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Nodules and mychorrhizae are both examples of symbiotic relationships where both the plants and the organisms involved benefit. The plants benefit by getting nutrients which they could not get normally through the roots. Often nodules and mychorrhizae occur in poor soils that do not have alot of nutrients. Nodules are a symbiotic relationship between a bacterium of the genus Rhizobia and the plant. The bacterium actually infects the root and produces the nodules. The bacterium takes nitrogen in the atmosphere and chemically transforms it in to ammonia which the plant can then absorb. Nitrogen is needed to make plant proteins. The plant in return provides the bacteria with energy in the form of carbohydrates (sugars lke glucose). Mycorrhizae are a type of fungus which infect the roots of a plant. The fungus is like microscopic threads and they are numerous. The fungus has a large surface area because the threads are so thin and there are so many of them. The large surface area allows the fungus to efficiently absorb water and nutrients which are transferred to the plant roots. In return, the plants provides the fungus with a steady source of energy (sucrose or glucose).
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