14 5 The photographs show leaves from six species of plant. Daffodil Frogbit floating on water Sunflower Maize Oak tree Pea Turn over 15 In an investigation into transpiration, a survey was carried out to measure the distribution of stomata on leaves. The table shows the results of this investigation. Plant species Density of stomata in leaf surface / number per mm2 Upper epidermis Lower epidermis Beech tree 0 340 Daffodil 65 68 Frogbit (floating leaf) 89 0 Maize 52 58 Oak tree 0 450 Pea 100 220 Sunflower 85 156 Sycamore tree 0 860 16 (a) Analyse the data and the photographs to explain the distribution of the stomata. 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(b) As part of this investigation, the effect of light on the transpiration rate of seven‑day‑old maize seedlings was measured. The transpiration rate of maize seedlings placed in dim light was measured every 30 minutes for 3.5 hours. Extra illumination was then added and the transpiration rate again measured every 30 minutes for another 3.5 hours. The graph shows the results of this investigation. Turn over 17 7 6 5 4 3 2 1 0 Transpiration rate / a.u. extra illumination added Time / hours dim light bright light 1 2 3 4 5 6 7 (i) Calculate the approximate percentage increase in the transpiration rate due to the extra illumination. (2) Answer .............................................................. (ii) Explain two factors that should have been controlled in this investigation. 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(Total for Question 5 = 9 marks)