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Plant Hormones
Stimulus
A change in organism’s
environment
Stimulus
Response
An organisms reaction to change.
Response
Tropisms
• Tropism = plant’s growth response toward
or away from a stimulus through the action
of auxins.
Phototropism
Plants grow toward a source of light
Explain how a plant grows
towards light. (4 marks)
1.Auxins are produced in the shady side of the tip.
2.The auxins diffuse down the shoot and
cause cells behind the tip to elongate.
3.There is greater growth on the shady
side of the young shoot.
4. The shoot grows towards the light - this
is known as PHOTOTROPISM.
Gravitropism
 A plant grows with or against gravity
A plant’s stems
or trunk grow
up, against the
pull of gravity.
A plant’s roots
grow down,
with the pull of
gravity
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Fresh fruits are shipped
around the world.
Plant hormones are used
to slow the ripening of
the fruit, so they are just
ripe as they reach the
supermarket.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
When a gardener takes cuttings
from a plant, the base of each
cutting is first dipped into a
rooting compound to stimulate
the growth of roots.
Many rooting compounds
contain auxin.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Auxins can be sprayed onto
flowers so that the fruits
develop without pollination or
fertilisation.
These fruits are seedless.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Applications of plant hormones
Can you explain the use of
hormones in each diagram.
Click to reveal the answer.
Auxins can be used as herbicides.
Weeds have broader leaves
than the grass on a lawn. The
weeds will take up more auxin
than the grass when the lawn
is sprayed.
The weeds will grow too quickly and die.
Task
• Describe three uses of auxins. (3 marks)
True or false?
Which of the following
statements is true?
Click to reveal the answer.
Young roots always grow downwards.
This is because roots are...
1. positively phototropic
2. negatively hydrotropic
3. positively geotropic
True or false?
Which of the following
statements is true?
Click to reveal the answer.
Young roots always grow downwards.
This is because roots are...
1. positively phototropic
2. negatively hydrotropic
3. positively geotropic 