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An action potential arrives at a presynaptic neurone, which causes calcium ion channels to open. Calcium ions enter the presynaptic knob, which causes synaptic vesicles containing neurotransmitter to detach ...

A barrier separates the original population into two groups. Due to the different environmental conditions (selection pressures) either side of the barrier, different alleles are selected that better adapt t...

Carbon dioxide diffuses into the cell leaf through the stomata, and diffuses into the water surrounding the mesophyll cell walls (main site of photosynthesis-packed with many chloroplasts). From here, the ca...

Homeostasis is the maintaining of a constant internal environment to allow for healthy functioning of the body. Three examples would be the control of water levels in the kidney via ADH, control of temperatu...

Compartmentalisation - as different organelle's different metabolic reaction require different optimum environments such as pH and temperature. Site of chemical reactions such as photosynthesis or respiratio...