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Draw a diagram showing a normal iris and what happens to the iris when a light in shined into the human eye. (1 mark). What causes this to happen? (2 marks)

(Any diagram showing an iris that has constricted) 1 mark In high light levels (1 mark) Accept reflex action due to increased photoreceptor action or words to that effect circular muscles relax and radial mu...
JP
Answered by James P. • Biology tutor
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How is blood glucose levels controlled by the body (homeostasis) ?

Controlling high blood glucose Blood glucose levels are important to control because glucose is our key source of energy in respiration. When blood glucose levels are too high, this is detected by the pancre...
NB
Answered by Nazeya B. • Biology tutor
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Using your knowledge of osmosis, describe what happens to a red blood cell when they are placed in a beaker of distilled water.

The distilled water is a hypotonic solution and so has a higher water potential than that of the red blood cell. Due to the difference in water potentials, water will move from the beaker into the red blood ...
KR
Answered by Karishma R. • Biology tutor
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Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar. Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria.

Sugar is a solute, so honey contains a high concentration of solutes. This increases the solute potential, and decreases the water potential of honey, which is therefore lower than the water potential in bac...
NK
Answered by Nighat K. • Biology tutor
3879 Views

Give three features of an efficient exchange surface. Provide an example for each feature.

An efficient exchange surface should have a high surface area as this increases the rate at which diffusion can occur across it. For instance, roots have many root hair cells. These root hair cells have thin...
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Answered by Elliot H. • Biology tutor
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