IBBiologyHLExam QuestionsInteraction & InterdependencePopulations & Communities

Syllabus Edition

First teaching 2023

First exams 2025

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Populations & Communities (HL IB Biology)

Exam Questions

31 mins13 questions

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Populations & Communities

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Populations & Communities

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1
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Which statement about estimating population size in motile organisms is correct?

  • Any marking method can be used to mark organisms in the first sample.

  • Population size can be estimated using quadrat sampling.

  • Marked individuals from the first sample must be allowed to randomly mix with the rest of the population before taking a second sample.

  • Simpson's index is used to calculate population size.

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2
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Why does exponential growth occur in the early stages of population increase?

  • There is competition for resources and increasing predation.

  • Death rate is equal to birth rate.

  • Birth rate is higher than death rate.

  • Resources are readily available and there is little or no predation.

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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 to determine population size are correct? 

  1. Random sampling avoids bias.
  2. Random sample sites can be selected by throwing a quadrat with eyes closed.
  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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4
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Sampling allows population size to be estimated; this can result in sampling errors. 

What is a sampling error?

  • The difference between an estimated population size and a true population size.

  • The process of counting small samples of a population that will represent a whole population.

  • When some members of a population are more likely to be counted than others.

  • When positions of the sampling points are not selected at random.

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1
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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
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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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