The energy animals need for their life functions are released when their cells carry out cellular respiration.
Cellular respiration is a metabolic process by which living organisms breaks down organic molecules using oxygen especially glucose to produce energy and gives off carbon dioxide and water in the process.
It is the reverse of photosynthesis.
During this process, chemical energy stored in food substances are released and converted to heat energy.
The process takes place in the mitochondria of a cell.
