RBSE Class 9 Science Notes Chapter 5 Concept of Life

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Rajasthan Board RBSE Class 9 Science Notes Chapter 4 Chemical Bond and Chemical Equation

Major differences between living and non-living:
In our surroundings there are many living and non-living things, some times it is difficult to differentiate them. There are many characteristics by which we can differentiate living from non-living.

Living World Non-living World
1. A living organism shows certain life processes like respiration, digestion, etc. 1. A non-living thing does not possess any such characteristics.
2. All living organisms has well developed cellular organisations. 2. Non-living things are not made up of cells.
3. The basis of all life processes is the metabolism process, taking place in cells. 3. A non-living thing is not made up of cells and hence, does not show metabolism.
4. All living organisms can grow and develop by several life processes. 4. Non-living organisms cannot grow and develop on their own.
5. All living organisms can reproduce to produce organisms of their own kinds. 5. Non-living organisms cannot reproduce on their own.
6. All living organisms have the ability to respond to the external stimuli. 6. Non-living organisms does not respond to the external stimuli.

Various Hypothesis Related to origin of life:

  • Earlier people believed in the spontaneous generation of life. It means that life arise spontaneously from the non-living matter. Van Helmont also supported the same idea, by his experiment. People believed that God is Almighty, he first made the earth, water, air, plants, fishes, birds, terrestrial animals and then, man. With the spread of education, scientists do not accept this concept.
  • The Greek philosophers, Aristotle, Plato define the theory that life originated from the lifeless or non-living substances, from which different types of animals and plants appeared suddenly or spontaneously, without any apparent cause. Ex-animals like frogs, toads appears spontaneously out of mud, while dung and mud gave rise to insect larvae worms, flies, moths, etc. Butterflies suddenly appeared out of farm manure, decaying wood, vinegar, and fruit, but this is rejected by the experimental demonstration of the fact that organism do not appear out of inanimate, lifeless objects.
  • Louis Pasteur, a French microbiologist, first time gave the scientific explanation that the life originates only from pre-existing life.
  • A.I. Oparin and Halden gave a biochemical theory of origin of life. They believed that complex organic molecules were formed through chemical reactions in earth’s hot primordial soup. Universe came into being as a result of interactions of mass, matter and energy. Earth is originated by big bang theory. The beginning of earth was in the form of a red hot ball of gas.
  • According to cosmozoic theory, the spores of life came to earth from some distant planet, via metiorites or by some unknown means. This theory has been rejected because the intense cold, extreme dryness and intense radiations of interplanetary space would not have allowed the spores of life to reach the earth, without damage.
  • Russian Scientist Alexander I. Oparin in his book The Origin of life’, tried to explain the origin of life on earth. He believed that the formation of protein molecules is extremely important for origin of life. His theory is known as theory of primary abiogenesis. In his book, he says that life is originated from lifeless chemicals.
  • A British Scientist J.B.S Haldane presented the similar hypothesis.

According to him, origin of life can be divided in the following eight stages:

    • Atomic stage
    • Molecular stage
    • Formation of organic compounds
    • Formation of colloids and coacervates
    • Formation of genes and virus
    • Production of Prokaryotic cells
    • Production of autotrophs
    • Production of cells with nucleus
    • In support of Halden Hypothesis, Stanley Miller performed an experiment. Stanley Miller prepared a special apparatus. Miller filled the chamber of the apparatus with methane (CH4), ammonia (NH3), hydrogen (H2) and water (H2O). In this mixture, he passed electric discharge of 60,000 volts for a week. In one side, boiled water and in other side, mixture with condensed water was circulated.
    • During this process, a red colored liquid was obtained. On analysis of this fluid, it was found that the liquid contained several aminoacids, glycerol and alanine. Abalson added carbon dioxide, carbon and water vapour to the experimental mixture of Miller. He got more than 20 amino acids which are present in living beings and some proteins.
    • Astronomers refused to believe that earth is the only planet that contains life in our solar system and other heavenly bodies in the universe do not have any traces of life. The two Apollo missions of National Aeronautics and Space Administration of USA have provided first hand information about the absence of life on moon.
    • Moon is lifeless, dry and without water. Venus has a surface temperature that constantly touches the boiling point. Mars is considered to have some possibility of life in its past history. This view is supported by the presence of frozen water on its poles and dry rivers on the surface, as if water had been an ultimate aim of finding the possibilities of life which might have existed on it. These explorations speak of man’s quest for detecting life on other planets.

RBSE Class 9 Science Notes