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Water is essential for the survival of all plants. It is one of the key reactants for photosynthesis (6H2O + 6CO2 in the presence of light energy → C6H12O6 + 6O2) which provides the nutrients needed for the production of energy that is essential for plants to survive. Water provides cell turgidity; where the vacuole swells and the cell’s contents are pushed up against the cell membrane, thus creating turgor pressure which is needed for the stomata to remain open for transpiration and effective diffusion of gases. This turgor pressure allows plants to stay upright, which is why during a shortage of water a plant may wilt because there is not enough water in the vacuoles to create enough turgor pressure. Water is also used to keep the cell membranes moist to allow for efficient gas exchange and to control the temperature of the plant allowing it to optimise its survival rates.
Plants need to maintain the correct water balance because if the plants take on too little water the cells will shrink, there will not be enough turgor pressure to keep the plant upright or the stomata open meaning that photosynthesis rates would dramatically decrease and the cells would eventually plasmolyse resulting in the plant dying. Too much water can reduce the availability of various nutrients and oxygen in the soil, too much water around the roots means that gases can no longer diffuse in and out, meaning that eventually the plant will die. Therefore meaning that plants must have enough water to keep the cells turgid (so the plant can remain upright) and to maintain high rates of photosynthesis, but not too much as to limit the life of the plant.
The main issue for water conservation in plants is the process of transpiration; where negative water potential draws water into the roots, cohesion (water molecules sticking to each other - water has positive and negative poles meaning that there is attraction between water molecules) and adhesion (water molecules sticking to the xylem wall) draw water up the xylem. The water then moves from the xylem and moves from cell to cell via osmosis; also through air spaces (lacunae) and out through the stomata. Water molecules are pulled up the xylem in a continuous stream so that when water vapour is lost through evaporation from the leaves it is immediately replaced by water from the xylem.
http://slideplayer.com/slide/58
Transpiration can cause huge problems for plants during times of little water and high temperatures. This is because, due to high temperatures evaporation rates would have increased (temperature increases the rate that water molecules move at therefore increasing the rate of diffusion. Greater temperature = greater transpiration rates.(Roberts 2011)) resulting in more water being pulled up into the roots from the soil. During times of drought or low water where the soil has very low water content, the plants cannot transpire without wilting because the water in the xylem that is evaporating through the leaves is not being replaced. This causes the leaves cells to lose turgor pressure and results in the stomata closing. If the loss of pressure continues the plant will wilt due to there not being enough pressure to keep it upright (Plant and Soil Sciences eLibrary). While transpiration is the main cause for water loss in plants it also allows for minerals, nutrients and water to move around the plant, as well as keeping the plant cool (TaliaPowell and Profile). During hot, dry or windy times the transpiration rate will increase because there is a greater water potential in the leaves then there is in the atmosphere, meaning that water molecules will move out of the stomata in order to try and achieve an isotonic state.
Plants need to maintain the correct water balance because if the plants take on too little water the cells will shrink, there will not be enough turgor pressure to keep the plant upright or the stomata open meaning that photosynthesis rates would dramatically decrease and the cells would eventually plasmolyse resulting in the plant dying. Too much water can reduce the availability of various nutrients and oxygen in the soil, too much water around the roots means that gases can no longer diffuse in and out, meaning that eventually the plant will die. Therefore meaning that plants must have enough water to keep the cells turgid (so the plant can remain upright) and to maintain high rates of photosynthesis, but not too much as to limit the life of the plant.
The main issue for water conservation in plants is the process of transpiration; where negative water potential draws water into the roots, cohesion (water molecules sticking to each other - water has positive and negative poles meaning that there is attraction between water molecules) and adhesion (water molecules sticking to the xylem wall) draw water up the xylem. The water then moves from the xylem and moves from cell to cell via osmosis; also through air spaces (lacunae) and out through the stomata. Water molecules are pulled up the xylem in a continuous stream so that when water vapour is lost through evaporation from the leaves it is immediately replaced by water from the xylem.
http://slideplayer.com/slide/58
Transpiration can cause huge problems for plants during times of little water and high temperatures. This is because, due to high temperatures evaporation rates would have increased (temperature increases the rate that water molecules move at therefore increasing the rate of diffusion. Greater temperature = greater transpiration rates.(Roberts 2011)) resulting in more water being pulled up into the roots from the soil. During times of drought or low water where the soil has very low water content, the plants cannot transpire without wilting because the water in the xylem that is evaporating through the leaves is not being replaced. This causes the leaves cells to lose turgor pressure and results in the stomata closing. If the loss of pressure continues the plant will wilt due to there not being enough pressure to keep it upright (Plant and Soil Sciences eLibrary). While transpiration is the main cause for water loss in plants it also allows for minerals, nutrients and water to move around the plant, as well as keeping the plant cool (TaliaPowell and Profile). During hot, dry or windy times the transpiration rate will increase because there is a greater water potential in the leaves then there is in the atmosphere, meaning that water molecules will move out of the stomata in order to try and achieve an isotonic state.