All living things, including plants and animals, need energy to survive and carry out their functions and other life processes. Animals get their energy from the food they eat and plants from the food they produce as a result of photosynthesis. In animals, including humans, nutrients, including carbohydrates, are transported around the body in blood cells and then into cells of the body. Here, the digested food is broken down so that the energy it contains can be released and put to use within the body. This process is called respiration. There are two types of respiration: aerobic, which occurs when oxygen is present; and anaerobic which occurs when there is no oxygen present.
Aerobic respiration is the process that results in glucose being oxygenated to produce carbon dioxide and water during which a great deal of energy is released. This energy is used by the body to help it function effectively. In anaerobic respiration, because of the lack of oxygen the glucose is turned not into carbon dioxide and water but into lactic acid. Organisms, such as yeasts and bacteria, can live entirely by anaerobic respiration and can be useful to humans. For example, respiration of yeast cells results in the production of ethanol, an alcohol and carbon dioxide substance used in brewing and bread-making respectively.
Respiration also occurs in plants. As they photosynthesise, plants build up food in the form of glucose and starch. Some of this food is broken down through respiration but plants make more food than they break down so their leaves take in carbon dioxide. At night, when the photosynthesis stops, plants continue to break down food by respiration but now their leaves need to take in oxygen due to the absence of light.
Glucose + oxygen – carbon dioxide + water + energy
