Cell:
The Smallest unit of living matter that can exist by itself is the cell. Some organisms, such as bacteria, consist of only a single cell. Others, such as humans and Oak trees, are composed of many billion cells.
Cells exist in a variety of shapes and sizes. Red blood cells are disk-shaped, while some skin cells resemble cubes. A single cell could be as large as the tennis ball or so small that thousands would fit on the period at the end of this sentence. Regardless of size, however, every cell contain the components needed to maintain life. Cells normally function with great efficiency, though they are vulnerable to disease.
Cell size is usually measured in microns. A micron is equal to about one millionth of a meter, and about 25000 microns equal 1 inch. The smallest bacteria are about 0.2 micron in diameter. The diameter of average human cell is roughly 10 microns, making it barely visible without a microscope.
The study of cell is branch of biology called cytology, and the scientists who specialize in this field, are called cytologists. A related field is molecular biology, which examines large molecules such as nuclei acids and proteins and their role in cell structure and function.

Prokaryotes and Eukaryotes:
Most scientists today agree that all living organisms can be divided into two major groups--prokaryotes and eukaryotes--based on fundamental differences in cell structure. Within these groups, the organisms are further classified into kingdoms, based on the variety of characteristics. Prokaryotes consist of single kingdom—Monera—that is made up entirely of bacteria. The eukaryotes include the animal, plant, fungi and protest kingdoms.
Prokaryotic and eukaryotic cells are distinguished by several key characteristics. Both cell types contain DNA as their genetic material. However, prokaryotic DNA is single-stranded and circular, and its floats freely inside the cell; eukaryotic DNA is double-stranded and linear and is enclosed inside a body called the nucleus. Eukaryotes also have membrane-bound organelles—specialized structures that do much of the cell’s work. Prokaryotes lack organelles, though they must accomplish many similar vital tasks. This inability to “delegate” tasks makes prokaryotes less metabolically efficient than eukaryotes.





Cell Structure and Function:

All cells consist of protoplasm, a living jellylike substance made up of water, proteins, and other molecules surrounded by a membrane. The protoplasm within the main body of the cell is called cytoplasm. This is the site of much of the cell’s work. Structures inside eukaryotic cells, such as organelles, contain their own protoplasm.

Cell Membrane:
Cells can survive only in a liquid medium that brings in food and carries away waste. For unicellular (Single-celled) organisms, such as bacteria, algae, and protists, this fluid is an external body of water, such as lake or stream. For multicellular (many-celled) organisms, the medium is part of the organism. In plants, for example, it is the sap; in animals, the blood.
The cell membrane is semipermeable—that is, some substances can pass through it but others cannot. This characteristic enables the cell to admit and reject substances from the surrounding fluid and enables the cell to excrete waste products into its environment.
The cell membrane is composed of two thin layers of phospholipid molecules studded with large proteins. Phospholipids are chemical similar to stored fat that give the membrane its fluid quality. Some of the membrane proteins are structural; others form pores that function as gateways to allow or prevent the transport of substances across the membrane.
Substances pass through the cell membrane in several ways. Small uncharged molecules, such as water, pass freely down their concentration gradient ( from the side of membrane where they are in higher concentration to the side of lower concentration ). This movement is called diffusion. Other materials, such as ions ( charged molecules ), must be transported through channels—membrane pores that are regulated by chemical signals from the cell. This facilitated transport requires energy for substances moving against a concentration gradient.

