IB Biology SL D4.2.4 Mesocosm Model Questions
Use controlled mesocosms to model ecosystems, manage exchanges and evaluate experimental validity.
- Syllabus
- First assessment 2025
- Course
- Biology SL
- Level
- SL
Exam points
- Explain how mesocosms control variables, isolate populations and allow replication while reducing effects on the natural habitat.
- Set up and validate a sealed mesocosm using suitable producers, decomposers, light, matter-energy exchange and controlled starting variables.
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IB Biology SL D4.2.4 Mesocosm Model Questions question 1
[Maximum number: 4]
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)
State one variable that should have been the same in all of the mesocosms when they were set up.
[ 1 ]
a. volume/source/composition of water;
b. initial numbers/type of organisms of each species;
c. size/volume/material of tanks;
d. type of nutrients;
"same" tanks is too vague. Do not accept amount of nutrients.
Marking guidance:
Do not accept same temperature/amount of light as all are in the same open space.
1 max
Question (b)
(b)
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 (c)
(c)
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; |
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