NCERT Solution Class X Science Heredity and Evolution Question 9 (Ex 9.7)

Question 9:

What evidence do we have for the origin of life from inanimate matter?

Answer:

A British scientist, J.B.S. Haldane, suggested that life originated from simple

inorganic molecules. He believed that when the earth was formed, it was a hot

gaseous mass containing elements such as nitrogen, oxygen, carbon, hydrogen,

etc. These elements combined to form molecules like water (H2O), carbon dioxide

(CO2), methane (CH4), ammonia (NH3), etc.

After the formation of water, slowly the earth surface cooled and the inorganic

molecules interacted with one another in water to form simple organic molecules

such as sugars, fatty acids, amino acids, etc. The energy for these reactions was

provided by solar radiations, lightning, volcanic eruptions, etc.

This was proved by the experiment of Stanley L. Miller and Harold C. Urey in 1953.

They took a mixture of water (H2O), methane (CH4), ammonia (NH3), and hydrogen

gas (H2) in a chamber and sparks were passed through this mixture using two

electrodes.

After one week, 15% of the carbon from methane was converted into amino acids,

sugars, etc. These organic molecules are polymerized and assembled to form protein

molecules that gave rise to life on earth.

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