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Old Wednesday, July 28, 2010
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Arrow Essential Notes For Botany

Chapter #1 Introduction to Botany

Botany, plant science(s), phytology, or plant biology is a branch of biology that involves the scientific study of plant life. Botany covers a wide range of scientific disciplines concerned with the study of plants, algae and fungi, including structure, growth, reproduction, metabolism, development, diseases, chemical properties, and evolutionary relationships between taxonomic groups.

The main subject matter in this course is:

A) Life : the characteristics of living things
B) Biochemistry : the important biological chemicals, like proteins and sugars
C) Cell structure : what plant cells contain
D) Chemical reactions : respiration and photosynthesis
E) Cell division : including meiosis
F) Plant ancestors and relatives : bacteria, protists and fungi
G) The plant kingdom : spore plants, seed plants
H) The applications of botany: crops, plant breeding and ecology


Why study Botany?
Plants are the source of many important products such as:
Food (including grass for animals)
Cotton and other fabrics
Paper
Wood
Coal and oil
Antibiotics and other medicines


Botany as a Science
Sciences, such as Biology, Chemistry and Physics, use a series of steps, called the scientific method, to try to understand the world around us. Some of the main steps are:

1-Make an observation (for example: plants in one part of my yard grow faster).
2-Come up with a hypothesis : an idea that can be tested. (eg. part of the yard gets more sunlight)
3-Make a prediction : a logical consequence of a hypothesis. (if slow growing plants are given more sunlight they will grow faster)
4-Test the prediction by conducting an experiment. Experiments are often designed to disprove the hypothesis. It is easy to disprove a hypothesis, but virtually impossible to prove that a hypothesis is correct in all possible situations.

The experimental group differs from the control group usually in one variable eg amount of sunlight. Experiments should be repeatable. Sample size : the larger the sample, the more accurate the results. It is better to do an experiment with 200 plants than with 2 plants.

Theory : a scientific theory has been supported by many experiments eg atomic theory, the theory of evolution.

The main areas of Botany

Plant anatomy: the structure of plants
Plant physiology: the function of parts of the plant
Plant taxonomy: the classification of plants
Plant ecology: the interactions of plants and other species
Genetics: the study of inheritance
Economic botany: the practical uses of plants and plant products.


Biological Classification
Organisms are classified (put into groups) using this system devised by the Swedish biologist Linnaeus, around 1750.

The example below is the classification of corn:

Kingdom Plantae
Phylum ( Phyla ) Magnoliophyta
Class Monocots (Liliopsida)
Order Commelinales
Family Poaceae (grasses)
Genus ( Genera ) Zea
Species mays

The scientific name is the Genus name followed by the species name eg Zea mays.
Members of the same species can interbreed to produce fertile offspring. Members of the same genus are similar, but do not interbreed in the wild. Example: wild perennial maize (Zea perennis ) is in the same genus as corn, but they do not interbreed.
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Arrow Chapter # 2 Basic Biochemistry

Philosophical considerations aside, organisms are basically ordered aggregations of chemicals and biological processes are merely biochemical reactions. Therefore an understanding of basic biochemistry is necessary in order to understand biology.


Attributes of Living things

1-They are composed of cells. Cells consist of a membrane around the outside, a nucleus containing DNA, and the cytoplasm.
2-Growth
3-Reproduction
Sexual reproduction: the offspring vary from the parents
Asexual reproduction: the offspring are identical clones
4-Respond to stimuli: for example plants respond to light, water, gravity, touch.
5-Metabolism: all the chemical reactions in an organism. The most critical reactions are respiration and photosynthesis.
6-Movement: for example sperm can swim, whole plants grow in particular directions, or there is cyclosis in cells.
7-Complexity: they are made of molecules and organelles.
8-Adaptation and evolution: populations evolve to become better adapted to their environment.


I. Matter is composed of elements

A. Matter

1. Matter refers to anything that takes up space and has mass

2. All matter (living and nonliving) is composed of basic elements

a. Elements = fundamental forms of matter that occupy space and have mass, cannot be broken down to substances with different chemical or physical properties

b. There are 92 naturally occurring elements. Living things contain a maximum of 25 elements.

c. Six elements (C, H, N, O, P, S) make up 98% of most organisms


II. Atoms form compounds and molecules
Atom - the smallest unit of an element.

A. Molecules = two or more atoms of same element bonded together (e.g., O2)

B. Compound = two or more different elements bonded together (e.g., H2O)

Atomic number = Number of Protons per atom. Atomic number also equals the number of electrons.
Example : Carbon has 6 protons and 6 electrons (Table 2.1).

Atomic mass = Number of Protons + Neutrons.
Example: carbon 14 has 8 neutrons (14 minus 6 ).

Isotopes : atoms of the same element that differ in the number of neutrons.

Radioactive atoms : large isotopes that break apart, releasing energy. The energy is either:
Alpha particles : weak, cannot penetrate paper.
Beta particles : stronger, can penetrate paper but not metal.
Gamma rays : very strong, can penetrate metal and harm living things.

Chemical Bond
Chemical bonds only involve electrons. Valence electrons - electrons in the outer shell ( the valence shell ) of an atom. All atoms try to fill their valence shell of electrons. Maximum number of electrons per shell :
First shell 2
Second shell 8
Third shell 8
Bonds are not physical links, they are links of pure energy.

Types Of Bond
1. Covalent bond - involves sharing of electron(s). Electrons possess energy; bonds that exist between atoms in molecules contain energy.

a. Sharing of a pair of electrons creates a single bond represented by single dash, e.g. water H2O is made of two single bonds H-O-H. Sharing two pairs of electrons is represented by two dashes, C=C

2. Ionic bond - electrons are transferred from one atom to another, e.g. salt NaCl

3. Hydrogen bond - weak attractive force between slightly positive hydrogen atom of one molecule and slightly negative atom in another or the same molecule. Hydrogen bonds are important in holding together proteins.

a. E.g. in a water molecule the electrons spend more time orbiting the oxygen than the hydrogens, therefore the oxygen becomes slightly negative and the two hydrogens become slightly positive

b. Such polar molecules attract each other like magnets

BASIC ORGANIC CHEMISTRY

Because carbon needs four electrons to fill its outer shell it can form millions of different combinations with other atoms - ten times more than all other atoms put together.

I. Organic molecules

A. Life as we know it is based on carbon

1. Carbon has four electrons in outer shell; bonds with up to four other atoms (usually H, O, N, or another C)

2. Ability of carbon to bond to itself makes possible carbon chains and rings which serve as the backbones of organic molecules

3. Organic molecules - contain carbon and hydrogen, most also contain nitrogen, and oxygen

4. Functional groups - clusters of atoms with characteristic structure and functions

B. Monomers and polymers

1. Most important biological compounds are polymers

a. Polymers - large compounds made of identical or nearly identical repeating subunits

b. Monomers - the subunits of polymers

2. Making and breaking polymers

a. Condensation - making polymers by lining up monomers and eliminating a water molecule, a hydroxyl (OH) group is removed from one monomer and a hydrogen (H) is removed from the other

b. Hydrolysis - breaking polymers apart by introducing a water molecule


PRINCIPLE ORGANIC POLYMERS

I. Carbohydrates- contain C, H and O in the proportion 1:2:1 (CH2O).

A. Most abundant organic compounds in nature

B. Serve both as structural compounds and as energy reserves to fuel life processes

C. Carbohydrate monomers are called monosaccharides

1. Alpha Glucose, a six carbon sugar (C6H12O6) is the immediate energy source to cells. You should know its structure

D. Carbohydrate polymers are called polysaccharides

1. Starch is straight chain of alpha glucose molecules with few side branches, mostly from plant sources

2. Glycogen is highly branched polymer of alpha glucose with many side branches; called "animal starch," it is storage carbohydrate of animals

3. Cellulose is a polymer of beta glucose molecules, it is primary constituent of plant cell walls

E. Disaccharides - 2 monosaccharides linked together

1. Sucrose (table sugar ) - glucose and fructose linked together, transported throughout plants

2. Lactose (milk sugar) is glucose + galactose

F. Virtually all carbohydrates come from plants which use the sun's energy to make alpha and beta glucose.

II. Lipids - fats, oils, fatlike substances, some vitamins and steroids

A. Primarily energy sources and structural compounds

B. Two principle characteristics:

1. Hydrophobic - insoluble in water
2. Large number of bonded hydrogens - therefore release a larger amount of energy than other organic compounds. Fats yield 9 cal/gm, carbohydrates 4 cal/gm

C. Major lipids:

1. Triglycerides (fats and oils) - three fatty acids joined to a glycerol molecule:

a. Fatty acid - long hydrocarbon chains with terminal carboxyl (COOH) group

Saturated fatty acids have no double bonds between their carbon atoms

Unsaturated fatty acids have double bonds in the carbon chain

b. Glycerol - three carbon molecule
1) Fats - triglycerides containing saturated fatty acids (e.g. butter is solid at room temperature)

2). Oils - triglycerides with unsaturated fatty acids (e.g. corn oil is liquid at room temperature)

c. Triglycerides are synthesized via condensation

2. Phospholipids - two fatty acids attached to phosphate group

a. phosphate heads are hydrophilic (water soluble) but tails are hydrophobic (water insoluble) therefore they spontaneously line up to form a lipid bilayer

b. very important because they form biological membranes

III. Polypeptides - polymers of nitrogen containing molecules called amino acids, joined together by peptide bonds

A. Amino acids consist of:

1. Amino group - NH2 (positive charge)

2. Carboxyl group - COOH (negative charge)

3. Central carbon atom

4. R group - different substitution to the molecule, determines nature of the amino acid

B. About 50,00 different proteins in humans, serve a variety of functions:

1. Structural - e.g. muscles, hair, fingernails, collagen
2. Enzymes - biological catalysts which regulate biochemical reactions

