The Molecular Basis of Life; Defining Life; Level of Organisation


Biology deals with living organisms. The living organisms are made up of protoplasm. Huxley (1868) has stated that protoplasm is the physical basis of life. At the molecular level there is no difference between nonliving object and living beings. Both exist on this earth and both are governed by same physico-chemical laws. Then, how are the living beings different from the nonliving?

level of organisation


The living beings are made up of protoplasm. Protoplasm is unique. It represents a characteristic level of organisation. The simple meaning of organisation is the manner in which smaller components of any structure, system or a situation are arranged in a hierarchy to coordinate with one another towards a goal. The levels of organisation of matter differ between the living and nonliving The organisational levels in the living becomes gradually more and more complex. In the figure a graphical representation has been made to show the difference between living and nonliving organisation right from the atomic and molecular level and in case of living, the organisation becomes more and more complex
beyond the individual level.

Regulation of organisation

There are four important operations to regulate the organisation at different levels. They are aggregation, interaction, equilibrium and change.
(i) Aggregation. It is formation of a larger unit by coming together of smaller units. For example-atoms aggregate to form molecules and compounds or cells aggregate to form a tissue.
(ii) Equilibrium. The interaction leads to a stability or equilibrium or a balance. For example, an aggregate of organs like nose, wind pipe, lungs, ribs and diaphragm interact among one another and finally come to a balance resulting breathing movements.
(iii) Change. In some cases the interaction may also result in a change or variation. For example, H and O interact in one manner to produce H20 but when they interact in a different manner, they produce H202 (hydrogen peroxide).
In the nonliving world, organisation is upto the level of molecules and compounds which may aggregate further to form mixtures, colloids, crystalloids. In the living world the same elements occur as that of nonliving world. Rather 99% of living matter is formed of C, H, O and N. Both are subjected to similar physico-chemical laws. In spite of all similarities, putting together all elements in a mixture in the right proportions and supplying them with the energy
does not create life This is because the highly complex way in which living matter is organised.In order to explain life one has to examine the essential aspects of living organisation such as the molecular basis of life, energy changes, reproduction, adaptation and ultimately their death.


(i) It is estimated that there are more than 5000 different chemicals are present in a cell.The number of chemical reactions that occur in a cell are several times this number.But all the biomolecules are predominantly made up of elements like carbon, hydrogen and oxygen. Therefore, molecular organisation in the living beings is basically organic in nature.

(ii) The biomolecules are of two typesmicromolecules and macromolecules. Both small and large molecules are important for life. But the nonlivings mostly consist of small molecules like gases, salts, ores and some forms of crystals. A few important small molecules of living are water, common salt, sugar etc. 70% to 80% of cellular weight is water. Most substances enter and are distributed within the organism in dissolved state. Most chemical reactions in the body are mediated by water. Above all, life originated in water. The common salt NaCl is no less significant for life. Ions of sodium and chloride play important roles in living processes of animals. Similarly glucose is the fuel for most of the cellular activities. It is synthesized in green plants, form the bulk of the plant body in form of cellulose, animals consume them as food, stored as glycogen for animal reserve, an important constituent of blood and brain. The big molecules of life are carbohydrates (starch, cellulose, glycogen), proteins (enzymes,some hormones and structural proteins), lipids or lats ànd nucleic acids. Most of the macromolecules of life are 1Ormed by polymerisation. Cellulose and starch are polymers of glucose., 20 types of amino acids combine in different sequences to form wide range of proteins. DNA is also a polymer. Hormones and enzymes are macromolecules which control the activities of other molecules.

(iii)Metabolism is the outcome of biochemical reactions in the cell. When more than 5000 kinds of biomolecules are available in suitable medium, they react among in many more ways. Majority or the chemical reactions can be grouped categories. (i) The first category is the building up reactions known as anabolism (Gk.ana = up, bole = throw). Reactions which build up complex substances from simpler ones are anabolism. These are constructive processes of the body. Energy is stored in the process.

6CO2 + 6H²O. light energy. C⁶H1206+ 602chlorophyl
Carbon dioxide Water. →. glucose. oxygen

(ii) The second category is breakdown reactions known as catabolism (Gk. kata =down; bole = throw). These are break down reactions that split up complex substances into simpler ones. These are destructive processes in the body. Energy is liberated in the process.


           enzymes.    6CO2.   + 6H²0+ Energy.
 CgH1206 + 602      →             carbon dioxide water
  glucose Oxygen

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