Respiration is how nutrients change into useful energy in a cell. During respiration, energy is released in a form that can be used by cells. All living things respire. Both plant and animal cells use respiration to release energy from glucose.
There are two types of respiration. One is aerobic respiration and the other is anaerobic respiration. Aerobic respiration happens in the presence of oxygen. Oxygen breaks down food (glucose) to release high amounts of energy. Anaerobic respiration happens in the absence of oxygen making lactic acid. During respiration in yeast and bacteria, oxygen is not involved in the oxidation of food. Food (glucose) is broken down into ethyl alcohol and carbon dioxide this 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.
Some use oxygen to break down glucose completely into CO2 (Carbon dioxide) and H2O (Water).
See these (in this order) for an outline of the biochemistry of aerobic respiration: