I think it's oxygen and water because they are the substance for cellular respiration.
Cellular respiration uses oxygen to release the energy stored in food.
Explanation:
In breathing living organisms take oxygen and release the carbon dioxide it is similar to the aerobic respiration.
There are two types of respiration:
1. Aerobic respiration
2. Anaerobic respiration
Aerobic respiration
It is the breakdown of glucose molecule in the presence of oxygen to yield large amount of energy. Water and carbon dioxide are also produced as a byproduct.
Glucose + oxygen → carbon dioxide + water + 38ATP
Anaerobic Respiration
It is the breakdown of glucose molecule in the absence of oxygen and produce small amount of energy. Alcohol or lactic acid and carbon dioxide are also produced as byproducts.
Glucose→ lactic acid/alcohol + 2ATP + carbon dioxide!