C. Proteins - large polypeptides with molecular weights from 10,000 - 1,000,000

D. Enzymes - large globular proteins from 12,000 to 1 million molecular weights that act as catalysts

1. Catalysts - substances that accelerate chemical reactions but which remain unchanged or unused in the process

2. Enzymes generally named by adding -ase to root name of substrate they react upon, e.g. amylase breaks down amylose (starch)

E. Polypeptide structure - due to interactions between adjacent hydrogen bonds and R groups proteins form complex three dimensional structures

C. Polypeptides can be denatured

1. Both temperature and pH can change polypeptide shape

a. Examples: heating egg white causes albumin to congeal; adding acid to milk causes curdling. When such proteins lose their normal configuration, the protein is denatured

b. Once a protein loses its normal shape, it cannot perform its usual function

IV. Nucleic Acids - polymers of nucleotides

A. Nucleotides made up of:

1. Phosphate group - PO4
2. Five carbon sugar called ribose (or deoxyribose)

3. Nitrogenous base - ring structure containing C & N

B. Important Nucleic Acids:

1. DNA (deoxyribonucleic acid) - the molecule which stores the genetic information passed on form parent to offspring

2. RNA (ribonucleic acid) - serves as the translator of the genetic information contained in DNA

SECONDARY METABOLITES

I. Proteins, lipids, carbohydrates and nucleic acids are called primary metabolites because they occur in all plant cells and they are necessary for the life of the plant.

II. Secondary metabolites are an assortment of many different compounds which serve a variety of functions, and that are restricted to different species of plants. They include:

A. Alkaloids - alkaline, nitrogen containing compounds which affect the human nervous system. At least 10,000 alkaloids have been isolated from plants. Many names end in -ine, e.g. morphine, caffeine, cocaine, nicotine, atropine.

B. Terpenoids - polymers of isoprene (see figure 2-26a, p. 33). Isoprene is emitted by leaves, causing a haze over forests on hot days. Other terpenoids include essential oils (volatile compounds) such as mint and menthol, taxol (cancer drug), digitalis (heart medicine) and rubber.

C. Phenolics - compounds based on an aromatic ring with an attached OH group. Flavonoids are important pigments, tannins are bitter tasting compounds which probably act as deterrents to herbivores, lignin is an important compound secreted into the cells of woody plants to provide structural support. Salicylic acid is the active ingredient in aspirin.
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Arrow Chapter # 3 Cell

Cells are the structural and functional units of life. The smallest organisms are composed of only a single cell while the largest are made up of billions of cells.

Even when comparing the most diverse and complex organisms, at the cellular level they are remarkably similar. Even though the human body has over 100 different cell types, they all share certain features and they even have many characteristics in common with plants.


I. Cells - Hooke (1663) - described cork "cells" and "nutritive juices"

A. Development of cell theory

1. Schleiden (1838) - cells are fundamental living unit of all plants

2. Schwann (1839) - cells are fundamental living unit of all animals

3. Virchow (1858) - all cells come from preexisting cells

B. Cell Theory:

1. all living organisms are composed of cells

2. cells are the fundamental units of all organisms and the chemical reactions of life take place within cells

3c. all cells come from preexisting cells

II. Two types of cells distinguish two fundamentally distinct groups of organisms

A. Prokaryotes (before, nucleus) - no nucleus, i.e. DNA not membrane bound

B. Eukaryotes (true, nucleus) - have a nucleus, i.e. DNA membrane bound
C. Prokaryotes perform most of the metabolic functions that Eukaryotes do but the reactions do not take place in distinct compartments called organelles. Prokaryotes have an outer plasma membrane and some also have a cell wall. Only a relatively small number of organisms are prokaryotes (3,000 species). The majority of organisms are Eukaryotes.


TYPICAL PLANT CELL

I. Cell Wall - plant cells have cell walls made of cellulose, beta glucose polymers.

A. Cell wall prevents the cell from being ruptured due to enlargement from water intake by vacuole. Helps keep plants erect.

B. Cell plays an important role in absorption, transport and secretion of many substances

C. Cell walls may have two or more layers and may vary in thickness depending on their role in the plant. All have at least two layers:

1. Primary wall - deposited before and during growth of the cell. In addition to cellulose may contain hemicellulose (polysaccharide) pectin and glycoproteins. Also can become lignified.

a. Actively dividing cells as well as most mature cells carrying on metabolic processes have only a primary wall. The cell wall is not of uniform thickness and may contain thin areas called primary pit fields.

b. Plasmodesmata, thin threads of cytoplasm which connect adjacent cells are aggregated in primary pit fields.

