Biology 9700 · AS & A Level · Control and coordination in plants
Control and coordination in plants — practice question
An experiment was conducted to investigate the effect of the plant growth regulator auxin on apical dominance.
• The apical buds of 20 pea plants were removed and thrown away.
• For 10 pea plants, the cut ends were covered with inert paste that contained auxin.
• The cut ends of the remaining 10 pea plants were covered only with the inert paste.
• Another 10 pea plants kept their apical buds intact and were not given paste. This served as the control group.
The lengths of the side shoots in each of the three groups were recorded at fixed time intervals, and mean values were then worked out.
The results are shown in Fig. 7.1.
(a)[3]
Explain why the side shoots become longer after the terminal buds are removed.
(b)[2]
Calculate the percentage difference, at 13 days, in the mean length of side shoots of plants treated with paste alone compared with the plants treated with paste and auxin.
Give your answer to the nearest whole number.
Show your working.
(c)[3]
Using data from Fig. 7.1, describe and explain the effect of auxin on the growth of side shoots.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Apical bud is source of auxin” …