Fig. 1 shows a red mangrove growing at the edge of a tropical estuary. Twice each day, seawater covers the muddy soil around the plant. The mud has little o...
Question 1 Report
Fig. 1 shows a red mangrove growing at the edge of a tropical estuary. Twice each day, seawater covers the muddy soil around the plant. The mud has little oxygen because water fills most of the air spaces. Some roots grow upwards above the mud. Salt water may enter root cells, so the plant must maintain the water concentration of its cells. A ranger is comparing this plant with a tree growing on dry land.
(a) Describe one feature visible in Fig. 1 that helps the mangrove obtain oxygen. [2]
(b) Explain why taking in salt water can cause a problem for mangrove cells. [2]
Table 1 shows growth of young bean plants grown in sterilised soil. In one set of pots, the roots were inoculated with mycorrhizal fungi. Fig. 1 shows fungal hyphae around and inside a root. The plants all received the same amount of water, light and carbon dioxide. Fungal hyphae increase the area from which mineral ions can be absorbed.
| Soil treatment | Mean dry mass after 28 days / g |
|---|---|
| No fungi added | 2.8 |
| Mycorrhizal fungi added | 4.6 |
(a) Describe the result shown in Table 1. [1]
(b) Explain how fungal hyphae can increase the growth of bean plants. [2]
(c) Give one substance supplied by the plant to the fungus. [1]
Answer Details
Labelled answer diagram:
Mangrove
- (a) The visible upward-growing roots project out of the mud. They are exposed to air, so oxygen can diffuse into them for respiration. [2]
- (b) Salt water is more concentrated, so has a lower water potential, than the cell contents. Water therefore leaves mangrove cells by osmosis; the cells lose water and may become plasmolysed. [2]
Mycorrhizal fungi and bean plants
- (a) Plants with mycorrhizal fungi had the greater mean dry mass: 4.6 g compared with 2.8 g without fungi. [1]
- (b) Fungal hyphae provide a large surface area, increasing absorption of mineral ions from soil. The plant uses these ions, for example to make proteins and new cells, so growth increases. [2]
- (c) The plant supplies glucose, or other sugars, to the fungus. [1]
Exam focus: In this mutualistic relationship, the fungus improves mineral-ion uptake and receives sugars made by photosynthesis.
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