notochords and all the rest. This stage lasts only a short time, after which they anchor to the seabed and live a sedentary life. They completely change shape at this point, and it is hard to believe that they are in the same phylum as humans. The adults lack the notochord but do keep the pharyngeal slits. They have a highly-developed internal structure, with a heart and other organs. Tunicates are named for their protective covering, known as a tunic. This tunic is made up of cellulose, which is very rare in animals. There are 2000 species in 4 classes:
Appendicularia or Larvacea (free swimming tunicates)
Ascidiaceae (sea squirts)
Sorberacea (benthic tunicates)
Thaliacea (salps)

3. [B]Vertebrata[/B]

This is the largest subphylum with the more well-known animals, including humans, reptiles, fish, etc. Every animal with a backbone is present in this subphylum. The notochord is developed at an early age, and is replaced with vertebrate. All vertebrates have a skeleton of either bone or cartilage. Their brain is protected by a boney cranium, and consists of three parts. They all have well-developed hearts with 2-4 chambers and have a closed circulatory system. There are 41700 species in 8 classes:

Amphibia (frogs, salamanders)
Aves (birds)
Cephalaspidomorphi (Lampreys)
Chondrichthyes (cartilaginous fish)
Mammalia (mammals)
Myxini (Hagfish)
Osteichthyes (bony fish)
Reptilia (crocodiles, snakes, turtles)


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Chordates
 

[CENTER][B][SIZE=3]Chordate evolution[/SIZE][/B]
[youtube]6LJewU1PhQo[/youtube]


[youtube]9CBAN3f6Qhg[/youtube]

[COLOR=white]................[/COLOR][/CENTER]

thanks!
 

afrms : you are indeed doing a selfless and virtuous job of posting zoology notes from different sources. i gained much from your notes for my zoology papers 2009. There was a question on placenta. the topic which you posted at the outset of your notes. there was question on canal system, on coral reef, conjugation. i have found your proposed notes quite relevant. May God bless you for your timely effort. it is indeed a hard job which you are doing.
thanks for being helping

regards

Chordates
 

Phylum Chordata

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[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/Image19.gif[/IMG]


[IMG]http://i723.photobucket.com/albums/ww237/alphamalik/tree4_large.jpg[/IMG]
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[LEFT][B]The following is a link to chordate ppt presentation[/B][/LEFT]

[URL="http://faculty.evansville.edu/de3/b10802/PPoint/Chordata/sld001.htm"][B]Click here[/B][/URL]

Parasites And Parasitism
 

[FONT=Times New Roman][B][FONT=Verdana][SIZE=3]PARASITES AND PARASITISM[/SIZE][/FONT][/B][/FONT]

[FONT=Times New Roman][FONT=Times New Roman][SIZE=3]Parasites are often described as occupying the third great environment, -aquatic, -terrestrial -parasitic, the body of another organism. So perhaps the first question about parasitism is how successful is it as a way of life? To some extent this depends on how you define parasitism, but all the major animal groups, except possibly the vertebrates (although some deep sea fish have parasitic males, and lampreys may be considered parasitic) have parasitic members, there are even parasitic cnidarians. It has been estimated that more than 50% of all known species are parasitic at some stage of their life cycle. Just as important as how many species of parasite are there, is how many plants and animals are themselves parasitized as individuals and the answer must approach 100%.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Parasitism is a form of animal association, but can we define it more rigorously, how does our concept of parasitism differ from other associations, say prey/predator interactions.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Start with some definitions:[/SIZE][/FONT]
[SIZE=3][FONT=Times New Roman][B]Symbiosis[/B] means literally living together. Coined in 1876 by DeBary, to describe two species of organisms that lived together, with no implication regarding the length or outcome of the association. So symbiosis as originally conceived covered a range of intimate interactions between organisms-the most common ones being [I]mutualism[/I], [I]commensalism[/I] and [I]parasitism[/I]. So symbiosis was an overarching term, there has been a move to restrict symbiosis to a particular sort of association, where both partners are seen to benefit, but most modern literature has now returned to using symbiosis as an umbrella term for organisms that live together. Using this concept then:[/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Mutualism,[/B] highly interdependent association, to the extent that the two associates cannot survive without one another. Example flagellate protozoa/termites or ruminants and rumen protozoa. In each case the protozoa have the enzymes that convert cellulose to glucose, the host provides a low redox potential environment. Two way benefit, no harm = Symbiosis of some authors.[/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Commensalism [/B]involves one way benefit, but as in the case of mutalism no harm is exerted in either direction. Clown Fish and sea anemone. The sea anemone provides protection against predators, the clown fish is highly evolved to survive the cnidarian nematocysts. Its external mucus layer is much thicker than that of related species and the chemical composition of clown fish mucus is different. Clown fish mucus consists largely of neutral polysaccharides and lacks the acidic sialic acid groups which trigger nematocyst discharge (although this makes the fish more susceptible to fungal infection). Commensalism usually involves a feeding relationship and generally does not involve metabolic independence. E.g. polychaete and hermit crabs.[/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Parasitism.[/B] Classical definition - intimate relationship between two organisms in which one (the parasite) lives on, off or at the expense of the other (host). This implies that one of the partners benefits, the other is harmed. One problem with this simple definition is that harm is a very difficult thing to quantify, the same problem applies to the definition of mutualism and commensalism. In animal associations it is often assumed that one organism is benefiting or not without any real evidence.[/FONT][/SIZE]
[FONT=Times New Roman][SIZE=3]Rats, infected with the intermediate stages of a tapeworm called [I]Spirometra[/I] grow larger than uninfected rats. The tapeworm larva produces an analogue of vertebrate growth hormone-is the growth boost harming the host or is it good for the host? Similarly many molluscs, when infected with the intermediate stages of Digenetic flukes develop thicker, heavier shells, which could be deemed an advantage. On closer investigation some of the classic examples of mutualism seem more like an armed standoff than mutual benefit. Given the right conditions many organisms which harbour symbiotic algae - like for example green hydra will digest the algae and carry on quite happily. Many trees have associated with their roots fungal mycorrhiza. The fungi get organic nutrients from the plant via the phloem, and in nutrient poor soil the trees seem to benefit by increased nutrient uptake, particularly phosphate by the fungus. But if soil nutrient levels are good it appears much more like a parasitic invasion by the fungus with the tree attempting to wall off infected cells. Depending on external conditions, the association switches between mutualism and parasitism.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]So the simple definition of parasitism where one of the partners benefits and the other is harmed is not really adequate and also it does not really differentiate between a parasite and a predator or a parasite and a micro-predator. e.g. mosquito.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]In order to develop the concept of the [I]host-parasite relationship[/I] different people have added to the classical definition that 'the parasite is metabolically or physiologically dependent on the host'. Or that there is 'genetic complementation between the parasite and its host'. That is that the parasite has lost the genetic ability to make certain vital metabolic intermediates and has to rely on the hosts genome for this or it may have to rely on the host genome to provide vital developmental stimuli. In extreme cases part of the parasites genome may have been lost and become integrated into that of the host.[/SIZE][/FONT]
[B][FONT=Times New Roman][SIZE=3]A more recent definition or perhaps description of parasitism is that given by Crofton.[/SIZE][/FONT][/B]
[FONT=Times New Roman][SIZE=3]Ecological relationship between two different organisms, one designated the parasite, the other the host. [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]The parasite is physiologically or metabolically dependent upon its host. [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Heavily infected hosts will be killed by their parasites. [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]The reproductive potential of the parasite exceeds that of their hosts. [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]There is an overdispersed frequency distribution of parasites within the host population. That is, the parasite population is not evenly distributed amongst the host population nor is it randomly distributed but clumped, so some hosts have a lot of parasites, most have very few. [/SIZE][/FONT]
[B][FONT=Times New Roman][SIZE=3]Let's look at some of these points in more detail.[/SIZE][/FONT][/B]
[FONT=Times New Roman][SIZE=3]Parasitism is, like most other animal associations defined in terms of two different species, who form a regular association, although this seems sensible, and it does exclude consideration of the mammalian foetus as being parasitic upon its mother, there are some very interesting immunological parallels between the mechanisms the foetus uses to avoid being rejected by the immune response of its mother and the ways in which the parasites of mammals seek to avoid their hosts immune response. Also in a number of deep-sea fish, the males are tiny and become parasitic on the females, nothing is known about the physiological basis of this.

Sometimes people add that the parasite is the smaller and the host the larger of the two organisms. This is generally true, although in some fish parasites, the plerocercoid stage of the tapeworm that lives in the body cavity of the fish can be heavier than the host. Size to a certain extent distinguishes parasites from predators, as predators are usually, but not always, larger than their prey. Any one parasite usually only infect a few different species of host during its life cycle (their are a few 4 host life cycles, no 5 host life cycles), this is in contrast to predators which usually eat a range of different prey species.[/SIZE][/FONT]
[FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][FONT=Times New Roman][SIZE=3]Physiological or metabolic dependence of the parasite on its host is central to most attempts to define parasitism. It does not of course distinguish parasitism from mutualism.

[/SIZE][/FONT]
[FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][FONT=Times New Roman][SIZE=3]Heavily infected hosts are killed, this introduces the concept of the cost to the host population of parasitism.

[/SIZE][/FONT]
[FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][FONT=Times New Roman][SIZE=3]Parasites have a higher reproductive potential than their hosts, this distinguishes parasites from predators. Predators have a lower reproductive potential than their prey, and are less numerous, whilst parasites have a higher reproductive potential and are more numerous.