2. Middle lamella - occurs between the primary walls of adjacent cells and made up of pectic substances and galacturonic acids (polysaccharides). Difficult to distinguish from primary wall, especially after lignification.

3. Secondary wall - if present is laid down by the protoplast of the cell on the inner surface of the primary wall. Usually occurs only after cell has stopped growing and the primary wall is no longer enlarging.

a. Very important for adding strength since different composition than primary wall. Lacks pectins and glycoproteins but has more hemicellulose and the cellulose is laid down in a much denser pattern.

b. Secondary wall also has three different layers called S1, S2, S3 in which the orientation of the fibers is different such that it provides more strength. These multiple layers plus lignin are found in wood and give it its strength. When secondary wall laid down it does not cover the primary pit fields of primary wall. Therefore there are depressions or pits in the secondary walls.

D. Growth of cell wall is poorly understood but requires loosening of wall structure which is regulated by hormones, and an increase in protein synthesis, respiration and water uptake. The new microfibrils are placed on top of older, layer upon layer.

II. Protoplast - the living contents of the cell. Contains the cytoplasm and the nucleus:

A. Cytoplasm - semifluid ground substance of the cell, forms most of the cell mass. About 70% water. Contains organelles, several membrane systems, cytoskeleton and ribosomes.

B. The cytoplasm is delimited from the cell wall by the plasma membrane - a semifluid, selectively permeable lipid bilayer embedded with proteins, carbohydrates and other chemicals. The proteins regulate the flow of materials in and out of the cell.

1. Called fluid mosaic model because phospholipids move about freely in the plane of the membrane and the proteins scattered about like a mosaic.

2. Plasma membrane - keeps cells distinct from the environment:

a. mediates transport of substances into and out of protoplast.

b. coordinates synthesis and assembly of cellulose microfibrils that make up cell wall.

c. translates hormonal and environmental signals involved in the control of cell growth and differentiation.

d. Plasma membrane is very sensitive and loses its integrity with excessive heat or cold, and some chemicals.

II. Nucleus - the cell control center. Usually most prominent structure in the cell.

A. Two major functions:

1. stores the genetic information in chromosomes and passes it on to daughter cells during cell division or replication.

2. controls ongoing activities of the cell by determining which protein molecules (enzymes) are produced and when they are produced, i.e. when genes are turned on and off.

B. Nucleus is enclosed by nuclear envelope made of two lipid bilayers and perforated by tiny pores which regulate passage of substances.

C. Contents of nucleus:

1. nucleoplasm - inner matrix of the nucleus.

2. chromatin (threadlike material) - the genetic material (DNA) which is combined with proteins called histones. When tightly coiled called chromosomes.

3. nucleolus (nucleoli) - one or two small bodies which are the sites of formation of ribosomal RNA.

CONTENTS OF THE CYTOPLASM

I. Mitochondrion (Mitochondria) - powerhouses of the cell - sites of respiration, i.e. where energy is produced by breaking down organic molecules.

A. May be 1 to 1,000's per cell,

B. Mitochondria have two lipid bilayer membranes:

1. smooth outer membrane.

2. inner membrane folded into pleats or projections called crista (cristae). Greatly increases surface area available for chemical reactions to take place.

C. Mitochondria have their own ribosomes, and DNA. And their DNA is arranged like that in prokaryotes, i.e. not associated with histones and arranged in a loop. Supports endosymbiont theory.

II. Plastids - organelles which contain pigments and produce or store food. Found only in plants.

A. Chloroplasts are the most common plastid.

1. contain chlorophyll in flattened sacs called thylakoids which are arranged in stacks called grana.

B. A single leaf cell may contain 40 -5 0 chloroplasts and a square millimeter of leaf may contain 500,000 chloroplasts.

C. Chlorophyll makes plants appear green because it absorbs reds and blues and reflects green. Chlorophyll uses the sun's energy to make food and structural materials.

D. Like mitochondria plastids have two membranes, their own ribosomes, and DNA. And their DNA is arranged like that in prokaryotes, i.e. not associated with histones and arranged in a loop. Supports endosymbiont theory.

III. Vacuole - large membrane bound sac found only in plants.

A. Tonoplast = vacuole membrane

B. Central vacuole may occupy up to 90% of the volume of a mature plant cell. It contains mostly water but often also contains sugars, salts, proteins, citric acid, and many pigments. The contents of the vacuole are often called the cell sap.

C. Central vacuoles help keep plants erect because when full of water they push against rigid cell walls.

IV. Ribosomes - small beadlike structures scattered throughout the cytoplasm or attached to the endoplasmic reticulum.

A. Made up primarily of protein and RNA.

B. Sites of protein (polypeptide) synthesis.

V. Endoplasmic reticulum (ER) - a complex 3-dimensional network of membranes which extends from the nuclear envelope to the plasma membrane.

A. May be smooth or rough. Rough ER has ribosomes attached for protein synthesis and transport.

B. The ER appears to function as a communication system within the cell as well as a system for channeling materials such as proteins and lipids throughout cell.

