Plant and animal responses: (f) the commercial use of plant hormones

The idea

Plant hormones are used commercially to control plant growth in agriculture and horticulture. Gibberellins can be applied to promote stem elongation and to break seed dormancy, for example in malting barley to increase germination and in grapes to increase berry size. Auxins are used as selective weedkillers because broad-leaved plants are affected more than narrow-leaved cereals, and as rooting powders to encourage cuttings to form roots. Ethene is used to ripen fruit such as bananas and tomatoes during transport and storage. Cytokinins can be used to delay leaf senescence, keeping cut foliage and produce fresh for longer. In each case you should link the hormone to the specific commercial outcome and the reason it is useful, such as improving yield, uniformity or shelf life.

What earns the marks

• Gibberellins are used to promote stem elongation and to break seed dormancy, for example in malting barley or to increase grape size.
• Auxins are used as selective weedkillers, affecting broad-leaved plants more than narrow-leaved cereals, and as rooting powders for cuttings.
• Ethene is used commercially to ripen fruit such as bananas and tomatoes during transport and storage.
• Cytokinins can be used to delay leaf senescence, extending the shelf life of cut foliage and produce.
• Each application is linked to a commercial benefit such as increased yield, uniformity of ripening or longer shelf life.

Common mistakes and how to put them right

• Confusing which hormone does which job.

  Put it right: Learn a clear pairing, for example ethene for fruit ripening and gibberellin for stem elongation and breaking dormancy.

• Assuming auxin weedkillers kill all plants equally.

  Put it right: They are selective, affecting broad-leaved plants more than narrow-leaved cereals.

• Giving an application without a commercial reason.

  Put it right: State the economic benefit, such as improved yield, uniform ripening or extended shelf life.

• Treating rooting powder as a gibberellin effect.

  Put it right: Rooting powders contain auxins, which promote root formation in cuttings.

Exam tips

• Learn each hormone with one concrete commercial example so you can match them quickly in a multiple-choice question.
• Read the question carefully to check whether it asks for the hormone, the application or the commercial benefit, since these are different.
• Eliminate options that pair a hormone with the wrong application before choosing your answer.