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Part A: Transpiration When a plant absorbs water, not all of it is used. It is instead lost through transpiration, the evaporation of water through the leaf surface and stomata. Transpiration is also the major process that powers the movement of water throughout a plant. The movement of water through a plant is due to water potential. Water always flows from areas of high water potential to areas of low water potential. However, the actual movement of water is favilitated by osmosis, root pressure, and adhesion and cohesion. Water also evaporates due to guttation. Guttation, which is the loss of water from the vascular tissues in the margins of leaves, is caused when root pressure pushes water up from the roots into leaves and stems. Guttation occurs during the night when stomata are closed and transpiration is over. When water moves through a plant, it first undergoes osmosis which creates root pressure that forces the water upward. However, transpiration soon takes over and “pulls” the water up through the plant. This “pull” is increased by water’s properties of adhesion and cohesion. Pressure begins to builds up in the leaves, and prevents the movement of water back down. Then transpiration and guttation occur. Loss of water through transpiration is controlled by the opening and closing of the stomata depending on environmental conditions such as rain, sun, humidity, wind, and temperature. Materials: 1. 0.1 mL pipette 2. clamp on a ring stand 3. 16 in clear plastic tubing 4. plant leaf with steam 5. water 6. plastic bag 7. food coloring(blue) 8. syringe 9. petroleum jelly 10. squirt bottle Problem/Hypothesis/Control: a) Does the rate of transpiration in plants occur faster in light or in the dark?

Lab Write Up: AP Bio Transpiration Lab

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Full lab write up (parts a and b) of AP Biology Transpiration Lab.

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Page 1: Lab Write Up:  AP Bio Transpiration Lab

Part A: Transpiration

When a plant absorbs water, not all of it is used. It is instead lost through transpiration, the evaporation of water through the leaf surface and stomata. Transpiration is also the major process that powers the movement of water throughout a plant. The movement of water through a plant is due to water potential. Water always flows from areas of high water potential to areas of low water potential. However, the actual movement of water is favilitated by osmosis, root pressure, and adhesion and cohesion. Water also evaporates due to guttation. Guttation, which is the loss of water from the vascular tissues in the margins of leaves, is caused when root pressure pushes water up from the roots into leaves and stems. Guttation occurs during the night when stomata are closed and transpiration is over. When water moves through a plant, it first undergoes osmosis which creates root pressure that forces the water upward. However, transpiration soon takes over and “pulls” the water up through the plant. This “pull” is increased by water’s properties of adhesion and cohesion. Pressure begins to builds up in the leaves, and prevents the movement of water back down. Then transpiration and guttation occur. Loss of water through transpiration is controlled by the opening and closing of the stomata depending on environmental conditions such as rain, sun, humidity, wind, and temperature.

Materials:

1. 0.1 mL pipette2. clamp on a ring stand3. 16 in clear plastic tubing4. plant leaf with steam5. water6. plastic bag7. food coloring(blue)8. syringe9. petroleum jelly10. squirt bottle

Problem/Hypothesis/Control:

a) Does the rate of transpiration in plants occur faster in light or in the dark?b) If the environment affects the rate of transpiration of plants than the plant in room conditions

will transpire more than the plant in the misty environment because the stomata opens bigger when there is a low water potential in the environment, therefore allowing more transpiration to occur.

c) The control group is the plant in regular room conditions.

Abstract:

This lab tested the rate of transpiration when the environment was changed. One set-up was placed in room conditions and another set-up was placed in a plastic bag and misted, for the experimental of “misty environment”. Each plant was then checked on in 3-minute intervals for 30 minutes to see if the plant had transpired and loss any water. After 30 minutes the set-up placed in room conditions lost .03 mL of water and lost water 8.33 mL per m2. The experimental group lost 0.005 mL of water and lost water 1.5625 mL per m2. Therefore the set-up in the dark transpired less than the one in room conditions.

