Which life function is primarily involved in the conversion of the energy stored in organic molecules to a form directly usable by a cell?
a) absorption
b) circulation
c) digestion
d) respiration

Respiration

Explanation:

Respiration can be defined as the biological process by which the organism breakdown the energy stored in the form of glucose.

The energy in the form of glucose is broken down to be converted into ATP which is a high energy molecule.

Cellular respiration takes place in the presence of oxygen in which the Glucose is broken down and the energy is transformed into ATP and carbon dioxide is released as a by-product of this process.

c should be the answer

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.