Passive transport:
Substances such as glucose or ions enter the cell through specific channels, travelling down their concentration gradient. Since the process does not require energy, it is called passive transport.
Active transport:
Molecules moving against their concentration gradient must be “escorted” across the cell membrane. This is called active transport, and it requires the cell to spend energy. Chemical signals in the cell tell the membrane channels when to start and when to stop the transport process.
Endocytosis and exocytosis:
Endocytosis is the process used by cells to take in certain materials. The cell membrane forms a pocket around a substance in its environment. The filled pocket breaks loose from the membrane, forming a bubblelike vacuole that drifts into the cytoplasm, where its contents are “digested”: the vacuole wall is broken down and the contents are released into the cytoplasm. The process is called pinocytosis (pino – is from the Greek pinein, meaning “to drink”) when the material is dissolved in fluid and phagocytosis (phago—is from the Greek phagein, meaning “to eat”) when the cell ingests larger, particulate matter, such as another cell. The reverse process, exocytosis, is used to remove material from the cell.
Cell Wall:
Almost all prokaryotes, as well as the cells of plants, fungi, and some algae, have a cell wall—a rigid structure that surrounds the cell membrane. Most cell walls are composed of polysaccharide—long chains of sugar molecules linked by strong bonds. The cell wall help maintain the cell’s shape and, in larger organisms such as plants, enables it to grow upright. The cell wall also protects the cell against bursting under certain osmotic conditions.
Plant cell walls, as well as those of green algae and some other protists, are made mostly of the polysaccharide cellulose. In Some plants, the cellulose is mixed with varying amounts of other polysaccharides, such as lignin, an important component of tree bark and wood. In some fungi the cell wall is composed of chitin, a polysaccharide that also forms the exoskeleton of many invertebrates such as insects and crabs. The bacterial cell wall is composed mostly of peptidoglycan, which is made up of polysaccharides and amino acids. Diatom cell walls have a high concentration of silica, which gives them a glasslike appearance.


Cytoplasm:
Water is the largest component of cytoplasm. Depending on the cell and its needs and conditions, water concentration varies from about 65 percent to roughly 95 percent. Suspended in the cytoplasm are various solids such as proteins, carbohydrates, fat droplets, and pigments. As such, cytoplasm is colloid rather than simply a solid or a liquid.
Changes in the concentration of solids produce an apparent streaming of the cytoplasm from place to place within a cell. When viewed through a microscope, membranes and fibrous structures are more readily visible in the cytoplasm when the concentration of solid increases. This visibility decreases as the solid content decreases.

Organelles and Their Functions:
Cells are constantly working to stay alive. Food molecules are changed into material needed for energy, and substances needed for growth and repair are synthesized, or manufactured. Some of these tasks occur in the cytoplasm; in eukaryotes, however, most specialized tasks take place inside membrane-bound bodies in the cytoplasm called organelles.
Plastids:
Plastids are found in the plant cells and in protists such as algae that use photosynthesis to manufacture and store food. Chloroplasts, chromoplasts, and leucoplasts are the most common plastids. Photosynthesis takes place inside chloroplasts, which contain chlorophyll, a green pigment that captures energy from the sun and converts it into sugar. Chromoplasts, most commonly found in fruits and flower petals, contain other pigments, such as orange carotenes, yellow xanthophylls, and red and blue anthocyanins. These pigments give fruits and flowers their colors and produce the brilliant fall hues seen in many trees species. Leucoplasts are colorless and usually contain starch granules or other materials.
All plastids have an inner and outer membrane; the inner membrane is highly impermeable, while the outer is semipermeable. Plastids have their own DNA; it is distinct from the DNA found in the cell’s nucleus and is replicated and inherited independently. Plastids manufacture some of their own proteins but rely on the cell’s DNA and ribosomes to synthesize others.

Mitochondria:
Often called the powerhouses of the cell, the sausage-shaped mitochondria produce the energy needed by the cell to function. Food molecules that pass into the cytoplasm are taken into the mitochondria and oxidized, or burned, for energy. Like plastids, mitochondria have an inner and an outer membrane. Also like plastids, they depend upon the cell’s DNA for certain proteins though they have their own DNA.

Endoplasmic reticulum and ribosomes:
The endoplasmic reticulum (ER), a network of membranous tubes and sacs, twists through the cytoplasm from the cell membrane to the membrane surrounding the nucleus. Located along portions of the endoplasmic reticulum are ribosomes, tiny bodies made of ribonucleic acid (RNA) that play a vital role in manufacture of proteins. Ribosomes are also found scattered throughout the cytoplasm; distinct sets of ribosomes are found in plastids and mitochondria.
The portions of the endoplasmic reticulum that contain ribosomes are called rough endoplasmic reticulum (RER). Areas of the network that do not contain ribosomes are called smooth endoplasmic reticulum (SER). The latter is predominant in cells involved in the synthesis and metabolism of lipids and the detoxification of some drugs.

