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Plant Transpiration Lab
Transcript of Plant Transpiration Lab
s = .00798 Environmental Factors Nitrogen Concentration Nitrogen Concentration
Humidity Data Conclusion Light Intensity Conclusion Wind Conclusion Data Data Overall Question How much influence do various environmental factors have on the rate of transpiration in common geranium plants? Overall
Knowledge Cells and organisms must exchange matter with the environment to grow. Transpiration is the loss of water by evaporation in plants, especially through the stomata; a process in which the water vapor escapes through the plant via its stomata into its external environment. Water vapor, CO2 and O2 are exchanged through the stomata. The effect of nitrogen supply on the transpiration rate and the stomata opening of plants was studied in a series of experiments. The transpiration rates of N-supplied plants were higher than those of N-deficient plants when soil moisture was relatively high.
~istor.org/discover Overall Procedure Fill one of the tubs with distilled water. Take the tubed-microrespirometer and completely submerge under water. Using a small syringe, place syringe into the tubed end of the micro-respirometer and pull back on the plunger to suck water into the tubes completely. Keep submerged until instructed to remove. Meanwhile, submerge a leaf and stem, and, using a razor, cut the stem at a 45 degree angle.
Note: Do not use scissors to prevent pinching the xylem. Insert the cut stem into the tubed end of the micro-respirometer while still submerged. Once held vertical in a U shape, release thumb and the water in the respirometer will drop to a measurable range. Record measurements. Attach the apparatus to the stand and make sure the tube is devoid of air pockets. If there are any air bubbles trapped, restart procedure and try again. Record observations. Perform individual environmental factor change. Prior Knowledge Question What influence does the concentration of Nitrogen in water have on the rate of transpiration in common geranium plants? Question Knowledge Probe Prediction Procedure Prediction Question Knowledge Probe Prediction Procedure Procedure Knowledge Probe Prediction Procedure Question Prediction Procedure Sources of Error Too low of a nitrogen concentration level
Too few trials
The plant was not exposed to the nitrogen rich environment for a long enough time
Differences in leaf size The rate of respiration will decrease when there are higher levels of nitrogen in the plants water 1. Follow the steps in the AP Biology Investigation Lab Book for calculating the surface area of geraniums and for the potometer Data s = .00583 mL/g x̄ = .0097964 mL/g control x̄ = .01262
control s = .00583 p = .20836
control > higher N concentration Light Intensity = 0 Claim Question: We would want to explore whether or not the rate of transpiration will be affected if there was a higher concentration of Nitrogen in the water.
Another theory we would like to explore would be if planting the seed in a Nitrogen rich soil would increase the overall rate of transpiration.
Prediction: We predict that with a higher nitrogen concentration, the rate of transpiration would increase Explanation Evaluation x̄ = .007004
s = .001759 control x̄ = .01262
control s = .00583 p = .0772
control > darkness Increasing light intensity increases the rate of transpiration. Light intensity under control conditions was only .0374
This is why a light intensity of zero had no statistically significant result Light intensity of .5738 and 1.0006 both had significantly higher rates of transpiration versus the control group. Does the intensity of light have an effect on the rate of transpiration in common geranium plants? light intensity = .5738 x̄ = .01971
s = .00187 As the light intensity increases, the rate of transpiration will remain the same because the stomata will either be open or closed depending on the absence of light and not by the amount of light. Plant stomata are open during the day if there is red light and at night if there is moonlight. Plants also open at sunrise in blue light. The light also increases temperature in the atmosphere which speeds up transpiration. Light induces photosynthesis in guard cells and and synthesizes sugar. This brings about and increase in the osmotic pressure when the stomata open and transpiration begins. Quality and intensity of light affect the rate of transpiration 1. Set up plant according the AP Biology Lab Manual procedure control x̄ = .01262
control s = .00583 p = .04675
control < lit light intensity = 1.0006 x̄ = .02431
s = .00308 control x̄ = .01262
control s = .00583 p = .0177
control < lit control x̄ = .01262
control s = .00583 p = .1418
control < wind How does wind affect transpiration?
-When wind is a present factor the rate of transpiration is high. This is because wind blows away water vapor from around the surface of the leaves, creating more room for evaporation.
-Wind alters the rate of transpiration by removing the boundary layer - the still layer of water vapor hugging the surface of leaves. Wind increases the movement of water from the leaf surface when it reduces the boundary layer because the path for water to reach the atmosphere is shorter. <passel.unl.edu>
-If there is little air movement, the water vapor leaving the stomata will tend to build up around the stomata. This will create high humidity directly outside, decreasing the rate of transpiration. Therefore, an increase in wind will lead to an increase in transpiration rates control x̄ = .03365
control s = .02567 x̄ = .00391
s = .00289 p = .173
dry > humid Does wind affect the rate of transpiration in common geranium plants? 1. Prepare potometer as usual. Mass the leaf before placing it in the tube.
