Plant hormones

What are plant hormones?

Chemical messengers that regulate plant growth and responses to the environment.

What is a tropism?

A directional growth response of a plant to a stimulus.

Name two types of tropisms.

• Phototropism → response to light.

• Gravitropism (geotropism) → response to gravity.

What is auxin?

A plant hormone that controls growth near the tips of shoots and roots.

How does auxin affect shoots?

Promotes cell elongation → shoots bend towards light (positive phototropism).

How does auxin affect roots?

Inhibits cell elongation → roots grow downwards (positive gravitropism).

What is the plant hormone required practical?

Investigating the effect of light or gravity on the growth of seedlings (e.g. placing cress seeds in different conditions and measuring growth direction).

What variables should be controlled in the tropism practical?

Same type of seed, amount of water, temperature, light intensity (unless it’s the independent variable).

What are gibberellins?

Plant hormones that stimulate seed germination, stem growth, and flowering.

What is ethene and what does it do?

A plant hormone that controls cell division and stimulates fruit ripening.

How is auxin used commercially?

• As a weed killer (kills broad-leaved weeds).

• In rooting powders (stimulates root growth in cuttings).

• In tissue culture (to grow cloned plants).

How are gibberellins used commercially?

• To promote seed germination in brewing industry.

• To increase fruit size.

• To promote flowering (all year round).

How is ethene used commercially?

To control fruit ripening during storage and transport.

Which plant hormone controls:

• Phototropism and gravitropism?

Auxin

Seed germination, stem growth, flowering?

Gibberellins

Fruit ripening?

Ethene