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Athena Banh AP Biology Pd. 3 Giannou 4/6/2014 I. Title Transpiration Rates of Plants Under Different Conditions, Visualize Plant Stem Cell Structure, and Observe the Epidermis of Plant Leaves that are Accustomed to Different Environments II. Introduction a. Problem/Purpose: Study the transpiration of a plant under different environmental conditions by applying knowledge of diffusion, osmosis, adhesion and water potential, and stomata concentration. b. Background Information: Plants may be divided into groups based on their structure and method of water transportation. The plant that will be researched in this experiment, the tomatillo plant, is one of the vascular group, meaning mean ing that water moves upward through the plant through the xylem tissue. The phloem tissue also aids water and solute movement in vascular plants. Vascular plants do not contain a physical pump that transports water, but rather instead rely on air pressure to push water from the roots, or hydrostatic root pressure, in which osmosis moves the water into the xylem. x ylem. The transport and movement of water in a plant is affected by water potential in which water moves to an area with a higher water potential. Vascular plants may also rely on the transpiration pull theory, or cohesion, to bring water into it. Transpiration occurs with a large water loss from the plant by b y evaporation from the opening of the stomata. The opening of the stomata causes evaporation due to the higher water potential of the
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surrounding air. The overall movement of water through the plant because of cohesion results in a transpirational pull from the leaves to the roots of a plant. Despite the many ways in which a plant obtains the solutes and water needed to sustain itself, environmental factors, factors, such as temperature, light intensity, and air currents, greatly impact the rate of transpiration, such factors have an effect on the opening and closing of the stomata and evaporation rate. The epidermis of plants that require more water to sustain itself differ from that of plants that are less dependent of water for survival. i. Terms Vascular Plants- plants that have tissues that are specifically designed for e fficient water and solute transport Xylem- vascular tissue in plants that conducts water and dissolved nutrients upward from the root Phloem- vascular tissue in plants that conducts sugars and other metabolic products downward from the leaves Osmosis- process of molecules passing through the plant membrane from a less concentrated solution to a more concentrated one Water potential- explains the water movement from cell to c ell over long distances in the plant Cohesion- process of water being pulled up the xylem from the roots and soil due to transpiration Stomata- pores in the epidermis of the leaf or stem of a plant that allow for exchange of water and air with the environment Potometer- a tool used to measure the rate of o f transpiration in a plant by
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determining the amount of water absorbed Parenchyma- plant tissues that are found in roots, stems and leaves Sclerenchyma- plant tissues that function as support Collenchyma- fundamental nonspecialized plant tissue Epidermis- outer covering of roots, stems and leaves that functions as a barrier to water loss and protection against injury c. Hypothesis: Because environmental factors affect the opening and closing of the stomata on the leaf surface, the rate of transpiration will change accordingly. d. Variables: For Part A (transpiration rate in different environments), the independent variables are the different environmental factors: air temperature, light intensity, and air current, and the dependent variable is the rate of transpiration. For Part B (visualizing the plan t stem cell structure), the independent variable is stem cell structure, and the dependent variable is also the stem cell structure because it is solely an observational procedure. For Part C (observing the epidermis of the of different plants), the independent variable va riable is the amount of water the plants require, and the dependent variable is the amount of stomata on the epidermis. III. Methods a. Materials Part A Materials: -potometer
-tomatillo plant
-water
-ring stand
-.1mL pipet
-16” vinyl tubing
-petroleum jelly
-timer
-100 Watt light bulb -fan
-mister
-marker
-paper towels
-ruler
-razor
-scale
-scissors
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Part B Materials: -microscope
-tomatillo plant
-razor
-nut and bolt microtome
-Pasteur pipet
-parawax
-spatula
-50% ethanol
-Toluidine blue O stain
-distilled water
-50% glycerol
-cover slip
-microscope
-microscope slides
-Impatiens plant
-succulent plant
-microscope
-microscope slides
-cellophane tape
-clear nail polish
-scissors
-petri plate
Part C Materials:
