Tropic responses

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KS4 Biology

Tropic Responses

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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?

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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

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Multiple-choice quiz