C. ER of adjacent cells is interconnected by threads called plasmodesmata.

VI. Golgi Complex - collective term for all the golgi bodies (dictyosomes) of a cell.

A. Golgi bodies are groups of flat, disk-shaped sacs, each of which is called a cisterna (pl. cisternae).

B. Involved in secretion, processing and packaging materials for storage or transport to other areas, e.g. in plants they help form cell wall.

OTHER CELLULAR STRUCTURES

I. Cytoskeleton - 3-D network of protein fibers which provides structural framework for the cell and suspends the organelles.

II. Ergastic substances - passive products, i.e. not directly involved in metabolism of cell. May be storage compounds or waste products.

A. May appear in the cytoplasm, cell wall or in organelles. E.g. starch grains, crystals (silica), pigments, oil droplets, resins, gums, tannins.

III. Flagella and cilia - hairlike structures which extend from the surface of some eukaryotic cells.

A. Mostly function in locomotion (movement).

B. Structurally flagella and cilia are the same but flagella are longer than cilia.

C. All cilia/flagella have 9 + 2 pattern, i.e. an outer ring of nine pairs of microtubules which surrounds two central microtubules. This supports the theory of evolution.
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Arrow Chapter # 4 Cell Cycle

Since organisms start from one cell, yet adults may contain billions of cells, a process for producing new identical cells is required. Likewise, most cells have a relatively short life so they must constantly be replaced.

I. How prokaryotic cells divide

A. Prokaryotic cells lack a nucleus and organelles

B. Prokaryotes have a single circular loop of DNA attached to the inside of the plasma membrane; about 1,000 times the length of the cell

C. Prokaryotes reproduce asexually via binary fission

D. Before cell division takes place, DNA is replicated so two chromosomes are attached inside the plasma membrane

E. Following DNA replication, the two chromosomes separate when cell lengthens and pulls them apart

F. When cell is approximately twice its original length, the plasma membrane grows inward, a new cell wall forms, dividing the cell into two approximately equal daughter cells

II. Eukaryotic chromosomes

A. DNA in the chromosomes of eukaryotic cells is associated with histone proteins

B. When a eukaryotic cell is not undergoing division, DNA within a nucleus is a tangled mass of threads called chromatin

C. At cell division, chromatin becomes highly coiled and condensed, and visible as chromosomes

D. Each species has a characteristic number of chromosomes

1. With the exception of bacteria virtually all organisms have two sets of each chromosome in their non-sex cells, one came from each parent

2. Diploid (2n) number = 2 sets of chromosomes in somatic (body) cells, e.g. humans have 2n = 46

3. Haploid (n) number = one set of chromosomes, usually restricted to sex cells, e.g. human sperm and eggs have n= 23

E.g., Humans have 23 pairs of homologous chromosomes - corresponding chromosomes, one from each parent, which contain the same genes

E. Cell division in eukaryotes involves nuclear division and cytokinesis (division of the cytoplasm)

1. Somatic (body) cells undergo mitosis in the development, growth, and repair of multicellular organisms

a. This nuclear division leaves the chromosome number constant

b. A 2n nucleus divides to provide daughter nuclei that are also 2n

2. A chromosome begins cell division with two sister chromatids

1) Sister chromatids are two parts of a chromosome, at the beginning of cell division, that are attached at a centromere; each consists of a DNA molecule identical to the DNA molecule of the other chromatid

2) Centromere = a region of constriction on a chromosome, where sister chromatids are attached.

III. The cell cycle has three continuous overlapping phases:

A. Interphase - the time between cell divisions

B. Mitosis - division of the nuclear material

C. Cytokinesis - division of the cytoplasm

A. Interphase - the phase between successive mitotic divisions. It is the period of normal metabolic activity

1. Three phases:

a. G1 - period of normal metabolic cellular activities: transcription, translation (protein synthesis) and growth of the cytoplasmic materials including the organelles

b. S - the genetic material (DNA) is duplicated, chromosomes now consist of two chromatids joined at the centromere

c. G2 - metabolic activities in preparation for mitosis

B. Mitosis - the process by which a nucleus gives rise to two identical daughter nuclei, four overlapping phases:

1. Prophase

a. Chromatin condenses and chromosomes become visible

b. Nucleolus and nuclear envelope disappear

2. Metaphase

a. Spindle forms and attaches to kinetochores

Kinetochores are protein containing structures, one on each chromatid, associated with the centromere.

b. chromosomes align on the equatorial plane (metaphase plate)

3. Anaphase

a. centromeres divide

b. daughter chromosomes move towards opposite poles

4. Telophase

a. Spindle disappears

b. Chromosomes decondense and return to chromatin

c. Nuclear envelope reforms and nucleoli reappear.

