Diffusion and respiration GapFill

Respiration is the process used by organisms to generate energy for movement and all  electricalnucleicmetabolicnervous reactions. Because it is  an endogenousan endothermican exothermican anabolic reaction, respiration is also important for keeping organisms warm.

When there is  oxygenmethanewaterglucose available, aerobic respiration converts oxygen and  ethanolglucosenitratecarbon monoxide to carbon dioxide and water, but if it is lacking,  anaerobichyperaerobichypoaerobiclactoaerobic respiration in muscles converts glucose to lactic acid, which can cause a painful or burning sensation. This yields less energy than aerobic respiration because of the incomplete oxidation of glucose, and the lactic acid produced must eventually be converted back to glucose by the  small intestineliverthyroid glandpancreas.

 Active transportSelective reabsorptionDiffusionFiltration is the passive movement of substances from an area of higher concentration to an area of lower concentration. Examples of this in nature are the movement of the waste product  carbon monoxideglucoseureabile from the liver cells into the blood (where it is transported to the kidneys) and the movement of  plasmawaterantibodiesurea and dissolved mineral ions from the soil into plant roots.

This process can be sped up by several factors, including increasing the concentration gradient, increasing the  volumetemperaturefrictionpH or increasing the surface area of the membrane. Having a  variablesmalllargeconstant surface-area-to-volume ratio allows this process to occur rapidly, which allows single-celled organisms to exist without complex transport systems, and is also one reason why alveoli are efficient at gas exchange.

A cube-shaped cell with sides measuring 3 µm has a surface area of  18366054 µm² and a volume of  729544227 µm³. The surface-area-to-volume ratio is  2 : 14 : 32 : 33 : 1.