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Updated Mar 22, 2026

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3 pages

Plant Hormones and Their Functions

Seren White

@serenwhite_muwd

Plant hormones are chemical messengers that control how plants grow... Show more

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Plant homones

Auxins are made in the tip of the plant and the
Side of the root dosest to the ground.

roots have a positive tropism co grav

How Auxins Control Plant Movement

Ever wondered why plants always seem to grow towards windows? Auxins are the clever chemicals behind this behaviour. These hormones are produced in plant tips and control growth by making cells elongate rather than multiply.

When light hits a plant evenly from all sides, auxins spread equally throughout the stem, causing straight upward growth. But here's where it gets interesting - when light comes from just one direction, auxins move to the shaded side of the plant.

This uneven distribution makes only the shaded cells elongate, causing the plant to bend towards the light source. It's basically the plant's way of maximising photosynthesis by chasing the best light available.

Quick Tip: Remember that roots show positive gravitropism (grow towards gravity) whilst shoots show negative gravitropism (grow away from gravity).

Gravitropism and Root Growth

Roots are brilliant at finding their way down, even in complete darkness. Gravitropism explains how auxins help roots navigate towards water and nutrients underground.

When gravity affects a root, auxins accumulate on the bottom side where gravitational pull is strongest. Unlike in shoots, auxins actually inhibit growth in roots. This means the bottom cells stop growing whilst the top cells continue, forcing the root to curve downward.

Without gravity (like in space), roots would grow horizontally because auxins can't tell which way is down. Phototropism experiments show that removing the tip of a plant stops this bending response entirely, proving that's where the auxins are made.

Remember: Auxins promote growth in shoots but inhibit growth in roots - they work opposite ways in different parts of the plant!

Commercial Uses of Plant Hormones

Plant hormones aren't just fascinating science - they're big business in agriculture and horticulture. Gibberellins are particularly useful because they control seed germination, shoot elongation, and flowering timing.

Ethene gas is the reason bananas ripen faster when you put them in a bag together. This hydrocarbon hormone speeds up fruit ripening, which is why citrus fruits that stay green when ripe can be treated to turn the familiar orange colour we expect.

Gardeners and farmers use synthetic auxins in rooting powder to help plant cuttings develop strong root systems quickly. The natural version, Indoleacetic acid (IAA), can be cheaply manufactured to break seed dormancy and force buds to flower on command.

Commercial Advantage: Understanding these hormones means farmers can control when crops germinate, flower, and ripen - making food production more predictable and profitable.

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Updated Mar 22, 2026

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3 pages

Plant Hormones and Their Functions

Seren White

@serenwhite_muwd

Plant hormones are chemical messengers that control how plants grow and respond to their environment. Understanding how auxins, gibberellins, and ethene work helps explain why plants bend towards light, grow roots downward, and how farmers can manipulate these processes for... Show more

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How Auxins Control Plant Movement

Quick Tip: Remember that roots show positive gravitropism (grow towards gravity) whilst shoots show negative gravitropism (grow away from gravity).

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Gravitropism and Root Growth

Roots are brilliant at finding their way down, even in complete darkness. Gravitropism explains how auxins help roots navigate towards water and nutrients underground.

Remember: Auxins promote growth in shoots but inhibit growth in roots - they work opposite ways in different parts of the plant!

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Commercial Uses of Plant Hormones

Commercial Advantage: Understanding these hormones means farmers can control when crops germinate, flower, and ripen - making food production more predictable and profitable.