How does xylem and phloem work?

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trophyhunter1 | College Teacher | (Level 1) Educator Emeritus

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Xylem cells are non-living cells that are part of a plant's vascular or conducting tissue. Xylem transports water from the roots upward through the plant, along with nutrients. Xylem is found in vascular bundles, that can be arranged in a circular fashion or a scattered fashion in woody and non-woody parts of plants with wood. The veins found in leaves, stems and roots which are interconnected contain xylem. Transpirational pull is a method that helps pull water up from the roots to the leaves of plants. As transpiration occurs, and water molecules leave the stomates, this allows menisci to form in the mesophyll cell wall. Surface tension causes water to be pulled into a plant from the roots and soil. Osmosis of water from soil into the roots also occurs. Capillary action which is the attraction of water molecules to the xylem tubes also helps force water up against gravity. Phloem, also part of the vascular tissue, conducts nutrients to parts of the plant where needed, particularly sugar produced by photosynthesis. Phloem cells are living and transport sap from the leaves, to roots or to storage areas in a plant such as a bulb. Phloem sap moves from sugar sources to sugar sinks due to turgor pressure gradient. Turgor has to do with osmotic flow of water from low solute outside the cell into the cell's vacuole, where there is a higher solute concentration. A sugar source is where photosynthesis is occurring in the plant and sugar is produced. Transport in phloem is multidirectional and allows sugar to be transported where needed. Transport in xylem is one-direction upward from the roots.


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