Golgi complex:
The Golgi complex, or Golgi apparatus, is a membranous structure composed of stacks of thin sacs. Newly made proteins and lipids move from the RER and SER, respectively, to the Golgi complex. The materials are transported inside the vesicles formed from the ER membrane. At the Golgi complex, the vesicles fuse with the Golgi membrane and the contents move inside the Golgi’s lumen, or centre, where they are further modified and stored. When the cell signals that certain proteins are needed, the latter are ‘packaged’ by the Golgi for export—part of the Golgi membrane forms a vesicle that then buds off, or breaks away, from the larger apparatus. The vesicle may migrate to the cell membrane and export its contents via exocytosis or it may travel to an intracellular location if its contents are needed by the cell. Lipids are processed by the same methods.
Vacuoles:
Vacuoles drift through the cytoplasm and usually carry food molecules in solution. Vacuoles are regulate the water content of some unicellular organisms. For example, when an amoeba absorbs too much water, it forms a contractile vacuole against the membrane. The vacuole fills with the water and then contracts to squeeze the excess liquid out of the cell.
Vacuoles in cambium cells in plants develop large central vacuoles that play a role in building stalks and stems. If a cambium cell is to become bark or wood, its membrane grows into the vacuole and deposits layers of cell wall to increase stiffness. In cells that become part of vascular bundle that transmits sap, the vacuole becomes cylindrical and develops openings at each end that pass sap from cell to cell.

Lysosomes and peroxisomes:
Lysosomes are similar in appearance to vacuoles. Each lysosome is filled with enzymes that help the cell to digest certain material, such as cell plants that are no longer functional, and foreign particles, such as bacteria. Similar to lysosomes are peroxisomes, which contain enzymes that destroy toxic material such as peroxide. Lysosomes are produced in the Golgi complex, while peroxisomes are self-replicating.
Centrosomes:
Near the nucleus of animal, fungus, and algae cells is a spherical structure called the centrosome. During cell division, the centrosome divides into two centrosomes. Each of these then travels to opposite ends of the cell. The centrosomes contain a pair of structures called centrioles, which produce microtubules. These protein tubes form “spindles” that extend toward the nucleus and help the cell’s chromosomes separate during cell division. Plant cells lack centrioles, but they do have the centrosomes, which serve a function similar to that in animal cells.

Cytoskeleton:
The cytoskeleton helps the cell maintain its shape, aids in cellular movement, and helps with internal movement. Found only in eukaryotic cells, the cytoskeleton is the network of proteins filaments and tubules that extends throughout the cytoplasm. Microtubules help form structures such as cilia and flagella, which help in cell movement, and the spindle fibers that help chromosomes moving during cell division. Mircofilaments give the cell its shape and help it contract; intermediate filaments give it strength.

Nucleus:
Near the center of the cell is nucleus. The nucleus is the control center of the cell. It also contains the structures that transmit hereditary traits. A nucleus not undergoing division has at least one nucleolus, which is the site of RNA synthesis and storage.
The nucleus is enclosed by a two-layered membrane and contains a syrupy nucleoplasm and strands of DNA wrapped around proteins in a manner that resembles a string of beads. Each strand contains a long series of genes—segments of DNA inherited from the previous generation. Each gene determines a heritable characteristics of the organism. Genes also regulate the production of RNA, which in turn controls the manufacture of specific proteins.
The DNA strands, which are called chromatin because they readily stain with dyes, are usually too thin to be seen with an optical microscope. When a cell begins to divide, the chromatin-protein strands coil repeatedly around themselves, condensing into thicker structures called chromosomes.

Nitrogen:
About two thirds of the air in the atmosphere is composed of the inert gas nitrogen. During breathing nitrogen is exhaled from the lungs chemically unchanged. Most nitrogen exists as a free element in the atmosphere. The compounds it forms are extremely active and essential to all living things.
Protoplasm in living cells requires nitrogen for its formation. Protein, which is essential to life, is composed of nitrogen compounds linked together. Despite the abundance of free nitrogen in the air, it must be combined in compounds to be used by living things. The process by which free nitrogen is joined to other elements is called nitrogen fixation.

