Holding on through the hurricane
320 words over 28 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.
Holding on through the hurricane
In the summer of 2017, a team of biologists visited two small islands
in the Caribbean to study a species of small brown lizard. They caught
lizards, photographed their legs and feet, and measured the area of
the sticky pads on their toes before releasing them. The lizards in
each population varied: some had larger toe pads than others. Lizards
of this species spend most of their lives on tree trunks and branches,
where they hunt insects and hide from birds.
A few days after the scientists left, a powerful hurricane struck the
islands, followed two weeks later by a second one. Winds of more than
200 kilometres per hour tore leaves and branches from the trees where
the lizards live. Six weeks after the storms, the team returned and
measured the lizards that had survived.
The survivors were different. On average, they had larger toe pads on
their front feet and longer front legs than the lizards measured
before the hurricanes. Figure 1 shows illustrative mean values. The
survivors were also slightly smaller overall, perhaps because a
lighter body is easier to hold in place in a strong wind. The same
changes were found on both islands.
To find out why, the scientists placed lizards on a perch in front of
a powerful fan in the laboratory. As the wind speed increased, the
lizards clung on with their front feet. Those with larger toe pads
held on for longer before they were blown into a safety net.
The hurricanes seem to have acted as a strong force of natural
selection. However, this will only change the next generation if the
size of toe pads is at least partly controlled by genes. Some
features, such as body mass, are also affected by the environment, for
example by how much food an animal finds. The team plans to return to
the islands to measure the young lizards born after the storms.
Figure 1 Mean area of front toe pads in lizards before and after the hurricanes
Based on Donihue C M et al. (2018) Nature 560: 88–91, which reported a 9% increase in mean front toe pad area. The values in Figure 1 and the article text are 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 variation.
(1)Use Figure 1 to calculate the percentage increase in the mean area of front toe pads. Give your answer to one decimal place.
(2)Explain how the hurricanes caused the mean toe pad area of the lizard population to increase.
(3)Explain why the next generation of lizards will have larger toe pads only if toe pad size is controlled by genes.
(2)Suggest why the scientists studied lizards on two islands rather than one.
(2)Give two control variables the scientists should have kept the same in the fan experiment.
(2)Total for this question: 12 marks
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