[/SIZE][/FONT]
[FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][FONT=Times New Roman][SIZE=3]Overdispersed or clumped frequency distribution is important in that it is something that can be quantified and we shall return to it when we look at parasite populations. This frequency distribution helps to exclude micro-predators from our definition. [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]No definition of parasitism is ever going to be completely satisfactory if we try hard enough we can always find an exception and there are always going to be grey areas where parasitism, mutualism and commensalism overlap.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]But it is a mistake to think of animal associations forming a linear sequence with commensalism leading to parasitism leading to mutualism. Each association is independent with different endpoints. People have argued that for parasitism to evolve the two species must have been living in close association, possibly in a prey-predator relationship. In the early stages of association the host and parasite are not going to be well adapted to each other so you might expect recently evolved parasites to be virulent and cause a lot of host damage, but gradually the host would evolve to be more tolerant of the parasite and so you might expect a series.[/SIZE][/FONT]
[SIZE=3][B][FONT=Times New Roman]Acute --[/FONT][/B][B][FONT=Symbol]>[/FONT][FONT=Times New Roman] Chronic --[/FONT][/B][B][FONT=Symbol]>[/FONT][FONT=Times New Roman] Mutualism?[/FONT][/B][/SIZE]
[FONT=Times New Roman][SIZE=3]Equally you can argue that a parasite that elicits a very strong host response is not likely to get established in the first place and it is much more likely in the early stages of the evolution of a parasitic association that the parasite would cause little if any host response and that virulence is something that evolved later. It is just as likely that a mutualistic association will evolve into parasitism as a commensal relationship and although some parasitic relationships may evolve into mutualistic ones, they may equally well not.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Once a parasitic association has evolved, say a nematode in a fish, the parasite could radiate within the body of the host to occupy new niches, so you could get new species of parasite evolving from the original progenitor. The concept of the parasite niche is one that has undergone quite a lot of revision lately. The original concept was that the host could be divided up into a large number of separate niches, each one being a separate entity that might or might not be occupied by a parasite. In the same way in free-living animals you might describe a niche for a large carnivore which might be filled with a bear in one ecosystem or a tiger in another. They occupy a particular niche, but even if they are not there, the niche still exists.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]A more compelling concept is that the parasite creates its own niche. It is the parasite that determines the niche not the host. A particular parasite may occupy a specific site and utilize certain host resources and this defines its niche. So a niche is a description of the parasites requirements, not of host attributes. One thing parasite ecologists are agreed on is that current parasites have not exhausted the number of possible host niches. So there is still plenty of room left for new parasite species.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Another way of course that parasites can be acquired is by host capture, when the parasite transfers from one host to another one in the same ecosystem. Since parasites can effect the reproductive success of their hosts, either by removing resources or by ultimately killing the host, parasites can exert an influence on host evolution. We will talk about the influence of hosts on parasite evolution in a later lecture. So parasites can influence host evolution.[/SIZE][/FONT]
[SIZE=3][FONT=Times New Roman][B]Macroevolution:[/B] Animals show a high degree of protein polymorphism. That is, if you take virtually any protein you find that there are a large number of different isoforms. These isoforms differ by perhaps just a few amino acid residues, different individuals have different isoforms, but the isoforms seem to be biologically identical. Where is the driving force coming from to maintain this high degree of protein heterogeneity? One suggestion is that most of this polymorphism represents neutral mutations. The proteins biological function is not altered by these mutations so they are neither selected for nor selected against. An alternative explanation is that protein polymorphism is a host response to parasitism. If every individual had identical proteins, a parasite could evolve a surface coat that was identical to one of these proteins and so hosts would not recognize the parasite as foreign and would not mount any defensive immune attack. Host polymorphism prevents the parasite using molecular mimicry. The main process which maintains polymorphism in animals is of course sexual reproduction, so parasites may be one of the driving influences behind the evolution of sex.[/FONT][/SIZE]
[SIZE=3][FONT=Times New Roman][B]Micro-evolution[/B]: Parasites may also have a role in sexual selection. In many bird species the males have brightly coloured plumage and females select males with the biggest and brightest feathers. To grow this plumage is a considerable metabolic investment for males and may also make them more vulnerable to predation. One explanation is that it is a red queen effect, females prefer males with big tails so males evolve bigger and bigger tails. Females mate with males with big tails so their own sons will have big tails and so be more successful in their turn.[/FONT][/SIZE]
[FONT=Times New Roman][SIZE=3]A second explanation is that females use the condition of the male plumage to inform her of the physiological fitness of the male. Only healthy birds can grow a big tail, and female birds because they invest so much in reproduction want to make sure that they mate with only the fittest males. There is some experimental evidence that heavily parasitized individuals cannot grow the requisite plumage, so females can use the state of the male plumage to ensure that they mate with parasite free-males. A similar argument can be put forward for birds that have an energetic courting display where the males jump up and down (lek system).[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]There is also some evidence in mice that females discriminate against parasitized males, and that the cue may be smell.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]So parasites then may influence the evolution of their hosts.[/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]Useful definitions:[/SIZE][/FONT]
[SIZE=3][B]Ectoparasite[/B][/SIZE]
[FONT=Times New Roman][SIZE=3]lives on surface. [/SIZE][/FONT]
[SIZE=3][B]Endoparasite[/B][/SIZE]
[FONT=Times New Roman][SIZE=3]live inside host. [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3][B]Mesoparasite[/B][I]-[/I] [/SIZE][/FONT]
[FONT=Times New Roman][SIZE=3]penetrates external openings - buccal cavity, cloaca, external ear. [/SIZE][/FONT]
[SIZE=3][B]Definitive host- [/B][/SIZE]

[FONT=Times New Roman][SIZE=3]where parasite reaches sexual maturity. [/SIZE][/FONT]
[SIZE=3][B]Intermediate host- [/B][/SIZE]

[FONT=Times New Roman][SIZE=3]required by parasite to complete its life cycle. Usually undergoes morphological or physiological change in it. [/SIZE][/FONT]
[SIZE=3][B]Paratenic host- [/B][/SIZE]

[FONT=Times New Roman][SIZE=3]optional transport host - no detectable morphological change in parasite [/SIZE][/FONT]
[SIZE=3][B]Vector[/B]- [/SIZE]

[FONT=Times New Roman][SIZE=3]host that plays an active role in transmission, can be a definitive or an intermediate host. [/SIZE][/FONT]

[/FONT]

Invertebrate Short Notes
 

[CENTER][B][SIZE=3]Flame cell[/SIZE][/B][/CENTER]


[COLOR=black][FONT=Times New Roman][SIZE=3]A [B]flame cell[/B] is a specialized excretory cell found in most "lower" freshwater [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Invertebrates"][COLOR=black][FONT=Times New Roman][SIZE=3]invertebrates[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], including [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Nematode"][COLOR=black][FONT=Times New Roman][SIZE=3]Nematode[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Platyhelminthes"][COLOR=black][FONT=Times New Roman][SIZE=3]Platyhelminthes[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] (except the tubellarian [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Order_(biology)"][COLOR=black][FONT=Times New Roman][SIZE=3]order[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] [I]Acoela[/I]), flatworms, [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Rotifers"][COLOR=black][FONT=Times New Roman][SIZE=3]rotifers[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and [/SIZE][/FONT][URL="http://www.cssforum.com.pk/w/index.php?title=Nemerteans&action=edit&redlink=1"][COLOR=black][FONT=Times New Roman][SIZE=3]nemerteans[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]; these are the simplest animals to have a dedicated [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Excretory_system"][COLOR=black][FONT=Times New Roman][SIZE=3]excretory system[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. Flame cells function like a [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Kidney"][COLOR=black][FONT=Times New Roman][SIZE=3]kidney[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], removing waste materials. Bundles of flame cells are called [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Protonephridia"][COLOR=black][FONT=Times New Roman][SIZE=3]protonephridia[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman].[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]The flame cell has a [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Nucleus_(biology)"][COLOR=black][FONT=Times New Roman][SIZE=3]nucleated[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] cell body, with a "cup-shaped" projection, with [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Flagella"][COLOR=black][FONT=Times New Roman][SIZE=3]flagella[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] covering the inner surface of the cup. The beating of these flagella resemble a flame, giving the cell its name. The cup is attached to a [B]tube cell[/B]. The inner surface of the tube cell is coated in [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Flagella"][COLOR=black][FONT=Times New Roman][SIZE=3]flagella[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. The beating of the cilia and flagella help move liquid through the tube cell. The tube opens externally through a [I]nephropore[/I], or, in the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Trematoda"][COLOR=black][FONT=Times New Roman][SIZE=3]trematoda[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], into an excretory [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Urinary_bladder"][COLOR=black][FONT=Times New Roman][SIZE=3]bladder[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. The function of these cells is to regulate the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Osmotic_pressure"][COLOR=black][FONT=Times New Roman][SIZE=3]osmotic pressure[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] of the worm, and maintain its ionic balance. [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Microvilli"][COLOR=black][FONT=Times New Roman][SIZE=3]Microvilli[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] in the tube cell may be used to reabsorb some [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Ion"][COLOR=black][FONT=Times New Roman][SIZE=3]ions[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3].[/SIZE][/FONT][/COLOR]




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[COLOR=black][B][SIZE=3]Tube Feet[/SIZE][/B][/COLOR]

