Light and the Rate of Transpiration - Lab Report Example

BIOL 134

Light and the Rate of Transpiration

ABSTRACT

This experiment will document the effects of temperature on water facilitation from an outside source to within the plant structure under light density. A LabQuest pressure sensor was used to record the increasing or decreasing rate of pressure when different samples of water were applied to three separate samples of vegetation in high and low light density. Water temperature did not play a significant role in the process, nor did the application of low and high light emission. The density of the plant walls proved to be the determining factor for which plant transferred more water than others. The thick-skinned plants started at a lower pressure and determined to have a slower rate of pressure decrease, whereas the thinner-walled plants were more successful with water intake within the time parameters set on the sensor. The rate of photosynthesis, amount of light intensity and the rate of transpiration are dependent on each other. As light intensity increases the rate of photosynthesis increases, the water potential of the leaf decreases due to the increased amount of glucose stored in the guard cells. The decrease in water potential causes more water to enter into the guard cell, increasing turgidity. The turgor pressure leads to the opening up of the stomata, and transpiration takes place consequently occurs.

INTRODUCTION

When thinking of the complexities of plant photosynthesis and growth, one would think that the roots of the plant would be one of the primary sources of its life source, water. 97% of a plants water source arise from a secondary source, which is the leaves. Through a process called transpiration, plants transport water from the underbelly of its foliage using the stomata to open and close its pores as needed. The process works like how waterworks for the human body. In times of over exertion, water is used as the primary source of cooling the human body down to a reasonable temperature.  The process of transpiration works in the same capacity within its initial purpose. It is necessary for cooling down the plant, help in the transport of water from the soil, water transport through the xylem, regulating the concentration of the cell sap and distribution of salts and minerals in the plant. Three samples of water (room temperature, hot, and cold) were used in sequence with three plant sources (honeysuckle, crape myrtle, and eucalyptus) in conjunction with high and low levels of light emission. Greater light intensity will lead to a higher rate of transpiration.

METHODS

Three samples of vegetation were procured from their natural habitat.  Each sample was cut on a 45-degree angle to increase the surface area for the uptake of water through the xylem. Also so as not to crush any of the veins in the stem, to prevent t water transfer would not be blocked due to a crushed sample. The stem is cut underwater, the reason being to avoid the air bubbles from entering the xylem vessel. The reason for the testing was to document how light density affects water transfer at different rates through vegetation and finding a determining factor of why different plants move at different rates. The LabQuest system was set up so that the pressure sensor was placed above the test pieces so that each run would give accurate results. The first test run used room temperature water that was injected into the pressure line. The plant samples were tested for all three phases at high light emission and low light emission. The crape myrtle was test subject A, the Honey Suckle was B, and the Eucalyptus was C. The last phases used ice-cold water at 2.7 degrees Celsius and hot water at 65.1 degrees Celsius.

RESULTS

Before the initial tests were started, atmospheric pressure registered in at 100 KPa. The first tests were conducted on the crape myrtle using the LabQuest sensor and tap water, with the lights on. The pressure tube was filled with the fluid and drained properly to release all air bubbles so that the results would not be distorted. The test subject sat for 5 minutes before recording data. The first reading was 114.57 KPa with the lights on before starting the timer. Each test lasted for approximately 15 minutes. The graph showed a slight decrease in pressure within the first few seconds. After the time elapsed, the pressure dropped 13 points to 100.82 KPa. The next test used ice-cold water. The results were consistent with the tap water, except for the fact that it started dropping pressure a little slower. It started at 111.41 and fell to 102.11. The hot sample registered in at 111.86 and bottomed out at 105.92. The tests were then run with the lights off. The numbers were the same as the readings with the lights on.

The second test subject was the honeysuckle. Pressure registered similar to sample A at 103.08 KPa with the lights on. The decrease in pressure was much more consistent compared to that of the first sample. This material was far better suited for water transfer as the readings dropped by a total of 10 points to 93.33 KPa. The cold test run started at 113.8 and dropped to 92.3. The hot run introduced itself at 116.38 and fell to 96.95. As the case with sample A, the numbers were the same when taken with low light density.

The last sample was eucalyptus. The pressure reading was low with the lights on, registering at 96.17 KPa. The results for this test subject was vastly different from the first two. As the test began, the data was relatively stagnant. There was not any movement for the first 4-5 seconds. The rate eventually bottomed out at 95.46 KPa. They were moving less than one point. The second run was with cold water. Pressure started at 96.17 and dropped slightly once again to 95.85. The last sample was with the hot water, and the results were the same. Pressure began at 96.3 and only fell to 95.53. With low density light introduced to it, the sample had minimal change as well.

{light intensity on plants} (cd)

{water pressure} (psi)

Trial 1 *

Average {normal light on plants} (cd)

Trial 2 *

Control

{45 minutes}

DO NOT

INCLUDE

DATA

{45 minutes}

DO NOT

INCLUDE

DATA

{45 minutes}

DO NOT

INCLUDE

DATA

DISCUSSION

Overall, the experiment proved that the density of plants plays a massive role in transpiration. Sample B moved less than 1KPa because of the thickness of its bark. It seemed to act as a shield and an extra barrier to allow the flow of water. The benefits of this are that it also retains more water compared to the other specimen so that when it gets hot, it will stay hydrated. Sample A and C pressure dropped over ten points apiece, showing that they reacted instantly and consistently to their introduction to the water samples. There was not any difference in pressure related to the multiple water temperatures, or light density. All three samples graded out similar regardless of both factors. The project needed more variables like saturation rates and outside factors like humidity and sun exposure. I would conduct the experiment with the LabQuest attached to the source. By doing this, the data would be more consistent with that of its natural environment. Several factors affect the rate of transpiration; they are dependent on the plant structure, such as the environment the plant grows and the type of stem the plant possess. Regarding the stem capillary action determines the upward movement of water, the forces of attraction between molecules causes the liquid to move up the plant.

Consequently, the amount of water that runs through capillary action determines the amount of water transpired by the plant. Water potential also affects water movement in plants in the aspect of resistance such as cuticle resistance, boundary layer resistance and stomata resistance—the higher any plants resistance, the slower the rate of transpiration. Transpiration is as a result of the water potential of the leaf minus the water potential of the atmosphere divided by the resistance the plant offers.