Levels of Biological Organization

The structure and function of living things are dependent upon chemicals. Any think that takes up space and has mass is called matter. A matter can exist in as a solid, liquid and gas form. All matters are composed of basic substances called elements. There are six elements commonly found in all living things. These are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur, which are also called bioelements.

A matter is made up of atom. Every atom is made up of subatomic particles protons, neutrons and electrons. Protons and neutrons are found in the nucleus of the atom. Electrons revolve around the nucleus. 
Levels of Biological Organization

Molecules (L moles, mass) are collection of atoms bound together. Molecules can be made up of atoms of the same elements and atoms of different elements combined in a definite ratio are called compound.

Organic molecules are those that always contain carbon and hydrogen. It is the organic molecules that characterize the structure and the function of the living things. The small organic molecules, or a unit, can join together and form a large organic molecule is called macro-molecule. There are four major groups of biologically important macromolecules, i.e. Carbohydrates, proteins, lipids and nucleic acids.

All organisms are made up of cells. And a cell is the smallest unit of living thing. A cell contains organelles e.g. Mitochondrion, chloroplast etc. which are made up of organic molecules. A group of cell performing a similar function forms a tissue. Nerve cells are grouped together to form a nerve tissue which carries messages. The thick walled cells in a tree trunk form tissues that support the tree Tissues of various kinds are often grouped together to form an organ. Our heart, eyes and even skin are all organs e.g. Leaves, roots etc Organs working together are often combined into system  e.g. Many organs like liver, pancreas, gall bladder, oesophagus, stomach, intestine etc form the digestive system of human beings. A system carries out life function for the living things. Systems work together to make up an entire organisms e .g. Man, cow, mustard, rose etc.

A population is a group of individuals of the same species that interbreed and occupy a given area at a given time. All the grasses in the lawn make up grass population. All the fish in the pond make up the fish population of the pond.

Phyletic lineages
 A Phyletic lineage is an unbroken series of species arranged in an ancestor to descendent sequence with each later species having evolved from one that immediately preceded it.

Different groups of organisms show common characteristics, which indicate their common ancestry. For example, jawless fish gave rise to higher bony fishes, the amphibians evolved from these fishes. Reptiles evolved from amphibians. The reptiles gave rise to birds and mammals.

The number and variety of species in a place is called biodiversity .Various estimates put the total number of species between 5 and 30 millions out of these only 2.5 million species have been identified so far.

Many different kinds of populations may live together in harmony in the same habitat. Together they make up the community. We may find population of plants, insects, frogs, turtles, and fish in a pond or lake forming a community.  The organisms interact in a community. It may be predation, parasitism, commensalism, mutualism etc.

Living world in space and time
Almost all parts of the world are full of living things. Different types of organisms are found in different parts of the world. It is called distribution of organism in space. It can studied through biomes.

A biome is the largest regional biogeographical unit of life on earth. A biome has a particular group of plants and animals that are adapted to live under certain environmental conditions, of which climate has a great influence e. g.  Tropical rain forest, temperate deciduous forest, coniferous forest, tundra etc.

Scientists think that about 15 billion years ago all materials of the universe were condensed into a single small space. It then, exploded in an event called the big bang the universe, as it is known today did not exist before the time. The gases and dust form the big bang produced an early generation of stars. Then cover billions of years these stars exploded and their space debris formed other stars and planets. The stars formed in this way some 4-6 billion years ago. For almost a billion years or so the molten earth cooled. Intense heat produced by gravitational energy and radioactivity caused the earth to become stratified into several layers. Heavier atoms of iron and nickel become the molten liquid core, and dense silicate minerals become the semi liquid mantle. Upwelling of volcanic lava produced the first crest. This event happened about 3.8 billion years ago. After that time some 3.5 billion years ago life began.

Since then different organisms evolved. They dominated the earth on various periods of geological area. This is evident from the fossils record of animals and plants. The great majority of fossils are found embedded in sedimentary rocks. Sedimentation is a process that has been going on since the earth was formed. Sediment becomes stratum. Any given stratum (plural: strata) is older then the above it and younger then the one immediately below it. The fossils trapped in the strata are the fossil record that tells us about the history of life. The age of the fossils and the age of the strata which contains the fossils is the same. The absolute dating method that relies on radioactive dating techniques assigns an actual date to a fossil. Each radioactive isotope has a particular half-life, the length of time it takes for half of the radioactive isotopes to change into another stable element. If the fossil has an organic matter, half of the C14, it will have changed to C12 in 5,730 years. Thus fossils, which can be dated relatively according to their location in strata and absolutely according to their content of radioactive isotopes, give us information about the history of life.

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