IB Biology SL D4.2 Stability and Change Question Bank
Practise IB Biology SL D4.2 by evaluating energy input, nutrient cycling, biodiversity and disturbance in ecosystem evidence.
- Syllabus
- First assessment 2025
- Course
- Biology SL
- Level
- SL
Exam points
- explain mesocosm sustainability through light input, autotrophs, decomposers and nutrient recycling
- predict how keystone-species removal or reintroduction changes biodiversity and food-web stability
- trace eutrophication, biomagnification or plastic pollution through ecosystem data and trophic levels
Covered syllabus points
D4.2.1—Stability of natural ecosystemsD4.2.2—Requirements for stabilityD4.2.3—Amazon rainforest deforestationD4.2.4—Mesocosm modelD4.2.5—Keystone speciesD4.2.6—Sustainable resource harvestingD4.2.7—Agriculture sustainability factorsD4.2.8—EutrophicationD4.2.9—BiomagnificationD4.2.10—Plastic pollution of oceansD4.2.11—Rewilding
D4.2 Stability and change question 1
Beavers (Castor fiber) have been reintroduced into many European countries. They cut down trees and use them as a source of food as well as for building their homes and dams.
Question (a)
(a)
Beavers are a keystone species. Outline the importance of keystone species.
[ 2 ]
Question (b)
(b)
Studies show that species richness of large invertebrates increases in the presence of beavers. Suggest reasons why biodiversity is important in an ecosystem.
[ 2 ]
Question (c)
(c)
Outline two methods of restoration of natural processes in ecosystems by rewilding, other than reintroducing a keystone species.
1.
2.
[ 2 ]
D4.2 Stability and change question 2
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.
Removed for copyright reasons
Question (a)
(a)
Suggest one reason for using netting to cover the mesocosms.
[ 1 ]
Question (b)
(b)
Explain the advantages of using mesocosms instead of doing the experiment in the natural habitat.
[ 2 ]
D4.2 Stability and change question 3
The sea snail Nucella ostrina and the sea star Pisaster ochraceus are predators of the mussel Mytilus trossulus. The mussels live on rocks at the edge of the sea and feed on phytoplankton and zooplankton. The zooplankton feed on the phytoplankton.
Nucella ostrina
Pisaster ochraceus
Mytilus trossulus
Groups of 50 mussels were transplanted to an experimental area and protected from predation until the start of the experiment. Researchers then investigated the effect of the predators on the population of the mussels over a period of 60 days.
Sea stars along the pacific coast of the US are dying from "sea star wasting syndrome". Suggest the effect this will have on the ecosystem.
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