- As plants moved to the land from a water environment, desiccation (drying out) became a problem to overcome. The cuticle, which is a thick, waxy layer on a plant's surface helps to prevent water loss.
- The cuticle however, also prevents the exchange of oxygen and carbon dioxide with the environment. Because photosynthesis requires the exchange of these two gases, the plant needs a way to allow for this exchange. Small pores con the leaves, called stomata enable the intake of carbon dioxide and the release of oxygen during photosynthesis.
- Most plants loose 90% of the water taken into the roots as a result of the process of transpiration. Transpiration is the movement of water molecules from the plant into the air. Most water loss is through the stomata when they are open for photosynthesis.
- Environmental conditions can cause changes in the opening and closing of the stomata. Some environmental conditions will increase the rate of transpiration, while others will slow it down.
MATERIALS:
Plant misting bottle
Small plastic bag (to fit over plant)
Twist-tie
Fan
Lamp with 100 W bulb
1 mL graduated pipette (graduated in 0.01mL graduations)
40 cm of plastic tubing
2 utility clamps
Ring stand
Eyedropper
Distilled water
4 bean seedlings (approximately 2-weeks old)
Scalpel or single-edged razor blade
Cotton
Petroleum jelly
4 different colored pencilsPROCEDURE:
You will investigate four environmental conditions. Your instructor will assign you one of the environments.
If you are doing all 4 yourself, be sure to use a new plant for each one.The following are the environmental conditions:
A. Normal room environment
B. Rain forest simulation: Mist leaves with water and cover the plant with the small plastic bag. secure with twist-tie.
C. Windy: Create a breeze with a fan placed 1 m from the plant.
D. Hot (desert): Place a lamp with a 100 W bulb 1 m from the plant.
1. Insert the tip of a 1 mL graduated pipette into a 40 cm length of clear plastic tubing. BE CAREFUL! the glass is fragile and can break. Bend the tubing into a U shape. Use the ring-stand and clamps to hold both upright sections of the U in place as shown in the diagram.2. Use an eyedropper to fill the open end of the tubing with distilled water until the water exits the pipette.
3. Set up the environmental condition you will be examining.
4. Use a scalpel or single-edged razor blade to cut the stem of a bean seedling at an angle. Quickly submerge the seedling in the water at the open end of the tube. Use some cotton to secure it into the tube. Make an airtight seal by applying petroleum jelly to the stem and tube (completely covering any cotton). Make sure no petroleum jelly comes into contact with the cut end of the stem.
5. adjust the apparatus so you have a starting volume on the graduations of the pipette.
6. Record the water level at the "0 time value" in the DATA TABLE. Record the water level every 10 minutes for 30 minutes, and record in the DATA TABLE. Be sure to record the environmental condition you tested.
DATA TABLE: Change in the Tube Over Time Environmental conditions:_____________________
Time (min) Water level (mL)
0
10
20
30CALCULATIONS:
7. Calculate the total amount of water lost (in milliliters) after each time interval, and record these data in the table below. To calculate this loss, subtract the water level measured at the start of each interval from the water level at the end of each interval. Note: some pipettes are graduated to deliver, and some to take-up. You may need to adjust how you read and calculate, to your individual pipette. Be sure to record the environmental condition you tested.
Total Water Loss After Each 10-minute Time interval Environmental conditions:_____________________
Time interval Water loss (mL)
1
level at 10 minutes - level at 0 minutes = _______
2
level at 20 minutes - level at 0 minutes = _______
3
level at 30 minutes - level at 0 minutes = _______8. Share your data with the other students who tested the same environment as you. Calculate the average amount of water loss for each of the three intervals. Give your data to your instructor, who will write the averages for each interval for all of the environments on the chalkboard. Copy these data into the table below.
Average Amount of Water Lost by Transpiration Over Time (in mL) Environmental conditions Time
intervalNormal Rain forest Windy Hot
1
2
39. Graph the data from the table of average water loss for each environmental condition (from step 8). Title the graph "Water Loss Over Time for Four Environments". Graph "Water loss (mL)" on the vertical axis, and "Time (Min)" on the horizontal axis. Make a Key with a different color for each environment.
10. Remove your seedling from the tubing. Carefully cut off all the leaves. Lay them on graph paper with 1 cm squares and trace around each one. Estimate the total area of the leaves by counting the full squares within the tracings, and adding together the partial squares into full squares.Record your answer
Total leaf surface area = _________ cm2
11. Use the equation below to calculate the water loss per unit of leaf surface area for your seedling in milliliters per square centimeter (mL/cm2).
Total water loss after 30 min (mL) Leaf surface area (cm2 Water loss per surface area = ____________ mL/cm2
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Back to Lab Dad's Laboratory
- The cuticle however, also prevents the exchange of oxygen and carbon dioxide with the environment. Because photosynthesis requires the exchange of these two gases, the plant needs a way to allow for this exchange. Small pores con the leaves, called stomata enable the intake of carbon dioxide and the release of oxygen during photosynthesis.
MEASURING PLANT
TRANSPIRATION
INTRODUCTION: