There are two types of respiration. One is aerobic respiration and the other is anaerobic respiration. Breaking down of food in presence of oxygen is called aerobic respiration, whereas breaking down food in the absence of oxygen is called anaerobic respiration.
- Animals obtain carbohydrates, such as starch and sugars, by eating them. Some heat is released by these chemical reactions in cells, and it is this we experience as body heat.
- Plants make their own carbohydrates during photosynthesis. They get carbon dioxide from the environment and their energy from the sun.
See these (in this order) for an outline of the biochemistry of aerobic respiration:
Respiration Facts for Kids. Kiddle Encyclopedia.