Nitrogen Fixation and Circulation of Nitrogen:
Nitrogen fixation occurs in nature by the actions of lightning and bacteria. A flesh of lightning unites nitrogen with oxygen to form nitric oxide (NO), which changes to nitrogen dioxide (NO2) upon cooling. Nitrogen dioxide combines with water to form nitric acid (HNO3). The dilute acid falls to the earth and reacts with minerals in the soil to produce nitrates. The nitrates form compounds necessary for cell growth. A greater amount of nitrogen is fixed by the action of bacteria in the soil and plant roots.
Among nitrogen-fixing bacteria are Clostridium pasteurianum and species of the genera Azotobacter and Rhizobium. Plant-dwelling bacteria live only on the roots of legumes. However, they fix more nitrogen than these plant require. The surplus is stored in the roots and escapes to the soil when the plant dies. Both soil and plant-dwelling bacteria take nitrogen from the air and combine it with hydrogen to form compounds that join to form proteins.
Nitrogen in living tissues can be used repeatedly. If a plant or animal dies, bacteria of decay break up proteins, and nitrogen is released in ammonia (NH3). Part of this escapes into the air. The remainder is acted upon by another type of bacteria to convert ammonia to nitrites. Still another type of bacteria changes the nitrites to nitrates, which plants use to create proteins. The bacteria that do this vital work are called nitrifying bacteria. The opposite result is produced by denitrifying bacteria. They act on protein during the decay process to release nitrogen to the atmosphere. This continual loss is made up, in part, by the action of the nitrifying bacteria. The circulation of nitrogen between the atmosphere and the soil is called the nitrogen cycle.


Artificial fixation of Nitrogen:
When plants die they return nitrogen to the soil. When crops are harvested, however, nitrogen is removed and is not returned. For this reason, it is necessary to cover the soil periodically with nitrogen compounds called fertilizers. Sodium nitrate, ammonium sulfate, and the waste products of animals are substances that provide the soil with nitrogen.
Nitrogen processes do not produce the necessary amounts of such nitrogen compounds. Chemists have devised a number of processes for converting free nitrogen into usable nitrogen compounds. The Haber-Bosch process subjects a mixture of nitrogen and hydrogen to tremendous pressure in the presence of an iron catalyst. The gases unite to form ammonia. This is the most widely used industrial method of nitrogen fixation. The Casale process and the Claude process are variations of the Haber-Bosch method.
A second important method is the electric arc process. In this process, air is blown through an electric furnace. Nitrogen and oxygen unite to form nitrogen peroxide which is then passed through a spray of water to form nitric acid. This method requires a large supply of low-cost electric power. In the cyanamide process, nitrogen is passed over hot calcium carbide (CaC2). The resulting reaction produces calcium cyanamide (CaCN2). This compound Can be used directly as a fertilizer or can be converted to ammonia.

Chemistry of Nitrogen:
Nitrogen was first identified by the British chemist Daniel Rutherford in 1772. It is a colorless gas at standard temperature and has an atomic weight of 14.0067. It liquefies at -198.8* C (-320.4 * F) and freezes at -209.9* C (-345.8* F). The valence of nitrogen ranges from one to five. The combinations are illustrated by its compounds with divalent oxygen. It forms nitrous oxide (N2O), nitric acid (NO), nitrogen dioxide (NO2) and nitrogen penoxide (N2O5). In most cases, however, the valence of nitrogen in its compounds is three or five.

Photosynthesis

Introduction

 Without photosynthesis, the replenishment of the Earth's fundamental food supply would halt, and the planet would become devoid of oxygen. During photosynthesis the radiant energy from the sun is harnessed and converted to the chemical energy stored in green plants and certain bacteria. In green plants this energy is used to convert carbon dioxide, water, and minerals from the environment into organic compounds and gaseous oxygen—the food we eat and the air we breathe. The process is an almost exclusive property of the varied members of the plant kingdom.


Photosynthesis Reactions

The chemical equation for the process of photosynthesis is as follows:

6CO2 + 6H2O +  light  →  C6H12O6 +  6O2

The actual process, however, is far more complex than the equation might suggest. The equation indicates that atmospheric carbon dioxide, CO2, is “fixed,” or converted from a gas to the solid sugar C6H12O6, water (H2O) is consumed, and oxygen (O2) is liberated. Yet within this deceptively simple reaction are two distinctly different processes. The first is photochemical and the second is biochemical; they are the so-called light and dark reactions.

All photosynthetic organisms—with the exception of a small group of bacteria—contain the light-absorbing pigment called chlorophyll. This pigment plays a very important role in the transfer of energy from light to chemical compounds.

