The effect of wind speed on the rate of transpiration.
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The effect of wind speed on the rate of transpiration. I was asked to design an experiment to investigate the effect wind or air movement on leaves on the rate of transpiration. Most of the water entering a plant does so via the root hairs. It travels across the root cortex to the xylem, ascends in the xylem to the leaves and is lost by evaporation from the surface of the mesophyll cells before diffusing out through the stomata. This process is called transpiration, and the flow of water from the roots to the transpiring surfaces forms the transpiration stream. Apparatus 1 plant pot with plant 1 electronic scale 1 anemometer 1 thermometer 1 hydrometer 1 Stopwatch 1 meter stick 1 fan 1 plastic bag I will start the experiment by first wrapping the plant pot/plant roots in the plastic bag. This is to prevent water loss via evaporation, I don't want this to happen because I am trying to measure transpiration and it will interfere with my experiment dramatically. Then I will weigh the plant pot/ plant using an electronic scale, which should be very accurate. I will record this in my table of results. I will then use a hydrometer to measure the humidity of the room and use a thermometer to measure the temperature of the room.
My independent variable will be the distance from the fan, which in reality is wind speed, which I will change, each time. The wind will come from a fan and will measured using an anemometer. WIND- Air movements carry away water vapour from leaves and this prevents air around them from becoming saturated with water vapour. Consequently, depending upon temperature and humidity, transpiration is faster on a windy day than in still air. Wind moves the air and water vapour away from the leaf, this increases the water potential gradient from the plant to the air. The best conditions for a higher rate of transpiration are the same as those needed for drying washing on a line: a warm, dry, sunny, windy day. Variables that I will keep the same are: Weber LIGHT- effects transpiration because stomata usually open in light and close in darkness. At night therefore, and only small amounts of water are lost through the waxy cuticle: As stomata open in the morning, transpiration rates increase. TEMPERATURE- the higher the temperature, the greater the rate of evaporation of water from mesophyll cells. It increases the capacity of air to absorb water from leaves and it warms the water inside leaves making it evaporate more quickly. Direct sunlight has the same effect since it warms leaves to a higher temperature than the atmosphere.
This pulls up water from the roots. Water molecules stick together to form a column. The mechanism which provides the force that pulls water up the plant is called the cohesion-tension hypothesis. Some plants such as the cactus are adapted to prevent water loss these are called xerophytes. These plants have special features that prevent them from loosing too much water. They have special features like a leaf that is rolled inwards this traps humid air around the leaf surface. Some have hairs that reduce air movement around the surface of the plant. Others have a swollen stem, which gives it a low surface to volume ratio and acts as a reservoir for water. I will try and make it fair by sticking to the plan. I will use a stopwatch to measure the time and will stand equal distance from the leaf. There is nothing in this experiment that I feel is of any danger to others or me. I will hang my coat up and have my bag under the table. I will use the same fan each time because different fans have different wind speeds and different diameters. I will use a meter stick to measure the distance accurately and precisely. Once I have obtained my results I will plot them on a graph. This will enable me to see the results more accurately and I will be able to see the rate of transpiration better. The graph will look something like this. Water loss (%)
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