4 2 Plant growth substances and phytochromes are chemicals that affect the growth of plants. (a) (i) Which row of the table shows the concentrations required for the fastest growth of lateral buds? (1) A B C D Auxin concentration Cytokinin concentration high high high low low high low low (ii) Some types of auxin affect the activity of cells in the same way as hormones such as oestrogen affect human cells. These auxins pass through the cell membrane and affect the synthesis of enzymes. Explain how these auxins affect the synthesis of enzymes. 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Turn over 5 BLANK PAGE 6 (b) Phytochrome is involved in the germination of seeds. The effect of red (R) light and far-red (FR) light on the germination of lettuce seeds was investigated. A scientist exposed five groups of 50 seeds to red light for one minute. The seeds were planted and the mean number that germinated was calculated. Another five groups each of 50 seeds were then exposed to red light for one minute, followed by far-red light for four minutes. These seeds were planted and the mean number that germinated was calculated. The experiment was repeated with different combinations of red light and far‑red light. The results are shown in the table. Sequence of red (R) and far‑red (FR) light Mean number of seeds that germinated Standard deviation (SD) R 45 ± 4 R, FR 5 ± 2 R, FR, R 45 ± 5 R, FR, R, FR 10 ± 4 R, FR, R, FR, R 40 ± 9 Turn over 7 Analyse the data to comment on the effect of red (R) and far-red (FR) light on the germination of lettuce seeds. 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(Total for Question 2 = 8 marks)