[COLOR=black][COLOR=black][FONT=Times New Roman][SIZE=3]Tube feet are the many small tubular projections found most famously on the oral face of a [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Sea_star"][COLOR=black][FONT=Times New Roman][SIZE=3]sea star[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]'s arms, but are characteristic of the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Water_vascular_system"][COLOR=black][FONT=Times New Roman][SIZE=3]water vascular system[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] of the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Echinoderm"][COLOR=black][FONT=Times New Roman][SIZE=3]echinoderm[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] phylum which also includes [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Sea_urchin"][COLOR=black][FONT=Times New Roman][SIZE=3]sea urchins[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Sand_dollar"][COLOR=black][FONT=Times New Roman][SIZE=3]sand dollars[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Sea_cucumber"][COLOR=black][FONT=Times New Roman][SIZE=3]sea cucumbers[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] and many other sea creatures.[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]Tube feet function in locomotion and feeding. The tube feet in a sea star are arranged in grooves along the arms. They operate through [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Hydraulics"][COLOR=black][FONT=Times New Roman][SIZE=3]hydraulic pressure[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]. They are used to pass food to the oral mouth at the center, and can attach to surfaces. A sea star that is overturned simply turns one arm over and attaches it to a solid surface, and levers itself the right way up.[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]Tube feet allow these different types of animals to stick to the ocean floor and move very slowly.[/FONT][/SIZE][/COLOR]

[COLOR=black][FONT=Times New Roman][SIZE=3]The tube feet also help the starfish in reproduction. Tube feet consist of two parts: ampulla and podia. Ampulla contain both circular muscles and longitudinal muscle, whereas the podia contain the latter only. Thus the podia use suction to attach to the substratum.[/SIZE][/FONT][/COLOR]



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Chordates
 

[CENTER][B]Cleavage[/B][/CENTER]
[COLOR=black][FONT=Times New Roman][SIZE=3]In [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Embryology"][COLOR=black][FONT=Times New Roman][SIZE=3]embryology[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], [B]cleavage[/B] is the division of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cell_(biology)"][COLOR=black][FONT=Times New Roman][SIZE=3]cells[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] in the early [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Embryo"][COLOR=black][FONT=Times New Roman][SIZE=3]embryo[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. The [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Zygote"][COLOR=black][FONT=Times New Roman][SIZE=3]zygotes[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] of many species undergo rapid [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cell_cycle"][COLOR=black][FONT=Times New Roman][SIZE=3]cell cycles[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Blastomere"][COLOR=black][FONT=Times New Roman][SIZE=3]blastomeres[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and form a compact mass called the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Morula"][COLOR=black][FONT=Times New Roman][SIZE=3]morula[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. Cleavage ends with the formation of the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Blastula"][COLOR=black][FONT=Times New Roman][SIZE=3]blastula[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman].[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]Depending mostly on the amount of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Yolk"][COLOR=black][FONT=Times New Roman][SIZE=3]yolk[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] in the egg, the cleavage can be [B]holoblastic[/B] (total or entire cleavage) or [B]meroblastic[/B] (partial cleavage). The pole of the egg with the highest concentration of yolk is referred to as the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Vegetal_pole"][COLOR=black][FONT=Times New Roman][SIZE=3]vegetal pole[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] while the opposite is referred to as the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Animal_pole"][COLOR=black][FONT=Times New Roman][SIZE=3]animal pole[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman].[/FONT][/SIZE][/COLOR]
[B][FONT=Times New Roman][SIZE=3]Mechanism[/SIZE][/FONT][/B]

[COLOR=black][FONT=Times New Roman][SIZE=3]The rapid cell cycles are facilitated by maintaining high levels of proteins that control cell cycle progression such as the cyclins and their associated [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cyclin-dependent_kinase"][COLOR=black][FONT=Times New Roman][SIZE=3]cyclin-dependent kinases[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] (cdk). The complex CyclinB/cdc2 a.k.a. MPF ([/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Maturation_promoting_factor"][COLOR=black][FONT=Times New Roman][SIZE=3]maturation promoting factor[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]) promotes entry into mitosis.[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]The processes of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Karyokinesis"][COLOR=black][FONT=Times New Roman][SIZE=3]karyokinesis[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] (mitosis) and [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cytokinesis"][COLOR=black][FONT=Times New Roman][SIZE=3]cytokinesis[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] work together to result in cleavage. The mitotic apparatus is made up of a [/SIZE][/FONT][URL="http://www.cssforum.com.pk/w/index.php?title=Central_spindle&action=edit&redlink=1"][COLOR=black][FONT=Times New Roman][SIZE=3]central spindle[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and polar [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Asters"][COLOR=black][FONT=Times New Roman][SIZE=3]asters[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] made up of polymers of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Tubulin"][COLOR=black][FONT=Times New Roman][SIZE=3]tubulin[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] protein called [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Microtubules"][COLOR=black][FONT=Times New Roman][SIZE=3]microtubules[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. The asters are nucleated by [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Centrosomes"][COLOR=black][FONT=Times New Roman][SIZE=3]centrosomes[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and the centrosomes are organized by centrioles brought into the egg by the sperm as basal bodies. Cytokinesis is mediated by the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Contractile_ring"][COLOR=black][FONT=Times New Roman][SIZE=3]contractile ring[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] made up of polymers of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Actin"][COLOR=black][FONT=Times New Roman][SIZE=3]actin[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] protein called [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Microfilaments"][COLOR=black][FONT=Times New Roman][SIZE=3]microfilaments[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]. Karyokinesis and cytokinesis are independent but spatially and temporally coordinated processes. While mitosis can occur in the absence of cytokinesis, cytokinesis requires the mitotic apparatus.[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]The end of cleavage coincides with the beginning of zygotic transcription. This point is referred to as the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Midblastula"][COLOR=black][FONT=Times New Roman][SIZE=3]midblastula transition[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] and appears to be controlled by the nuclear/cytoplasmic ratio (about 1/6).[/FONT][/SIZE][/COLOR]
[B][COLOR=black][SIZE=3][FONT=Times New Roman]Types of cleavage[/FONT][/SIZE][/COLOR][/B]

[B][COLOR=black][SIZE=3][FONT=Times New Roman]Determinate[/FONT][/SIZE][/COLOR][/B]

