Question 1
Paper 1A style
A bacterium grows only at the bottom of a tube of broth, where no oxygen is present. Which type of organism is it?
- Obligate aerobe
- Facultative anaerobe
- Obligate anaerobe
- Facultative mixotroph
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Answer: C [1]
Question 2
Paper 1A style
What distinguishes saprotrophic nutrition from holozoic nutrition?
- Saprotrophs are autotrophic, whereas holozoic organisms are heterotrophic
- Saprotrophs digest food outside their cells, whereas holozoic organisms digest food internally
- Saprotrophs ingest food, whereas holozoic organisms absorb food directly
- Saprotrophs feed on living organisms, whereas holozoic organisms feed only on dead matter
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Answer: B [1]
Question 3
Paper 1A style
Which forest plant starts life on the branch of a tree and later sends roots down to the soil that enclose the host trunk?
- Liana
- Strangler epiphyte
- Shade-tolerant herb
- Canopy tree
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Answer: B [1]
Question 4
Paper 2A style
Euglena is a freshwater protist that contains chloroplasts. Outline why Euglena is described as a facultative mixotroph.
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- mixotroph: both autotrophic and heterotrophic [1]
- photosynthesises / autotrophic in light, using chloroplasts [1]
- takes in / absorbs carbon compounds from surroundings (heterotrophic) [1]
- facultative: can survive using one mode alone, e.g. heterotrophically in the dark [1]
- max 3
Question 5
Paper 2A style
A skull of Paranthropus robustus has a sagittal crest and very large molars with thick enamel. Deduce the diet of this species, giving reasons.
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- herbivorous / tough, hard plant material, e.g. seeds, roots, tubers [1]
- large flat molars give large surface area for grinding [1]
- thick enamel resists wear from hard / abrasive food [1]
- sagittal crest anchors large jaw / temporalis muscles for powerful chewing [1]
- max 3
Question 6
Paper 1B style
Two species of Paramecium, A and B, which feed on the same bacteria, were grown in separate cultures and then together in a mixed culture. The data are for practice. (a) Calculate the percentage decrease in the population of species B in the mixed culture compared with the separate culture on day 16. [2] (b) Explain the results of the mixed culture with reference to competitive exclusion. [3]
| Day | A alone / cells per cm³ | B alone / cells per cm³ | A in mixed culture / cells per cm³ | B in mixed culture / cells per cm³ |
|---|---|---|---|---|
| 0 | 2 | 2 | 2 | 2 |
| 4 | 60 | 40 | 50 | 30 |
| 8 | 190 | 120 | 150 | 40 |
| 12 | 200 | 130 | 180 | 15 |
| 16 | 200 | 125 | 195 | 5 |
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- (a) (125 − 5) ÷ 125 × 100 [1]
- (a) = 96% [1]
- (b) both species occupy the same niche / compete for the same food [1]
- (b) species A is the better competitor / uses the bacteria more efficiently [1]
- (b) species B is eliminated / declines towards extinction in mixed culture [1]
- (b) two species cannot share the same niche indefinitely / competitive exclusion [1]
- (b) species A reaches similar density in mixed culture as alone, so is little affected [1]
- max 5; ECF in (a)
Question 7
Paper 2A style
Distinguish between the fundamental niche and the realized niche of a species.
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- fundamental niche is the potential niche based on adaptations / tolerance limits [1]
- realized niche is the actual extent of the niche when in competition with other species [1]
- realized niche is usually smaller than / part of the fundamental niche [1]
- example, e.g. barnacle Chthamalus restricted to upper shore by competition from Semibalanus [1]
- max 3
Question 8
Paper 2B style
Describe adaptations of herbivores for feeding on plants and of plants for resisting herbivory, and outline chemical, physical and behavioural adaptations of prey animals for resisting predation.
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- chewing mouthparts / mandibles in leaf-eating insects, e.g. caterpillars, bite and grind leaves [1]
- piercing mouthparts / stylets of insects, e.g. aphids, reach phloem sap [1]
- plants have thorns / spines / physical structures that deter herbivores [1]
- plants produce toxic secondary compounds in seeds and leaves [1]
- named toxin, e.g. alkaloids / nicotine / cyanogenic glycosides [1]
- some herbivores have metabolic adaptations to detoxify the toxins, e.g. koala / eucalyptus [1]
- prey chemical adaptation, e.g. toxins / distasteful chemicals / defensive sprays [1]
- prey physical adaptation, e.g. camouflage / spines / shells / speed [1]
- warning colours advertise toxicity, so predators learn to avoid prey [1]
- prey behavioural adaptation, e.g. herding / shoaling / alarm calls / fleeing / playing dead [1]
- max 8