C. Cytokinesis (cytoplasmic cleavage)

1. In plant cells golgi apparatus produces vesicles that fuse, forming a cell plate

2. In animals a cleavage furrow indents the plasma membrane between the two daughter nuclei at a midpoint; then constriction separates the cytoplasm

IV. Consequences of the cell division

1. Nuclear material was duplicated prior to division

2. Therefore two new genetically identical cells are formed

V. Duration of cell cycle - varies with the tissues and organism involved. Average time for events in plant root tip:

Interphase: 12 - 30 hrs.

Prophase: 1 - 2 hrs.

Metaphase: 5 - 15 min.

Anaphase: 2 - 10 min.

Telophase: 10 - 30 min.
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Arrow Chapter # 5 Meiosis

Unlike single celled prokaryotes, most organisms are diploid and multicellular. At a particular time in their life cycle certain cells will differentiate, via meiosis, into haploid cells. During sexual reproduction two haploid cells called gametes will unite, thus restoring the diploid chromosome number in the next generation. Meiosis is especially important because it produces genetic variation, the raw material for evolution.

I. Halving the chromosome number

A. Sexual reproduction

1. Requires gamete formation and then fusion of gametes (syngamy) to form a zygote

a. Gamete = a sex cell (sperm or egg)

b. Zygote = first diploid cell resulting from syngamy (fertilization)

2. If gametes contained same number of chromosomes as body cells, doubling would soon fill cells


B. Life cycles

1. Life cycle refers to all reproductive events between one generation and next

2. Mitosis = nuclear division that maintains a constant chromosome number

3. Meiosis = nuclear division reducing chromosome number from diploid (2n) to haploid (n) number

4. Meiosis occurs at different points during life cycle of various organisms

C. Three basic types of life cycles:

1. gametic meiosis - meiosis give rise to gametes which fuse together in syngamy (fertilization). Characteristic of animals and some types of algae. Therefore, in animals, sexual reproduction involves a regular alternation between meiosis and syngamy.

2. sporic meiosis - in true plants (and some algae) meiosis results in the production of haploid spores, cells that can grow directly into a new haploid individual. Therefore, in plants there is a regular alternation of generations between haploid and diploid individuals.

a. In most plants meiosis takes place within flowers.

3. zygotic meiosis - haploid individuals (or cells) fuse to form a diploid zygote which immediately undergoes meiosis. This is the simplest type of life cycle and occurs in unicellular haploid organisms such as some algae and all fungi.

D. Chromosomes occur in homologous pairs

1. In a diploid cell, chromosomes occur as pairs

a. Each set of chromosomes is a homologous pair; each member is a homologous chromosome or homologue

Homologous chromosomes - corresponding chromosomes, one from each parent, which contain the same genes

b. Homologues look alike; they have same length and centromere position; have similar banding pattern human karyotype

c. A locus (location) on one homologue contains the same types of gene which occur at the same locus on the other homologue

2. Chromosomes duplicate just before nuclear division

a. Duplication produces two identical parts called sister chromatids, held together at centromere

3. One member of each homologous pair is inherited from either male or female parent; one member of each homologous pair is placed in each sperm or egg

II. Overview of meiosis

A. Purpose of Meiosis

1. Meiosis keeps chromosome number constant across the generations

2. Makes sure that each gamete contains only one member of each homologous pair

B. Meiosis has two divisions

1. Since meiosis involves two nuclear divisions it produces four haploid daughter cells; each, containing half the total number of chromosomes as the diploid parent nucleus

2. Meiosis I - the first nuclear division

a. Prior to meiosis I, DNA replication occurs and each chromosome has two sister chromatids

b. During meiosis I, homologous chromosomes pair; come together and line up in synapsis

c. During synapsis, the two sets of paired chromosomes lay alongside each other as bivalents

d. While paired up the chromosomes have equal exchanges of genetic material; this is called crossing over

e. After crossing-over occurs, sister chromatids of a chromosome are no longer identical

3. Meiosis II - second nuclear division, nearly identical to mitosis

a. No replication of DNA needed between meiosis I and II because chromosomes were already doubled

b. During meiosis II, centromeres divide; daughter chromosomes derived as sister chromatids separate

c. Chromosomes in the four daughter cells have only one chromatid

C. Crossing-over produces genetic variation, the raw material for evolution

1. Crossing-over results in exchange of genetic material between nonsister chromatids

2. Due to crossing-over, daughter chromosomes derived from sister chromatids have different mix of genes

PHASES OF MEIOSIS

I. Prophase I

A. Nucleolus disappears; nuclear envelope fragments; and spindle fibers assemble

B. Homologous chromosomes undergo synapsis forming bivalents; crossing-over may occur at this time in which case sister chromatids are no longer identical

C. Chromatin condenses and chromosomes become visible

II. Metaphase I

A. Bivalents independently align themselves at the equatorial plane (metaphase plate)

B. This independent assortment during metaphase I is another form of genetic recombination; produces more genetic variation

