B2 Transpiration

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Transpiration is the loss of water from a plant. It is caused by the evaporation and diffusion of water from inside the leaves. It explains how water moves up the plant against gravity in tubes made of xylem cells without the use of a pump.

In the leaves, water moves out of the xylem and enters the leaf cells by osmosis (the movement of water molecules from an area of high concentration to an area of lowconcentration.) Water evaporates from the surface of the cells inside the leaf and then diffuses out through the open stomata. The evaporation of the water cause more water to rise up the xylem from the roots. This is known as transpiration.

Transpiration creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it. The flow of water through the plant from the roots to the leaves



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