Other pigments may also be involved, depending on the type of organism in which the photosynthesis occurs. These pigments come in many colors; for instance, chlorophylls are green and phycocyanins are blue. Light for photosynthesis is harvested from the visible spectrum (see Color; Light), and each of these pigments is responsible for absorbing the light from a particular range within that spectrum. The result is a form of light-absorption array, or antenna, that neatly matches the entire visible spectrum.

During the light reaction the pigments absorb light energy. A captured photon, or “particle” of light, is passed through the pigment antenna to specialized chlorophylls that carry out a process called free-charge separation. In this process an electron (e–) is separated from the chlorophyll molecule and is passed, at a higher energy, to a molecule called a carrier, thereby converting the energy of the photon into chemical energy. The electrons lost by the chlorophylls are replaced by splitting off electrons from water. This process is called photolysis, and it is the source of gaseous oxygen. The photolytic reaction can be described as an equation, which is written in the following manner:

H2O → 2H+ + 2e– + 1/2O2

Two such free-charge separations, called photoacts, are connected in series. As electrons pass between photoacts, the energy-rich compound adenosine triphosphate (ATP) is formed by the addition of an inorganic phosphate group (Pi) to a molecule of adenosine diphosphate (ADP), and the electron loses energy. This process is called photophosphorylation, and it can be described as an equation, which is written in the following manner:

ADP + Pi → ATP + H2O

In the second photoact, the compound NADP+ is reduced—that is, it gains electrons—to form the electron donor compound nicotinamide adenine dinucleotide phosphate (NADPH):

NADP+ + H+ + 2e– → NADPH

The compounds ATP and NADPH are used in the next stage of photosynthesis, the dark reaction. In nature, for every ten photons absorbed, two to three molecules of ATP and two molecules of NADPH are formed. This translates into an energy conversion efficiency of about 38 percent.

In the dark reaction, the ATP and NADPH formed in the light reaction are used to transform inorganic carbon dioxide (CO2) into organic carbon compounds, a process called carbon fixation. The process is a biochemical cycle and involves the formation of intermediate compounds called sugar phosphates. The input is the sugar ribulose bisphosphate (RuBP) and carbon dioxide (CO2); the output is the sugar triose phosphate (TP). The reaction is brought about, or catalyzed, by the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO). The reaction can be described as an equation, which is shown in the following line:

RuBP + CO2 → (RuBisCO) → 2TP

The cycle then regenerates RuBP through a complex series of reactions. The sugars produced by these reactions are used to synthesize higher carbohydrates, proteins, and fats—the plant foodstuffs that are the end products of photosynthesis.

SOLAR SYSTEM:

THE SUN

Our closest star, the Sun, is the center of the solar system. All the
planets and asteroids are held in their orbits by its immense gravity.
It also attracts objects from the farthest reaches of the solar system,
such as comets. For billions of years, the Sun has been providing Earth with
light that green plants use as an energy source for living and growing.
Herbivorous animals eat the plants, and carnivorous animals eat the herbivores.
In this way, the Sun powers life on Earth.

STAR PROFILE:

Diameter at Equator 864,938 miles
(109 time Earth’s)
Surface area 109109 sq miles
(12,000 times Earth)
Mass 2x1027 tons
(333,000 times Earth)
Volume 33 x 1016 cubic miles
(1.3 million times Earth)
Overall density 99 lbs. per square foot
Gravity (Earth = 1) 27.9
Number of main planets 9 (debated)



MERCURY

Known by most ancient people by its brief periods of visibility at
dawn and dusk, Mercury was named after the Roman winged
messenger of the gods. It has the fastest orbital speed of any planet,
averaging 30 miles every second. Being the closest planet to the Sun, it is
blasted by solar heat and other radiation. This has an extremely weak
atmosphere. Mercury’s daytime side heats to incredible temperatures, however,
the night side plunges to within -275°F.

PLANET PROFILE:

Diameter at Equator 3032 miles
Surface area 75 million sq km
Tilt of axis 0.01º
Mass (Earth = 1) 0.055
Volume (Earth = 1) 0.056
Overall density 5.42 g per cm3
Gravity (Earth = 1) 0.377
Number of moons 0




VENUS

Venus, the second planet from the Sun, is named after the Roman
goddess of love and is shrouded in mystery. It is covered by thick
swirling clouds of poisonous gases and droplets of acid that hide its
surface from the view of outsiders. Although Venus is about the same size
and mass as Earth, it could not be more different. It is the hottest of all the
planets, partly because its thick atmosphere traps in vast amounts of heat
from the nearby Sun in a greenhouse effect far more extreme than on Earth.