[COLOR=black][FONT=Times New Roman][SIZE=3]Determinate is the form of cleavage in most [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Protostomes"][COLOR=black][FONT=Times New Roman][SIZE=3]protostomes[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. It results in the developmental fate of the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cell_(biology)"][COLOR=black][FONT=Times New Roman][SIZE=3]cells[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] being set early in the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Embryo"][COLOR=black][FONT=Times New Roman][SIZE=3]embryo[/SIZE][/FONT][/COLOR][/URL][URL="http://www.cssforum.com.pk/wiki/Morphogenesis"][COLOR=black][FONT=Times New Roman][SIZE=3]development[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. Each cell produced by early embryonic cleavage does not have the capacity to develop into a complete [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Embryo"][COLOR=black][FONT=Times New Roman][SIZE=3]embryo[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman].[/FONT][/SIZE][/COLOR]
[B][COLOR=black][FONT=Times New Roman]Indeterminate[/FONT][/COLOR][/B]
[COLOR=black][FONT=Times New Roman][SIZE=3]A cell can only be indeterminate if it has a complete set of undisturbed animal/vegetal cytoarchitectural features. It is a characteristic of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Deuterostomes"][COLOR=black][FONT=Times New Roman][SIZE=3]deuterostomes[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] - when the original cell in a deuterostome embryo divides, the two resulting cells can be separated, and each one can individually develop into a whole organism[/FONT][/SIZE][/COLOR]
[B][COLOR=black][FONT=Times New Roman]Holoblastic[/FONT][/COLOR][/B]
[COLOR=black][FONT=Times New Roman][SIZE=3]In the absence of a large concentration of yolk, four major cleavage types can be observed in [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Isolecithal"][COLOR=black][FONT=Times New Roman][SIZE=3]isolecithal[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] cells (cells with a small even distribution of yolk) or in [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Centrolecithal"][COLOR=black][FONT=Times New Roman][SIZE=3]mesolecithal[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] cells (moderate amount of yolk in a gradient) - [B]bilateral[/B] holoblastic, [B]radial[/B] holoblastic, [B]rotational[/B] holoblastic, and [B]spiral[/B] holoblastic, cleavage.[/SIZE][/FONT][URL="http://www.cssforum.com.pk/l%20"][COLOR=black][FONT=Times New Roman][SIZE=3][1][/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] These holoblastic cleavage planes pass all the way through isolecithal zygotes during the process of cytokinesis. Coeloblastula is the next stage of development for eggs that undergo these radial cleavaging. In holoblastic eggs the first cleavage always occurs along the vegetal-animal axis of the egg, the second cleavage is perpendicular to the first. From here the spatial arrangement of blastomeres can follow various patterns, due to different planes of cleavage, in various organisms.[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][/COLOR][COLOR=black][SIZE=3][FONT=Times New Roman]Bilateral [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]The first cleavage results in bisection of the zygote into left and right halves. The following cleavage planes are centered on this axis and result in the two halves being mirror images of one another. In bilateral holoblastic cleavage, the divisions of the blastomeres are complete and separate; compared with bilateral meroblastic cleavage, in which the blastomeres stay partially connected. [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][/COLOR][COLOR=black][SIZE=3][FONT=Times New Roman]Radial [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]Radial cleavage is characteristic of the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Deuterostomes"][COLOR=black][FONT=Times New Roman][SIZE=3]deuterostomes[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], which include some [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Vertebrate"][COLOR=black][FONT=Times New Roman][SIZE=3]vertebrates[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Echinoderm"][COLOR=black][FONT=Times New Roman][SIZE=3]echinoderms[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], in which the spindle axes are parallel or at right angles to the polar axis of the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Oocyte"][COLOR=black][FONT=Times New Roman][SIZE=3]oocyte[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]. [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][/COLOR][COLOR=black][SIZE=3][FONT=Times New Roman]Rotational [/FONT][/SIZE][/COLOR]
[COLOR=black][URL="http://www.cssforum.com.pk/wiki/Mammal"][COLOR=black][FONT=Times New Roman][SIZE=3]Mammals[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] display rotational cleavage, and an [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Isolecithal"][COLOR=black][FONT=Times New Roman][SIZE=3]isolecithal[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] distribution of yolk (sparsely and evenly distributed). Because the cells have only a small amount of yolk, they require immediate implantation onto the uterine wall in order to receive nutrients. [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]Rotational cleavage involves a normal first division along the meridional axis, giving rise to two daughter cells. The way in which this cleavage differs is that one of the daughter cells divides meridionally, whilst the other divides equatorially. [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][/COLOR][COLOR=black][SIZE=3][FONT=Times New Roman]Spiral [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]In spiral cleavage, the cleavage planes are oriented obliquely to the polar axis of the oocyte. At the third cleavage the halves are oblique to the polar axis and typically produce an upper quartet of smaller cells that come to be set between the furrows of the lower quartet. All groups showing spiral cleavage are [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Protostomia"][COLOR=black][FONT=Times New Roman][SIZE=3]protostomia[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], such as [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Annelid"][COLOR=black][FONT=Times New Roman][SIZE=3]annelids[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] and [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Mollusk"][COLOR=black][FONT=Times New Roman][SIZE=3]mollusks[/SIZE][/FONT][/COLOR][/URL][/COLOR]
[B][COLOR=black][FONT=Times New Roman]Meroblastic[/FONT][/COLOR][/B]
[COLOR=black][FONT=Times New Roman][SIZE=3]In the presence of a large amount of yolk in the fertilized egg cell, the cell can undergo partial, or meroblastic, cleavage. Two major types of meroblastic cleavage are [B]discoidal[/B] and [B]superficial[/B].[/SIZE][/FONT][URL="http://www.cssforum.com.pk/l%20"][COLOR=black][FONT=Times New Roman][SIZE=3][2][/SIZE][/FONT][/COLOR][/URL][/COLOR]
[COLOR=black][FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][/COLOR][COLOR=black][SIZE=3][FONT=Times New Roman]Discoidal [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]In discoidal cleavage, the cleavage furrows do not penetrate the yolk. The embryo forms a disc of cells, called a blastodisc, on top of the yolk. Discoidal cleavage is commonly found in [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Birds"][COLOR=black][FONT=Times New Roman][SIZE=3]birds[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Reptiles"][COLOR=black][FONT=Times New Roman][SIZE=3]reptiles[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], and [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Fish"][COLOR=black][FONT=Times New Roman][SIZE=3]fish[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] which have [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Telolecithal"][COLOR=black][FONT=Times New Roman][SIZE=3]telolecithal[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] egg cells (egg cells with the yolk concentrated at one end). [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Symbol][SIZE=3]·[/SIZE] [/FONT][/COLOR][COLOR=black][SIZE=3][FONT=Times New Roman]Superficial [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]In superficial cleavage, [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Mitosis"][COLOR=black][FONT=Times New Roman][SIZE=3]mitosis[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] occurs but not [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cytokinesis"][COLOR=black][FONT=Times New Roman][SIZE=3]cytokinesis[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], resulting in a polynuclear cell. With the yolk positioned in the center of the egg cell, the nuclei migrate to the periphery of the egg, and the plasma membrane grows inward, partitioning the nuclei into individual cells. Superficial cleavage occurs in [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Arthropods"][COLOR=black][FONT=Times New Roman][SIZE=3]arthropods[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] which have [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Centrolecithal"][COLOR=black][FONT=Times New Roman][SIZE=3]centrolecithal[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] egg cells (egg cells with the yolk located in the center of the cell). [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman][B]Mammals[/B][/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]There are several differences between the cleavage in mammals and the cleavage in other animals. Mammals have a slow rate of division that is between 12 and 24 hours. These cellular division are asynchronous. Zygotic transcription starts at the two, four, or eight-cell stage. Cleavage is holoblastic and rotational.[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]At the eight-cell stage, the embryo goes through some changes. Most of the blastomeres in this stage become polarized and develop tight junctions with the other blastomeres. This process leads to the development of two different populations of cells: polar cells on the outside and apolar cells on the inside. The outer cells, called the [B]trophoblast[/B] cells, pump sodium in from the outside which automatically brings water in with it to the basal (inner) surface to form a blastocoel cavity in a process called compaction. The embryo is now called a blastula or early blastocyst. The trophoblast cells will eventually give rise to the embryonic contribution to the placenta called the [B]chorion[/B]. The inner cells are pushed to one side of the cavity (because the embryo isn't getting any bigger) to form the [B]inner cell mass[/B] (ICM) and will give rise to the embryo and some extraembryonic membranes. At this stage, the embryo is called a [B]blastocyst.[/B][/FONT][/SIZE][/COLOR]

[CENTER][COLOR=black][SIZE=3][FONT=Times New Roman][B]Complete Cleavage[/B][/FONT][/SIZE][/COLOR][/CENTER]

[CENTER][COLOR=black][SIZE=3][FONT=Times New Roman][B][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/Frog2-4-cell.gif[/IMG][/B][/FONT][/SIZE][/COLOR][/CENTER]

[CENTER][COLOR=black][SIZE=3][FONT=Times New Roman][B][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/BirdCleavage.jpg[/IMG][/B][/FONT][/SIZE][/COLOR][/CENTER]

[CENTER][COLOR=black][SIZE=3][FONT=Times New Roman][B][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/6JBM0507.gif[/IMG][/B][/FONT][/SIZE][/COLOR][/CENTER]

[CENTER][COLOR=black][SIZE=3][FONT=Times New Roman][B][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/40-6a.jpg[/IMG][/B][/FONT][/SIZE][/COLOR]

[IMG]http://i723.photobucket.com/albums/ww237/alphamalik/06720Cleavage20of20a20sygote.jpg[/IMG][/CENTER]

mashallah! u have a gr8 job......have u done masters in zoology?.....or its ur kind effort at ur own for css?

[quote=prissygirl]mashallah! u have a gr8 job......have u done masters in zoology?.....or its ur kind effort at ur own for css?[/quote]

Salam
yes i have done masters in zoology :D and M phil in zoology;) .this is for those who want to opt zoology:closedeye for css.
thanks and regards

Invertebrate Short Notes
 

[CENTER][B][SIZE=4]Spicules[/SIZE][/B][/CENTER]
[SIZE=3][FONT=Times New Roman][B][COLOR=black]Spicules[/COLOR][/B][COLOR=black] are tiny spike-like structures of diverse origin and function found in many organisms, such as the [URL="http://www.cssforum.com.pk/wiki/Copulation"][COLOR=black]copulatory[/COLOR][/URL] spicules of certain [URL="http://www.cssforum.com.pk/wiki/Roundworm"][COLOR=black]nematodes[/COLOR][/URL] or the grains on the skin of some [URL="http://www.cssforum.com.pk/wiki/Frog"][COLOR=black]frogs[/COLOR][/URL].[/COLOR][/FONT][/SIZE]

[COLOR=black][FONT=Times New Roman][SIZE=3]This article discusses the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Skeleton"][COLOR=black][FONT=Times New Roman][SIZE=3]skeletal[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] spicules that occur in most [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Sea_sponge"][COLOR=black][FONT=Times New Roman][SIZE=3]sponges[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. They provide structural support and deter [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Predator"][COLOR=black][FONT=Times New Roman][SIZE=3]predators[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]. Large spicules, visible to the naked eye are referred to as [B]megascleres[/B], while smaller, microscopic ones are termed [B]microscleres[/B].[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]Spicules have four major symmetry types: Monaxon (simple cylinders with pointed ends), triaxon, tetraxon, and polyaxon. Sponges can be [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Calcium_carbonate"][COLOR=black][FONT=Times New Roman][SIZE=3]calcareous[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Biogenic_silica"][COLOR=black][FONT=Times New Roman][SIZE=3]siliceous[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], or composed of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Spongin"][COLOR=black][FONT=Times New Roman][SIZE=3]spongin[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. The meshing of many spicules serves as the sponge’s [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Skeleton"][COLOR=black][FONT=Times New Roman][SIZE=3]skeleton[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. The composition, size, and shape of spicules is one of the largest determining factors in sponge [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Taxonomy"][COLOR=black][FONT=Times New Roman][SIZE=3]taxonomy[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman].[/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]Spicules are formed by [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Sclerocyte"][COLOR=black][FONT=Times New Roman][SIZE=3]sclerocytes[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], which are derived from archaeocytes. The sclerocyte begins with an organic [/SIZE][/FONT][URL="http://en.wiktionary.org/wiki/Filament"][COLOR=black][FONT=Times New Roman][SIZE=3]filament[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3], and adds silica to it. Spicules are generally elongated at a rate of 1-10 μm per hour. Once the spicule reaches a certain length it protrudes from the sclerocyte [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cell_(biology)"][COLOR=black][FONT=Times New Roman][SIZE=3]cell[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] body, but remains within the cell’s [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Cell_membrane"][COLOR=black][FONT=Times New Roman][SIZE=3]membrane[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]. On occasion, sclerocytes may begin a second spicule while the first is still in progress.[/FONT][/SIZE][/COLOR]
[LEFT][COLOR=black][FONT=Times New Roman][SIZE=3]Research on the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Venus%27_Flower_Basket"][SIZE=3][FONT=Times New Roman][I][COLOR=black]Euplectella aspergillum[/COLOR][/I][COLOR=black] (Venus' Flower Basket)[/COLOR][/FONT][/SIZE][/URL][FONT=Times New Roman][SIZE=3] demonstrated that the spicules of certain deep-sea sponges have similar traits to [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Optical_fibre"][COLOR=black][FONT=Times New Roman][SIZE=3]Optical fibre[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. In addition to being able to trap and transport light, these spicules have a number of advantages over commercial fibre optic wire. They are stronger, resist stress easier, and form their own support elements. Also, the low-temperature formation of the spicules, as compared to the high temperature stretching process of commercial fibre optics, allows for the addition of [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Impurity"][COLOR=black][FONT=Times New Roman][SIZE=3]impurities[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] which improve the [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Refractive_index"][COLOR=black][FONT=Times New Roman][SIZE=3]refractive index[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3]. In addition, these spicules have built-in [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Lens_(optics)"][COLOR=black][FONT=Times New Roman][SIZE=3]lenses[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] in the ends which gather and focus light in dark conditions. It has been theorized that this ability may function as a light source for [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Symbiosis"][COLOR=black][FONT=Times New Roman][SIZE=3]symbiotic[/SIZE][/FONT][/COLOR][/URL][URL="http://www.cssforum.com.pk/wiki/Algae"][COLOR=black][FONT=Times New Roman][SIZE=3]algae[/SIZE][/FONT][/COLOR][/URL][FONT=Times New Roman][SIZE=3] (as with [I]Rosella racovitzae[/I]) or as an attractor for [/SIZE][/FONT][URL="http://www.cssforum.com.pk/wiki/Shrimp"][COLOR=black][FONT=Times New Roman][SIZE=3]shrimp[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] which live inside the Venus' Flower Basket. However, a conclusive decision has not been reached; it may be that the light capabilities are simply a coincidental trait from a purely structural element.[/FONT][/SIZE][/COLOR][/LEFT]
[CENTER][COLOR=black][FONT=Arial][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/SPICULES.gif[/IMG][/FONT][/COLOR]


