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First teaching 2023

First exams 2025

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Stability & Change (HL IB Biology)

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11 mark

A simple aquatic mesocosm is shown below.

chTYgEST_e-5

Why is A an important component of the mesocosm?

  • A provides protection for the primary consumers from predators.

  • A converts heat energy to chemical energy.

  • A provides carbohydrates and oxygen to support the mesocosm.

  • A helps to maintain a stable temperature.

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2
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What is required for an ecosystem to be stable over an extended time period?

I.
An external supply of soil nutrients
II.
Genetic diversity
III.
An energy supply

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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3
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Which of the following statements about keystone species is correct?

  • Keystone species are always top predators.

  • Keystone species do not affect the diversity of their surrounding ecosystems.

  • The influence of a keystone species on its ecosystem is equivalent to that of any other species.

  • Removing a keystone species risks ecosystem collapse.

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11 mark

Which of the following considerations should be taken into account when building a mesocosm to test the impact of a particular environmental variable?

A Any type of container can be used No secondary consumers Inclusion of autotrophs Producers should be slow-growing
B Transparent container Food chains of up to three organisms can be included Inclusion of autotrophs Producers should be slow-growing
C Transparent container No secondary consumers Inclusion of autotrophs A control mesocosm should be built
D Transparent container

No secondary consumers

Inclusion of autotrophs

  Soil should be sterilised to prevent contamination

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    2
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    Which of the statements relating to deforestation in the Amazon rainforest is correct?

    • Only a small area of rainforest is needed to sustain the cycle of transpiration and rainfall that maintains the ecosystem.

    • A region of rainforest with an area of 4 100 000 km2 was reduced to an area of 3 855 000 km2 over a ten year period, resulting in a percentage decrease of 6 %.

    • Scientists know the area of rainforest that needs to be maintained in order to avoid passing a tipping point in rainforest stability.

    • The Amazon rainforest will be able to recover even if deforestation continues until the stability tipping point is reached.

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    3
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    Which of the statements about ecological succession is correct?

    • Succession can only be triggered by changes in abiotic conditions.

    • During primary succession the arrival of new species can alter the abiotic conditions present in a habitat.

    • Succession always results in a stable climax community.

    • A climax community will always be more diverse than the ecosystems that occur during the process of succession.

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    4
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    The stability of an ecosystem can be investigated using a mesocosm.

    What ethical guidelines should be followed when using animals in a mesocosm?

    I.
    Animals should be used in preference to alternative organisms.
    II.
    Enough food should be available for any animals present.
    III.
    Animals must be returned to their natural environment at the end of an investigation.

    • I and II only

    • II and III only

    • I and III only

    • I, II and III

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    5
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    A team of scientists used mesocosms to investigate the effect of invasive species A and B on native species of frog, toad and newt that would normally be found in a wetland ecosystem. Their mesocosms contained the frog, toad and newt species in the absence of invasive species, in the presence of each invasive species individually, and in the presence of both invasive species at the same time. 20 mesocosms, set up on land in 400 litre tanks, allowed each condition to be replicated 5 times. Some of the results are shown in the graph. The error bars show standard error.

    mesocosm-invasive-species-graph-1

    Which of the statements about the mesocosm experiment are correct?

    • It can be concluded that introducing species B to a wetland ecosystem would damage populations of frogs.

    • The mesocosms provide a realistic representation of the wetland habitat of the frog, newt and toad species.

    • The mesocosms provided a model that allowed data on the effect of the invasive species to be collected.

    • Invasive species B had a significant impact on all of the native amphibian species.

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    1
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    Which of the following is not true about mesocosms?

    • Mesocosms allow the control of environmental conditions

    • Mesocosms allow collection of reliable data

    • Continuous data can be collected from a mesocosm

    • It is easy to mimic natural environmental conditions in a mesocosm

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