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Question

Assertion: Organic compounds first evolved on Earth to support the origin of life were proteins, fatty acids, and nucleic acids.
Reason: All life forms were formed in water environment only.

A
Both the assertion and reason are true and the reason is the correct explanation of the assertion
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B
Both assertion and reason are true but the reason is not the correct explanation of the assertion
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C
Assertion is true but the reason is false
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D
Both assertion and reason are false
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Solution

The correct option is B Both assertion and reason are true but the reason is not the correct explanation of the assertion
Early Earth crust was in a molten state as a result of high temperature and pressure. It cooled down, when both pressure and temperature dropped. At this point, the shallow sunken parts of the Earth’s crust began getting filled with water and came to be known as the primitive oceans (prebiotic soup).

Now, in this prebiotic soup, the origin of life occurred. Origin of life required the presence of the correct mixture of chemicals and free energy. The molecules (ammonia, hydrogen cyanide, methane, hydrogen and water molecules) necessary for life were created in the atmosphere of early Earth by forces like lightning, electric discharges from the sun wind, ultraviolet rays and meteorites.

These molecules once formed in the atmosphere, along with rain reached the primitive oceans, where the free energy necessary for organization of life was supplied by deep-sea hydrothermal vents, hot springs, volcanoes and earthquakes. As the Earth surface cooled down the simple inorganic molecules interacted with one another in the ocean water to form simple organic molecules (sugars, amino acids, fatty acids, purines and pyrimidines), necessary to support life on early Earth. This process took millions of years.

Once formed the organic molecules accumulated in water as their degradation was slow in the absence of any life or enzymes. Slowly these compounds joined to form complex compounds such as proteins, fatty acids and nucleic acids.

It is important to note that all these processes occur in an aqueous environment, as it provided a more protective environment than land. So both assertion and reason are true but the reason is not the correct explanation of the assertion.

Figure : Formation of organic molecules on early Earth

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