[COLOR=black][FONT=Arial][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/Spiculesff.gif[/IMG][/FONT][/COLOR][/CENTER]

Invertebrate protozoa (Movements)
 

[COLOR=white].........................................................................[/COLOR]
[youtube]QGAm6hMysTA[/youtube]

Chordates
 

[B][B]Germ layers[/B]

[/B][COLOR=black]A [B]germ layer[/B] is a group of [/COLOR][URL="http://www.cssforum.com.pk/wiki/Cell_(biology)"][COLOR=black]cells[/COLOR][/URL][COLOR=black], formed during animal [/COLOR][URL="http://www.cssforum.com.pk/wiki/Embryogenesis"][COLOR=black]embryogenesis[/COLOR][/URL][COLOR=black]. Germ layers are particularly pronounced in the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Vertebrate"][COLOR=black]vertebrates[/COLOR][/URL][COLOR=black]; however, all [/COLOR][URL="http://www.cssforum.com.pk/wiki/Animal"][COLOR=black]animals[/COLOR][/URL][COLOR=black] more complex than [/COLOR][URL="http://www.cssforum.com.pk/wiki/Sea_sponge"][COLOR=black]sponges[/COLOR][/URL][COLOR=black] ([/COLOR][URL="http://www.cssforum.com.pk/wiki/Eumetazoa"][COLOR=black]eumetazoans[/COLOR][/URL][COLOR=black] and [/COLOR][URL="http://species.wikimedia.org/wiki/agnotozoa"][COLOR=black]agnotozoans[/COLOR][/URL][COLOR=black]) produce two or three [B]primary tissue layers[/B] (sometimes called primary germ layers). Animals with [/COLOR][URL="http://www.cssforum.com.pk/wiki/Symmetry_(biology)/lRadial_symmetry"][COLOR=black]radial symmetry[/COLOR][/URL][COLOR=black], like [/COLOR][URL="http://www.cssforum.com.pk/wiki/Cnidaria"][COLOR=black]cnidarians[/COLOR][/URL][COLOR=black], produce two germ layers (the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Ectoderm"][COLOR=black]ectoderm[/COLOR][/URL][COLOR=black] and [/COLOR][URL="http://www.cssforum.com.pk/wiki/Endoderm"][COLOR=black]endoderm[/COLOR][/URL][COLOR=black]) making them [/COLOR][URL="http://www.cssforum.com.pk/wiki/Diploblastic"][COLOR=black]diploblastic[/COLOR][/URL][COLOR=black]. Animals with [/COLOR][URL="http://www.cssforum.com.pk/wiki/Symmetry_(biology)/lBilateral_symmetry"][COLOR=black]bilateral symmetry[/COLOR][/URL][COLOR=black] produce a third layer between these two layers (appropriately called the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Mesoderm"][COLOR=black]mesoderm[/COLOR][/URL][COLOR=black]) making them [/COLOR][URL="http://www.cssforum.com.pk/wiki/Triploblastic"][COLOR=black]triploblastic[/COLOR][/URL][COLOR=black]. Germ layers eventually give rise to all of an animal’s [/COLOR][URL="http://www.cssforum.com.pk/wiki/Biological_tissue"][COLOR=black]tissues[/COLOR][/URL][COLOR=black] and [/COLOR][URL="http://www.cssforum.com.pk/wiki/Organ_(anatomy)"][COLOR=black]organs[/COLOR][/URL][COLOR=black] through the process of [/COLOR][URL="http://www.cssforum.com.pk/wiki/Organogenesis"][COLOR=black]organogenesis[/COLOR][/URL][COLOR=black].[/COLOR]
[COLOR=black]Among [/COLOR][URL="http://www.cssforum.com.pk/wiki/Animal"][COLOR=black]animals[/COLOR][/URL][COLOR=black], [/COLOR][URL="http://www.cssforum.com.pk/wiki/Sea_sponge"][COLOR=black]sponges[/COLOR][/URL][COLOR=black] show the simplest organization, having a single germ layer. Although they have differentiated cells (e.g. [/COLOR][URL="http://www.cssforum.com.pk/wiki/Choanocyte"][COLOR=black]collar cells[/COLOR][/URL][COLOR=black]), they lack true tissue coordination. [/COLOR][URL="http://www.cssforum.com.pk/wiki/Diploblastic"][COLOR=black]Diploblastic[/COLOR][/URL][COLOR=black] animals, [/COLOR][URL="http://www.cssforum.com.pk/wiki/Cnidaria"][COLOR=black]Cnidaria[/COLOR][/URL][COLOR=black] and [/COLOR][URL="http://www.cssforum.com.pk/wiki/Ctenophores"][COLOR=black]ctenophores[/COLOR][/URL][COLOR=black], show an increase in complexity, having two germ layers, the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Endoderm"][COLOR=black]endoderm[/COLOR][/URL][COLOR=black] and [/COLOR][URL="http://www.cssforum.com.pk/wiki/Ectoderm"][COLOR=black]ectoderm[/COLOR][/URL][COLOR=black]. Diploblastic animals are organized into recognisable tissues. All higher animals (from flatworms to humans) are [/COLOR][URL="http://www.cssforum.com.pk/wiki/Triploblastic"][COLOR=black]triploblastic[/COLOR][/URL][COLOR=black], possessing a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Mesoderm"][COLOR=black]mesoderm[/COLOR][/URL][COLOR=black] in additition to the germ layers found in Diploblasts. Triploblastic animals develop recognisable organs.[/COLOR]

[B][COLOR=black]Development[/COLOR][/B]
[URL="http://www.cssforum.com.pk/wiki/Fertilisation"][COLOR=black]Fertilization[/COLOR][/URL][COLOR=black] leads to the formation of a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Zygote"][COLOR=black]zygote[/COLOR][/URL][COLOR=black]. During the next stage, [/COLOR][URL="http://www.cssforum.com.pk/wiki/Cleavage_(embryo)"][COLOR=black]cleavage[/COLOR][/URL][COLOR=black], [/COLOR][URL="http://www.cssforum.com.pk/wiki/Mitosis"][COLOR=black]mitotic[/COLOR][/URL][COLOR=black] cell divisions transform the zygote into a tiny ball of cells, a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Blastula"][COLOR=black]blastula[/COLOR][/URL][COLOR=black]. This early embryonic form undergoes [/COLOR][URL="http://www.cssforum.com.pk/wiki/Gastrulation"][COLOR=black]gastrulation[/COLOR][/URL][COLOR=black], forming a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Gastrula"][COLOR=black]gastrula[/COLOR][/URL][COLOR=black] with either two or three layers (the germ layers). In all [/COLOR][URL="http://www.cssforum.com.pk/wiki/Vertebrate"][COLOR=black]vertebrates[/COLOR][/URL][COLOR=black], these are the forerunners of all adult tissues and organs.[/COLOR]
[COLOR=black]The appearance of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Archenteron"][COLOR=black]archenteron[/COLOR][/URL][COLOR=black] marks the onset of gastrulation.[/COLOR]
[COLOR=black]In humans, after about three days, the zygote forms a solid mass of cells by mitotic division, called a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Morula"][COLOR=black]morula[/COLOR][/URL][COLOR=black]. This then changes to a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Blastocyst"][COLOR=black]blastocyst[/COLOR][/URL][COLOR=black], consisting of an outer layer called a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Trophoblast"][COLOR=black]trophoblast[/COLOR][/URL][COLOR=black], and an inner cell mass called the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Embryoblast"][COLOR=black]embryoblast[/COLOR][/URL][COLOR=black]. Filled with uterine fluid, the blastocyst breaks out of the zona pellucida and undergoes [/COLOR][URL="http://www.cssforum.com.pk/wiki/Implantation"][COLOR=black]implantation[/COLOR][/URL][COLOR=black]. The inner cell mass initially has two layers: the hypoblast and epiblast. At the end of the second week, a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Primitive_streak"][COLOR=black]primitive streak[/COLOR][/URL][COLOR=black] appears. The epiblast in this region moves towards the primitive streak, dives down into it, and forms a new layer, called the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Endoderm"][COLOR=black]endoderm[/COLOR][/URL][COLOR=black], pushing the hypoblast out of the way (this goes on to form the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Amnion"][COLOR=black]amnion[/COLOR][/URL][COLOR=black].) The epiblast keeps moving and forms a second layer, the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Mesoderm"][COLOR=black]mesoderm[/COLOR][/URL][COLOR=black]. The top layer is now called the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Ectoderm"][COLOR=black]ectoderm[/COLOR][/URL][COLOR=black].[/COLOR]

