Question 1
Paper 1A style
Which statement correctly describes a habitat?
- The role of a species in an ecosystem, including how it obtains food
- The place in which a community, species, population or organism lives
- All the populations of different species living and interacting in an area
- The range of an abiotic factor within which a species can survive
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Answer: B (A describes a niche, C a community, D a range of tolerance) [1]
Question 2
Paper 1A style
Why do coral reefs form mainly in shallow water, usually less than about 30 m deep?
- The water pressure dissolves calcium carbonate skeletons
- The salinity of deep water is too high for coral polyps
- Too little light reaches the zooxanthellae for photosynthesis
- The water is too warm for coral polyps to survive
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Answer: C [1]
Question 3
Paper 1A style
Cacti in American deserts and spurges in African deserts are not closely related, but both have succulent stems, spines and reduced leaves. What explains this similarity?
- Convergent evolution under similar selection pressures
- Inheritance of the features from a recent common ancestor
- Competitive exclusion between the two groups
- Adaptive radiation from a single desert species
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Answer: A [1]
Question 4
Paper 2A style
Explain how a named tree species is adapted to the abiotic conditions of a mangrove swamp.
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- named species, e.g. red mangrove / Rhizophora mangle [1]
- stilt / prop roots anchor tree in soft mud [1]
- lenticels in aerial roots allow oxygen uptake / gas exchange [1]
- because waterlogged mud is anoxic / low in oxygen [1]
- roots exclude salt during water uptake [1]
- salt accumulated in older leaves that are shed [1]
- viviparous seeds / propagules germinate on parent and float to establish in mud [1]
- thick waxy leaves reduce water loss OWTTE [1]
- max 4
Question 5
Paper 1B style
Students used a belt transect from the edge of a woodland into its interior. At each point they measured light intensity with a sensor and estimated the percentage cover of a moss species in three quadrats. The data are for practice. (a) Describe the relationship between light intensity and moss cover. [2] (b) Suggest one abiotic variable other than light that could have changed along the transect and affected moss cover. [1] (c) Evaluate the conclusion that low light intensity causes the moss to grow. [2]
| Distance from edge / m | Light intensity / lux | Mean moss cover / % |
|---|---|---|
| 0 | 12000 | 2 |
| 5 | 6500 | 8 |
| 10 | 3000 | 21 |
| 15 | 1400 | 34 |
| 20 | 900 | 38 |
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- (a) negative correlation / moss cover increases as light intensity decreases [1]
- (a) use of data, e.g. 2% at 12000 lux rising to 38% at 900 lux / change levels off at low light [1]
- (b) soil / air humidity OR soil moisture OR temperature OR soil pH [1]
- (c) correlation does not prove causation [1]
- (c) other variables such as humidity also change with distance / were not controlled [1]
- (c) only one transect / three quadrats per point, so limited replication [1]
- (c) moss may tolerate shade rather than need it / may be outcompeted in bright light OWTTE [1]
- max 5
Question 6
Paper 2A style
Outline how temperature and rainfall determine the distribution of terrestrial biomes, using two named biomes.
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- for a given temperature and rainfall pattern one natural ecosystem type / biome is likely to develop [1]
- tropical forest where temperature is high all year and rainfall very high [1]
- hot desert where rainfall is very low and daytime temperatures are high [1]
- tundra where temperatures are very low / below 0 °C most of the year and precipitation is low [1]
- accept other correct biome–climate pairs: taiga, temperate forest, grassland [1]
- max 3
Question 7
Paper 2B style
Explain how named species of plants and animals are adapted to life in hot deserts and in tropical rainforest.
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- desert plant named, e.g. saguaro cactus / Carnegiea gigantea [1]
- leaves reduced to spines reduce surface area for water loss / deter herbivores [1]
- stem stores water / pleated stem swells after rain [1]
- shallow, widespread roots absorb rain quickly [1]
- CAM photosynthesis / stomata open at night, reducing water loss [1]
- desert animal named, e.g. dromedary camel [1]
- body temperature allowed to rise during day, so less water used for sweating [1]
- concentrated urine / dry faeces reduce water loss [1]
- rainforest plant named, e.g. kapok / Ceiba pentandra [1]
- tall / emergent trunk reaches light above canopy OR buttress roots support tree in shallow soil [1]
- leaves with drip tips shed rainwater quickly [1]
- rainforest animal named, e.g. spider monkey with prehensile tail for moving in canopy / poison frog with toxins and warning colours [1]
- Note: credit adaptations only when linked to a named species; accept common or scientific names
- max 7