PLANET PROFILE:

Diameter at Equator 7,520 miles
Surface area 460 million sq km
Tilt of axis 177.36º
Mass (Earth = 1) 0.815
Volume (Earth = 1) 0.856
Overall density 5.2 g per cm3
Gravity (Earth = 1) 0.90
Number of moons 0

EARTH

Human beings may think of Earth as an “average” planet, but the
more we learn about the rest of the solar system, the more we see
that Earth is very unusual. This is mainly because its average
surface temperature is just above 71°F. Earth has the smallest range of
surface temperatures of any planet. Also, more than three-quarters of Earth’s
surface is rivers, lakes, seas, oceans, and frozen water as glaciers and icecaps.

PLANET PROFILE:

Diameter at Equator 7,926 miles
Surface area 196.9 million sq miles
Tilt of axis 23.4º
Mass 6.6 sextillion tons
Volume 259.8 billion miles3
Overall density 5.517 g per cm3
Gravity 1g (9.8 miles per second2)
Number of moons 1


THE MOON

A moon, also called a satellite, is a natural object of reasonable size
going around a planet. The one human beings call the Moon is
Earth’s single moon. It has also been known to scientists as Luna.
The word luna comes from the Latin word for moon. Seen from Earth, the
Moon is about the same size as the Sun. It appears to change shape during its
29.5-day orbit because we can only see the sunlit part of its surface, creating
the phases of the Moon. Its pull of gravity also makes the water in seas and
oceans rise and fall, calle tides.

MOON PROFILE:

Diameter at Equator 2160 miles
Surface area 14.6 million sq miles
Tilt of axis 1.5º
Mass (Earth = 1) 0.074
Volume (Earth = 1) 0.020
Overall density 3.34 g per cm3
Gravity (Earth = 1) 0.165
Number of moons None


MARS

Named after the Roman god of war, Mars is also called the Red Planet,
because its surface rocks and dust contain large amounts of the
substance iron oxide, also known as rust. Like Earth, Mars has polar ice
caps, volcanoes, canyons, winds, and swirling dust storms. Features resembling
river beds and shorelines suggest that great rivers, probably of water, once flowed
across Mars’ surface. Despite many visits by space probes, landers, and rovers,
there are no signs of life.

PLANET PROFILE:

Diameter at Equator 4228 miles
Surface area 55.9 million sq miles
Tilt of axis 25.1º
Mass (Earth = 1) 0.107
Volume (Earth = 1) 0.151
Overall density 3.9 g per cm3
Gravity (Earth = 1) 0.38
Number of moons 2


JUPITER

Jupiter is by far the biggest planet in the solar system. It is a vast planet
of swirling gases and storms of unimaginable fury. As the fifth planet
out, it is the nearest gas giant, a planet made almost completely of
gases, to the Sun. It is not much smaller than some of the stars called brown
dwarfs. Jupiter does not shine itself, but reflects sunlight as all planets do.
Even so, its huge pull of gravity holds more than 60 moons in orbit around it.
Jupiter is named after the Roman king of the gods, also called Jove.


PLANET PROFILE:

Diameter at Equator 88,850 miles
Surface area 33.7 billion sq miles
Tilt of axis 3.13º
Mass (Earth = 1) 318
Volume (Earth = 1) 1,236
Overall density 1.33 g per cm3
Gravity (Earth = 1) 2.36
Number of moons more than 60


SATURN

Known for its glistening, breathtakingly beautiful rings, Saturn is the
solar system’s second-largest planet after its neighbor, Jupiter. Saturn
was the Roman god of farming, civilization, prosperity, and also the
name of the rockets that powered the Apollo astronauts to the Moon. Due to its
fast spin, gas giant make-up, and very light weight compared to its size, Saturn
bulges around its equator as it rotates. This means the planet is 7,456 miles
wider than it is tall.

