Respiration has two common meanings in biology.
Respiration uses oxygen and fuel (food) to produce energy for cellss. The products of respiration are carbon dioxide and water. A demonstration that carbon dioxide is a product of respiration is often shown in schools. See School science experiment- Huff & Puff Apparatus for details.
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4 Tissue Engineering
5 See Also
Respiration in Animals
Respiration in animals is divided into:
Respiration can be measured using a device called a respirometer.
Plant respiration is limited by the process of diffusion. Even a baobab tree is mostly dead because air can penetrate only skin deep. However, most plants are not involved in highly metabolic activities like hunting, i.e. they do not need the energy necessary for predators, and thus their breathing is limited.
Insects have no concentrated respiratory organs. (Perkins, 2003) Instead insects use a system of tracheae, thin channels, that run through their body, to improve on simple diffusion and let air flow more freely throughout the organism. Spiracles are small holes that open to the outside of the body and allow air in. Spiracles can be found along the abdomen and thorax of the insect body but never on the head. (Perkins, 2003) The spiracles can control the amount of air that is let into the insect. The spiracles lead to the trachea which act like "large distribution tubes" for the air being carried. (Perkins, 2003) The trachea lead to smaller tubes called tracheoles. The insects' cells can't be too far from these tracheoles because this is where oxygen and carbon dioxide diffuse in and out of the hemolymph. This simple system limits their size because insects are purely diffusive. No modern insect exists that is larger then a foot or so (in metric units, about half a meter). Many people fear big bugs, and they should be comforted by this fact.
In tissue engineering, respiration is an essential problem. The small depth of diffusion respiration sufficient to support the metabolism of an average human cell is less than a milimetre in metric units, or less than a quarter of a quarter of an inch in Imperial units. Various substances can be used to enhance this depth, essentially having a haemoglobising role.