Why are so many children short-sighted?
313 words over 30 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.
Why are so many children short-sighted?
In some cities in East Asia, more than eight out of ten young people
leaving school are short-sighted. They can see nearby objects clearly,
but distant objects look blurred. Fifty years ago, short sight was far
less common. Genes cannot change that quickly, so scientists have
looked for causes in the way children now live.
Light enters the eye through the cornea, which bends the light. It
then passes through the pupil, the hole in the centre of the iris, and
through the lens. The lens focuses the light on the retina, which
contains receptor cells that are sensitive to light. Impulses then
travel to the brain along the optic nerve.
To focus on a near object, the ciliary muscles contract and the
suspensory ligaments slacken, so the lens becomes fatter and bends
light more. This change of focus is called accommodation. In a
short-sighted eye, the eyeball has usually grown too long, so light
from distant objects is focused in front of the retina.
Many scientists suspected that children who spend more time outdoors
are less likely to become short-sighted. Outdoor light is much
brighter than indoor light, and children outside look at distant
objects more often. In bright light, the pupil becomes smaller.
In a trial in Guangzhou, China, twelve primary schools were randomly
placed into two groups of six. In the first group, children had an
extra forty-minute class outdoors at the end of each school day, and
parents were encouraged to take them outside at weekends. Children in
the control group schools carried on as normal. After three years, the
scientists measured how many of the children who had normal sight at
the start had become short-sighted. Their results are shown in Figure
1.
The trial did not stop short sight, but it reduced the number of new
cases. Some schools now hold lessons outdoors whenever the weather
allows.
Figure 1 Children who became short-sighted within three years
Figure 1 uses results reported in He M et al. (2015) JAMA 314(11): 1142–1148. The article text is illustrative.
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 accommodation.
(1)Name the part of the eye that contains light receptors.
(1)Describe how the eye changes so that it can focus on a distant object after looking at a book.
(3)Use Figure 1 to calculate the percentage decrease in children becoming short-sighted in the schools with an extra outdoor class, compared with the control group schools. Give your answer to one decimal place.
(2)Explain why the trial included a control group.
(2)Explain how the eye responds when a child walks from a classroom into bright sunlight.
(3)Total for this question: 12 marks
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