Describe and explain the importance of a water potential gradient for plants

Unlike animal cells, plant cells have a rigid cell wall surrounding the plasma membrane. In terms of water exchange, in animals we need to only worry about osmosis, but in plants we plants we care about osmosis (concentration of solutes) and the pressure of the cell wall pushing against the living part of the cell located to its interior. So therefore we have this equation: water potential= osmotic potential+pressure potential Water moves from areas of high water potential to areas of lower water potential. Plants need to transport water from roots to the top leaves of the plants. This is achieves by maintaining a negative pressure in the Xylem. At the top of the plant the is losing water through transpiration, as water is evaporating from the leaves. Water has high surface tension so when water evaporates it creates a tension at the air/water interface. This causes a negative pressure potential which according the to water potential equation, lowers water potential. Since water moves from areas of high water potential to areas of lower water potential, this will cause water in the xylem to be pulled up into the spaces made available by the water that just evaporated. Also the cohesive and adhesive properties of water molecules aid in 'pulling up' the water in the xylem.

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