[B][COLOR=black]Endoderm[/COLOR][/B]
[COLOR=black]The [B]endoderm[/B] is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Endoderm"][COLOR=black]endoderm[/COLOR][/URL][COLOR=black].[/COLOR]
[COLOR=black]The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm). It also forms the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas; the epithelium of the auditory tube and tympanic cavity; the trachea, bronchi, and air cells of the lungs; the urinary bladder and part of the urethra; and the follicle lining of the thyroid gland and thymus.[/COLOR]
[COLOR=black]The [/COLOR][URL="http://www.cssforum.com.pk/wiki/Endoderm"][COLOR=black]endoderm[/COLOR][/URL][COLOR=black] forms: the stomach, the colon, the liver, the pancreas, the urinary bladder, the lining of the urethra, the epithelial parts of trachea, the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Lungs"][COLOR=black]lungs[/COLOR][/URL][COLOR=black], the pharynx, the thyroid, the parathyroid, and the intestines.[/COLOR]

[B][COLOR=black]Mesoderm[/COLOR][/B]
[COLOR=black]The [B]mesoderm[/B] germ layer forms in the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Embryo"][COLOR=black]embryos[/COLOR][/URL][COLOR=black] of [/COLOR][URL="http://www.cssforum.com.pk/wiki/Triploblastic"][COLOR=black]triploblastic[/COLOR][/URL][URL="http://www.cssforum.com.pk/wiki/Animal"][COLOR=black]animals[/COLOR][/URL][COLOR=black]. During [/COLOR][URL="http://www.cssforum.com.pk/wiki/Gastrulation"][COLOR=black]gastrulation[/COLOR][/URL][COLOR=black], some of the cells migrating inward contribute to the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Mesoderm"][COLOR=black]mesoderm[/COLOR][/URL][COLOR=black], an additional layer between the endoderm and the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Ectoderm"][COLOR=black]ectoderm[/COLOR][/URL][COLOR=black].[/COLOR]
[COLOR=black]This key innovation evolved hundreds of millions of years ago and led to the evolution of nearly all large, complex animals. The formation of a mesoderm led to the development of a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Body_cavity"][COLOR=black]coelom[/COLOR][/URL][COLOR=black]. Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks.[/COLOR]
[COLOR=black]The [/COLOR][URL="http://www.cssforum.com.pk/wiki/Mesoderm"][COLOR=black]mesoderm[/COLOR][/URL][COLOR=black] forms: skeletal muscle, the skeleton, the dermis of skin, connective tissue, the urogenital system, the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Heart"][COLOR=black]heart[/COLOR][/URL][COLOR=black], blood ([/COLOR][URL="http://www.cssforum.com.pk/wiki/Lymph"][COLOR=black]lymph[/COLOR][/URL][COLOR=black] cells), and the spleen.[/COLOR]

[B][COLOR=black]Ectoderm[/COLOR][/B]
[COLOR=black]The [B]ectoderm[/B] is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.[/COLOR]
[COLOR=black]The [/COLOR][URL="http://www.cssforum.com.pk/wiki/Ectoderm"][COLOR=black]ectoderm[/COLOR][/URL][COLOR=black] forms: the central nervous system, the lens of the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands[/COLOR]

[SIZE=4][COLOR=black][B]Neural crest[/B]
[/COLOR][/SIZE][COLOR=black]Because of its great importance, the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Neural_crest"][COLOR=black]neural crest[/COLOR][/URL][COLOR=black] is sometimes considered a fourth germ layer. It is, however, derived from the ectoderm.[/COLOR]



[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/Cell_differentiation.gif[/IMG][/CENTER]



[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/I10-55-gastrulation.jpg[/IMG][/CENTER]



[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/germ-layers.jpg[/IMG][/CENTER]


[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/Gastrulation.gif[/IMG][/CENTER]

Chordates
 

[LEFT][B]Embryonic Membranes[/B][/LEFT]

The embryos of reptiles, birds, and mammals produce 4 extraembryonic membranes, the
amnion
yolk sac
chorion, and
allantois
In birds and most reptiles, the embryo with its extraembryonic membranes develops within a shelled egg.
The [B]amnion[/B] protects the embryo in a sac filled with [B]amniotic fluid[/B].
The [B]yolk sac[/B] contains yolk — the sole source of food until hatching. Yolk is a mixture of proteins and [URL="http://www.cssforum.com.pk/../C/Cholesterol.html/llipoprotein"][U][COLOR=#0000ff]lipoproteins[/COLOR][/U][/URL].
The [B]chorion[/B] lines the inner surface of the shell (which is permeable to gases) and participates in the exchange of O2 and CO2 between the embryo and the outside air.
The [B]allantois[/B] stores metabolic wastes (chiefly [URL="http://www.cssforum.com.pk/../U/UreaCycle.html/lUricAcid"][U][COLOR=#0000ff]uric acid[/COLOR][/U][/URL]) of the embryo and, as it grows larger, also participates in gas exchange.
With these four membranes, the developing embryo is able to carry on essential metabolism while sealed within the egg. Surrounded by amniotic fluid, the embryo is kept as moist as a fish embryo in a pond.
Although (most) mammals do not make a shelled egg, they do also enclose their embryo in an amnion. For this reason, the reptiles, birds, and mammals are collectively referred to as the [URL="http://www.cssforum.com.pk/../V/Vertebrates.html/lAmniota"][B][COLOR=#0000ff]amniota[/COLOR][/B][/URL].
Mammals fall into three groups that differ in the way they use the amniotic egg.

[B][LEFT]Monotremes[/LEFT]
[/B]
[LEFT]These primitive mammals produce a shelled egg like their reptilian ancestors. Only four species exist today: three species of spiny anteater (echidna) and the duckbill platypus[/LEFT]

[B][LEFT]Marsupial[/LEFT]
[/B]
[LEFT]Marsupials do not produce a shelled egg. The egg, which is poorly supplied with yolk, is retained for a time within the reproductive tract of the mother. The embryo penetrates the wall of the [B]uterus[/B]. The yolk sac provides a rudimentary connection to the mother's blood supply from which it receives food, oxygen, and other essentials. However, this interface between the tissues of the uterus and the extraembryonic membranes never becomes elaborately developed, and the young are born in a very immature state. [/LEFT]

[B][LEFT]Placental mammals[/LEFT]
[/B][LEFT]
In placental mammals, the extraembryonic membranes form a [B]placenta[/B] and [B]umbilical cord[/B], which connect the embryo to the mother's uterus in a more elaborate and efficient way. The blood supply of the developing fetus is continuous with that of the placenta. The placenta extracts food and oxygen from the uterus. Carbon dioxide and other wastes (e.g., urea) are transferred to the mother for disposal by her excretory organs.
Humans are placental mammals.
[/LEFT]

[CENTER][/CENTER]

[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/I10-82-membranes.jpg[/IMG][/CENTER]




[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/amnion.jpg[/IMG][/CENTER]


[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/AmnioticEgg.gif[/IMG][/CENTER]

Chordates
 

[CENTER][SIZE=3]EGG TYPES[/SIZE][/CENTER]
The Zygote
The zygote is [I]totipotent[/I] - it has the potential to develop into any other cell
Zygotes from different species differ in their yolk content:
[B]- [I]oligolecithal[/I] eggs - little yolk[/B]
[B]- [I]mesolecithal[/I] eggs - moderate amounts of yolk[/B]
[B]- [I]macrolecithal[/I] eggs - large amounts of yolk[/B]
[B]The distribution of yolk also differs:[/B]
[B]- oligolecithal eggs tend to be [I]isolecithal[/I] - yolk is distributed throughout the egg[/B]
[B]- meso- and macrolecithal eggs tend to be [I]telolecithal[/I] - yolk is segregated toward the [I]vegetal pole[/I], away from the [I]animal[/I] pole.[/B]






[B][CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/6JBM0504.gif[/IMG][/CENTER]
[/B]







[B][CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/6JBM0508.gif[/IMG][/CENTER]
[/B]





[B][CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/Image99.jpg[/IMG][/CENTER]
[/B]



[B]Cleavage[/B]

[B]Early cell division occurs without cell growth, and is termed cleavage[/B]
[B]The presence of yolk slows cleavage in proportion to its concentration[/B]
[B]- in [I]holoblastic cleavage[/I] cell divisions are complete[/B]
[B]- in [I]meroblastic cleavage[/I], the yolk is not completely divided[/B]
[B]Cleavage results in the [I]blastula[/I] - a mass of undifferentiated cells[/B]
[B]- cells have a high nucleus:cytoplasm ratio[/B]
[B]- cells are undifferentiated[/B]
[B]- the blastula contains a central cavity or [I]blastocoel[/I] [/B]