PLANET PROFILE

Diameter at Equator 74,897 miles
Surface area 16.48 billion sq miles
Tilt of axis 26.7º
Mass (Earth = 1) 95.2
Volume (Earth = 1) 688.9
Overall density 0.69 g per cm3
Gravity (Earth = 1) 0.91
Number of moons 50-plus


URANUS

Uranus is the third gas giant and seventh planet from the Sun.
It is very similar in size and structure to Neptune, being partly gas,
but also containing much rocky and frozen material. The axis of
Uranus is almost at right angles to the Sun. Some scientists believe an Earthsized
object crashed into Uranus soon after it was created, giving it its
unique axis. The planet is named after the Greek god of the heavens, who
was also the father of Saturn.

PLANET PROFILE

Diameter at Equator 31,763.25 miles
Surface area 3.118 billion sq miles
Tilt of axis 97.8º (almost at a
right angle to the Sun)
Mass (Earth = 1) 14.54
Volume (Earth = 1) 63.1
Overall density 1.32 g per cm3
Gravity (Earth = 1) 0.89
Number of moons approaching
30 and counting


NEPTUNE

Neptune’s deep blue color of the fourth gas giant inspired its
name, the Roman god of the sea. Neptune’s atmosphere is ravaged
by the fastest winds in the solar system. Although it is the fourth
largest planet, it is third heaviest, being denser than its neighbor, Uranus.
Also like Uranus, Neptune’s atmosphere probably extends about one-fifth of
the way toward the center. Then, it gives way to a mix of semi-liquid ice,
rocks, methane, and ammonia, with a central core of maily partly molten
rocks and metals.

PLANET PROFILE

Diameter at Equator 30,775 miles
Surface area 2.94 billion sq miles
Tilt of axis 28.3º
Mass (Earth = 1) 17.15
Volume (Earth = 1) 57.7
Overall density 1.64 g per cm3
Gravity (Earth = 1) 1.14
Number of moons about 13



PLUTO

Pluto has held the honor of being the smallest and farthest planet in the
solar system, since its discovery in 1930. However, discoveries in
2003 and 2005 may threaten this record. A tiny, frozen, distant world,
Pluto is the least known of all planets. Our information comes from
telescopes only, since no space probe has visited it. Pluto also has a highly
unusual orbit, being very oval. For part of its immensely long year, Pluto is
actually nearer to the Sun than its neighbor, Neptune.

PLANET PROFILE:

Diameter at Equator 1,412 miles
Surface area 6.9 million sq miles
Tilt of axis 122.5º to its
orbit, 115º to orbits of
other planets
Mass (Earth = 1) 0.002
Volume (Earth = 1) 0.007
Overall density 1.75 g per cm3
Gravity (Earth = 1) 0.06
Number of moons 1



ASTEROIDS

Asteroids are chunks of rock that orbit the Sun. They are pieces
of rock left over from the formation of the planets and moons.
Most asteroids are too far away and too faint to be seen clearly
without a telescope. Most orbit far away, beyond Mars, but occasionally one
may come closer to the Sun or Earth. Asteroids have hit the Earth in the past.
A major impact about 65 million years ago may be linked to the extinction of
the dinosaurs.

THE TROJANS

If asteroids stray too close to the
giant Jupiter, they can get trapped
in its orbit. There are two groups
of asteroids that circle around the
solar system in front and behind
Jupiter. Scientists have named
these asteroids the Trojans.
Sometimes, they fall into Jupiter’s
gravitational pull and become
satellites of Jupiter.


METEORS

Look up into a clear sky on any night and you may be lucky enough
to see a streak of light. It appears for only a fraction of a second and
then it is gone. The bright streak is made by a particle of dust from a
meteor entering the Earth’s atmosphere from space and burning up. Large
meteors that travel down through the atmosphere are called meteorioids.
When meteoroids hit the ground, they are called meteorites.


COMETS

Every few years, an object that looks like a fuzzy star with a long,
bright tail appears in the sky. These strange objects are not stars. They
are comets. A comet is a chunk of dust and ice left over from the
formation of the solar system. Comets orbit the Sun. When a comet nears the
Sun, some of the ice on its surface evaporates and releases gas and dust to
form the tail. Most comets are too dim to be seen with the naked eye, but every
ten years or so an especially bright comet appears in the sky.


