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Factors affecting the rate of transpiration

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Introduction

Biology Lab Design Factors affecting the rate of transpiration Elric Balrog Introduction There are several factors which can affect the rate transpiration of plants; these could either increase the rate of water uptake or decrease the rate of water uptake. These factors could be internal or external. In this investigation we will be looking at the external factors which affect the rate of respiration, such as temperature, light intensity... etc. Transpiration is known as the loss of water vapour through the stomata of the leaves. It is needed to keep the cells of the spongy and palisade mesophyll cells moist as this allows carbon dioxide to dissolve before diffusing into the cells for photosynthesis. A suction force is created on the column of water below it in the xylem when water is evaporated. The upwards force on the column of water created by transpiration and the downwards force due to gravity created a tension in the column of water. As there is a difference in the upwards pull, which is greater than the downwards pull, the column of water moves up the xylem. As the cohesion tension theory explains it, water molecules are polar, meaning that they stick to one another. ...read more.

Middle

thermometer 1 x 1 Balsam leafy shoot 1 x 1 beaker 1 x 1 candle 1 x 1 match box 1 x 1 30 cm ruler 1 x 2 syringe with needle 50 ml DCPIP 1 x 1 black polythene bag 1 x 1 rubber bung Method 1. The apparatus was set up as shown on the protocol diagram. 2. The conical filter flask was filled with water. 3. The leafy shoot was transferred from the water filled beaker to the sink and a slanting cut was made few centimeters above the last cut in water. 4. The shoot was fit into the bung of the flask under water and pushed in to make a tight fit. 5. The end of the rubber bung with wax was sealed using a candle and matches. 6. DCPIP, the indictor, was inserted into one end of the graduated capillary tube using a syringe. 7. The shoot was left to equilibrate for 5 minutes as it adjusts to its external conditions whilst regularly replacing the water taken up. 8. The time taken for the water to move 30 cm along the capillary tubes were measured every 2 minutes. ...read more.

Conclusion

The experiment took roughly about 3 hours 30 minutes to complete as the set up of the equipment took a lot of time as well as the preparation of the shoot and adjustments which had to be made to limit air loss from the rubber bung. An unbalance in the pressure between the potometer and the graduated capillary tube would disrupt cohesion tension in the shoot. Seeing as only 3 environmental conditions were tested, a broader understanding of the effect of external factors on the rate of water uptake by a leafy shoot would be possible if other conditions were tested for, such as humidity, increased light intensity and vaselining the upper and lower epidermises of the leaves. More readings over a longer period of time could have been taking to obtain more accurate average. Moreover, an estimate of the water loss per unit in leaf area could have been derived by measuring the volume of water lost and then removing all the leaves in order to determine the surface area. Overall, I would have preferred looking at more factors which could have influenced the rate of water uptake by the Balsam leafy shoot, but because of time restraints I could not do so. It was interesting to see how external factors affect the rate of transpiration in plants. ?? ?? ?? ?? IB Biology Lab Design Page 9 of 9 ...read more.

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