transpiration essays

transpiration essays Transpiration is the evaporation of water from cells and tissues. In the plants studied this is the loss of water from the leaves. The water enters the stem of the leaf from the potometers tube via osmosis. Because the water potential in the stem is lower then that in the tube the water molecules enter the stem down a water potential gradient. Once in the stem, in the xylem cells this occurs again as the next cell along has a lower water potential from the one before it. The theory of how the water moves up the stem and out the leaves is called cohesion tension theory. As the water molecules move from cell to cell, they pull other water molecules with them. This pulling affect, known as the transpiration pull is possible due to cohesive forces between the molecules. The pull creates tension in the xylem cells, which pulls the water through the stem. The water potential in the atmosphere is usually lower then that in the leaf. If the stomata in the leaf are open, the water molecules are able to go down the concentration gradient into the atmosphere. If there is some air movement this water is moved away from the leaf as it leaves the stomata. This is replaced by more water evaporating from the surrounding the substomatal space. The water is taken fro these cells in 2 ways: Apoplast method- Water travels along the cell wall along spaces in-between cellulose fibres. As this water evaporates into the substomatal space from the wall of 1 cell, it creates a tension, which pulls water from the cell walls of other cells. The pull is transmitted through the plant by cohesive forces between each of the water molecules. Symplast method Cells are connected to each other by tiny gaps called plasmodesmata. Water can move into the cell via osmosis through these gaps. If water is lost from the cell through the stomata, the water potential of this cell is lowered. Water will now flow into this cell from the cells near the xylem vesse...