Faster than thought
323 words over 29 numbered lines, then 6 parts worth 12 marks (Modular Unit 2 (4WBI2) style, 12–13 marks). Read the article, answer each part, then open its mark scheme and set your mark.
Illustrative article written for Scholar Lab, not a Pearson text. The biology is real; the studies, people and figures are invented or rounded for practice unless a source is named.
Faster than thought
A child running barefoot across a carpet steps on a drawing pin.
Before she has even felt the pain, her foot has already lifted off the
pin. She did not have to think about it. This rapid, automatic
response is a reflex action.
Pain receptors in the skin of her foot detect the stimulus. They start
electrical impulses in a sensory neurone, which carries them to the
spinal cord. In the spinal cord, the impulses pass to a relay neurone
and then to a motor neurone. The motor neurone carries impulses to
muscles in the leg, which contract and lift the foot. The pathway from
receptor to effector is called a reflex arc.
The brain and spinal cord together make up the central nervous system.
In a reflex, the impulses do not need to travel to the brain before
the muscles respond. Impulses also travel up the spinal cord to the
brain, so a moment later the child feels the pain and may cry out.
Where one neurone meets the next there is a tiny gap called a synapse.
When an impulse reaches the end of a neurone, a chemical called a
neurotransmitter is released. It diffuses across the gap and starts an
impulse in the next neurone. Synapses make sure that impulses travel
in one direction only.
A group of students compared the time taken for a reflex with the time
taken for a voluntary response. For the voluntary response, one
student dropped a ruler between the open finger and thumb of another
student, who caught it as quickly as possible. The distance the ruler
fell was converted into a time. Each test was repeated ten times. The
mean results are shown in Figure 1.
Doctors test reflexes, such as the knee-jerk reflex, to check whether
the nervous system is working normally after an injury. A missing
reflex may show that a nerve or part of the spinal cord has been
damaged.
Figure 1 Mean time taken for a reflex and for a voluntary response
Read the article and study the figure. Use the information in the article and your own knowledge to answer the questions. The lines in brackets show where to look; select them to highlight the text.
Use the information in the article and your own knowledge to answer the questions. The lines in brackets show you where to look; select them to highlight the text.
State what is meant by the term effector.
(1)Describe the pathway taken by impulses in the reflex arc that lifts the child’s foot.
(3)Explain how an impulse passes from one neurone to the next across a synapse.
(2)Use Figure 1 to calculate how many times longer the voluntary response took than the reflex. Give your answer to one decimal place.
(2)Explain why the reflex is faster than the voluntary response.
(2)Give two control variables the students should keep the same when using the ruler-drop test.
(2)Total for this question: 12 marks
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