Fig She took readings of the height of the meniscus every 10 seconds for 90 seconds. Her results are below.

Transcription

1 1 A student did an experiment to compare the rates of transpiration of leafy shoots from two different plants, elder and pyrocantha. She selected shoots from both plants of the same mass and stem diameter. She used the potometer shown in Fig Examiner s rubber tubing, making an air-tight seal between the cut end of the shoot and the water in the capillary tubing capillary tubing containing water meniscus scale marked in cm Fig. 1.1 She took readings of the height of the meniscus every 10 seconds for 90 seconds. Her results are below. results for elder reading of meniscus at start = 1.6 cm reading / cm results for pyrocantha reading of meniscus at start = 0.8 cm reading / cm /06/M/J/03

2 (a) Construct a table showing times and readings in the space below. 3 Examiner s [3] (b) Work out the average water loss for each plant in centimetres of water per second. Show your working. elder average water loss =... cm / s pyrocantha average water loss =... cm / s [4] (c) Suggest one difference between the shoots that could account for the different rates of water loss. Explain your answer. difference... explanation......[2] (d) Name one environmental factor that could account for the different rates of water loss of the two shoots /06/M/J/03 [Turn over

3 14 5 Some plants show differences between leaves found in sunny areas of the plant (sun leaves), and leaves found in shaded areas (shade leaves). (a) A student was supplied with two leaves, labelled sun leaf and shade leaf. Drawings of the two leaves are shown in Fig (i) Measure the maximum length of each leaf, excluding the petiole (stalk). Write your measurements below each diagram. (ii) Fig. 5.1 sun leaf shade leaf length = mm length = mm [2] (ii) The leaves clearly have different areas. One leaf has a larger surface than the other. Suggest an advantage to the leaf with the larger area. UCLES /61/M/J/10

4 15 (b) The diagrams in Fig. 5.2 show cross-sections of a sun leaf and a shade leaf as viewed using a microscope. waxy cuticle palisade cells sun leaf shade leaf Fig. 5.2 Construct a table to compare these two diagrams. Include the following features; thickness of leaf, number of palisade cells, size of air spaces. [4] (c) Choose any one feature of the sun leaf in Fig. 5.2 and explain how this feature is a good adaptation for photosynthesis. feature explanation [2] UCLES /61/M/J/10 [Turn over

5 16 (d) The sun leaf usually has a thicker cuticle than the shade leaf. The cuticle is a waxy layer covering the leaf. Suggest an advantage that this thicker cuticle gives to the sun leaf. UCLES /61/M/J/10

6 13 4 A student used the apparatus shown in Fig. 4.1 to study the transpiration rate in a leafy shoot. As water vapour is transpired from the leaves, water is drawn through the apparatus. The rate of movement of the small bubble along the tube is used as an indication of the rate of transpiration. The student wanted to find which surface of the leaves lost the greater amount of water vapour. The student did two experiments, the first with the leaves untreated and a second with grease applied to the upper surface of the leaves. leafy shoot grease reservoir water scale (cm) air bubble bubble moves in this direction Fig. 4.1 (a) The student prepared the shoot by cutting the stem under water. He placed the shoot in the rubber tubing at the top of the apparatus as shown in Fig He added water from the reservoir to move the bubble to the zero mark. He then started timing. He read the position of the bubble every minute for three minutes and recorded the readings in Table 4.1. UCLES /61/O/N/12 [Turn over

7 14 condition of leaves time / minutes reading on scale / cm Table 4.1 distance moved by bubble per minute / cm average distance moved by bubble per minute / cm untreated (i) Take the readings from the scales illustrated in Fig. 4.2 and record them in Table 4.1. Read the value from the left side of the bubble. (ii) Calculate the distance moved by the bubble during each minute and enter the values in column 4 of Table 4.1. (iii) Using the three values found in (a)(ii) calculate the average distance moved by the bubble per minute and enter this value in column 5 of Table 4.1. scale (cm) first reading scale (cm) second reading scale (cm) third reading Fig. 4.2 UCLES /61/O/N/12

8 15 (b) The student then applied grease to all of the upper surfaces of the leaves to prevent loss of water vapour. He added water from the reservoir to return the bubble to zero. He repeated the procedure as in part (a) and calculated a new average distance moved by the bubble per minute. This new value was 1.2 cm. (i) the average value from (a)(iii) and the average value given in (b) to calculate the percentage of water vapour loss that took place from the lower surface of the leaf. percentage loss from lower surface [2] (ii) The student concluded that the rest of the water vapour was lost from the upper surface of the leaf. Describe what the student could do to confirm this. (c) Study column 4 of Table 4.1. The three values for the distance the bubble moved per minute are not identical to each other. Suggest two environmental conditions that could cause the differences. first condition second condition [2] UCLES /61/O/N/12 [Turn over

9 16 (d) (i) Explain why the student cut the stem of the leafy shoot under water before putting it into the apparatus. (ii) Suggest a possible reason why the amount of water taken up by the plant shoot may not be exactly the same as the amount lost by transpiration. UCLES /61/O/N/12