b. Procedures: Part A Procedures: 1. Place non-tapered end of a .1mL pipet into one end of a 16” piece of vinyl tubing. Petroleum jelly may be placed on the outside of the pipet to help the insertion of it into the tubing. 2. Bend the tube into a U-shape and place it onto a ring stand with clamps. The top of the tubing and the tops of the pipet must be level. 3. Fill the tubing and pipet with water from the tubing end using a .1mL .1m L pipet. No air bubbles should be present. 4. Insert a freshly cut stem from a tomatillo plant into the end of the tubing and seal with petroleum jelly. 5. Expose the stem to one of the following conditions: -room conditions -100 watt light source place 1 meter from the stem -Fan 1 meter from the stem on low
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-mist of water from plant mister, covering the potometer immediately with a plastic bag 6. After a 10 minute equilibrium period, read the water level of the pipet and record as time 0. Use a marker to draw d raw a line at the water level for each time point. 7. Obtain a reading once every 5 minutes for 30 minutes. 8. After 30 minutes, cut off the leaves of plant and blot off any an y excess water. Weigh the leaves. 9. Estimate the total leave surface area for the plant. pl ant. Part B Procedures: 1. Assemble the nut and bolt microtome to where there is a small cup at the end. 2. Cut a slice of the tomatillo stem about a bout 5-6mm in length. 3. Place the cut stem into the microtome so that it stands up. Use a Pasteur pipet to fill the cup with melted parawax. 4. Wait 5-10 minutes for the parawax to solidify. When it has solidified, lay the microtome on its side and with a razor, slice away the excess wax. 5. Twist the bolt to expose a thin piece of wax. Slice off a thin section of the wax/stem. Using a spatula, place the sections in a petri dishes with 50% ethanol. Prepare 10-12 10 -12 sections. Let the sections soak for 5 minutes. 6. Transfer the sections to the Toluidine blue O stain solution in another petri plate. Stain for 5-10 minutes. 7. Transfer the stained sections to the petri plate with distilled water. 8. Place the sections onto a microscope slide and add a drop of 50$ glycerol, and cover with a cover slip.
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9. Observe the sections under a compound light microscope. 10. Draw the observed structures. Part C Procedures: 1. Obtain a succulent leaf and an Impatiens leaf. 2. Paint a solid patch of clear nail polish on the top and bottom of the leaves of each plant. Make the patch at least one square centimeter. 3. Allow the nail polish to completely dry. 4. Press a piece of clear cellophane tape onto the dried nail polish patch. 5. Peel the tape away carefully. 6. Tape the peeled impression to a microscope slide. 7. Examine the leaf impressions under a light microscope. 8. Observe and draw the structures, including the stomata. IV. Data and Calulations a. Data Tables: Potometer Readings (Room Conditions) Time (min) Reading (mL)
0
5
10
15
20
25
30
.009
.0125
.0167
.0192
.0225
.0258
.0283
Individual Water Loss in mL/m² (Room Conditions) Time (min)
0
5
10
15
20
25
30
Water Loss (mL)
.009
.0125
.0167
.0192
.0225
.0258
.0283
Water Loss per m²
3.33
1.29
2.85
3.78
5
6.22
7.15
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Class Average in Water Loss in mL/m2 Time (min) Treatment 0
5
10
15
20
25
30
Room
2.79
1.71
2.80 2.8 0
3.64
4.6
5.74
6.58
Light
3.62
.878
1.82
2.58 2 .58
3.08
3.95
4.46
Fan
1.49
1.51
2.66
3.37
4.18
4.81
5.56
Mist
1
-.88
-.75
1
1
1
1
b. Graphs Individual Potometer Readings (Room Conditions) 0.03 0.025
) L m ( g n i d a e R
0.02 0.015 0.01 0.005 0 0
5
10
15
20
25
30
35
Time (min)
Individual Water Loss (Room Conditions) 8
² m r e p s s o L r e t a
6 4 2 0 0
5
10
15
20
Time (min)
25
30
35
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Class Average Water Loss 7 6 5
) ² m / L m ( s s o L r e t a W
4
Series1
3
Series2
2
Series3
1
Series4
0 -1
0
5
10
15
20
25
30
35
-2
Time (min)
c. Calculations: Total Leaf Surface Area:
Water Loss:
= = .0027 m²
= =
1.29 mL/m²
V. Conclusion and Evaluation a. Concluding: As seen in the results of the differing environmental conditions of Part A’s procedures, the plant that was exposed to the classroom conditions experienced the greatest
loss of water. Factors that contributed to the water loss o f the plants in the room conditions were the temperature, air flow, and exposure expo sure to light. This plant probably showed the most dramatic loss in water because it was exposed to two of the other three conditions, both b oth of which caused a loss individually as well. The plant that was exposed to the mist conditions retained the most water throughout the experiment as the humidity hu midity in the plastic bag kept water from escaping both the plant and its environment. Part P art C’s procedures of observing the stomata density of plants that
require different water levels to survive revealed that the co nditions of a plant’s natural habitat
