IB Biology SL 4.2.4 Mesocosms
Practise designing and evaluating sealed mesocosm investigations, including controls, variable exchange and ecosystem requirements.
- Syllabus
- First assessment 2025
- Course
- Biology SL
- Level
- SL
Exam points
- Explain why mesocosms help control variables when studying ecological relationships.
- Identify errors, required components and material exchange in sealed mesocosm experiments.
D4.2.4—Mesocosm model question 1
[Maximum number: 3]
Mosquitofish (Gambusia affinis) are aquatic organisms that feed on mosquito larvae, other insects, zooplankton and detritus. Open mesocosms were established outdoors in 30 large water tanks designed to match natural aquatic habitats in California, USA.
Experiments were set up to measure the effect of extra nutrient availability on the community in the presence or absence of mosquitofish. Each tank was covered with netting. Six tanks were used for each of the different experimental conditions.
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Question (a)
(a)
Suggest one reason for using netting to cover the mesocosms.
[ 1 ]
a. prevent entering/leaving of organisms/leaves/organic matter;
b. allow gases/air to circulate/enter;
c. prevent animals from eating organisms/drinking water/damaging mesocosm;
d. allow light to penetrate;
Marking guidance:
Do not accept microorganisms.
1 max
Question (b)
(b)
Explain the advantages of using mesocosms instead of doing the experiment in the natural habitat.
[ 2 ]
a. ability to control/measure variables/nutrients/physical factors (to determine their effects);
b. isolation of populations / can compare with and without mosquitofish (to determine specific effects);
c. not affect/impact/contaminate the natural ecosystem;
d. avoid unpredictable effects that could occur in the natural ecosystem;
e. possible to have exact replicates;
2 max
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