Living things respire. Respiration is a complex sequence of chemical reactions which result in the release of energy from food. There are two types of respiratory process:

Aerobic respiration Carried out by the vast majority of organisms, this involves oxygen. The by-products of the reaction are water and carbon dioxide both of which are eliminated as waste products. Oxygen is obtained from the air or water using organs designed to optimise gaseous exchange. These include the stomata in plants (small, size regulated pores), spiracles in arthropods, gills in fish and lungs in mammals. The uptake of oxygen and simultaneous elimination of carbon dioxide and water is commonly referred to as breathing. It is important to distinguish between breathing and respiration. It is tempting, particularly with younger children to use the well used term breathing as an all embracing description of the respiratory process. However, this is not correct and could lead to the reinforcement of misconceptions.


Anaerobic respiration When oxygen levels are at a low level, it is possible for some simpler organisms and parts of more complex ones to release energy from food without oxygen. This is a far less efficient process but a necessary alternative in some cases. The by-products of anaerobic respiration are different to aerobic. In humans, oxygen starved muscle cells will respire anaerobically under stress such as heavy physical activity. The by-product of this is lactic acid and it is this that causes the puffed out feeling. Yeast cells respire anaerobically in sugar solution producing alcohol as the by-product.


Movement, Growth
Sensitivity, Excretion
Self assessment