D4.2 Stability and change questions for IB Biology
37 questions on Stability and change, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.
- IB Biology
- Part of D Continuity and change
- SL and HL
Questions by paper and level
SL and HL questions are for students at either level. HL only questions cover what only HL students study.
| Paper | SL and HL | HL only | All |
|---|---|---|---|
| Paper 1A | 15 | 5 | 20 |
| Paper 1B | 4 | 1 | 5 |
| Paper 2 | 8 | 4 | 12 |
| Every paper | 27 | 10 | 37 |
Counted on
Questions to try
Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.
Which observation provides the strongest evidence that an ecosystem has been stable over a long period of time?
Students set up 15 mesocosms in sealed 1 dm3 glass jars. Each jar contained 100 g of pond sediment, 800 cm3 of pond water, five shoots of Canadian pondweed (Elodea canadensis) and two pond snails (Lymnaea stagnalis). The dissolved oxygen concentration in every jar was 8.0 mg dm-3 at the start.
Three jars were placed under each of five lighting regimes, with 0 to 16 hours of light per day from LED lamps, at 20 °C. After 14 days the dissolved oxygen concentration was measured with an oxygen probe and the number of living snails was counted.
Light per day / hours | Mean dissolved oxygen after 14 days / mg dm-3 | Standard deviation / mg dm-3 | Living snails after 14 days (out of 6) |
|---|---|---|---|
0 | 1.2 | 0.4 | 0 |
4 | 4.1 | 0.6 | 3 |
8 | 7.6 | 0.5 | 6 |
12 | 9.8 | 0.7 | 6 |
16 | 10.4 | 0.9 | 6 |
- (a)
State the independent variable in this investigation.
1 mark
- (b)
Outline why sealed glass jars were used for the mesocosms rather than open tanks.
2 marks
- (c)
Calculate the percentage change in the dissolved oxygen concentration over the 14 days for the jars given 4 hours of light per day.
1 mark
- (d)
Discuss whether the difference in mean dissolved oxygen between the 12-hour and 16-hour treatments is likely to be significant.
2 marks
- (e)
Explain the results for the jars kept with no light.
2 marks
- (f)
Suggest two changes that would bring the care of animals in this investigation into line with experimental guidelines.
2 marks
Human activities are changing ecosystems across the world.
- (a)
Describe how the leaching of fertilizers can lead to eutrophication of lakes and rivers.
4 marks
- (b)
Outline the causes of the loss of mixed dipterocarp forest in Southeast Asia.
4 marks
- (c)
Explain why a combination of different approaches is needed to conserve biodiversity.
7 marks
Which are requirements for the stability of an ecosystem?
I. A continuous supply of energy
II. Recycling of nutrients
III. Climatic variables that stay exactly the same from year to year
Students investigated the effect of drainage water from farmland on a stream. A drainage pipe from fields treated with nitrate fertilizer discharged into the stream. Water samples were taken at one site upstream of the pipe (A) and at four sites downstream (B–E).
At each site the nitrate concentration and the dissolved oxygen concentration were measured. A second sample from each site was sealed in a bottle, incubated in the dark at 20 °C for 5 days and its dissolved oxygen concentration measured again. The biochemical oxygen demand (BOD) is the decrease in dissolved oxygen over the 5 days.
Site | Distance from pipe / m | Nitrate / mg dm-3 | Dissolved oxygen at start / mg dm-3 | Dissolved oxygen after 5 days / mg dm-3 | BOD / mg dm-3 |
|---|---|---|---|---|---|
A | 50 upstream | 1.2 | 9.6 | 8.4 | 1.2 |
B | 50 downstream | 9.8 | 8.1 | 2.3 | |
C | 200 downstream | 7.5 | 7.4 | 2.9 | 4.5 |
D | 500 downstream | 4.6 | 8.0 | 5.1 | 2.9 |
E | 1000 downstream | 2.4 | 8.9 | 7.0 | 1.9 |
- (a)
Calculate the BOD of the water at site B.
1 mark
- (b)
Suggest why the bottles were incubated in the dark.
1 mark
- (c)
Describe the relationship between nitrate concentration and BOD shown by these data.
2 marks
- (d)
Explain how a high nitrate concentration could lead to a high BOD.
3 marks
- (e)
Evaluate the method used to show that drainage water from the farmland affects the stream.
2 marks
Researchers used satellite images to estimate the area of rainforest remaining in a large region of the Amazon basin. Mean annual rainfall over the remaining forest in the region was calculated from weather station records for the ten years up to each date.
Year | Area of rainforest / km2 | Mean annual rainfall / mm |
|---|---|---|
1970 | 410 000 | 2300 |
1990 | 362 000 | 2260 |
2010 | 318 000 | 2180 |
2020 | 297 000 | 2120 |
- (a)
Calculate the percentage change in the area of rainforest between 1970 and 2020.
2 marks
- (b)
Describe the relationship between the area of rainforest and the mean annual rainfall.
2 marks
- (c)
Explain how the loss of rainforest could reduce the rainfall over the remaining forest.
3 marks
- (d)
Scientists are uncertain about the minimum area of rainforest needed to maintain rainfall over the Amazon basin. Suggest reasons for this uncertainty.
2 marks
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More questions in Continuity and change
- D1.1DNA replication
- D1.2Protein synthesis
- D1.3Mutations and gene editing
- D2.1Cell and nuclear division
- D2.2Gene expressionHL only
- D2.3Water potential
- D3.1Reproduction
- D3.2Inheritance
- D3.3Homeostasis
- D4.1Natural selection
- D4.2Stability and changeThis page
- D4.3Climate change
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