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Firstly, capillaries are one cell thick and so this makes them very thin. This reduces the diffusion pathway between the capillary and other cells thus allowing efficient diffusion. Secondly, capillaries ...

Directional selection occurs when a phenotype at the extreme end of a distribution is favoured and so over time the distribution shifts in the direction of the favoured phenotype. An exam...

Oxidative phosphorylation is a critical component of the cell's metabolic pathway, and is responsible for the generation of most of the cell's ATP. Overall, reducing potential in the form of NADH and FADH...

The human gas exchange system includes the trachea, the bronchioles and the alveoli. During inhalation (breathing in) the diaphragm contracts and the external intercostal muscles contract. This increases ...

A reflex arc is made up of a receptor (which detects a stimulus), a sensory neurone, a relay neurone, a motor neurone and an effector (which brings about a respon...