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Describe three properties that all respiratory surfaces must have and explain why they must have them.

Respiratory surfaces must be thin (such as in alveoli which have walls that are 1 cell thick) to create a small diffusion distance for the gases to be exchanged through. They must also have a large surface a...
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Answered by Isabel M. • Biology tutor
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The herbicide atrazine works by disabling plastoquinone, one of the proton pumps in photosystem II. Explain how atrazine would kill a susceptible plant (5 marks) (OCR A specimen paper 3)

Atrazine prevents photophosphorylation from occurring because when plastoquinone is disabled H+ ions cannot be pumped into the thylakoid space therefore their will be a reduced proton motive force . ATP and ...
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Answered by Tamara T. • Biology tutor
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How does the environment influence the growth of roots and shoots of plants?

There are 3 main environmental influences; water, light and gravity. The effect of water is known as hydrotropism. This can be positive (the plant grows towards the stimulus in this case water) or negative (...
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Answered by Ella G. • Biology tutor
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Describe the mechanism of a reflex action.

A receptor detects a stimulus and generates electrical signals which are conducted by the neurones in the reflex arc. Firstly, the sensory neurone conducts the signal to the spinal cord. There is then a syna...
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Answered by Ella G. • Biology tutor
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Explain how the human circulatory system is adapted to: 1. supply oxygen to the tissues 2. remove waste products from tissues.

The human circulatory system has dual / double system which means that it has higher blood pressure and a greater flow of blood to the tissues. The heart is made of specialised (cardiac) muscle cells which h...
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Answered by Mariam B. • Biology tutor
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