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Roots grow through the soil towards moisture.

Unit 1 - Auxin and Plant Growth

In this GCSE Biology quiz you will explore how auxin controls plant growth, helping shoots bend towards light and roots respond to gravity and water.

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Fascinating Fact:

In shoots, auxin promotes cell elongation, so higher auxin concentrations usually cause the shoot to grow faster on that side.

In GCSE Biology, you learn how the plant hormone auxin controls growth in shoots and roots. Auxin helps plants respond to light and gravity, guiding shoots towards light for photosynthesis and roots deeper into the soil for water and minerals.

Key Terms

Auxin: A plant hormone that controls growth, especially by affecting how quickly cells elongate in shoots and roots.
Phototropism: The growth response of a plant towards or away from light, usually causing shoots to bend towards a light source.
Gravitropism: The growth response of a plant to gravity, with roots growing downwards and shoots growing upwards.

Frequently Asked Questions (Click to see answers)

What is auxin in GCSE Biology?

Auxin is a plant hormone studied in GCSE Biology that controls the rate of growth in shoots and roots, mainly by changing how quickly plant cells elongate.

How does auxin make a shoot bend towards light?

Auxin builds up on the shaded side of a shoot, causing cells there to elongate more. This side grows faster, so the shoot bends towards the light source.

What is the difference between phototropism and gravitropism?

Phototropism is a plant’s growth response to light, while gravitropism is its growth response to gravity, helping shoots grow up and roots grow down.

Try These Related Quizzes

To see a larger image, click on the picture.

1 .

This picture shows the growth of a seed. Growth is controlled by auxin. What is auxin?

Auxin is a type of plant chemical

Auxin is a type of plant hormone

Auxin is a type of plant regulator

Auxin is a type of plant pesticide

Hormones carry messages to cells

2 .

In the following picture, where would the auxin be found?

Photograph courtesy of Wikimedia Commons

You might think that auxin is a single hormone, it isn't it is a whole family of plant hormones

3 .

Plants grow towards the light. What is this known as?

Geotropism

Phototropism

Hydrotropism

Photosynthesis

This means that even if a seed is planted upside-down, the plant will grow the right way up

4 .

In experiments on auxins, scientists cut the tip as shown in the following picture. The distribution of auxin is...

Photograph courtesy of Wikimedia Commons

unequal

equal

unchanged

normal

Auxins are growth hormones and so are mainly found in the areas of a plant that is actively growing

5 .

This picture shows a growing plant where the growing regions have been stained with a special glow in the dark substance called luciferin. What is the first factor that affects roots' growth?

Photograph courtesy of Wikimedia Commons

Light

Food

Water

Gravity

The root is the first part of the plant that grows out from a seed

6 .

This is a picture of a healthy plant. What is the plant shoot growing towards?

The sky

Dark

Water

Light

Plant shoots grow towards the light which is usually upwards!

7 .

What are the plants in this picture demonstrating?

Photograph courtesy of Lequerik at Wikimedia Commons

Negative phototropism

Positive phototropism

Positive geotropism

Positive chemotaxis

If the main source of light was moved to the side, the plant leaves (and stems in most cases) would gradually turn towards the new location of the light

8 .

The trees in this image grow upwards due to an effect of gravity. What is this known as?

Photograph courtesy of Rbastien~commonswiki at Wikimedia Commons

Phototropism

Geotropism

Photosensitivity

Gravity

A very interesting image showing the entire tree trunk bending and growing upwards under the influence of auxins present on the right side of these tree trunks

9 .

This is a citrus plant cutting which will eventually grow into a lemon tree. What can auxins be used to stimulate?

Flower production

Root development

Buds to form

Stem

Auxins can be applied to cuttings to stimulate them to produce roots. They are found in rooting powders and liquids. Using too much will actually harm the cutting and prevent root formation

10 .

Cereal crops like this one can be protected from overgrowth of unwanted plants. Plant hormones can be used by farmers to kill what?