Why is nutrition, respiration, and excretion necessary for every living being?

Breath. All living organisms must be able to release the energy stored in food molecules through a chemical process known as cellular respiration. Aerobic respiration absorbs oxygen and releases carbon dioxide.

Food. Living things require energy to survive. Energy is obtained from nutrients or food. Green plants, algae and some archaea and bacteria can produce food from water and carbon dioxide through photosynthesis.

Selection. All living organisms create waste through life processes. Most of the waste comes from food. The rest is movement, growth and other functions of life.