State the theory of biogenesis. How does Miller's experiment support this theory?
class 12th CBSE Biology sample paper
Answers
The theory or biogenesis was given by Louis Pasteur.
He stated that all life originated from pre-existing life form present .
Cells that later evolves from the given organic compounds. So, coincidentely the life may have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and that formation of life was comes by the chemical evolution, i.e., formation of complex organic molecules from inorganic molecules.
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Miller conducted an experiment that prove this theory.
He created the conditions of primitive nacent earth -
so high temperature, volcanic storms & eruption cond., reducing atmosphere containing CH4, NH3,H2O, H2 .at laboratory scale in flask. They then stimulated electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 8000°C.
then he observed the formation of amino acids. In similar experiments others observed, formation of sugars, nitrogen bases etc.. These little organic molecules are the major building blocks for the proteins & other components. Hence, this experiment should supported that life has come from preexisting non-living organic molecules that are present already over there.
* It is most widely accepted theory to explain how life originated on Earth. This concept was given by a A.I. Oprain and J.B.S. Haldane.
* According to this theory 'life originated from in a inanimate matter through a series of chemical reaction occurring on primitive Earth'.
* According to Oparin, life first originated in water, so water is essential for origin of life. At that time free oxygen was absent so first life was anaerobic. In the primitive atmosphere, oxygen in free gaseous state was virtually absent, that is atmosphere was reducing.
* Alexander I.Oparin and J.B.S. Haldane put forward the concept of First living being evolved from simple organic molecules which were present on earth soon after it was formed. According to Oparin and Haldane, spontaneous generation of earlier molecules might have taken place if the earth had atmosphere as compared to the present oxidising atmosphere.
* Stanley L. Miller and Harold C. Urey in 1953, illustrated occurrence of organic molecules on earth. They experimentally proved the theory of chemical evolution given by Oparin and Haldane. They assemble an Atmosphere similar to that thought to existence of primitive Earth. Mixture of water vapours (H2O), Methane (CH4), Ammonia (NH3) and hydrogen (H2) was added in Miller's apparatus (spark-discharge apparatus). This was maintained at a temperature just below 100 degree Celsius and sparks were passed through the mixture of gases to stimulate lightning. They allowed the experiment to run and after few days, they got red colour liquid in which organic compound were present and the products of chemical reaction led to the formation of amino acids, which make up protein molecules. Thus, life first originated from inorganic matter and then from pre-existing life.
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