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Transpiration

Transpiration. Objectives.... -Be able to explain how transpiration is affected by light intensity, wind speed, temperature and humidity. -Perform an investigation into the affects of wind speed on transpiration. . Transpiration. -What is it? Loss of water from the leaves.

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Transpiration

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  1. Transpiration Objectives.... -Be able to explain how transpiration is affected by light intensity, wind speed, temperature and humidity. -Perform an investigation into the affects of wind speed on transpiration.

  2. Transpiration -What is it? Loss of water from the leaves. -Where does it occur? Water is lost from the stomata (pores). Guard cells control whether or not the stomata are open. -Why is it important? Decreases the water pressure in the leaf-pulls water up through the xylem.

  3. Light intensity Temperature Explain how each of these factors affects transpiration Humidity Wind speed

  4. Light intensity Temperature Stomata are stimulated to open by light. So if its light there will be more transpiration because more stomata will be open. The intensity of the light does not directly affect transpiration. A rise in temperature increases the rate of diffusion of molecules-more likely to pass through stomata. Humidity Wind speed Movement of wind across the leaf clears the water vapour away from the stomata. This increases the water potential gradient and increases transpiration. Humid air has a higher water potential. This decreases the rate of transpiration as there is less of a water potential gradient between the leaf and the surrounding air.

  5. Measuring transpiration Potometer.

  6. Method: 1. Submerge the capillary tube in the bowl or sink of water. 2. Squeeze and release the rubber tubing several times to remove air from the capillary tube. 3. Submerge the cut end of the leafy stem in the water. 4. Use the scissors or secateurs to cut about 2cm off the end of the stem at an angle of about 45o (Make sure the cut is not just below where a leaf joins the stem) 5. While both tubing and cut stem are still submerged push the cut end of the stem into the rubber tubing as far as it will go. Smear the joint with petroleum jelly. 6. Lift the apparatus out of the water, holding on to the stem to do so. 7. Clamp the stem above the bench so that the capillary tube hangs freely. Dry off any damp leaves. 8. A small bubble will appear at the bottom of the capillary tube. Record the movement of this bubble over time. 9. Turn on the fan or hair dryer (set on ‘cold’) so it is close to the leafy stem. 10. After one minute, record further movements of the bubble. 11. Repeat with the fan at different distances from the leafy stem.

  7. Understanding transpiration 2 parts... • Complete potometer worksheet. • Mini essay. Xerophytes such as Marram grass are adapted to live in dry conditions. Write a short (1 page) essay explaining the adaptations of xerophytes.

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