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affect transpiration rate. The Impatiens plant, one that requires a sufficient amount of water, had a significantly higher stomata density on both the upper and lower epidermis when compared to that of the succulent, a cacti, ca cti, thus requiring less water. b. Evaluating Procedures: Part A of the experiment had very clear and detailed instructions and diagrams that displayed the intentions of the ex periment thoroughly and were easy to follow. Part B proved to be slightly more difficult to follow as the diagrams only on ly showed one step of the process, which seemed tedious and difficult at times. Though I did not physically do Part B except for observing the end product through the microscope, my group members seemed confused and lost at times. Part C’s procedures were clearly numbered and listed and the
procedure was easy to follow overall as its minimal tasks were were very simple. c. Improving the Investigation: The investigation could have been improved had we had more time to complete the experiment so that th at each individual could partake p artake in all three of the procedures so that we could more fully understand the objective of each procedure. Both Part A and Part C had instructions that were organized logically and easy to follow. Part B could be improved by providing clearer instructions and more diagrams dia grams to demonstrate what was supposed to be achieved per number instruction. VI. Questions: 1. How can you calculate the total leaf surface area expressed in cm²? In m²? The total leaf surface area in m² can be found through weighing w eighing all of the leaves in grams and then separately weighing a 1 cm² section of the leaf in grams. Multiply the cut section mass by 10,000 to get the mass per square meter of the leaf and then divide the total weight by the mass per square meter to get the total surface area.
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2. How can you estimate the leaf surface area of the entire plant without measuring every leaf? The leaf surface area of the entire plant can be measured without measuring every ever y leaf by finding that of one leaf and then estimating the amount of leaves on the plant, and then multiplying the single leaf surface are by the estimation of the total amount of leaves. 3. What predictions and/or hypotheses can you make about the number of stomata per mm² and the rate of transpiration? The greater the number of stomata that can be observed through a microscope, the greater the transpiration rate of the plant. 4. Is the leaf surface area directly related to the rate of transpiration? Yes, the greater the leaf surface area, the greater the rate of respiration. 5. What predictions can you make about the rate of transpiration in plants with smaller or fewer leaves? The rate of transpiration in plants with smaller or fewer leaves is less than th at of a plant with bigger or more leaves. 6. Because most leaves have two sides, do you think you have to double your calculation to obtain the surface area of one leaf? Why or why not? No, because surface area is only in regards to one side of the leaf. 7. Water is transpired through the stomata, but carbon dioxide must pass through the stomata into a leaf for photosynthesis to occur. There is evidence that the level of carbon dioxide in the atmosphere had not always been the same over the history of life on Earth.
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Explain how the presence of a higher or lower concentration of atmospheric carbon dioxide would impact the evolution of stomata density in plants. A higher concentration of atmospheric carbon dioxide dio xide would result in plants having a lower stomata density. The reverse of a lower concentration of atmospheric carbon dioxide would result in plants with a higher density of stomata. 8. Based on the data in the following following table, is there a relationship between the habitat (in (in terms of moisture) to which the plants are adapted and the density of stomata in their leaves? What evidence from the data supports your answer? The plants with a greater stomata density in its lower epidermis most likely live in a warmer, more humid region, as the stomata on the bottom of the leaf would butter prevent water of evaporating. The plants with a greater stomata density in its upper epidermis are most likely in a cooler region where water is less likely to evaporate from the plant. As seen in the table, most plants have greater stomata stoma ta densities in their lower epidermis compared to their upper epidermis which reflects on the fact that having the stomata in the lower epidermis is more reliable in terms of water and carbon dioxide maintenance in the plant. VII. Literature Citation; ED VOTEK: Principles of Transpiration. Washington, DC: ED VOTEK, 2014: Pages 4-14.
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