BIOLOGY 5090 · STRUCTURED PRACTICE
A student investigated the tropic responses of cereal coleoptiles.
Define the term phototropism.
State the precise site of auxin synthesis in a shoot, and describe how auxin is transported to the sub-apical growth zone.
The student exposed three intact oat coleoptiles, A, B, and C, to unilateral light from the left:
- Coleoptile A: Intact and untreated.
- Coleoptile B: An opaque aluminium foil cap was placed securely over the top 3 mm of the tip.
- Coleoptile C: A thin, impermeable sheet of mica was inserted horizontally halfway through the shaded (right) side just below the tip.
Predict the appearance of coleoptile A and coleoptile B after 48 hours.
Explain the growth response observed in coleoptile C.
In a separate experiment, agar blocks containing auxin were placed onto the left side of decapitated coleoptile stumps kept in complete darkness.
Describe the appearance of the stumps after 24 hours.
Explain, in terms of cellular mechanisms, why this curvature occurred in the absence of light.
Total: 11 marks