Transpiration Lab

Question: Is the rate of transpiration in a plant, represented by the amount of water that escapes out through the stomata, affected by environmental factors? If so, which environmental factor will cause the greatest increase in the rate of transpiration? Will it be an increase in temperature, which will increase evaporation, an increase in light, which will increase photosynthesis, or an increase in wind, which will cause water to blow out of the leaves? This question is solvable through perfuming tests on a number of different plants. The environmental factors can be replicated through the use of a fan for the wind, a heater for the temperature increase, and a lamp for the light increase.

Hypothesis: If a number of plants are tested under different environmental factors, then the trials where heat is added will cause the greatest rate of transpiration for all of the plants, because if the temperature is raised, then more water will be evaporated out of the plant through the stomata, because the kinetic energy/molecular motion of the water molecules will increase, and the water molecules will vaporize. I also hypothesize that the tails with the fan will show the second highest transpiration rate in all the plants, because the wind will cause many of the water droplets hanging around the stomata to blow out of the plant, without the need of evaporation.

Plant Transpiration Data Table
	Normal	With Fan	With Heater	With Lamp
Arrowhead	3.6 mL	7.5 mL	6.6 mL	4.0 mL
Coleus	0.9 mL	6.0 mL	3.9 mL	3.0 mL
Devil’s Ivy	2.9 mL	4.6 mL	4.1 mL	3.0 mL
Dieffenbachia	4.1 mL	7.7 mL	6.0 mL	3.9 mL
English Ivy	1.8 mL	5.1 mL	3.2 mL	2.1 mL
Geranium	1.2 mL	4.7 mL	5.8 mL	2.4 mL
Rubber Plant	4.9 mL	8.4 mL	6.8 mL	4.3 mL
Weeping Fig	3.3 mL	6.1 mL	4.9 mL	2.5 mL
Zebra Plant	4.2 mL	7.6 mL	6.1 mL	3.2 mL

Question 1: Describe the process of transpiration in vascular plants.

Answer: Water is evaporated through the stomata in the leaves, which are usually on the underside of the leaves. Water in the plant is brought up from the roots to the leaves because water is pulled by the water molecules that are being evaporated (cohesion and adhesion). The water is let out when the stomata open to release oxygen and take in carbon dioxide.

Question 2: Describe any experimental controls used in the investigation.

Answer: The experimental control in this investigation is the normal experiment. It allows us to compare the environmental changes to normal environmental conditions. 

Question 3: What environmental factors that you tested increased the rate of transpiration? Was the rate of transpiration increased for all plants tested?

Answer: The introduction of wind, represented by the fan, and the introduction of heat, represented by the heater, both increased the rate of transpiration, with the fan causing the greatest increase. For those two factors, the rate of transpiration increased for all nine plants.

Question 4: Did any of the environmental factors (heat, light, or wind) increase the transpiration rate more than the others? Why?

Answer: The rate of transpiration was increased the most by introducing wind, with Geranium being the only plant who's rate of transpiration increase more with the introduction of heat than with the introduction of wind. This is because the wind causes the water molecules sitting at the stomata to be blown out of the leaves, without even evaporating. The reason the heat increased the rate of transpiration, though not as much as the wind, is because the increase in temperature meant that the molecular motion of the water molecules increased, and more were able to evaporate.

Question 5: Which species of plant that you tested had the highest transpiration rates? Why do you think different species of plants transpire at different rates?

Answer: The Rubber Plant had the highest rate of transpiration in all four tests. This is because the Rubber Plant, pictured below, has the large leaves and probably has more, and larger, stomata than other plants. Different species of plants probably have different rates of transpiration because they have to survive different environments. The Rubber Plant probably lives in a wetter environment than the Coleus, and therefore will not die if it loses a lot of water through transpiration. Also, Coleus looks like its texture may make it harder for water to escape, compared to the Rubber Plant, which looks like water can slide right off of it.

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Question 6: Suppose you coated the leaves of the plant with petroleum jelly. How would the plant's rate of transpiration be affected?

Answer: The rate of transpiration would decrease because the stomata would be covered, and water would not be able to escape.

Question 7: Of what value to a plant is the ability to lose water through transpiration?

Answer: Just like people in sweating, plants use transpiration to cool themselves. As the water is evaporated, heat is lost with the water molecules. When evaporation occurs, water is pulled up to the leaves through cohesion and adhesion, carrying nutrients up to the leaves.