STARS

A star is a giant ball of glowing gas in space fuelled by nuclear
reactions in its core. You can see several thousand stars with the
naked eye. But these are only the brightest stars. Astronomers have
found tens of millions more stars by using powerful telescopes to probe the
sky. Our star, the Sun, is an ordinary star. Compared to the Sun, some stars
are giants. They each contain enough matter to make tens or hundreds of suns.

@seniors..

Please... guide me.. i am zero in science subjcts.. from where i should study..?
Should i begin with the science starting from 9th to 12th class..????
which subjects base one must know to cover the syllabus of EDS..???

__________________
Live and Let Live!

extremely helpful notes and definitions... thanks a lot for sharing.. share more if u can

MUHAMMAD BIN MUSA AL-KHWARIZMI:

Of all the great thinkers who have enriched the diverse branches of knowledge during the era of early Islam, Muhammad bin Musa Khwarizmi occupies an outstanding place. Being one of the greatest scientists of all times and the greatest of his age, Khwarizmi was a versatile genius. who made lasting contributions to the field of Mathematics, Astronomy, Music. Geography and History.
Muhammad bin Musa al-Khwarizmi (780--847 A.C.) was born in Khwarizm (Modern Khiva ) situated on the lower course of Amu Darya. His forefathers had migrated from their native place and settled in Qutrubulli, a district West of Baghdad. Little is known about his early life.Khwarizmi soon acquired a prominent place in the Darul Hukania founded by Mamoon, the celebrated Abbaside Caliph. He was entrusted with the astronomical researches conducted under the patronage of the talented Caliph.
As a mathematician, Khwarizmi has left ineffaceable marks on the pages of the mathematical history of the world. His mathematical works were the principal source of knowledge on the subject to the world for a pretty long time.AI Khwarizmi is the author of Hisab al Jabr wal Muqabla, an outstanding work on the subject which contains analytical solutions of linear and Quadratic equations. His great book contains calculations of integration and equations presented through over 800 examples.
Khwarizmi was also a Geographer of repute. His Kitab Surat al Ard (The work on the shape of the earth) laid the foundation of geographical science in Arabic. This book was illustrated with maps.
He wrote two books on astrolable namely 'Kitab al Amal bil Asturlab', and 'Kitab Amal al Asturlab'. The former dealt with the manner of using the astrolabe and the latter dealt with the art of making astrolabe.
Khwarizmi wrote a book on history known as Kitab al-Tarikh, which served as a source for Masudi and Tabari. The history written by Tabari contains a passage about the return of Caliph Mamoon to Baghdad which was probably taken from this book.

MUHAMMAD BIN MUSA AL-KHWARIZMI:

Of all the great thinkers who have enriched the diverse branches of knowledge during the era of early Islam, Muhammad bin Musa Khwarizmi occupies an outstanding place. Being one of the greatest scientists of all times and the greatest of his age, Khwarizmi was a versatile genius. who made lasting contributions to the field of Mathematics, Astronomy, Music. Geography and History.
Muhammad bin Musa al-Khwarizmi (780--847 A.C.) was born in Khwarizm (Modern Khiva ) situated on the lower course of Amu Darya. His forefathers had migrated from their native place and settled in Qutrubulli, a district West of Baghdad. Little is known about his early life.Khwarizmi soon acquired a prominent place in the Darul Hukania founded by Mamoon, the celebrated Abbaside Caliph. He was entrusted with the astronomical researches conducted under the patronage of the talented Caliph.
As a mathematician, Khwarizmi has left ineffaceable marks on the pages of the mathematical history of the world. His mathematical works were the principal source of knowledge on the subject to the world for a pretty long time.AI Khwarizmi is the author of Hisab al Jabr wal Muqabla, an outstanding work on the subject which contains analytical solutions of linear and Quadratic equations. His great book contains calculations of integration and equations presented through over 800 examples.
Khwarizmi was also a Geographer of repute. His Kitab Surat al Ard (The work on the shape of the earth) laid the foundation of geographical science in Arabic. This book was illustrated with maps.
He wrote two books on astrolable namely 'Kitab al Amal bil Asturlab', and 'Kitab Amal al Asturlab'. The former dealt with the manner of using the astrolabe and the latter dealt with the art of making astrolabe.
Khwarizmi wrote a book on history known as Kitab al-Tarikh, which served as a source for Masudi and Tabari. The history written by Tabari contains a passage about the return of Caliph Mamoon to Baghdad which was probably taken from this book.