C. The different possibilities can be calculated using the formula 2n where n = haploid chromosome number. E.g. in humans 8,388,608 different ways homologous pairs can line up (223)

D. Note centromeres are on opposite sides of the equatorial plane

III. Anaphase I

A. The homologues of each bivalent separate and move toward opposite poles

B. Each chromosome still has two chromatids

C. Note the centromeres do not divide

IV. Telophase I

A. Only occurs in some species

B. When it occurs, the nuclear envelope reforms, nucleoli reappear and chromosomes may decondense

V. Interkinesis

A. Period between meiosis I and meiosis II

B. No DNA replication occurs


THE SECOND MEIOTIC DIVISION IS NEARLY IDENTICAL TO MITOSIS

VI. Prophase II

A. If need be the nuclear envelope and nucleoli dissolve and chromatin condenses into chromosomes

VII. Metaphase II

A. The chromosomes align with their centromeres on the equatorial plane

VIII. Anaphase II

A. Centromeres divide and daughter chromosomes move toward the poles

IX. Telophase II

A. Nuclear envelope reforms, nucleoli reappear and chromosomes decondense

B. Cytokinesis produces four haploid daughter cells

X. Comparison of meiosis and mitosis:

A. Mitosis occurs more often because it allows growth and repair of body tissues in multicellular organisms; meiosis only occurs at certain times in the life cycle of sexually reproducing organisms

B. DNA is replicated only once before both mitosis and meiosis; in mitosis there is only one nuclear division; in meiosis there are two nuclear divisions

C. There is no crossing-over in mitotic prophase; there is crossing-over in prophase I of meiosis

D. Duplicated chromosomes align on metaphase plate in mitosis; bivalents align on the metaphase I plate

E. Sister chromatids separate to form daughter chromosomes in anaphase of mitosis; homologous chromosomes separate in anaphase I of meiosis

F. Meiosis II is like mitosis except the meiosis nuclei are haploid

G. Mitosis produces two daughter cells; meiosis produces four daughter cells

H. In mitosis, two daughter cells have same chromosome number as parent cell; in meiosis, four daughter cells are haploid

I. In mitosis, the daughter cells are genetically identical to each other and to the parent cell; in meiosis, the daughter cells are not genetically identical to each other or to the parent cell

XI. Significance of Meiosis

A. Meiosis produces genetic variation

1. Without meiosis, chromosome numbers would continually increase

2. Meiosis ensures daughter cells receive one of each kind of gene; precisely halves the chromosome number

3. Independent assortment provides 2n possible combinations of chromosomes in daughter cells

4. In humans with 23 haploid chromosomes, 2n = 223 = 8,388,608 possible combinations.

5. Variation is added by crossing-over; if only one crossover occurs within each bivalent, 423 or 70,368,744,000,000 combinations are possible

6. Fertilization also contributes to genetic variation; (223)2 = 70,368,744,000,000 possible combinations without crossing-over

7. With fertilization and crossing-over, (423)2 = 4,951,760,200,000,000,000,000,000,000 combinations are possible

B. Advantages of Meiosis

1. Tremendous storehouse of genetic variation provides for adaptations to changing environment

2. Asexual organisms depend primarily on mutations to generate variation
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Arrow chapter # 6 Introduction To Vascular plants

INTRODUCTION TO VASCULAR PLANTS

I. Two major types of true plants:

A. Vascular (higher) plants:

1. Have true conducting tissues (xylem and phloem), leaves, stems and roots

2. The sporophytes are the dominant phase and the gametophytes are much reduced

3. Constitutes the majority of plants

B. Non-vascular (lower) plants

1. Lack true conducting tissues, leaves and roots. Since they lack elaborate conducting tissues they are relatively small

2. The gametophytes are the dominant phase and the sporophytes are dependent upon them

3. Require water for fertilization so they must grow in moist or seasonally moist habitats

II. Earliest land plants:

A. The invasion of land by plants probably occurred about 450 million years ago because by 430 million years ago there were many fossil land plants

B. The earliest land plants were relatively simple and undifferentiated (see p. 433)

1. They had dichotomously branched photosynthetic axes that lacked true leaves and roots

2. Specialization led to differentiation of these simple axes into roots, stems and leaves

ORGANIZATION OF THE VASCULAR PLANT BODY

I. Vascular plants have three systems:

A. Root system - collective term for roots which anchor the plant and also absorb water and minerals from the soil

B. Shoot system - made up of the stems and leaves together. Leaves are specialized photosynthetic organs

C. Vascular system - conducts water and minerals to the leaves and the photosynthetic products away from the leaves to the rest of the plant

II. Tissue systems:

A. Different kinds of cells are arranged into tissues, and the tissues are further arranged into tissue systems, which are arranged into the organs (either roots, stems or leaves)

