A coastal restoration team shows a young mangrove plant growing where sea water enters a river estuary. The plant absorbs water through roots in mud, but th...
Question 1 Report
A coastal restoration team shows a young mangrove plant growing where sea water enters a river estuary. The plant absorbs water through roots in mud, but the salty water makes uptake difficult. Some mangroves lose salt through special leaf glands. Fig. 1 shows a leaf with a salt gland on its upper surface and a stoma on its lower surface. The team measured the mass of salt crystals collected from leaves after 24 hours. They also recorded the mean number of open stomata at 10:00 and at 14:00. These measurements help the team judge whether the plants can conserve water while obtaining carbon dioxide.
| time | mean open stomata per mm2 | salt crystal mass per leaf / mg |
|---|---|---|
| 10:00 | 64 | 3.1 |
| 14:00 | 29 | 5.8 |
(a) Describe the change in mean number of open stomata between 10:00 and 14:00. [2]
(b) Suggest why fewer stomata are open at 14:00. [2]
(c) Use Fig. 1 and Table 1 to suggest how the leaf helps the mangrove survive in salty conditions. [3]
(d) Name the process by which water enters root hair cells when the root cell has a lower water potential than the mud water. [1]
(e) Which dissolved substance is transported in phloem from a leaf to a root? [1]
Answer Details
- (a) The mean number of open stomata decreases from \(64\) to \(29\) per mm2, a decrease of \(35\) per mm2. [2]
- (b) Conditions at 14:00 are likely to be hotter or drier. Closing stomata reduces water loss by transpiration. [2]
- (c) Salt glands remove salt from the leaf. The rise in salt crystal mass from \(3.1\) mg to \(5.8\) mg supports this. Stomata can close to limit water loss, helping the mangrove conserve water in salty conditions. [3]
- (d) Water enters root hair cells by osmosis. [1]
- (e) The dissolved substance transported in phloem from leaf to root is sucrose. [1]
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