GCSE Biology revision

Use of plant hormones (HT only)

Plant hormones (biology only)

AQA 4.1.1.1

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AQA student objectives

Learning pathway

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Identify and describe Auxin as a Growth Hormone, Auxin as a Selective Weed Killer and Gibberellin and Seed Dormancy in the context of use of plant hormones (HT only).

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Explain the relationships between Auxin as a Growth Hormone, Auxin as a Selective Weed Killer and Gibberellin and Seed Dormancy and how they contribute to use of plant hormones (HT only).

SOME 🎯🎯🎯

Apply and analyse knowledge of Auxin as a Growth Hormone, Auxin as a Selective Weed Killer and Gibberellin and Seed Dormancy to interpret unfamiliar information about use of plant hormones (HT only).

Revision summary

Key knowledge

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Auxin as a Growth Hormone

Auxins are growth hormones that stimulate plant cells to grow and divide
In tissue culture, auxin is added to a growth medium to stimulate the growth of plant clones from a collection of plant cells
Rooting powder contains auxin and is applied to cuttings (small sections of a plant, such as the tip of a branch) to encourage root development and growth into a new plant

1. Auxin as a Growth HormoneAQA

Notes

Auxins are growth hormones that stimulate plant cells to grow and divide
In tissue culture, auxin is added to a growth medium to stimulate the growth of plant clones from a collection of plant cells
Rooting powder contains auxin and is applied to cuttings (small sections of a plant, such as the tip of a branch) to encourage root development and growth into a new plant

Auxin as a Selective Weed Killer

At high concentrations, auxin completely disrupts a plant's growth patterns, causing it to die
Most weeds are broad-leaved plants, whilst commercial crops such as cereals are narrow-leaved, allowing selective weed killers to target only the weeds
Selective weed killers containing auxin can be sprayed across a field, killing only the broad-leaved weeds without harming the narrow-leaved crops

2. Auxin as a Selective Weed KillerAQA

Notes

At high concentrations, auxin completely disrupts a plant's growth patterns, causing it to die
Most weeds are broad-leaved plants, whilst commercial crops such as cereals are narrow-leaved, allowing selective weed killers to target only the weeds
Selective weed killers containing auxin can be sprayed across a field, killing only the broad-leaved weeds without harming the narrow-leaved crops

Gibberellin and Seed Dormancy

Dormancy is the period before a seed germinates, during which it waits for the right conditions of warmth, oxygen, and water
Exposing seeds to gibberellin can induce germination at times of year when it would not naturally occur, allowing farmers to grow multiple crops per year
Gibberellin also ensures that all plants begin growing at the same time, making harvesting more efficient

3. Gibberellin and Seed DormancyAQA

Notes

Dormancy is the period before a seed germinates, during which it waits for the right conditions of warmth, oxygen, and water
Exposing seeds to gibberellin can induce germination at times of year when it would not naturally occur, allowing farmers to grow multiple crops per year
Gibberellin also ensures that all plants begin growing at the same time, making harvesting more efficient

Gibberellin for Flowering and Fruit Growth

Gibberellin can induce flowering on demand, even when the natural environmental conditions required for flowering are not present
Applying gibberellin can encourage plants to produce more flowers or larger flowers than they would naturally
Seedless varieties of fruit naturally grow smaller than seeded relatives, but treating them with gibberellin promotes larger fruit growth

4. Gibberellin for Flowering and Fruit GrowthAQA

Notes

Gibberellin can induce flowering on demand, even when the natural environmental conditions required for flowering are not present
Applying gibberellin can encourage plants to produce more flowers or larger flowers than they would naturally
Seedless varieties of fruit naturally grow smaller than seeded relatives, but treating them with gibberellin promotes larger fruit growth

Ethene and the Ripening of Fruit

Ethene is a plant hormone that stimulates the ripening of fruit by activating an enzyme responsible for the ripening process at the cellular level
Fruit is often picked before it is ripe so there is sufficient time to transport it across the world without it spoiling
Once fruit reaches its destination, it is exposed to ethene so that it ripens quickly and is ready for sale
During transportation, the natural production of ethene by plants is often blocked to prevent premature ripening

5. Ethene and the Ripening of FruitAQA

Notes

Ethene is a plant hormone that stimulates the ripening of fruit by activating an enzyme responsible for the ripening process at the cellular level
Fruit is often picked before it is ripe so there is sufficient time to transport it across the world without it spoiling
Once fruit reaches its destination, it is exposed to ethene so that it ripens quickly and is ready for sale
During transportation, the natural production of ethene by plants is often blocked to prevent premature ripening

Summary of Commercial Uses

Auxin is used in tissue culture, rooting powders, and selective weed killers
Gibberellin is used to control dormancy, induce flowering, and increase fruit size
Ethene is used to control the timing of fruit ripening during storage and after transportation