Question

Assertion :- Oxygen is compulsory for growth of all organisms.
Reason:- Oxygen is must for releasing metabolic energy essential for growth.

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

Answer 1

The correct option is D Both assertion and reason are false

$O_2$ is required for growth, but it is not compulsory. There are many organisms that thrive well without $O_2$.

Facultative anaerobes are the organisms which usually prefer anaerobic respiration when $O_2$ is not present in adequate amounts but are also capable of performing aerobic respiration in case $O_2$ is available in adequate quantity. For example, E. coli, Salmonella, Staphylococcus sp. and Yersinia pestis.

Obligate anaerobes are the organisms which can survive only in the absence of $O_2$. They die when they come in contact with the $O_2$ in the atmosphere. For example, Clostridium.

Obligate aerobes are the organisms that require $O_2$ for their growth. They cannot grow in the absence of $O_2$. For example, humans and plants.

Thus $O_2$ is not essentially required for releasing metabolic energy essential for growth.