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The Effect of Light on Transpiration

AP Biology

Cristi Marie

on 11 April 2013

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Transcript of The Effect of Light on Transpiration

The Effect of Light on Transpiration Cristina Knowles & Rosario Huamani Introduction Results Discussion Research Question Background Hypothesis Two potted pansies
Plastic bags or wrap
Light Intensity meter
Scale Obtain two small potted plants of the same species.
Remove each plant from its pot without destroying the roots or removing the soil.
Remove all blooms/flowers from the plants.
Enclose the entire root ball of each plant in a plastic bag, making sure each bag is tight snugly around the stem with string. This will keep water from evaporating.
Label each plant.
Determine and record the mass of each plant.
Place the plant labeled “With Light” in a sunny location. Place the other plant labeled “Without Light” in a shady location.
Use a thermometer and a light intensity meter to record temperature and light.
Return each day to record the mass, light, and temperature of the plants and their locations over the course of one week. Materials and Methods Materials Procedure Set Up Variables
& Groups Independent variable: Intensity of light

Dependent variable: Rate of transpiration (determined by mass measurements) One plant placed in a sunny location where it will receive light One plant placed in a shady location where it receives less light Mass is used to measure the transpiration rates in each plant to see how it is affected by light intensity. Both plants had a major decrease in mass, meaning there was a decrease in water from the plants. Variables That Were Monitored: Light Plant Dark Plant Light Intensity Temperature(C) Light Intensity Temperature(C)
Day 1- 250 26.5 8 18
Day 2- 1000 23.5 12 19.4
Day 3- 400 22.4 13 21.5 How does the presence of light affect the rate of transpiration in plants? Transpiration refers to the process of water entering plants through the roots and then leaving through the stomata. Water is able to do this by cohesion and adhesion. It is important for plants to obtain water because it provides the H+ ions needed to perform photosynthesis.

Besides light and water, plants also need CO2, for which they would need to open their stomata in order to obtain. Open stomata allow for the entrance of CO2 but it also for the loss of water.
It's possible that due to these processes, the presence of light might increase the rate of transpiration more than the absence of light. If two plants are placed in different conditions: one with light and one in a shady spot, then the plant exposed to light will have a higher rate of transpiration. The hypothesis for this experiment was that Plant 1 (Light) would have a higher transpiration rate than Plant 2 (Dark). Our hypothesis was incorrect because the plant exposed to light lost 16.15 grams (49.3% of its mass) and the plant which was in the dark lost 19.9 grams (51% of its mass). Each day that data was recorded, Plant 2 lost more mass than Plant 1. This means that Plant 1 retained more water than the other plant and had a lower transpiration rate. A reason for this may be the fact that Plant 1 was constantly in the sunlight and therefore was exposed to higher temperature. Sensing this, the plant probably closed the stomata in order to prevent too much water loss. Meanwhile the other plant wasn't exactly at a "risk" of water loss, thus the stomata remained open for the most part, and a higher rate of transpiration occurred.
If the experiment were to be repeated, a heat sink would have been placed in order to reduce the influence the heat may have had on Plant 1. Also, Plant 2 would be placed in a better location. Even though its location was dark in comparison to that of Plant 1, some light still reached it. Day 4- 65 26 10 24
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