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Describe how allopatric speciation occurs.

In a population of a species a barrier forms (for example the formation of a new river, or the division between two islands). This leads to two isolated groups of the original species. In the two isolated gr...
AP
Answered by Amelia P. • Biology tutor
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Can you name for four chambers of the human heart?

left atrium, right atrium, left ventricle, right ventricle
AJ
Answered by Ashley J. • Biology tutor
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Describe the structure of glycogen and explain why it is a suitable molecule to store energy.

Glycogen is a polysaccharide. Polysaccharides are carbohydrates made up from a large number of monosaccharides joined together by glycosidic bonds formed in condensation reactions. Glycogen, sometimes referr...
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Sodium atoms react with chlorine atoms to produce sodium chloride (NaCl). Describe what happens when a sodium atom reacts with a chlorine atom.

Sodium and chloride form an ionic bond. Therefore the sodium atom loses one electron from its outer shell and the chlorine atom gains one electron. As this happens, the electron is transferred from the sodiu...
DS
Answered by Dominic S. • Biology tutor
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When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob. Describe how.

A nerve impulse is an electrical current that is transmitted down the axon of a neurone and to the synaptic knob. The impulse depolarises the membrane and causes a change in voltage across the membrane. This...
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