Question 1
Paper 1A style
When is harvesting of a wild fish population sustainable?
- When only adult fish are caught
- When the population is above its carrying capacity
- When the rate of harvesting is lower than the rate of replacement
- When the catch is the same every year
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Answer: C [1]
Question 2
Paper 1A style
Why is a sealed glass vessel preferred to an open tank for a mesocosm?
- It stops light energy entering
- It prevents entry and exit of matter but allows energy transfer
- It keeps the temperature constant
- It prevents decomposers from growing
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Answer: B [1]
Question 3
Paper 2A style
(a) The forest area of a part of the Amazon basin fell from 520 000 km² to 442 000 km² (practice figures). Calculate the percentage change in forest area. [2] (b) Explain how deforestation on this scale could reduce rainfall over the remaining forest. [3]
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- (a) (442 000 − 520 000) ÷ 520 000 × 100 [1]
- (a) −15% / decrease of 15% [1]
- (b) fewer trees so less transpiration / less water vapour released into the atmosphere [1]
- (b) less evaporative cooling / less driving of air flows that bring in moist air [1]
- (b) water vapour from transpiration normally condenses and falls as rain further inland / water is recycled [1]
- (b) longer dry season / drought stress / more fires reduce forest further (positive feedback) [1]
- max 5
Question 4
Paper 1B style
The table shows DDT concentrations in an estuary food chain (practice data). (a) Calculate how many times greater the concentration is in the fish-eating birds than in the zooplankton. [1] (b) Explain the pattern shown in the data. [3]
| Sample | DDT concentration / parts per million |
|---|---|
| Water | 0.00005 |
| Zooplankton | 0.04 |
| Small fish | 0.5 |
| Large fish | 2.0 |
| Fish-eating birds | 25 |
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- (a) 25 ÷ 0.04 = 625 times [1]
- (b) concentration increases at each higher trophic level / biomagnification [1]
- (b) DDT is persistent / not broken down [1]
- (b) DDT is fat-soluble / stored in fatty tissue / not excreted [1]
- (b) each consumer eats many organisms from the level below, taking in all their DDT [1]
- max 4
Question 5
Paper 2B style
Explain how the use of fertilizers on farmland can lead to the death of fish in a nearby lake.
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- nitrate / phosphate fertilizers leach from soil (into the lake) [1]
- nutrient enrichment of the water is eutrophication [1]
- rapid growth of algae / algal bloom [1]
- algae block light so plants below cannot photosynthesise and die [1]
- algae / plants die and are decomposed by bacteria [1]
- decomposers respire aerobically / use oxygen [1]
- biochemical oxygen demand / BOD increases [1]
- dissolved oxygen concentration falls / water becomes hypoxic [1]
- fish cannot respire aerobically and die [1]
- Do not accept 'algae use up oxygen by photosynthesis'
- max 6
Question 6
Paper 2A style
Outline the effects of plastic pollution on marine life.
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- plastics are non-biodegradable / persist for a long time [1]
- macroplastic / nets / bags cause entanglement, e.g. of seals / turtles / seabirds [1]
- macroplastic swallowed, e.g. bags mistaken for jellyfish by turtles, blocking the gut / starvation [1]
- microplastics eaten by zooplankton / filter feeders / fish [1]
- microplastics pass along food chains / carry toxic chemicals [1]
- max 3
Question 7
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanUsing a named example, describe the changes that occur during primary succession.
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- named example, e.g. sand dunes / land exposed by a retreating glacier / volcanic island [1]
- pioneer species colonise bare ground / sand with no soil [1]
- organisms change conditions, e.g. add humus / form soil / stabilise sand, allowing new species to colonise [1]
- plants increase in size, e.g. grasses to shrubs to trees [1]
- primary production increases [1]
- species diversity increases [1]
- food webs become more complex [1]
- nutrient cycling increases [1]
- max 4
Question 8
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain how grazing by farm livestock can cause arrested succession.
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- livestock eat / trample tree seedlings / young shrubs [1]
- so woodland cannot develop and grassland / moorland persists [1]
- community is prevented from reaching the climax community / plagioclimax [1]
- max 2