CAMBRIDGE IGCSE™ BIOLOGY: END-OF-CHAPTER TEST 6
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Name Date
End-of-chapter 6 test
Palm trees belong to the botanical family Arecaceae. These species of tree have grown for more than
80 million years.
1 Fossilised Arecaceae show that ancient leaves had lower numbers of stomata per
unit surface area than modern leaves. Suggest what this indicates about the
ancient atmosphere.
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2 A study was carried out to investigate the effect of light intensity on the rate of
transpiration in two varieties of Arecaceae. One is native to sandy deserts, where there is
little rainfall and low humidity. The other grows in tropical rainforests, which have high
rainfall and high humidity.
A learner took a young sapling of each palm and attached them to separate items of equipment
in a laboratory at a range of light intensities (Figure 6.1).
Figure 6.1
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CAMBRIDGE IGCSE™ BIOLOGY: END-OF-CHAPTER TEST 6
In each case, the learner measured the rate of transpiration by recording how far the air bubble
moved in the tube attached to the flask containing the saplings (Table 6.1).
Light intensity / Mean distance moved by the air bubble in 20 minutes / mm
lux × 1000 Desert palm tree sampling Rainforest palm tree sampling
0 0 0
20 5 9
40 7 11
60 10 16
80 12 18
100 12 20
Table 6.1
a Identify the item of equipment used by the learner to measure the rate of transpiration.
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b Young trees such as those used in this study do not need as much lignin in their stems as
mature trees. Suggest why.
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c Plot a graph to show the results for both palm trees. You should select appropriate scales
for your axes and join your plotted points with straight lines to make two separate lines of
best fit.
[4]
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CAMBRIDGE IGCSE™ BIOLOGY: END-OF-CHAPTER TEST 6
d It was important that the total surface area of all leaves on both saplings was identical in this
investigation. Explain why.
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e Explain how the learner could improve the reliability of these results.
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[Total: 10]
3 Table 6.2 shows some features of the habitats of desert and rainforest palm trees.
Average humidity / % Average rainfall / mm/year
Desert 25 100
Rainforest 70 2000
Table 6.2
a Using your knowledge of leaf structure and the information provided in the table, explain the
results of the study in question 2. Use the term limiting factor in your answer.
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CAMBRIDGE IGCSE™ BIOLOGY: END-OF-CHAPTER TEST 6
b The learner noticed that some of the leaves of the desert palm sapling were yellow. Explain
the likely cause of this discoloration and suggest why this may mean that comparison of the
results in Table 6.1 is not valid.
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[Total: 8]
[Test total: 20]
END OF TEST
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