B. Three tissue systems occur, in different proportions, in all organs of the plant

1. Dermal - makes up the outer protective coating of the plant

2. Vascular - xylem and phloem, the conducting tissues

3. Ground - all other tissue

C. All three tissues systems occur in all organs of the plant and they are continuous from organ to organ

D. The principle differences between roots, stems and leaves lie primarily in the relative distribution of the vascular and ground tissue systems

GROWTH

I. Growth in plants is restricted primarily to meristems

A. meristem = undifferentiated tissue from which new cells arise

B. There are two types of growth:

1. Primary growth - it occurs relatively close to the tips of roots and stems

a. It is initiated by apical meristems and it is primarily involved in the extension of the plant body

b. The tissues that arise during primary growth are called primary tissues and the plant body composed of these tissues is called the primary plant body

c. Most primitive vascular plants are entirely made up of primary tissues

2. Secondary growth - in addition to primary growth some plants undergo additional growth that thickens the stems and roots

a. Secondary growth results from the activity of lateral meristems

Lateral meristems are called cambia (cambium) and there are two types:

1) Vascular cambium - gives rise to secondary vascular tissues (secondary xylem and phloem). The vascular cambium gives rise to xylem to the inside and phloem to the outside

2) Cork cambium - which forms the periderm. The periderm replaces the epidermis in woody plants.

b. The secondary vascular tissues and periderm make up the secondary plant body

c. Secondary growth appeared in the fossil record about 380 million years ago

VASCULAR SYSTEM

I. The vascular system is made up of:

A. Phloem - the food conducting system

1. The individual cells are called sieve elements. They have soft walls and they often collapse after they die. Therefore they are rarely preserved in fossils

B. Xylem - water conducting system. The principal conducting cells are called tracheary elements. They have rigid and persistent walls, and they are usually well preserved in the fossil record. There are two major types:

1. Tracheids - long, thin cells with imperforate end walls

a. Most primitive type of conducting cells and they are found in most of the seedless vascular plants and gymnosperms

2. Vessels (vessel members) - shorter, wider cells with perforate end walls

a. Vessels members are strung end to end to make continuous "tubes" for conducting water throughout the plant

b. They are the principle water conducting cells in the flowering plants and a few other groups

II. Arrangement of primary vascular tissues:

A. Stele = the arrangement of the primary vascular tissues and the pith, if present. There are three types of steles:

1. Protostele - consists of a solid strand of vascular tissue in which the phloem either surrounds the xylem or is interspersed within it

a. Most primitive type and it is found in extinct seedless vascular plants as well as the Psilotophyta, Lycophyta and the roots of most extant plants

2. Siphonostele - consists of a central column of ground tissue called the pith, which is surrounded by the vascular tissue. The phloem may form outside the cylinder of xylem or on both sides of it

a. Found mostly in ferns, the Pterophyta

3. Eustele - consists of a system of discrete vascular strands around a central pith

a. Eusteles are found in Sphenophyta, and both the gymnosperms and angiosperms

ORIGIN OF ROOTS

I. Roots are relatively simple structures and they probably are just derived from subterranean stems

A. The roots of nearly all extant plants are protosteles, indicating how little they have changed during the course of evolution

ORIGIN OF LEAVES

I. Two very different kinds of leaves occur in the vascular plants, suggesting there were probably two different ways they evolved

A. Microphylls

1. Have only one vascular strand and they appear to have originated as outgrowths of the stem

2. Found in groups that have protosteles

3. They were probably first just scale like growths in which leaf traces developed

B. Megaphylls

1. Have more than one vascular trace and they appear be derived from webbing and fusion of several branches

2. They are associated with siphonosteles and eusteles

VASCULAR PLANT REPRODUCTION

I. All vascular plants are oogamous and they have alternation of generations in which most of the gametophytes are reduced and nutritionally dependent upon the dominant sporophyte

A. Alternation of generations = a reproductive cycle in which a haploid organism (or tissue) gives rise to a diploid organism (or tissue) which later undergoes meiosis, the products of which later grow into a haploid organism (or tissue)

1. The haploid, gamete-producing phase is called the gametophyte

2. The diploid spore-producing phase is called the sporophyte

II. The earliest vascular plants produced one kind of spore so they are called homosporous

A. Following meiosis the spore germinates into a bisexual gametophyte which gives rise to antheridia and archegonia, which produce sperm and egg, respectively

B. Homospory is common in most of the extinct, primitive vascular plants as well as the Psilotophyta, Sphenophyta, some Lycophyta, and most ferns, the Pterophyta

III. More advanced (recent) plants are heterosporous

A. Plants produce two types of spores in two different kinds of sporangia

B. The spores are called microspores (male) and megaspores (female), and they are produced in microsporangia and megasporangia

C. Microspores give rise to microgametophytes (male) and megaspores give rise to megagametophytes (female)

D. Heterospory occurs in some Lycophyta, a few ferns and all seed plants

E. Heterospory evolved by at least by 370 million years ago
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