Procedure/Protocol

Page 2: Lab Write Up:  AP Bio Transpiration Lab

1. Place the tip of a 0.1-mL pipette into a 16-inch piece of clear plastic tubing2. Submerge the tubing and pipette in a shallow tray of water. Draw water through the tubing until all bubbles are eliminated.3. Carefully cut the plant stem under water. This step is very important, because no air bubbles must be introduced into the xylem. 4. While your plant and tubing are submerged, insert the freshly cut stem into the open end of the tubing. 5. Bend the tubing upward into a “U” and use the clamp on a ring stand to hold both the pipette and the tubing6. If necessary, use petroleum jelly to make an airtight seal surrounding the steam after it has been inserted into the tube. Make sure that the end of the stem is immersed in the water. Do not put petroleum jelly on the cut end of the stem.7. Let the potometer equilibrate for 10 minutes before recording the time zero reading.-Repeat steps 1-7 to create a second setup (one will be placed in room conditions, the other in a “misty environment”)-8. Read the level of water in the pipette at the beginning of your experiment (time zero) and record your finding in Table 9.19. Continue to record the water level in the pipette every 3 minutes for 30 minutes and record the data in Table 9.110. Calculate the water loss per square meter of leaf surface by dividing the water loss at each reading (Table 9.1) by the leaf surface area you calculated. Record your results in Table 9.211. Record the averages of the class data for each treatment in Table 9.3

Data:ControlTime (min)

0 3 6 9 12 15 18 21 24 27 30

Reading (mL)

.1 .09 .08 .08 .079 .077 .075 .074 .073 .072 .07

Water Loss(mL)

0 .01 .02 .02 .0205 .023 .025 .026 .027 .028 .03

Water Loss

per m2

0 2.77 5.55 5.55 5.69 6.38 6.94 7.22 7.5 7.7 8.33

Surface area of leaf: .0036 m2

Experimental: MistTime (min)

0 3 6 9 12 15 18 21 24 27 30

Reading (mL)

.1 .1 .095 .095 .095 .095 .095 .095 .095 .095 .095

Water Loss(mL)

0 0 .005 .005 .005 .005 .005 .005 .005 .005 .005

Water Loss

per m2

0 0 1.5625

1.5625

1.5625

1.5625

1.5625

1.5625

1.5625

1.5625

1.5625

Surface area of leaf: .0032 m2

Page 3: Lab Write Up:  AP Bio Transpiration Lab
Page 4: Lab Write Up:  AP Bio Transpiration Lab

Analysis/Conclusion:

1. Calculate the rate (average amount of water loss per minute per square meter) for each of the treatments.

Room: = 0.105 m2/minuteDark: = 0.0 m2/minuteMist: = 0.0 m2/minuteLight: = 0.413 m2/minuteNo Leaves: = 0.0 m2/minute

Condition Effect Reason

Dark DecreaseNo light would not allow the stomata to

open big which causes a decrease in transpiration

No Leaves DecreaseNo leaves means there is no way for the leaf to lose water, it destroys the

system of transpiration with no leaves.

Light IncreaseAn increase in light would cause the plant to transpire more because the

stomata would open bigger

Mist Decrease

There is more water outside of the plant than inside which means the leaf does not need to transpire and the stomata will close keeping the water inside..

3. Explain the role of water potential in the movement of water from soil through the plant and into the air.

Page 5: Lab Write Up:  AP Bio Transpiration Lab

The water potential defines whether the plant will take up water or not. For example, If there is low water potential in the plant, the water will move up into the plant.

4. What is the advantage of closed stomata to a plant when water is in short supply? What are th6e disadvantages?The closed stomata prevents water being lost to the environment by transpiration. However, closing stomata prevents the exchange of gases in plants and limits their carbon supplies.

5. Describe several adaptations that enable plants to reduce water loss from their leaves. Include both structural and physiological adaptations.Structural-Opening and closing the stomata, guard cellsPhysiological-Potassium pumps let water enter the guard cells

6. Why did you need to calculate leaf surface area in tabulating your results?The surface area has to be calculated because this greatly affects the amount of water lost through transpiration. Smaller leaves may lose less water than the larger ones, but by calculated water loss by surface area creates comparable data that is constant and consistent. To calculate the water loss per square meter of leaf surface we had to divide the water loss at each reading by the leaf surface area that was calculated.

Page 6: Lab Write Up:  AP Bio Transpiration Lab

Bibliography

1. "Lab 9 Transpiration Example 2 Ap." Lab 9 Transpiration Example 2 Ap. N.p., n.d. Web. 06 Jan. 2014. <http://www.biologyjunction.com/lab_9_transpiration_example_2_ap.htm>.

2. Writer, Contributing. "What Are the Causes of Guttation in Plants?" EHow. Demand Media, 27 May 2009. Web. 06 Jan. 2014. <http://www.ehow.com/about_5052727_causes-guttation-plants.html>.