IBBiologyHLTopic QuestionsInteraction & InterdependencePopulations & Communities

Syllabus Edition

First teaching 2023

First exams 2025

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Populations & Communities (HL IB Biology)

Topic Questions

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1
Sme Calculator1 mark

The graph shows changes in percentage cover of four plant species on a sand dune ecosystem over 500 years.

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Which of the following explanations cannot be supported using the information in this graph.

  • All four species never formed part of the same community

  • Beech grass became extinct after 100 years

  • Interspecific competition between conifer trees and shrub bunchgrass occurs leading to a decrease in shrub bunchgrass

  • Intraspecific competition results in a decrease in conifer trees after around 400 years

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2
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A water quality investigation was carried out after some cases of heavy metal poisoning were detected in a countryside village with a river running through it. The investigators were trying to establish if poisoning was worse on the north or the south of the river.

  North of the river South of the river
Number of cases of heavy metal poisoning 26 12

The results from a chi-squared test were:

Chi-squared value: 5.2
Degrees of freedom: 1

Critical values table:

Degrees of Freedom P = 0.05 P = 0.01 P = 0.001
1 3.83 6.64 10.83
2 5.99 9.21 13.82
3 7.82 11.35 16.27

What conclusions can be drawn from the information above?

  • The χ2 value is greater than the critical value so there is an association between heavy metal poisoning and location

  • The  χ2 value is lower than the critical value so there is no association between heavy metal poisoning and location

  • Poisoning from heavy metals is worse in villages

  • Heavy metals are found in both locations, north and south of the river

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3
Sme Calculator1 mark

Certain plants have developed a mutualistic relationship with soil fungi, in which the plant provides sugars to the fungus for respiration.

In what way does the plant receive a benefit in return?

  • The fungus helps to stabilise the plant's root network in poor / stony soils.

  • The fungus acts like a sponge to retain water in dry soils after (infrequent) rainfall.

  • The fungus fixes atmospheric nitrogen and supplies nitrate ions to the plant. 

  • The fungus accesses mineral ions in mineral-deficient soils and supplies them to the plant's roots.

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11 mark

In a woodland habitat, blue tits and other small birds feed on various species of caterpillar and beetle, which themselves feed on the leaves of trees and herbaceous plants. 

Which of the following statements accurately describes a population within this example?

  • All of the organisms living in the habitat, together with their living and non-living interactions.

  • All of the small birds living in the habitat.

  • All of the blue tits living in the habitat.

  • All of the living organisms in the habitat.

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21 mark

Which of the following statements about quadrat sampling are true? 

  1. Sampling must be random to avoid bias.
  2. Random samples can be achieved by closing your eyes and throwing a quadrat.
  3. Quadrat sampling is only useful for small organisms.

  • I only

  • I and II only

  • I and III only

  • I, II, and III

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31 mark

A chi-squared test was carried out to test for association between species A and species B.  The results of the chi-squared test are given below. 

Results of chi-squared test:

Chi-squared value 5.89
Degrees of freedom 1

Critical values table:

Degrees of freedom Probability level
0.1 0.05 0.01 0.001
1 2.71 3.84 6.64 10.83
2 4.60 5.99 9.21 13.82

What can be concluded from the chi-squared test for association carried out to test for association between species A and species B?

  • There is no significant association between species A and species B

  • Species A competes with species B for resources

  • There is a statistically significant association between species A and species B at the 5% probability level

  • There is a statistically significant association between species A and species B at the 1% probability level

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