Investigating the Effect of Temperature on the Rate of Transpiration - Research Paper Example

Investigating the Effect of Temperature on the rate of transpiration Introduction The transport and the transfer of water from a plant surface into the atmosphere is called transpiration. This takes place via a process called evapotranspiration during which water which is absorbed by the root of the plant, travel to the leaves through the plant body through tissues called xylem.1 The transpiration is similar to the breathing process of humans during which tiny water molecules are released into the atmosphere from the leaf surface through tiny pores on its surface called the stomata. Effect of temperature on the rate of photosynthesis Photosynthesis is the process by which plants convert carbon dioxide and water into organic compounds in the presence of sunlight releasing oxygen as a byproduct.2 At low temperatures, the chemical enzymes in the chlorophyll do not have sufficient energy and are hence inactive. The rate of photosynthesis is thus slow. With increase in temperature, the enzymes get more energy and the rate increases. At a critical temperature the enzymes lose their chemical characteristics and begin to disintegrate and the rate of photosynthesis comes down.3 At higher temperatures the stomata responsible for the water and gas exchange also closes thus stalling the process of photosynthesis even further. Plastic bags tied around 2 identical plants kept in pots are placed in a dark room and the other in the open atmosphere.1 After a certain time period, the 1-(The Encyclopedia of Earth, 2010) 2-(Higher Level Biology, Fourth edition 2007, p.84) 3-(Effect of temperature on Photosynthesis and Co2 evolution in light and darkness by Green leaves, November 1968, p.673) amount of water that has collected on the inner surface of the plastic can be compared using a cobalt chloride paper. This paper turns from blue to pink in the presence of water. Also, a leaf specimen is immersed in hot water and the number of bubbles coming from both the surfaces is noted. The two findings that one could infer are (1) The quantity of water collected in plant exposed to the open atmosphere is more. (2) More water bubbles come out from the underside of the leaf. Hypothesis Thus a co-relation can be found out between temperature, transpiration and photosynthesis. At higher temperatures which are sensed by the plants, the rate of transpiration is low which indirectly results in reduced rate of photosynthesis. Since the top surface of the leaf is directly exposed to sunlight the stomata density is more at the bottom surface compared to the top, hence more the bubbles from the bottom surface.1 Factors affecting Transpiration 2 (i) Independent Variables (a) Temperature- The increase in temperature leads to more opening of the stomata leading to more exchange of water into the atmosphere. (b) Relative humidity- Low humidity means that the amount of water vapour present in the atmosphere is of a very low percentage. Hence the plant has more tendencies to give off water to 1-(Effect of temperature on Photosynthesis and Co2 evolution in light and darkness by Green leaves, November 1968, p.273) 2- (Higher Level Biology, Fourth edition 2007, p.290) the atmosphere during these times. (c) Wind and air movement- This is related to humidity. As water evaporates from the surface of the leaf the area around the leaf gets saturated with vapour. If the area around the plant has sufficient air movement this saturated air can be displaced with fresh air of low humidity leading to increase in transpiration. (d) Soil moisture availability- Some plants lose soil around their roots due to erosion, landslides and other external factors which leads to leaf loss. This thereby reduces the rate of transpiration. (e) Type of plant- Some plants like cacti which grow in the desert regions have low transpiration rates in order to preserve the precious water. (ii) Dependent Variable A potometer is used to measure the rate of transpiration. The dependent variables in measuring the transpiration rate are (a) the weight of water lost as would be indicated in the potometer (b) the distance travelled by the bubble in a given time in a bubble photometer. (iii) Control variable 1 These are the variables that can control the outcome of the transpiration experiment. The independent variables can all be controlled to a certain extent if put in a simulated environment. The efficiency and reliability of the photometer also forms a control variable for the experiment. 1- (Higher Level Biology, Fourth edition 2007, p.291) The Transpiration experiment 1 Material & Apparatus 1.Plant species taken for the experiment eg: Impatiens (moisture loving plant) and Oleander (drought tolerant) 2.Large sink to assemble the setup under water. 3. Potometer 4. Beaker to hold 500ml of water 5. Miscellaneous items like scissors. Clamp stand with boss and clamp, marker pen, stop clock, 0.1ml pipette, 16 inch long flexible tube, petroleum jelly, thermometer and paper towels. Method 1. The tip of the 0.1 ml pipette should be placed into the 16 inch clear plastic tubing and submerged in the sink of water. The water should fill the entire tube and pipette setup so that no bubbles are entrapped. The plant shoot is placed in the beaker and cut under water before inserting it into the open end of the tubing. The flexible tube is then bend into a U shape and a clamp is used to hold both the tube piece and the pipette. Petroleum jelly may be used to make the seal airtight. 2.The setup is then exposed to different conditions like room condition, with a bulb of 100 Watt placed in the room, with a fan placed at 1m distance from the plant and with by spraying the leaves with water to simulate a humid atmosphere. 1-(Higher Level Biology, Fourth edition 2007, p.303) 3. Record the water level in the pipette at the beginning. Then continue to do so for 3 minutes for 30 minutes using the stopwatch. After conducting this experiment an inference as to how each of these affect transpiration rate can be summarized as follows:1 Variable How will you control Why it affects? Light (bulb) The light intensity increased Increased light stimulate more stomata the transpiration rate. openings leading to increased transpiration Fan speed The fan speed can be adjusted using Increased fan speed leads to removal of the regulator. Increased speeds lead saturated air from the surface to transpiration increase. of leaves. Spraying mist This lead to decrease in rate of Increased spraying leads to more transpiration. humid conditions leading to decrease in transpiration. Safety 1. Some people may find the sap of the plant extremely irritating, hence proper gloves need to be used when handling these plants, 2. Care should be taken when cutting the plant shoot using a knife and the photometer made of glass should also be handled with care to avoid breakage. 1-(Transpiration rates under controlled environment: Species, humidity and available water as variables, 1962, p.20) Bibliography 1. Effect of temperature on Photosynthesis and Co2 evolution in light and darkness by Green leaves, Choy-Sin Hew, G Krotkov and David T. Canvin, November 1968 2. Transpiration rates under controlled environment: Species, Humidity and available water as variables, Atwell M Wallace and Norman B. Stout, January 1962 3. The Encyclopedia of Earth, George Burba & Michael Pidwirny, August 2010. 4. Higher Level Biology, Rita Y Ghalayani, Forth edition 2007. Read More