Download Coordination and Response in Flowering Plants

What are hormones?
What do they do?
What function do hormones have in plants?
What are hormones?
What do they do?
Auxin controls plant growth. Auxin promotes growth in
the shoot and inhibits growth in the root
Coordination and Response in
Flowering Plants
In order to be successful in this lesson you must be able to:
Learning Objective:
explain that auxin distribution causes unequal
growth in roots and shoots.
Coordination and Response in Flowering Plants
State that
plants respond
to light , gravity
and moisture
Describe
negative and
positive
tropisms in
plants
PROGRESS
Explain that auxin
stimulates cell
elongation in
shoots and
inhibits cell
elongation in roots
Plants respond to their environment by altering
their growth. This is called tropism.
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3 main tropisms:
Phototropism (Light)
Geotropism (Gravity)
Hydrotropism
(all of which are controlled by auxin)
Tropisms can be described as positive and
negative:
positive tropism – the plant grows towards the
stimulus
negative tropism – the plant grows away from
the stimulus.
Does the shoot
grow towards
or away from
the light?
Plant sensitivity: Glossary
Key Word
Sensitivity
Meaning
Stimulus
hydrotropism
phototropism
geotropism
Negative
tropism
Positive tropism
Use p 155 and 156 in
iGCSE Biology to help
Phototropism
Shoots grow towards light = positive
phototropism
How?
The hormone auxin
moves away from
the light and
stimulates the cells
to elongate on the
‘dark side’
Geotropism
Roots grow in the direction of the force of
gravity = positive geotropism
auxin reduces cell
elongation in the
root, so the root
curves downwards
Geotropism
Roots grow in the direction of the force of
gravity = positive geotropism
Shoots grow against the force of gravity =
negative geotropism
auxin reduces cell
elongation in the
root, so the root
curves downwards
auxin stimulates cell
elongation in the
shoot, so the shoot
curves upwards
Summary of the different types of tropism
Part of plant
shoot
root
Light stimulus
Gravity stimulus
positive phototropism negative gravitropism
(grows towards the (grows against the
light)
force of gravity)
positive gravitropism
negative
(grows in the
phototropism (grows
direction of the force
away from the light)
of gravity)
Uses of plant hormones
Rooting powder contains growth
hormones that make stem cuttings
develop roots quickly.
Selective weedkillers kill some
plants but not others. This can
be useful for getting rid of
dandelions in a lawn without
killing the grass
Plant hormones
are useful for
delaying ripening
during transport
or when fruit is
displayed in shops
Coordination and Response in Flowering Plants
State that
plants respond
to light , gravity
and water.
Describe
negative and
positive
tropisms in
plants
PROGRESS
Explain that auxin
stimulates cell
elongation in
shoots and
inhibits cell
elongation in roots