Uses of Plant Hormones (AQA GCSE Biology): Revision Note

Plant hormones can be extracted or artificially made and used by gardeners and farmers in horticulture and agriculture to usefully control plant growth (e.g. to obtain larger yields)

The use of auxins, ethene and gibberellins commercially has been very beneficial is helping to produce plants for food and decoration

However, the everyday use of hormones as weed killers can have a negative effect on biodiversity

• Many different species of plants are classed as weeds commercially, but to other organisms they are a food source and potential habitat, so destroying them can have negative effects on other organisms in the ecosystem

Auxins can be used as selective weed killers; negatively affecting the growth of broad-leaved plants which are weeds in comparison to the narrow-leaved grasses and cereals grown as crops for food production (which are desired)

The growth of weeds is controlled by farmers who don’t want their yields to be smaller as a result of competition between crops and weeds for space and nutrients from the soil

• Selective weed killers disrupt the growth of weeds only, causing them to die

• However once applied to a crop their spread cannot be controlled, and they could affect other plant species negatively

If a gardener or farmer wants to easily and cheaply produce lots of clones of a desirable plant, then they can take cuttings of the plant and dip the tips in auxins which are sold as ‘rooting powders’ as they encourage the rapid development of roots

The same principle as above can be used to clone plants in the lab; auxins in this way are used to promote growth in tissue culture where scrapings of cells can be taken from a desirable plant and used to produce clones in a petri dish that are then planted and allowed to grow in soil

Ethene is used in the food industry to control ripening of fruit during storage and transport

It is far more effective to transport unripe fruit, as ripe fruit is softer and therefore more easily damaged and spoiled

The production of ethene can be inhibited to delay ripening of fruits in storage; this can either be achieved directly by adding chemicals that prevent ethene from being produced, or by reacting ethene in the air around fruit with substances that can remove it

When ripening needs to be encouraged (e.g. when fruit is in the supermarket), artificially produced ethene gas can be released to speed up the process

Gibberellin levels naturally rise after a period of dormancy (exposure to cold and dry conditions)

• Dormancy usually ends with an intake of water into the seed and warmer weather

Gibberellins can be used to:

• end seed dormancy, as a high concentration of gibberellin promotes seed germination

• promote flowering regardless of the weather conditions the plant is in

• increase fruit size – higher levels of gibberellin promote the development and growth of fruit