[B]Gastrulation[/B]
[B][I]Gastrulation [/I]is the transformation of the blastula into a [I]gastrula, [/I]a structure with three [I]germ layers[/I] and a [I]gastrocoel[/I][/B]
[B]Gastrulation begins at the [I]blastopore[/I] - a spot where proliferating cells fold into the blastocoel[/B]
[B]The gastrula has several important characters[/B]
[B]the three main body axes are defined [/B]
[B]cells acquire developmental fates[/B]
[B]- the [I]ectoderm[/I] will form the epidermis, nervous system, and sense organs[/B]
[B]- the [I]endoderm[/I] will form the gut lining and derivatives[/B]
[B]- the [I]mesoderm[/I] will form everything else[/B]


[B]Neurulation [/B]
[B][I]Neurulation[/I] is the initial formation of the nervous system[/B]
[B]- growth, cell differentiation and organogenesis begin[/B]
[B][I]Chordamesoderm[/I] cells aggregate to form the notochord[/B]
[B]The chordamesoderm [I]induces[/I] the dorsal ectoderm to form the neural tube[/B]
[B]- [I]induction [/I]involves turning on or off of specific genetic pathways in one type of cell following contact by another type of cell[/B]
[B]Mesoderm flanking the notochord becomes segmented into laterally paired blocks or [I]somites[/I][/B]
[B]different regions of the somites and lateral mesoderm have different developmental fates [/B]
[B][I]Pharyngeal pouches[/I] (6-9) develop by evaginations of the pharyngeal endoderm, which meet indentations of the ectoderm[/B]
[B]- they give rise to several important structures:[/B]
[B](e.g., the eardrum, jaws, glands)[/B]
[B][I]Placodes[/I] are ectodermal thickenings in the head[/B]
[B]- they contribute to the sense organs, and to the wandering cells[/B]
[B][I]Mesenchyme[/I] is the embryonic connective tissue [/B]
[B][I]- Wandering cells[/I] are mesenchyme cells that migrate through the embryo and form specific structures[/B]
[B][I]- Neural crest cells[/I] are wandering cells derived from ectoderm dorsal to the neural tube.[/B]
[B]- unique to vertebrates[/B]


[B]Organogenesis[/B]
[B][I]Organogenesis[/I] involves continued specialization of cells to form tissues[/B]
[B]- ectoderm and endoderm form predominantly [I]epithelium[/I] - sheets with tight intercellular junctions, flanking open space[/B]
[B]- mesoderm forms the matrix of the organs, including a variety of tissues [/B]
[B]Tissues combine to form organs[/B]
[B]Organs unite into organ systems[/B]

Chordates
 

[CENTER][FONT=Times New Roman][B]Differences between the hearts: Vertebrates[/B][/FONT][/CENTER]

[FONT=Times New Roman]

[FONT=Times New Roman][SIZE=3]The fish heart (figure 1a) is much different than the amphibian/reptile/bird/mammal heart (figures 1b and c). Hearts are very complex--they're not just a bunch of random arteries and veins connecting tissue. Fish hearts simply draw in deoxygenated blood in a single atrium, and pump it out through a ventricle. This system is termed "single circulation", as blood enters the heart, gets pumped through the gills and out to the body, Blood pressure is low for oxygenated blood leaving the gills.

3 and 4 chambered hearts have a pulmonary circuit (pathways taking blood from heart to lung and back to heart) that is very complex and must be set up such that blood can travel from the heart to become oxygenated in the lungs and then be properly pumped back the heart and out to the body. The 3 (and 4) chambered heart has "double circulation" (figure 1b and c) and is quite different from "single circulation" (figure 1a) of fishes.

"Double circulation" has an interior circuit within the heart--blood enters the heart, leaves the heart and gets oxygenated, enters the heart again, and then gets pumped out to the body. Because "Double circulation" allows oxygenated blood to be pumped back into the heart before going out to the body, it pumps blood with much more pressure and much more vigorously than "single circulation". [/SIZE][/FONT]


[FONT=Times New Roman][SIZE=3]Though the 4 chambered heart has 2 atrium-ventricle pairs, both pairs do not do the same thing. There are 4 steps involved with blood entering the heart: 1) oxygen poor blood enters the first atrium. 2) oxygen poor blood is fed to the first ventricle, which pumps it out to the pulmonary circuit (lungs) where it is enriched in oxygen. 3) Oxygen rich blood just leaving the lungs is pumped back into the second atria. 4) Oxygen rich blood is then fed to the second ventricle, which pumps the oxygen rich blood out of the heart and back into the body for usage.

The 4 chambered heart differs from the 3 chambered heart in that it keeps oxygenated blood completely separate from de-oxygnated blood, because there is one ventricle for deoxgynated blood and one for oxygenated blood. In the 3 chambered heart, a single ventricle pumps both out of the heart, and there is some mixing between fresh and old blood. The 2 ventricle-4 chamber heart prevents mixing allows the blood leaving the heart to have far more oxygen than it would otherwise. This is good for enhancing the more fast paced lifestyle that birds and mammals tend to have, giving an advantage to having a 4 chambered heart.[/SIZE][/FONT]


[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/hearts.jpg[/IMG][/CENTER]


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Chordates
 

[CENTER][B]Hepatic portal system[/B][/CENTER]

[COLOR=black]In [/COLOR][URL="http://www.cssforum.com.pk/wiki/Human_anatomy"][COLOR=black]human anatomy[/COLOR][/URL][COLOR=black], the [B]hepatic portal system[/B] is the system of [/COLOR][URL="http://www.cssforum.com.pk/wiki/Vein"][COLOR=black]veins[/COLOR][/URL][COLOR=black] comprised of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Hepatic_portal_vein"][COLOR=black]hepatic portal vein[/COLOR][/URL][COLOR=black] and its tributaries. It is also called the [B]portal venous system[/B], although it is not the only example of a [/COLOR][URL="http://www.cssforum.com.pk/wiki/Portal_venous_system"][COLOR=black]portal venous system[/COLOR][/URL][COLOR=black], and [B]splanchnic veins[/B], which is [I]not[/I] [/COLOR][URL="http://www.cssforum.com.pk/wiki/Synonymous"][COLOR=black]synonymous[/COLOR][/URL][COLOR=black] with [I]hepatic portal system[/I] and is imprecise (as it means [/COLOR][URL="http://www.cssforum.com.pk/wiki/Viscera"][I][COLOR=black]visceral[/COLOR][/I][/URL][COLOR=black][I] veins[/I] and not necessarily the [I]veins of the [/I][/COLOR][URL="http://www.cssforum.com.pk/wiki/Abdominal"][I][COLOR=black]abdominal[/COLOR][/I][/URL][COLOR=black][I] viscera[/I]).[/COLOR]

[SIZE=5][B][SIZE=4]Function[/SIZE][/B]

[/SIZE][COLOR=black]The portal venous system is responsible for directing blood from parts of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Gastrointestinal_tract"][COLOR=black]gastrointestinal tract[/COLOR][/URL][COLOR=black] to the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Liver"][COLOR=black]liver[/COLOR][/URL][COLOR=black]. Substances absorbed in the small intestine travel first to the liver for processing before continuing to the heart. Not all of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Gastrointestinal_tract"][COLOR=black]gastrointestinal tract[/COLOR][/URL][COLOR=black] is part of this system. The system extends from about the lower portion of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Esophagus"][COLOR=black]esophagus[/COLOR][/URL][COLOR=black] to the upper part of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Anal_canal"][COLOR=black]anal canal[/COLOR][/URL][COLOR=black]. It also includes venous drainage from the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Spleen"][COLOR=black]spleen[/COLOR][/URL][COLOR=black] and [/COLOR][URL="http://www.cssforum.com.pk/wiki/Pancreas"][COLOR=black]pancreas[/COLOR][/URL][COLOR=black].[/COLOR]
[COLOR=black]Many drugs that are absorbed through the [/COLOR][URL="http://www.cssforum.com.pk/wiki/GI_tract"][COLOR=black]GI tract[/COLOR][/URL][COLOR=black] are substantially metabolized by the liver before reaching general circulation. This is known as the [/COLOR][URL="http://www.cssforum.com.pk/wiki/First_pass_effect"][COLOR=black]first pass effect[/COLOR][/URL][COLOR=black]. As a consequence, certain drugs can only be taken via certain routes. For example, [/COLOR][URL="http://www.cssforum.com.pk/wiki/Nitroglycerin"][COLOR=black]nitroglycerin[/COLOR][/URL][COLOR=black] cannot be swallowed because the liver would inactivate the medication, but it can be taken [/COLOR][URL="http://www.cssforum.com.pk/wiki/Sublingual"][COLOR=black]under the tongue[/COLOR][/URL][COLOR=black] or transdermal (through the skin) and thus is absorbed in a way that bypasses the portal venous system.[/COLOR]
[COLOR=black]Blood flow to the liver is unique in that it receives both oxygenated and deoxygenated blood. As a result, the partial pressure of oxygen (pO2) and perfusion pressure of portal blood are lower than in other organs of the body. Blood passes from branches of the portal vein through cavities between "plates" of [/COLOR][URL="http://www.cssforum.com.pk/wiki/Hepatocytes"][COLOR=black]hepatocytes[/COLOR][/URL][COLOR=black] called [/COLOR][URL="http://www.cssforum.com.pk/wiki/Liver_sinusoid"][COLOR=black]sinusoids[/COLOR][/URL][COLOR=black]. Blood also flows from branches of the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Hepatic_artery"][COLOR=black]hepatic artery[/COLOR][/URL][COLOR=black] and mixes in the sinusoids to supply the hepatocytes with oxygen. This mixture [/COLOR][URL="http://www.cssforum.com.pk/wiki/Percolation"][COLOR=black]percolates[/COLOR][/URL][COLOR=black] through the sinusoids and collects in a central vein which drains into the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Hepatic_vein"][COLOR=black]hepatic vein[/COLOR][/URL][COLOR=black]. The hepatic vein subsequently drains into the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Inferior_vena_cava"][COLOR=black]inferior vena cava[/COLOR][/URL][COLOR=black].[/COLOR]
[COLOR=black]Large veins that are considered part of the [I]portal venous system[/I] are the:[/COLOR]
[URL="http://www.cssforum.com.pk/wiki/Hepatic_portal_vein"][COLOR=black]Hepatic portal vein[/COLOR][/URL]
[URL="http://www.cssforum.com.pk/wiki/Splenic_vein"][COLOR=black]Splenic vein[/COLOR][/URL]
[COLOR=black]Roughly, the portal venous system corresponds to areas supplied by the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Celiac_trunk"][COLOR=black]celiac trunk[/COLOR][/URL][COLOR=black], the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Superior_mesenteric_artery"][COLOR=black]superior mesenteric artery[/COLOR][/URL][COLOR=black], and the [/COLOR][URL="http://www.cssforum.com.pk/wiki/Inferior_mesenteric_artery"][COLOR=black]inferior mesenteric artery[/COLOR][/URL][COLOR=black].[/COLOR]


