1[1 mark]
Which plant tissue is found at the growing tips of shoots and roots?
- Xylem
- Phloem
- Meristem
- Epidermal tissue
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Answer: C C (1)
2[3 marks]
Explain how a root hair cell is adapted for taking in mineral ions from the soil.
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- long root hair gives a large surface area (1)
- mineral ions are taken in by active transport (1)
- which needs energy from respiration / many mitochondria (1)
3[3 marks]
Compare the transport of substances in xylem and phloem.
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- xylem transports water and mineral ions (1)
- phloem transports dissolved sugars (1)
- xylem: from roots to stems and leaves; phloem: from the leaves to the rest of the plant (1)
- allow xylem has lignin / hollow tubes; phloem has pores in end walls
4[3 marks]
Describe the role of stomata and guard cells in a leaf.
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- stomata are pores that allow gases to move in and out / gas exchange (1)
- guard cells control the opening and closing of the stomata (1)
- closing stomata reduces water loss (1)
5[3 marks]
A student used a potometer to measure the distance an air bubble moved in 5 minutes. Three repeats gave: 24 mm, 27 mm and 21 mm. Calculate the mean rate of transpiration in mm per minute.
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- mean distance = (24 + 27 + 21) ÷ 3 = 24 mm (1)
- 24 ÷ 5 (1)
- 4.8 mm/min (1)
- allow 3 marks for the correct answer with no working
6[6 marks]
Explain how temperature, humidity, air movement and light intensity affect the rate of transpiration in a plant.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A clear, correct explanation of the effects of all four factors, with reasons linked to evaporation, diffusion or stomata. |
| 2 | 3–4 | Correct effects given for at least three factors, with some reasons. |
| 1 | 1–2 | Some correct effects given, with few or no reasons. |
Indicative content
- Higher temperature increases the rate: water evaporates and diffuses out faster
- Higher humidity decreases the rate: smaller concentration gradient of water vapour between the leaf and the air
- More air movement increases the rate: removes water vapour from around the stomata so the concentration gradient stays steep
- Higher light intensity increases the rate: stomata open wider so more water vapour escapes
- The opposite changes reduce the rate