Which genus oxidises sulphur compounds and can markedly acidify soil?
Answer: C
Thiobacillus oxidises elemental sulphur and sulphides to sulphuric acid, which is why sulphur is used to lower the pH of alkaline soils and why the genus is central to acid mine drainage. The other three take no part in sulphur oxidation.
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Sulphate is reduced to hydrogen sulphide in waterlogged soil by
Answer: D
Desulfovibrio is an obligate anaerobe that uses sulphate as an electron acceptor, producing the hydrogen sulphide responsible for the rotten-egg smell and the black iron sulphide of gleyed soils. Thiobacillus runs the same cycle in the opposite direction.
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A mycorrhiza is an association between a fungus and
Answer: A
Correct answer: A plant root
A mycorrhiza is the symbiosis between a fungus and a plant root, and it is the normal condition for the great majority of land plants rather than an exception. The fungal hyphae extend far beyond the root hairs and supply phosphorus and water the root could not reach, receiving photosynthate in return. An association between a fungus and an alga is a lichen, which is a different partnership entirely.
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In an ectomycorrhiza the fungal hyphae
Answer: B
An ectomycorrhiza forms a sheath around the root and a Hartig net that threads BETWEEN cortical cells, with no penetration of the cells themselves. Penetrating the cell to form arbuscules is the defining feature of the arbuscular type instead.
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The network of hyphae growing between root cortical cells in an ectomycorrhiza is called
Answer: C
The Hartig net is the labyrinth of hyphae between the cortical cells, and it is where nutrients are exchanged. The mantle is the sheath enclosing the root from outside, while arbuscules and vesicles belong to the arbuscular type of mycorrhiza.
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Arbuscular mycorrhizal fungi are classified in the division
Answer: D
All arbuscular mycorrhizal fungi belong to the Glomeromycota, a small division of roughly a hundred and fifty species that nonetheless colonises the majority of land plants. Most ectomycorrhizal partners are Basidiomycota, and Oomycota are not fungi at all.
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The tree-like structures formed inside root cortical cells by arbuscular mycorrhizal fungi are
Answer: A
Arbuscules are finely branched structures within the cell that give the association its name and provide the enormous surface area across which phosphorus and carbon are exchanged. Vesicles in the same association are rounded storage bodies, and conidia are asexual spores.
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The main nutritional benefit a mycorrhiza gives its host plant is improved uptake of
Answer: B
Phosphate moves very slowly through soil, so a root quickly exhausts the supply immediately around it; fungal hyphae are thin enough to explore far beyond that zone and deliver phosphorus back. Mycorrhizas do not fix nitrogen, which is the work of bacteria.
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Ectomycorrhizas are most characteristic of
Answer: C
The ectomycorrhizal habit is concentrated in temperate forest trees, notably pines, oaks and birches, and the visible mushrooms of many woodland fungi are the fruiting bodies of these partners. Cereals and most other crops form arbuscular mycorrhizas instead.
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A biofertiliser is best defined as
Answer: D
The defining feature is that the product contains live organisms, such as Rhizobium, Azotobacter or mycorrhizal inoculum, which go on working in the soil. A manufactured nutrient salt is a chemical fertiliser however it was made, and compost is an organic amendment rather than an inoculant.
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