[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/hepatic.gif[/IMG][/CENTER]


[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/hepatic20portal20system.jpg[/IMG][/CENTER]

[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/portsys.gif[/IMG][/CENTER]



The hepatic portal system begins in the capillaries of the digestive organs and ends in the portal vein. Consequently, portal blood contains substances absorbed by the stomach and intestines. Portal blood is passed through the hepatic lobules where nutrients and toxins are absorbed, excreted or converted.
Restriction of outflow through the hepatic portal system can lead to portal hypertension. Portal hypertension is most often associated with cirrhosis. Patients usually present with splenomegaly, ascites, GI bleeding and/or portal systemic encephalopathy.
The consequences of portal hypertension are due to portal systemic anastomosis formed by the body as an attempt to bypass the obstructed liver circulation. These collateral vessels form along the falciform ligament, diaphragm, spleen, stomach and peritoneum. The collaterals find their way to the renal vein where blood drained from the digestive organs is let into the systemic circulation.

[CENTER][B]Blood[/B][/CENTER]


[B][I][SIZE=6][COLOR=#808080][SIZE=6][COLOR=#808080][CENTER]Blood Components[/CENTER]
[/COLOR][/SIZE][/COLOR][/SIZE][/I][/B][SIZE=6][COLOR=#808080][SIZE=6][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=6][COLOR=#808080][SIZE=6][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE][FONT=Times New Roman][SIZE=1][FONT=Times New Roman][SIZE=1]
[/SIZE][/FONT][/SIZE][/FONT][SIZE=3]Normally, 7-8% of human body weight is from blood. In adults, this amounts to 4-5 quarts of blood. This essential fluid carries out the critical functions of transporting oxygen and nutrients to our cells and getting rid of carbon dioxide, ammonia, and other waste products. In addition, it plays a vital role in our immune system and in maintaining a relatively constant body temperature. Blood is a highly specialized tissue composed of many different kinds of components. Four of the most important ones are red cells, white cells, platelets, and plasma. All humans produce these blood components--there are no populational or regional differences.[/SIZE]

[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/19432.jpg[/IMG][/CENTER]



[B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080][CENTER]Red Cells[/CENTER]
[/COLOR][/SIZE][/COLOR][/SIZE][/B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE]Red cells, or [B]erythrocytes[/B]
, are relatively large microscopic cells without nuclei. In this latter trait, they are similar to the primitive [URL="http://www.cssforum.com.pk/glossary.htm/lprokaryotic"][U][COLOR=#0000ff]prokaryotic cells[/COLOR][/U][/URL] of bacteria. Red cells normally make up 40-50% of the total blood volume. They transport oxygen from the lungs to all of the living tissues of the body and carry away carbon dioxide. The red cells are produced continuously in our bone marrow from [URL="http://www.cssforum.com.pk/glossary.htm/lstem_cells"][U][COLOR=#0000ff]stem cells[/COLOR][/U][/URL] at a rate of about 2-3 million cells per second. [B]Hemoglobin[/B]
is the gas transporting [URL="http://www.cssforum.com.pk/glossary.htm/lproteins"][U][COLOR=#0000ff]protein[/COLOR][/U][/URL] molecule that makes up 95% of a red cell. Each red cell has about 270,000,000 iron-rich hemoglobin molecules. People who are anemic generally have a deficiency in red cells. The red color of blood is primarily due to oxygenated red cells. Human fetal hemoglobin molecules differ from those produced by adults in the number of amino acid chains. Fetal hemoglobin has three chains, while adults produce only two. As a consequence, fetal hemoglobin molecules attract and transport relatively more oxygen to the cells of the body.

[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/RBC-Production-Cycle.gif[/IMG][/CENTER]




[B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080][CENTER]White Cells[/CENTER]
[/COLOR][/SIZE][/COLOR][/SIZE][/B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE]White cells, or [B]leukocytes[/B]
, exist in variable numbers and types but make up a very small part of blood's volume--normally only about 1% in healthy people. Leukocytes are not limited to blood. They occur elsewhere in the body as well, most notably in the spleen, liver, and lymph glands. Most are produced in our bone marrow from the same kind of stem cells that produce red blood cells. Others are produced in the thymus gland, which is at the base of the neck. Some white cells (called lymphocytes
) are the first responders for our immune system. They seek out, identify, and bind to alien protein on [URL="http://www.cssforum.com.pk/glossary.htm/lbacteria"][U][COLOR=#0000ff]bacteria[/COLOR][/U][/URL], [URL="http://www.cssforum.com.pk/glossary.htm/lvirus"][U][COLOR=#0000ff]viruses[/COLOR][/U][/URL], and [URL="http://www.cssforum.com.pk/glossary.htm/lfungi"][U][COLOR=#0000ff]fungi[/COLOR][/U][/URL] so that they can be removed. Other white cells (called granulocytes
and macrophages
) then arrive to surround and destroy the alien cells. They also have the function of getting rid of dead or dying blood cells as well as foreign matter such as dust and asbestos. Red cells remain viable for only about 4 months before they are removed from the blood and their components recycled in the spleen. Individual white cells usually only last 18-36 hours before they also are removed, though some types live as much as a year. The description of white cells presented here is a simplification. There are actually many specialized sub-types of them that participate in different ways in our immune responses.


[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/untitled.jpg[/IMG][/CENTER]





[B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080][CENTER]Platelets[/CENTER]
[/COLOR][/SIZE][/COLOR][/SIZE][/B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE]Platelets
, or [B]thrombocytes[/B]
, are cell fragments without nuclei that work with blood clotting chemicals at the site of wounds. They do this by adhering to the walls of blood vessels, thereby plugging the rupture in the [URL="http://www.cssforum.com.pk/glossary.htm/lvascular"][U][COLOR=#0000ff]vascular[/COLOR][/U][/URL] wall. They also can release coagulating chemicals which cause clots to form in the blood that can plug up narrowed blood vessels. There are more than a dozen types of blood clotting factors and platelets that need to interact in the blood clotting process. Recent research has shown that platelets help fight infections by releasing proteins that kill invading bacteria and some other microorganisms. In addition, platelets stimulate the immune system. Individual platelets are about 1/3 the size of red cells. They have a lifespan of 9-10 days. Like the red and white blood cells, platelets are produced in bone marrow from stem cells.

[CENTER][IMG]http://i723.photobucket.com/albums/ww237/alphamalik/cell_platelets_web.jpg[/IMG][/CENTER]




[B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080][CENTER]Plasma[/CENTER]
[/COLOR][/SIZE][/COLOR][/SIZE][/B][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=5][COLOR=#808080][SIZE=5][COLOR=#808080]
[/COLOR][/SIZE][/COLOR][/SIZE]Plasma
is the relatively clear liquid water (92+%), sugar, fat, protein and salt solution which carries the red cells, white cells, platelets, and some other chemicals. Normally, 55% of our blood's volume is made up of plasma. About 95% of it consists of water. As the heart pumps blood to cells throughout the body, plasma brings nourishment to them and removes the waste products of [URL="http://www.cssforum.com.pk/glossary.htm/lmetabolism"][U][COLOR=#0000ff]metabolism[/COLOR][/U][/URL]. Plasma also contains blood clotting factors, sugars, [URL="http://www.cssforum.com.pk/glossary.htm/llipid"][U][COLOR=#0000ff]lipids[/COLOR][/U][/URL], vitamins, minerals, [URL="http://www.cssforum.com.pk/glossary.htm/lhormones"][U][COLOR=#0000ff]hormones[/COLOR][/U][/URL], [URL="http://www.cssforum.com.pk/glossary.htm/lenzyme"][U][COLOR=#0000ff]enzymes[/COLOR][/U][/URL], [URL="http://www.cssforum.com.pk/glossary.htm/lantibodies"][U][COLOR=#0000ff]antibodies[/COLOR][/U][/URL], and other [URL="http://www.cssforum.com.pk/glossary.htm/lproteins"][U][COLOR=#0000ff]proteins[/COLOR][/U][/URL]. It is likely that plasma contains some of every protein produced by the body--approximately 500 have been identified in human plasma so far.