Transcript KS4 Plant Responses

Contents
Plant Responses
What do plants respond to?
Response to light
Response to gravity
Response to water
Using plant hormones
Summary quiz
Which way up?
How do plants always grow the right way up?
What conditions will affect how a plant grows?
What do plants respond to?
Plants are very sensitive and their growth is affected by
their environmental conditions.
water
light
gravity
A condition that affects plant growth is called a stimulus.
What are the three types of stimuli that plants respond to?
What is a tropism?
Plants respond to stimuli by growing to or away from them.
A growth movement in response to a stimulus is a tropism.
water
light
gravity
Movement towards a stimulus is called a positive tropism.
What is a movement away from a stimulus called?
A negative tropism.
Different types of tropism
Plant responses to light, water and gravity are given
special names.
water
hydrotropism
light
phototropism
gravity
geotropism
Can you work out what the name of each tropism means?
Which parts of a plant respond to these different stimuli?
What do different tropisms mean?
Contents
Plant Responses
What do plants respond to?
Response to light
Response to gravity
Response to water
Using plant hormones
Summary quiz
How do plants respond to light?
A plant’s response to light is called phototropism.
Is phototropism a positive or negative tropism?
light
Plants grow towards light, which is a positive tropism.
Why do plants grow towards light?
Plants need light for photosynthesis, so they respond
to light by growing towards it.
Phototropism and auxins
Which part of a plant is involved in phototropism?
A growing shoot on a plant responds to light.
light
Auxins are made in the
tip of a growing shoot
and move down the stem.
These plant hormones
speed up growth in
a growing shoot.
Phototropism and auxins – light from above
When a shoot gets light from above, the auxins produced
at the tip are spread out evenly in the shoot.
How will this affect the growth of the shoot?
light
Phototropism and auxins – light from above
Why does a shoot grow straight up when light is from above?
There is an equal amount of auxins in all parts of the shoot,
which grow at the same rate, so the shoot grows straight up.
light
light
Phototropism and auxins – light from one side
When a shoot gets light from one side, the auxins are
not evenly spread out in the shoot.
How will this affect the growth of the shoot?
light
Phototropism and auxins – light from one side
Why does the shoot bend towards the light when it gets
light from one side?
There are more auxins on the shaded side of the shoot,
so the shaded side grows faster making the bright side
bend towards the light.
light
light
Phototropism experiment
Contents
Plant Responses
What do plants respond to?
Response to light
Response to gravity
Response to water
Using plant hormones
Summary quiz
How do plants respond to gravity?
A plant’s response to gravity is called a geotropism.
Different parts of a plant have different responses to gravity.
shoots grow up
negative geotropism
gravity
roots grow down
positive geotropism
Are these responses positive or negative geotropisms?
Why is important that roots grow down into the soil?
Geotropism and auxins
Auxins speed up growth in shoots and slow growth in roots.
If a plant is laid on its side, the auxins produced collect
in the lower side of the root and stem.
How will the auxins affect the growth of the root and stem?
Geotropism and auxins
If a plant is laid on its side, why does the root grow down
and the stem grow up?
Auxins slow down growth on the lower side of the root,
so the root curves down.
Auxins speed up growth on the lower side of the stem,
so the stem curves up.
Contents
Plant Responses
What do plants respond to?
Response to light
Response to gravity
Response to water
Using plant hormones
Summary quiz
How do plants respond to water?
A plant’s response to water is called hydrotropism.
Roots always grow towards water, a positive tropism.
dry soil
wet soil
Roots will grow sideways or even upwards, towards water.
Do roots have a stronger response to water or gravity?
Roots always have a stronger response to water than
gravity to ensure that a plant gets the water it needs.
Hydrotropism and auxins – water all around
When roots are well watered from all sides,
the auxins produced in the roots are spread out evenly.
How will this affect the growth of the roots?
wet
soil
wet
soil
Hydrotropism and auxins – water all around
Why do roots grow out in all directions when they are well
watered from all sides?
There is an equal amount of auxins in all parts of the roots,
which grow at the same rate, so the roots grow out in all
directions.
wet
soil
wet
soil
wet
soil
wet
soil
Hydrotropism and auxins – more water one side
When roots are in soil with more water on one side,
the auxins are not spread out evenly in the roots.
How will this affect the growth of the roots?
dry
soil
wet
soil
Hydrotropism and auxins – more water one side
Why do roots grow towards the wet side when they are
in soil with more water on one side?
There are more auxins on the wetter side of the roots,
which grows slower than the dryer side, so the roots bend
towards the water.
dry
soil
wet
soil
dry
soil
wet
soil
Contents
Plant Responses
What do plants respond to?
Response to light
Response to gravity
Response to water
Using plant hormones
Summary quiz
What are plant hormones used for?
Plant hormones can be used in gardening and
agriculture to control how plants grow and develop.
Plant hormones are naturally-occurring chemicals
but can also be produced synthetically for the following
commercial uses:
growing cuttings
killing weeds
ripening fruit
Using plant hormones – growing cuttings
A cutting is a part of plant that
is removed from the main shoot.
What does a cutting no longer have,
when it is removed from a plant?
A cutting does not have roots and
so has no supply of water or minerals.
Rooting powder contains plant growth
hormones. Dip a cutting into rooting
powder and the plant hormones
stimulate the cutting to grow new roots.
Why does the gardening business use
cuttings and rooting powder to grow
new plants?
Grow your own plant cutting
Using plant hormones – killing weeds
A surprising use of plant
hormones is for killing
weeds.
Why are weeds a problem
in farming and gardening?
Weeds are unwelcome plants that compete with the plants
being grown by gardeners and farmers.
Many chemicals that are potential weedkillers are toxic
to animals and humans as well as plants.
Why might a weedkiller with plant hormones that only
affects plants be a more favourable option?
Using plant hormones – killing weeds
Cereal crops like wheat are
grasses with narrow leaves.
Most weeds that grow in
fields and gardens have
broad leaves.
Selective weedkillers contain plant hormones at
concentrations that will only affect plants with broad leaves.
What effect will this type of weedkiller have on a field of
wheat overgrown with weeds?
These selective weedkillers upset the normal growth of
broad-leaved plants and so kill off any weeds.
The growth of cereal crops and grasses is not affected.
Using plant hormones – ripening fruit
Fruit is usually ripe and
ready to eat when it is
bought from a greengrocers
or supermarket.
Fruit farmers are able to
control when fruit ripens
using plant hormones.
Why is this important for their business?
Fruit has often travelled many miles before being bought
from the shops.
Is it better for fruit to be ripe or unripe during a long journey?
Using plant hormones – ripening fruit
Fruit that is picked before
it is ripe is usually hard.
There is less chance of
unripe fruit being damaged
when transported, which
is important to the farmer
and the buyer.
Plant hormones can be sprayed onto unripe fruit
during transportation. These hormones ripen fruit in
time for its arrival in the shops.
Why is it a good idea to wash fruit before you eat it?
Contents
Plant Responses
Plant hormones
Response to light
Response to gravity
Response to water
Using plant hormones
Summary quiz
Multiple-choice quiz