Question 15
HA scientist investigates how light affects the distribution of auxin in shoot tips.
- She cuts the tips off three shoots and stands each tip on an agar block.
- Each agar block is split into two halves, L and R, by a thin sheet of mica. Auxin cannot pass through mica.
- In tip 1, the mica sheet divides only the agar block.
- In tip 2, the mica sheet divides the agar block and the tip.
- Tips 1 and 2 are lit from the right-hand side. Tip 3 is set up in the same way as tip 1 but is kept in the dark.
The Figure shows tip 1 and tip 2.
Figure
After 3 hours, the scientist measures the amount of auxin in each half of each agar block.
The Table shows the results.
Table
| Set-up | Amount of auxin in block L in arbitrary units | Amount of auxin in block R in arbitrary units |
|---|---|---|
| tip 1 (lit from the right) | 65 | 35 |
| tip 2 (lit from the right) | 50 | 50 |
| tip 3 (kept in the dark) | 50 | 50 |
a.[2]
Explain the results for tip 1.
b.[2]
Explain why the results for tip 2 are different from the results for tip 1.
c.[3]
The scientist places block L from tip 1 on the left-hand side of the cut end of a shoot that has had its tip removed. The shoot is kept in the dark.
Predict and explain how the shoot will grow.
d.[1]
Use the results for tip 1 and tip 3 to suggest how light affects auxin in the shoot tip.
3.2 Coordination and control – the endocrine system Questions
84 exam-style questions on OCR GCSE Biology 3.2 Coordination and control – the endocrine system, covering 3.2.1 Principles of hormonal coordination and control, 3.2.2 Roles of thyroxine and adrenaline, 3.2.3 Hormones in human reproduction, 3.2.4 Interactions of reproductive hormones, 3.2.5 Hormones in contraception, 3.2.6 Hormones in reproductive technologies, 3.2.7 Plant hormones in growth and coordination, 3.2.8 Effects of plant hormones, and 3.2.9 Uses of plant hormones. Each one has a worked solution and a mark scheme showing where the marks go.