Question 1
A student counted the number of dandelions in 8 quadrats: 3, 8, 5, 8, 6, 4, 8, 6. (a) Calculate the mean, and give the mode and the median number of dandelions per quadrat. (3) (b) Each quadrat has an area of 0.25 m². The field has an area of 200 m². Estimate the number of dandelions in the field. (2)
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- (a) mean = 48 ÷ 8 = 6 (1)
- mode = 8 (1)
- median = 6 (1) (middle values 6 and 6)
- (b) 6 ÷ 0.25 = 24 per m² (1)
- 24 × 200 = 4800 dandelions (1) allow 4800 with no working for 2 marks; allow ecf from their mean
Question 2
A student wants to investigate the effect of light intensity on the distribution of a plant species in a woodland. The light intensity falls from the edge of the woodland into the middle. Describe a method the student could use. Include how the student would make the results valid and safe.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A clear, logical method using a transect and quadrats at regular intervals, with measurement of light intensity, repeated or random sampling, and results processed. Control variables and a safety point are included. |
| 2 | 3–4 | A method which uses a transect or quadrats and records the number of plants and light intensity, but with some detail or sequence missing. |
| 1 | 1–2 | Simple statements about counting plants or measuring light, with no clear method. |
Indicative content
- lay a tape measure / transect from the edge into the woodland
- place a quadrat at regular intervals, for example every 2 m
- count the number of the plant species in each quadrat
- measure the light intensity at each position with a light meter
- repeat the transect / use more than one transect and calculate means
- same size of quadrat, same time of day, same person counting
- plot a graph of number of plants against distance or light intensity
- safety, for example wear gloves / avoid harmful plants / wash hands afterwards
Question 3
In a stable community, the numbers of hares and lynx rise and fall in cycles. Each time, the peak in the number of lynx is a short time after the peak in the number of hares. (a) State which animal is the predator. (1) (b) Explain why the number of lynx peaks after the number of hares. (3)
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- (a) lynx (1)
- (b) when there are many hares there is more food for the lynx (1)
- so more lynx survive and breed, and the number of lynx increases (1)
- breeding takes time, so the rise in lynx lags behind the rise in hares (1)
- the lynx then eat more hares, so hare numbers fall, and then lynx numbers fall from lack of food (1)
- Max 3 for (b)
Question 4
Describe how the carbon in a dead leaf can become the carbon in the glucose of a new plant.
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- microorganisms / decomposers break down the leaf / decay (1)
- carbon is released as carbon dioxide by respiration (of the microorganisms) (1)
- carbon dioxide is taken in by a plant / used in photosynthesis to make glucose (1)
Question 5
Explain why the water cycle is important to land plants and animals.
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- it provides fresh water (1)
- which plants and animals need to survive / for photosynthesis / for cells (1)