FreeScienceLessons · AQA BiologyPlant Hormones — auxins and tropisms
Key facts
Auxins and tropisms — fill in the table
Term
Explanation
Auxins
Phototropism
Gravitropism (geotropism)
Mechanism (shoot bending)
In roots
Commercial uses of plant hormones — fill in the table
Product / hormone
Use
Rooting powder
Selective weedkillers
Ripening fruit (ethene)
Gibberellins
Exam questions — 3 questions · 11 marks
⚡ Extended questions included. Read the hint. Write in full sentences. AI marks against the AQA mark scheme.
1 markPhototropism mechanismAQA 8461 P2 style
Explain why a shoot grows towards a light source.
A The side of the shoot facing the light photosynthesises more, producing more energy for growth
B Auxin moves to the shaded side of the shoot, causing greater cell elongation on that side, bending the shoot towards the light
C The light side of the shoot loses water by evaporation, causing it to shrink
D Auxin is destroyed by light, so cells on the light side grow faster due to lack of auxin inhibition
1 markGibberellins useAQA 8461 style
A fruit grower wants to produce larger seedless grapes. Which plant hormone should they use?
A Auxin
B Ethene
C Gibberellin
D Cytokinin
4 marksCompare root and shoot responseAQA 8461 P2 Higher style
A seedling is placed on its side in the dark. Explain, using your knowledge of auxins, how the shoot and root will respond over the next few hours. (4 marks)
Hint: Same auxin distribution (lower side) → opposite effects because roots and shoots respond differently to auxin. Shoot: more auxin = more growth (upward). Root: more auxin = less growth (downward).