Which is a reactant in the cellular respiration reaction?

A. water

B. oxygen

C. mitochondria

D. cytoplasm

The answer should be B, oxygen.

Take a look at the word equation for cellular respiration:

Glucose + oxygen ➡️ Carbon dioxide + water + energy

It is where the cell uses glucose and oxygen to make carbon dioxide, water and energy.

Therefore, since reactant is the substance that is involved in the reaction, so the only choice is oxygen.

Meanwhile water is the product of the reaction, and mitochondria and cytoplasm is the structures of cell.