Plant growth hormones are used in agriculture and horticulture.

The idea

Agriculture and horticulture both rely on plant growth hormones to manage crops and ornamental plants. In agriculture, auxin-based selective weed killers reduce competition from broad-leaved weeds in cereal fields, improving yield. In horticulture, rooting powders containing auxins help cuttings such as pelargonium or rosemary develop roots quickly and uniformly, producing many identical plants. Tissue culture uses auxins and other hormones to multiply rare or valuable plants from small pieces of tissue under sterile conditions. Growers may also use hormones to control fruit ripening, delay leaf fall or regulate growth so plants are a convenient size for transport and sale. These uses show how understanding hormone action allows people to manipulate plant growth deliberately.

What earns the marks

• States that plant growth hormones are used commercially in agriculture and horticulture to control plant growth.
• Gives an agricultural example, such as auxin selective weed killers reducing competition from broad-leaved weeds in cereal crops.
• Gives a horticultural example, such as auxin rooting powder encouraging cuttings to form roots.
• Explains that tissue culture uses plant hormones to produce many genetically identical plants from small explants.
• Links each use to the underlying hormone effect, such as cell elongation, root initiation or controlled development.

Common mistakes and how to put them right

• Describing agriculture and horticulture as identical.

  Put it right: Agriculture mainly involves crop production while horticulture involves garden and ornamental plant production, though both use plant hormones.

• Naming a use without naming the hormone or its effect.

  Put it right: State the hormone involved and the growth response it produces.

• Assuming all plant hormone uses increase growth.

  Put it right: Some uses, such as weed killers, disrupt or inhibit normal growth.

Exam tips

• Give one clear agricultural use and one clear horticultural use, each with the hormone and its effect, to cover the statement fully.
• Use precise terms such as selective weed killer, rooting powder and tissue culture rather than vague phrases like chemicals for plants.
• If asked to compare uses, comment on whether the hormone promotes or disrupts growth and which plants are affected.