Biology 5090 · Question 1[11 marks]
A student investigated the tropic responses of cereal coleoptiles.
(a)[3]
(i)[1]
Define the term phototropism.
(ii)[2]
State the precise site of auxin synthesis in a shoot, and describe how auxin is transported to the sub-apical growth zone.
(b)[4]
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.
(i)[2]
Predict the appearance of coleoptile A and coleoptile B after 48 hours.
(ii)[2]
Explain the growth response observed in coleoptile C.
(c)[4]
In a separate experiment, agar blocks containing auxin were placed onto the left side of decapitated coleoptile stumps kept in complete darkness.
(i)[1]
Describe the appearance of the stumps after 24 hours.
(ii)[3]
Explain, in terms of cellular mechanisms, why this curvature occurred in the absence of light.