AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The role of mycorrhizae in facilitating the uptake of water and inorganic…
Full specification wording
Nutrient cycles (A-level only): The role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants.
Mycorrhizae are mutualistic associations between fungal hyphae and plant roots.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 4 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Mycorrhizae are mutualistic associations between fungal hyphae and plant roots. The hyphae are extremely fine and grow far out into the soil, adding an enormous absorbing surface area to the root system and reaching water and ions in soil pores too small for root hairs to enter. This increases uptake of water and of inorganic ions, particularly phosphate, which diffuses very slowly through soil and is quickly depleted in the zone immediately around a root. The hyphal network also holds water around the root, helping the plant resist drought. In return the plant supplies the fungus with organic compounds, principally sugars from photosynthesis, so both partners gain. The effect is largest when a resource is scarce: with plenty of water, mycorrhizal and untreated plants may show no significant difference in yield, but under water shortage the treated plants grow significantly better.
What earns the marks
- The increased surface area of hyphae increasing uptake of water and inorganic ions.
- The plant supplying the fungus with organic compounds in return, making the relationship mutualistic.
- Describing a significant difference, or no significant difference, with the treatment named rather than just saying the results are significant.
- Using overlapping standard deviations to show no significant difference, or non-overlapping to show a significant one.
- A valid limitation, such as only one mycorrhizal species or one crop studied, or sterile soil and greenhouse rather than field conditions.
Common mistakes and how to put them right
Writing that 'the results are significant' with no statement of what is greater, lower or different, which is rejected.
Saying mycorrhizae give the plant minerals, rather than increasing the surface area for absorption.
Omitting the mutualism, so the fungus's gain of sugars from the plant is never mentioned.
Concluding that mycorrhizae always increase yield, when the data show no significant difference without water shortage.
Treating a large sample size as proof of a significant difference rather than as improved reliability.
Exam tips
- In evaluation questions, keep conclusions drawn from the data separate from limitations of the method; the mark scheme caps how many limitation marks you can earn.
- Quote the treatment or the letter from the table when stating a difference, for example greater in Q than in P.
- Overlapping error bars mean the difference is probably not significant; the phrase 'not due to chance' is accepted for significant.
Try the lesson
The start of the Nutrient cycles (A-level only): The role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants. lesson, made from checked teaching notes for this specification point.
Have a go first
How do mycorrhizae help a plant to take up water and inorganic ions?
Listen
Mycorrhizae are mutualistic associations between fungal hyphae and plant roots. The hyphae are extremely fine and grow far out into the soil, adding an enormous absorbing surface area to the root system and reaching water and ions in soil pores too small for root hairs to enter. This increases uptake of water and of inorganic ions, particularly phosphate, which diffuses very slowly through soil and is quickly depleted in the zone immediately around a root. The hyphal network also holds water around the root, helping the plant resist drought. In return the plant supplies the fungus with organic compounds, principally sugars from photosynthesis, so both partners gain. The effect is largest when a resource is scarce: with plenty of water, mycorrhizal and untreated plants may show no significant difference in yield, but under water shortage the treated plants grow significantly better. A strong answer earns marks for these points. the increased surface area of hyphae increasing uptake of water and inorganic ions. the plant supplying the fungus with organic compounds in return, making the relationship mutualistic. describing a significant difference, or no significant difference, with the treatment named rather than just saying the results are significant. using overlapping standard deviations to show no significant difference, or non-overlapping to show a significant one. Exam tip: In evaluation questions, keep conclusions drawn from the data separate from limitations of the method; the mark scheme caps how many limitation marks you can earn.
Key words
Say what each word means before you turn the card.
mycorrhizae
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mutualism
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surface area for absorption
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phosphate uptake
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See every definition
- mycorrhizae
- Mutualistic associations between fungal hyphae and plant roots, whose fine hyphae grow far out into the soil and add an enormous absorbing surface area to the root system.
- mutualism
- A relationship in which the fungus gains organic compounds, principally sugars from photosynthesis, and the plant gains increased uptake of water and inorganic ions, so both partners gain.
- surface area for absorption
- The enormous absorbing area added to the root system by extremely fine hyphae that reach water and ions in soil pores too small for root hairs to enter.
- phosphate uptake
- An increase in the uptake of inorganic ions, particularly phosphate, which diffuses very slowly through soil and is quickly depleted in the zone immediately around a root.
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