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KS4 Biology
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© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20041 of 35
KS4 Biology
Tropic Responses
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20042 of 35
Plant Responses
Response to light
Response to gravity
Contents
What do plants respond to?
Summary quiz
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Which way up?
How do plants always grow the right way up?
What conditions will affect how a plant grows?
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What do plants respond to?
Plants are very sensitive and their growth is affected by their environmental conditions.
A condition that affects plant growth is called a stimulus.
What are the three types of stimuli that plants respond to?
light
water
gravity
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What is a tropism?
Plants respond to stimuli by growing to or away from them.
Movement towards a stimulus is called a positive tropism.
What is a movement away from a stimulus called?
A growth movement in response to a stimulus is a tropism.
light
water
gravity
A negative tropism.
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Different types of tropism
Plant responses to light, water and gravity are givenspecial names.
Can you work out what the name of each tropism means?
water
gravity
light
hydrotropism
geotropism
phototropism
Which parts of a plant respond to these different stimuli?
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What do different tropisms mean?
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Plant Responses
Response to light
Response to gravity
Summary quiz
What do plants respond to?
Contents
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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.
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Phototropism and auxins
Which part of a plant is involved in phototropism?
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.
light
A growing shoot on a plant responds to light.
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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
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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
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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
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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
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Phototropism experiment
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Plant Responses
Response to light
Response to gravity
Contents
Summary quiz
What do plants respond to?
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200417 of 35
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.
Are these responses positive or negative geotropisms?
Why is important that roots grow down into the soil?
gravity
shoots grow up
roots grow down
negative geotropism
positive geotropism
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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?
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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.
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Plant Responses
Response to light
Response to gravity
Plant hormones
Summary quiz
Contents
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200421 of 35
Multiple-choice quiz
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