Concept: Mutualism is an interaction where two organisms benefit from each other.
Explanation:Plants require carbon dioxide,
CO2, to carry out photosynthesis.
Animals produce carbon dioxide,
CO2, as a waste product during respiration.
Animals require oxygen,
O2, for cellular respiration.
Plants release oxygen,
O2, as a by-product of photosynthesis.
Therefore, plants and animals supply each other’s essential respiratory gases.
This exchange of gases is a clear example of mutual benefit, not competition or mere coexistence.
Option A is wrong because rivals compete, but plants and animals do not compete for gases in this way.
Option B is too narrow because it ignores the benefit plants receive from animals.
Option D is incorrect because being neighbours does not guarantee any beneficial interaction.
Answer: C — plants and animals utilize the respiratory wastes of each other.