High metabolic demands, large size, surface area to volume ratio.
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Function of xylem
Transport of water and mineral ions and support.
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Structure of xylem
Made up of several types of cells, most of which are dead
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What are the two main cell types in xylem tissue?
Xylem vessel elements and tracheids
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Structure of xylem vessels.
Thickened with lignin, long and hollow structures made by several columns of cells fusing together end to end.
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What is the function of lignin?
Lignin strengthens the wall, providing support and waterproofs cell so it can conduct water. Lignin also helps reinforce xylem vessels so that they do not collapse under transpiration pull.
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Structure of phloem.
Living tissue that transports food in the form of organic solutes around the plant.
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Structure and function of sieve tube elements.
Made up of many cells joined end to end to form long, hollow structures. In areas between the cells, the walls are holed to form seive plates, which let phloem contents flow.
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Structure and function of companion cells.
These are closely linked to the sieve tube elements by many plasmodesmata which enable the cytoplasm of a companion cell to communicate with the cytoplasm of its neighbouring sieve tube elements.
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How are root hair cells adapted as exchange surfaces?
Thin hairs have large surface area to volume ratio.
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What is the symplast pathway?
Water moves through the continuous cytoplasm of the living plant cells that is conneced through the plasmodesmata by osmosis.
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What is the apoplast pathway?
Movement of water through the cell walls and intracellular spaces. As water moves into xylem, more water is pulled in from the apoplast due to the cohesive forces between the water molecules.
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