Hormones & Their Effects

Age Range 14-16Age Range 16-19

Page 9 of 10

  • Hormones and their Effects
  • Where are the Endocrine Glands?
  • Sex Hormones - Puberty
  • Sex Hormones - The Menstrual Cycle
  • Sex Hormones - Pregnancy
  • Insulin
  • More Hormones - Growth Hormones
  • More Hormones - Adrenaline & ADH
  • Plant Hormones
  • Quiz - Hormones

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Plant Hormones

A plant stem bends as it grows toward the light
Plant growing
towards the light

There are several different plant hormones. Those controlling the growth of roots and shoots are called auxins which stimulate cell growth.

Shoots grow upwards and roots downwards
Shoots grow upwards and roots downwards

Auxins can diffuse from cell to cell in solution or travel greater distances in the plant in the vascular bundles.

If a plant has light falling on it from one side only, it will grow towards the source of the light. This is as a result of auxin accumulating on the side of the plant away from the light, causing extra growth in this region and so causing the plant to bend towards the light.

Roots are not sensitive to light but grow downwards in response to the stimulus of gravity. Auxins are again involved, although scientists think another plant hormone might actually cause slowing of the growth of cells on one side of the root causing it to bend downwards.

Commercial Use of Plant Hormones

Plants hormones are used widely in agriculture in the following ways:

A plant cutting with initial root growth
Some time later new
roots are grown

A plant cutting with the base of its stem being dipped in rooting hormone powder
Cutting dipped in
rooting hormone powder
  • As selective weedkillers which are not harmful to the surrounding plants or to animals.
  • To produce new plants from cuttings. With the use of hormone rooting powder, cut stems can develop roots and grow into clones of the parent plant.
  • To promote the ripening of fruit or induce flowering when required.
  • To speed up or slow down the growth of plants.
  • To produce fruit without seeds. Unpollinated flowers are treated so that they grow fruit without seeds.

Question 8

Study the sentences below, then drag and drop
the missing word or phrase to complete the sentence.
Auxins can diffuse
  - upwards
Plants grow towards
  - from cell to cell in solution
Roots grow
  - clones of the parent plant
Shoots grow
  - are not harmful to animals
Auxins cause
  - a source of light
Hormone rooting powder
  - to ripen fruit
Cuttings can produce
  - causes roots to grow
Hormone weedkillers
  - downwards
Flowering can be induced
  - cell growth
Plant hormones can be used
  - by the use of plant hormones

A chemical messenger produced by a particular gland or cells of the endocrine system. Hormones are transported throughout the body in the blood stream but they produce a response only in specific target cells.
A plant hormone that regulates growth