Author: Kim Edgell
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Receptors homework 2
Name: ________________________   Percentage: __________________________
Q1.The diagram below shows a nerve pathway in an animal.
 
(a)     The nerve pathway shown in the diagram may be regarded as a simple reflex arc.Use the diagram to explain why.
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(b)     Suggest two advantages of simple reflexes.
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(c)     In the nerve pathway in the diagram, synapses ensure that nerve impulses only travel towards the muscle fibre. Explain how.
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(d)     Axon P was found to conduct impulses much faster than other axons in the nerve pathway shown in the diagram.

Describe and explain one feature of axon P that might cause this difference.
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Q2.The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how.
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 (Total 5 marks)
Q3.A frog’s heart was attached to an instrument which measured the force produced as the heart contracted. Graph 1 shows the changes in force when the heart was bathed in a solution of salts at 20 °C. Graph 2 shows the results when the heart was bathed in the same solution at the same temperature, but including acetylcholine.
 
(a)     Points A and B show when the atria and ventricle were contracting. Which point, A or B, shows contraction of the ventricle? Give two reasons for your answer.
Point ____________________
Reason 1 ___________________________________________________________
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Reason 2 ___________________________________________________________
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(b)     Calculate the frog’s heart rate when acetylcholine was not present. Show your working.

Heart rate = ____________________ beats per minute(2)
(c)     (i)      From the graphs, what can you conclude about the effect of acetylcholine on
heart rate;
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stroke volume?
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(ii)     Use your answer to part (i) to explain the effect of acetylcholine on cardiac output.
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(iii)     Addition of acetylcholine in the experiment mimics the effect of one branch of the autonomic nervous system. Which branch is this?
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(d)     (i)      Explain how nervous control in a human can cause increased cardiac output during exercise.
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(ii)     Explain why increased cardiac output is an advantage during exercise.
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Q4.When a person looks directly at an object, its image is focused on the fovea.
(a)     When the image is focused on the fovea, the person sees the object in colour.
Explain why.
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(b)     Vision using the fovea has high visual acuity but low sensitivity to light compared with vision using other parts of the retina.
(i)      Explain why vision using the fovea has high visual acuity.
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(ii)     Explain why vision using other parts of the retina has high sensitivity to light.
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