Question

Assertion: Chemoheterotrophs were the earliest organisms that appeared on earth and were presumably anaerobes.

Reason: Chemoheterotrophs utilised carbon dioxide from their surrounding to form their own organic compounds.

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

Answer 1

The correct option is C Assertion is true but reason is false

Early earth was devoid of oxygen, though it contained many elements like hydrogen, methane, ammonia, water vapour, etc. First living things that appeared on earth were anaerobic, and there was no oxygen, as oxygen can only come from organisms that carry out photosynthesis to make their own food. Organisms That cannot prepare their own food are called heterotrophs. That is why it is assumed that the first life or cells must have been heterotrophs, organisms that take their food from the surrounding.
Chemoheterotrophs are the organisms that obtain energy chemosynthesis rather than by photosynthesis. Microorganisms use organic chemical substances as the source of energy. Chemoheterotrophs were the earliest that appeared on earth which were presumably anaerobes. Early chemoheterotrophs did not have the capability of using carbon dioxide from their surroundings to make their own organic compounds. They directly consume organic molecules for both a source of carbon as well as energy. Photoautotrophs can derive energy from light and synthesise organic compounds from carbon dioxide.