2. Place potometer inside the vacuum capsule. It will not fit on a stand, so it must be taped to the inner walls of the capsule.
3. Put grease in between pressure capsule and rubber plate.
4. Connect vacuum to the capsule apparatus. Turn fume hood on before operating vacuum.
5. Replace the cork in the top of the vacuum tube with a cork that has a hole for a pressure sensor and connect the pressure sensor to a laptop.
6. Before pressurizing the capsule, make a reading on the water level.
7. Pressurize the capsule using the vacuum. Lower the pressure to about 80 kPa. After this pressure is achieved, close the valve to prevent air from entering the capsule, and turn the vacuum and fume hood off.
8. Make sure the capsule remains sealed for 20 minutes. Monitor the pressure using the laptop.
9. After 20 minutes, relieve pressure in the capsule by popping the cork off the top.
10. Before removing the potometer, make a reading of the water level. Less oxygen can be found in air at lower pressures. 2. Run a control experiment with two potometers using only distilled water. Record changes in water level every minute for 20 minutes.
3. Obtain a .5 molar nitrogenous (NaNO3) solution 4. Dilute 500 mL solution with 1000 mL distilled water in a large tub 5. Repeat general potometer procedure with the nitrogenous solution and record level every minute for 20 minutes Transpiration involves both movement of nutrients in water and gas exchange through the stomata. Pressure varies inversely with altitude.
Pressure of 80 kPa is reached at around 6,500 feet above sea level.
One peak at around this height is Mount Washington. We predict that under less pressure, a plant will transpire at a higher rate. Gas exchange (CO2 and O2) is involved in transpiration, so at a lower pressure, a plant should transpire more to compensate for lower concentration of these gases. How will a lower atmospheric pressure affect the rate of transpiration? ™ Reasoning The addition of a Nitrogenous solution has little to no effect on the rate of transpiration in geranium plants. Based on 2-Sample T-test, there is no significant evidence that the amount of Nitrogen in the water affects the rate of transpiration in geranium plants. 2. Use a light probe to record the intensity of the light as close to the plant as possible 3. For each light intensity test adjust the light level by moving the 100 watt light bulbs until the probe reads 0.000, 0.600, and 1.000 4. Record respirometer levels every 5 minutes 5. Repeat each light level twice Data Analysis for all factors excepting pressure was performed using a 2-Sample T-Test.
This test is appropriate because the rate of respiration for both the control and experimental groups is based on a sample of data, rather than known quantities. A 2-Sample T-test requires three things to be true 1. The populations (both experimental and control) that the samples are drawn from are approximately normal if the sample size is not greater than 25. 2. All trials are independent of one another. 3. Both population standard deviations are unknown T-test Output and Terminology T-value or T-statistic — the number of standard errors between the control mean and the experimental mean.
Standard error — the usual/expected difference between a control mean and an experimental mean (in either direction) if the true population means are the same. Due to natural variation.
P-value — the probability of getting your result or one even more extreme if the factor does not influence the rate of transpiration. A low p-value (below 5) means the factor does make a difference. Pressure analysis was done using a simpler analysis by necessity, because only one pressure trial gave viable results x = .0273935 p = .0056 Because of only one trial, the pressure was unable to be analyzed with a 2-Sample T-test. Instead, the experimental mean was transformed into a z-score (how many standard deviations from the control mean the experimental mean is), which is then transformed into a p-value. How does humidity affect the rate of transpiration in a geranium plant? We predict that as the humidity level increases, the transpiration rate will decrease. Transpiration increases with increasing air temperature and wind velocity. At constant temperature and wind velocity, transpiration rate is governed by moisture content of air. Transpiration also increases with decreasing relative humidity at constant wind velocity. The rate of diffusion of any substance increases as the difference in concentration of the substances in the two regions increases.When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly. The lack of statistically significant results does not deter the presumption that light is a factor. The difference in light intensity from the control (intensity = .0374) and the darkness (intensity = 0) is so slight that the odds of a significant difference between the two are slim.
More notable are the results where the light intensity was increased tenfold or more. Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast as it does at 20°C.
