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Home > Biology > The biosphere > Investigating an ecosystem


Investigating an ecosystem

Sample questions and answers

Here are some typical Standard Grade questions. Use the information on the other pages of this section to help you if you are unsure. Look at the answer after you have tried each one.


A group of pupils carried out an investigation to compare the number of invertebrates found in pitfall traps in areas A and B shown in the diagram below.

Multiple pitfall traps: trap A is placed in the open, trap B is placed under the trees and bushes

The number of invertebrates in each pitfall trap were sampled each day for five days. The results are shown in the table below.

Table: results of pitfall trap investigation

DayThe number of invertebrates found in the pitfall traps in Area AThe number of invertebrates found in the pitfall traps in Area B
Average 26

(a) Calculate the average number of invertebrates in Area A over the five days.


You should add up all the values and then divide by the number of sampling days:

13 + 7 + 21 + 14 + 20 = 75

75 divide by 5 = 15

Therefore number of sampling days = 15.


(b) Suggest a reason why there seem to be more invertebrates in Area B.


The most likely answer to this question is that there is more food, or that the woodland provides more habitats for the invertebrates.


(c) How could these pupils have improved the reliability of their results?


The pupils should have set more pitfall traps in the two areas.

Remember always repeat experiments for more reliable results.


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