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10 Cards in this Set
- Front
- Back
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Draw the apparatus used for the transpiration experiment |
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The potometer can be used to estimate the rate of transpiration what does it actually measure? |
It measures the rate of water uptake by a leafy shoot. Assuming that the cells are turgid, more than 95% of water taking up is lost by transpiration so this gives a reasonable estimate of transpiration rate |
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How does the potometer work? |
Water vapour lost by the leaves is replaced from the water in the capillary tube the movements of the meniscus at the end of the water column can be measured. |
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What 5 precautions should be made to ensure the results are valid? |
1) Set it up underwater to make sure there are no air bubbles inside the apparatus 2) Ensure that the shoot is healthy 3) Cut the stem under water to prevent air entering the xylem 4) Cut the stem at an angle to provide a large surface area in contact with the water 5) Dry the leaves |
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How do you measure the volume and transpiration rate? |
Measuring the volume of water taken up by the shoot involves calculating the volume of a cylinder the length of the capillary tube the volume of a cylinder is given by the formula: V=πr^2l Where r is the radius of the capillary tube and l is the length of the capillary tube The rate of transpiration is the volume calculated divided by the time taken. rate = volume/time |
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How does a light intensity affect transpiration rate? |
In light, the stomata open to allow a gaseous exchange for photosynthesis. Higher light intensity increases the transpiration rate |
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What are the three ways in which temperature affect transpiration rate? |
A higher temperature increase the rate of transpiration in three ways: 1) Increase the rate of evaporation from the cell surfaces so that the water-vapour potential in the leaf rises 2) Increase the rate of diffusion through the stomata because the water molecules have more kinetic energy 3) Decrease the relative water vapour potential in the air allow more diffusion of molecules out of the leaf |
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How does relative humidity affect transpiration rate? |
Higher relative humidity in the air will decrease the rate of water loss this is because there is a smaller water vapour potential gradient between the air spaces in the leaf and the air outside |
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How does air movement (wind) affect transpiration rate? |
Air moving outside the leaf will carry away the water vapour that has just diffused out of the leaf. This will maintain a high water vapour potential gradient. |
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How does water availability affect transpiration rate? |
If there is little water in the soil, then the plant cannot replace the water that is lost. If there is insufficient water in the soil then the stomata close and the leaves wilt |
