plant hormones

Hormones in plants

Move from where they are made to where they are needed to produce a response

Tropisms hormones are needed for

Gravitropism and phototropism

Positive phototropism

Shoots grow towards light

How auxin causes phototropism

Auxin moves to shaded side, stimulates growth, making shoot bend toward light

Why phototropism is useful

Plant receives more light so photosynthesis can occur at a faster rate

Negative gravitropism

Shoots grow upward, away from gravity

How auxin causes shoots to bend up

Auxin moves to lower side, cells grow faster, shoot bends upward

Why shoots show negative gravitropism

There is more light higher up

Positive gravitropism

Roots grow downward, towards gravity

How auxin causes positive gravitropism in roots

Auxin moves to lower side, slows growth there, upper side grows faster, root bends downward

Why positive gravitropism is useful

Provides stability and access to water/nutrients

Role of gibberellins

Stimulate seed germination

Role of ethene

Involved in cell division and the ripening of fruits

Human use of plant hormones

To alter plant growth for agriculture

Uses of auxin

Weed killers, rooting powders, promote growth in tissue culture

How auxin weed killers work

Cause uncontrolled growth, killing broad-leaved plants

Use of ethene in industry

Speeds up fruit ripening, used in the food industry

Uses of gibberellins

Ending seed dormancy, promoting flowering, increasing fruit size