Uses of Plant Hormones
Revise Uses of Plant Hormones for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) biology topic on how auxins, gibberellins and ethene are used in agriculture and horticulture.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Plant hormones are used widely in agriculture and horticulture. This is a Triple-only topic.
Auxins are used as weed killers, as rooting powders, and to promote growth in tissue culture. As selective weed killers they affect broad-leaved plants but not narrow-leaved crops such as grasses and cereals, which is what makes them commercially valuable.
Ethene controls cell division and the ripening of fruits, so it is used in the food industry to ripen fruit during transport and storage. Gibberellins end seed dormancy, promote flowering and increase fruit size.
Revision notes
Uses of auxins
As weed killers, particularly selective ones that kill broad-leaved weeds without harming narrow-leaved crops.
As rooting powders, to encourage cuttings to develop roots. In tissue culture, to promote growth of plant tissue in the laboratory.
Uses of ethene
Ethene controls cell division and the ripening of fruits.
It is used in the food industry to control ripening during transport and storage, so fruit can be picked unripe and ripened just before it reaches the shops.
Uses of gibberellins
Gibberellins end seed dormancy, allowing seeds to germinate at a chosen time.
They also promote flowering and increase the size of fruit. Together with auxins and ethene, they give growers considerable control over plant development.
Key points
- Auxins are used as weed killers and rooting powders.
- Selective weed killers kill broad-leaved plants only.
- Auxins promote growth in tissue culture.
- Ethene controls fruit ripening.
- Gibberellins end seed dormancy.
- Gibberellins promote flowering and increase fruit size.
Worked examples
Example 1
Explain why auxin can be used as a selective weed killer. [2 marks]
Model answer
Auxin affects broad-leaved plants such as weeds, causing uncontrolled growth that kills them (1 mark), but it does not affect narrow-leaved plants such as grasses and cereal crops, so the crop is unharmed (1 mark).
Example 2
Explain why ethene is useful to fruit growers. [2 marks]
Model answer
Ethene controls the ripening of fruit (1 mark), so fruit can be picked and transported while unripe and then ripened just before it reaches the shops, reducing damage and waste (1 mark).
Example 3
Give two commercial uses of gibberellins. [2 marks]
Model answer
Ending seed dormancy so seeds germinate when required (1 mark), and increasing the size of fruit (1 mark).
Common mistakes
Confusing the three hormones' uses.
Auxins for weed killers and rooting, ethene for ripening, gibberellins for dormancy and fruit size.
Saying weed killers kill all plants.
Selective ones target broad-leaved plants only, leaving cereal crops unharmed.
Saying ethene makes fruit grow.
It controls ripening, not growth.
Forgetting this is Triple-only.
It is not required for Combined Science.
Exam tips
- Learn each hormone with two uses.
- Explain selectivity in terms of broad versus narrow leaves.
- Give the commercial benefit, not just the effect.
- Remember this is a Triple-only topic.
Key terms
- Auxin
- A plant hormone used in weed killers and rooting powders.
- Ethene
- A plant hormone controlling fruit ripening.
- Gibberellin
- A plant hormone ending seed dormancy and increasing fruit size.
- Selective weed killer
- A herbicide affecting broad-leaved plants but not crops.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.