Rate of transpiration generally increases with an increase in temperature. Temperature enhances the rate of evaporation and induce enzyme activity. 1. Construct a box. The base made out of Comp wood, the four sides made of maple, the top sides made of treated maple hardwood. Dimensions: 11.5inches width, 1’1.5’’ length, 1’2’’ height. (Pegs should be bolted in. no glue used. Siding and top made of thin plastic (less than 1mm thick) should be sealed tight with masking tape. Small hole at bottom to set tube outside of the box.
2. Using previous directions set up a respirometer.
3. Using the box as an environment set up the leaf transpiration apparatus inside the box with the tube outside of the box using the hole drilled. The box should be at room humidity(unless conducting the humidity trial). Cut the stem under water inside the box. Tape to beaker to help support leaf in the air.
4. This Step Is Only Additional Step Used When Conducting Humidity Trial: Spray down The box with a squirt bottle that puts out 1 ml per spray. spray the box 15 times. Try to leave a dry spot to later tape a thermometer
5. Place a thermometer inside the box
6. Set up a light 1’’ from the top piece of plastic. Keep the light off until You are ready to begin experiment.
7. Turn on light and begin experiment. Every one minute make a mark of the temperature inside the box and measure the amount of transpiration from the calibrated pipette.
8. Take out leaves and follow Directions to calculate surface area. Based on the results of this experiment, we conclude that our prediction was correct, and geranium plants transpire faster at lower pressure (higher altitudes). Our data shows that there is an extremely small chance of attaining the results that we did given that pressure was not a factor. We believe that the higher transpiration rate is due to the lower concentration of gases such as O2 and CO2 outside of the plant. claim Humidity — to the degree of dry/wet that we tested — did not affect the rate of transpiration. evidence Results differing to the degree that our control and experimental groups did will occur by random natural fluctuations 17 percent of the time — a high enough percentage that it is reasonable to attribute the difference to random chance rather than humidity as a factor Evaluation Final Conclusion New Questions Prompted by this Research -Would greater humidity levels create a significant difference?
-If not, why wouldn't humidity cause a difference, considering the logistics of water potentials?
-Considering the intertwined nature of humidity and temperature, would it be more reminiscent of actual natural conditions if we hadn't controlled for temperature? Sources of Error Factors and Their Relevance Light — as light intensity increased, transpiration increased Wind — wind made no statistically relevant difference to the rate of transpiration Pressure — Decreasing the pressure increased the rate of transpiration Concentration of Nitrogen — the concentration made no statistically relevant difference to the rate of transpiration Humidity — humidity made no statistically relevant difference to the rate of transpiration at the levels we tested. New Questions Does this trend observed continue at pressures greater than sea level atmospheric pressure (101.325 kPa)? Could trend continue if concentrations of certain gases in the atmosphere were reduced without reducing pressure? Is there a minimum atmospheric pressure at which plants can no longer transpire? oops! -Two of the controls were performed in different rooms
-Temperature was not controlled for in any except the humidity experiment, and then only loosely
-Low trial count due to time constraints
-Human error reading the microrespirometers
-Potential non-linear relationship between mass and surface area of leaves — we assumed linear for calculations. Prediction: The trend does continue at higher pressures. Prediction: Yes, the concentration of gases was one of the primary reasons our low pressure plant transpired faster. Adding wind should increase the rate of transpiration, because the wind decreases the pressure outside the leaf, which essentially pulls the water out. Prediction: Yes. Plants will not be adapted to these environments, which would be both lower pressure and colder. APPLICATION There was a fourteen percent chance that the increase in transpiration seen in the wind trial was due to random chance, therefore wind is not a conclusive factor. This discovery could impact those living at higher elevations, such as the town of Durango, Colorado. Citizens of high altitude towns should water their plants more often to keep them healthier. New Questions Would a greater wind speed be a conclusive factor? Prediction: Yes Would the decrease in temperature that accompanies wind counteract the affects of the wind, negating it's effects? Prediction: somewhat, but not enough to be a significant difference. Graph from http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html A table of various pressures and altitudes can be found at http://www.avs.org/chapters/nccavs/pdf/AtmPres_at_Diff_Altitudes.pdf Experimental Error Our largest cause of error was our low number of trials due to time constraints. If the experiment were repeated, we would do more trials.
It was also hard to get a precise water level measurement due to the respirometer being tilted. This may Our largest cause of error was our low number of trials due to time constraints. If the experiment were repeated, we would do more trials.
It was also hard to get a precise water level measurement due to the respirometer being tilted. This may have slightly influenced our data. Ideally, this experiment could be repeated with a bigger pressure capsule. 1. Follow the general AP Biology Lab Manual procedure
2. Run a control trial
3. Set up a small fan to blow towards the bottoms of the leaves
4. Record data every three minutes