Roots213-page12

Roots213-page12 - threadlike cells of a fungus forming much...

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Roots - 12 Mycorrhizae We have learned that roots function to absorb water and minerals (nutrients). However, the majority of vascular plants form root associations with fungi to increase their absorption of mineral nutrients. Fungi, which live by absorbing nutrients from their surroundings, are ideal organisms to make these associations. The fungus obtains carbohydrates (the product of photosynthesis) from the host plant, and absorbs water and nutrients from the environment for the plant. The fungus can absorb nutrients actively so it can obtain nutrients even when they are in low supply. Roots absorb passively, so a gradient must exist from the soil to the root tissue. There are both endomycorrhizae and ectomycorrhizae. Endomycorrhizae penetrate cells of the cortex with their hyphae (the
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Unformatted text preview: threadlike cells of a fungus) forming much branched arbuscules, sometimes with swollen vesicles at their tips; some endomycorrhizae are found in the cortex spaces. • Ectomycorrhizae surround the exterior of roots, forming a hyphal sheath, or mantle, but do not penetrate the root cells. Ectomycorrhizae are important root associates in trees in most forest biomes. Ectomycorrhizae of conifers penetrate the epidermal layers to surround the cortex, forming a network of fungal cells called the Hartig net. Essentially, mycorrhizae can function as sophisticated root hairs, and plants that associate with ectomycorrhizae often do not produce root hairs. Some plants absolutely require mycorrhizae, such as orchids and the gametophytes of many lower vascular plants....
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This note was uploaded on 01/08/2012 for the course BIO 213 taught by Professor Makina during the Fall '09 term at SUNY Stony Brook.

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