This reduces the concentration gradient of water vapour between the air spaces in the leaf and the atmosphere, thus lowering the rate of transpiration of the leafy shoot. On the other hand, in windy conditions, water vapour coming out of the leaf is blown away rapidly. This maintains a high concentration gradient of water vapour between the air spaces in the leaf and the atmosphere. Thus a high rate of transpiration will be observed on the leafy shoot being placed under the fan. b) Compare and explain the transpiration rate of the leafy shoot when it is under normal light intensity and under higher light intensity. – Under high light intensity, the leafy shoot would have a higher transpiration rate. It is because when the light intensity increases, the size of the stomata increases too.
This causes water vapour to diffuse more rapidly out of the stomata. Also, an increase in light intensity leads to a rise in the leaf temperature, which raises the rate of evaporation of the water from the mesophyll cells. On the other hand, under normal light intensity, the leafy shoot would have a lower transpiration rate. It is because when the light intensity decreases, the size of the stomata decreases too. This causes water vapour to diffuse less rapidly out of the stomata. Also, an decrease in light intensity leads to a fall in the leaf temperature, which raises the rate of evaporation of the water from the mesophyll cells. It It is 3. Discuss two possible experimental errors.
Firstly, we need to cut the stem of a leafy shoot under water at the beginning of the experiment. If we don’t cut it the stem underwater, air would enter xylem vessels and leads to blockage, which lowers the amount of water uptake of the plant. Secondly, we should keep enough distance between the fan and the plant (e. g. 1metre). If we place the fan and the plant too closely together, strong wind would makes the stomata on the leaf closed, which would lower the amount of water uptake of the plant, thus leading to an anomalous result. 4. Suggest an improvement for the set up and procedure. -In the original set up, we can smear a thick layer Vaseline over the airtight seal.
This would further prevent air entering the set up. Besides prevent water leaking out, this could also prevent water vapour entering the atmosphere, and make the result more accurate. -Also, we can use a thinner capillary tube with markings to carry out this experiment, which shows more significant result. -Besides improving the procedure, there is a more convenient and accurate set up to study the transpiration rate of a leafy shoot. Here is the new set up: The reason that the previous set up (bubble photometer) is not good enough is that it measures the amount of water uptake only, including use of water in both metabolic activities and transpiration.
As we are studying the transpiration rate on the leafy shoot, this set up is not accurate enough since the transpiration rate of plant is about 99% only. On the other hand, the new set up (weight photometer) is more accurate, as the decrease in weight of the set up reflects water loss from transpiration, while water being used during metabolic activities is being kept in the plant. Unlike the previous set up, the water uptake for metabolic activities is not include in the measure of the whole amount of water uptake, therefore the second set up(weight photometer) is more accurate. Conclusion: To conclude, the rate of respiration varies with light intensity condition and air movement condition.