Unit 3 Problem solving questions
1. An investigation on the effects of the presence of plants on soil erosion was carried out.
The diagram below shows the apparatus used.
Tray A contained soil only.
Tray B contained the same type of soil but with grass growing on it.
Water from a spray was allowed to fall onto each tray. Any water running off was collected
and examined for soil washed from the tray.
a) Identify the variable which was altered in the investigation.
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b) Describe two variables which must be kept constant in both sets of apparatus during the
investigation.
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c) The investigation was set up to test the hypothesis that the presence of plants reduces soil
erosion.
Suggest one measurement or observation required in order to confirm or reject the
hypothesis.
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2. Four groups of students investigated the effect of light intensity on the time taken for
larvae to travel 10 cm. The light intensity was varied by moving the light source. The
diagram below shows the apparatus.
The table below shows the results of this investigation.
a) Complete the table to show the average time taken to travel 10 cm in very low light
intensity.
Space for calculation
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b) Which light intensity showed the greatest range of results?
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Question 2 continued
c) On the grid below, plot a bar graph to show the average time taken for larvae to travel 10
cm in high, medium and low light intensity levels only.
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d) Describe the relationship between light intensity and time taken for larvae to travel 10 cm.
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3. The small burrowing invertebrate, Corophium, is found in the mud of Scottish estuaries.
Corophium is the major prey of many species of migratory wading birds. These birds are
present in large numbers from August to April.
The graph below shows the results of a one year survey on the numbers of Corophium taken
on the first day of each month.
a) Describe the changes in the numbers of Corophium from January to December.
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b) How many times greater are the numbers of Corophium on 1st June compared to 1st
April?
Space for calculation
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Question 3 continued
c) Using all the information given, explain why there are high numbers of Corophium on 1st
August.
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d) Predict what would happen to the biodiversity of this estuary if the wading birds stayed all
year. Explain your answer.
Prediction __________________________________________________________________
Explanation _________________________________________________________________
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4. The leaves of black walnut trees produce a chemical which is released into the soil when
the leaves fall. This chemical prevents the germination (growth) of other plant seeds. The
chemical can be extracted from the leaves.
a) A student carried out an investigation into the effect of this chemical on mung bean seeds.
Leaf extracts containing different concentrations of the chemical were prepared. The student
was supplied with
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30 mung bean seeds
3 identical petri dishes
Cotton wool
Bottles of 0.1%, 1% and 10% leaf extract chemical
i) Complete the diagrams below to show how the investigation should have been set up.
Label the contents of each petri dish.
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Question 4. a) continued
ii) What observations and measurements should have been taken to obtain results for this
investigation?
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iii) A control petri dish should also have been set up to show that it was the leaf extaract
preventing the growth of the mung bean seeds. Complete the diagram below to show the
contents of the control petri dish.
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b) Explain why producing this chemical is an advantage to the black walnut trees.
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5. An investigation into the behaviour of blowfly larvae was carried out.
One blowfly larva was placed at X, then lamp A was switched on.
When the larva reached lamp Y, lamp A was switched off and lamp B was switched on.
The path taken by the larva is shown in the diagram below.
a) Describe the response of the larva to light.
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b) i) Suggest one change to the apparatus that would confirm that the response was due to the
light and not the heat from the lamp.
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ii) State one way in which the reliability of the results could be improved.
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