igcse biology - chemical coordination in plants

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MAKING SENSE OF TROPISMS IGCSE Biology 3.3 Chemical Coordination in Plants Copyright © 2014 Henry Exham Brought to you by MrExham.com

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This PowerPoint answers the following questions: Do you understand that plants respond to stimuli? Can you give an example of positive phototropism? How do plant roots and stems respond to gravity? It covers section 3.3 of the IGCSE Edexcel Biology Course.

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Page 1: IGCSE Biology - Chemical Coordination in Plants

MAKING SENSE OF TROPISMS

IGCSE Biology3.3 Chemical Coordination in

Plants

Copyright © 2014 Henry Exham

Brought to you by MrExham.com

Page 2: IGCSE Biology - Chemical Coordination in Plants

Terms and Conditions

This PowerPoint is protected under copyright.It is designed for educational use. Either personal study or to be presented to a class. It may be edited or duplicated for these purposes only.It must not be shared or distributed online in any format.Some images used are under a separate creative commons license, these are clearly marked.

Copyright © 2014 Henry Exham

Brought to you by MrExham.com

Page 3: IGCSE Biology - Chemical Coordination in Plants

Learning Objectives • Do you understand that plants respond

to stimuli?• Can you give an example of positive

phototropism?• How do plant roots and stems respond to

gravity?

Copyright © 2014 Henry Exham

Page 4: IGCSE Biology - Chemical Coordination in Plants

Plants respond to their environment

• Its not any animals that can respond to their environments.

Click on the images to watch the video about each plant

Venus Fly TrapMimosa Pudica

Copyright © 2014 Henry Exham

Page 5: IGCSE Biology - Chemical Coordination in Plants

Tropisms• These examples are very quick responses

which are not typical in plants.• A typical response in a plant is a change in

growth. • For example a plant may detect a certain

stimuli like light, and start growing towards it.

Copyright © 2014 Henry Exham

Page 6: IGCSE Biology - Chemical Coordination in Plants

Tropisms• A growth response of a plant to directional

stimuli is called a tropism. This is much slower as it involves cell division to see the results.

• If it grows towards the stimuli it is a positive tropism. If it grows away it is a negative tropism.

Copyright © 2014 Henry Exham

Page 7: IGCSE Biology - Chemical Coordination in Plants

Phototropism• Tropisms are given different

names dependent on the stimuli.

• A tropism where the stimuli is light is called phototropism.

• The shoot of a plant grows towards the light to maximise photosynthesis.

• This is called positive phototropism.

Copyright © 2014 Henry Exham

Cress seeds grown on a window sill

Page 8: IGCSE Biology - Chemical Coordination in Plants

PhototropismCopyright © 2014 Henry Exham

Page 9: IGCSE Biology - Chemical Coordination in Plants

Geotropism• If there is no light under the soil, how does a

germinating seed know which way to grow?

Copyright © 2014 Henry Exham

Page 10: IGCSE Biology - Chemical Coordination in Plants

Geotropism• If there is no light under the soil, how does a

germinating seed know which way to grow?

• Because the shoot is also negatively geotropic. • So will detect gravity and grow in the opposite

direction.

• The roots are positively geotropic. So will grow down to find mineral ions and water.

Copyright © 2014 Henry Exham

Page 11: IGCSE Biology - Chemical Coordination in Plants

Hydrotropism• The roots of some species show positive

hydrotropism.

Copyright © 2014 Henry Exham

Page 12: IGCSE Biology - Chemical Coordination in Plants

What causes these responses?

• The plant produces many different plant hormones (plant growth substances).

• The most important one of these is called auxin.

• It’s produced at the tip of the shoot and diffuses downwards.

• It causes cell elongation and division.

Copyright © 2014 Henry Exham

Page 13: IGCSE Biology - Chemical Coordination in Plants

What causes phototropism?• Auxin is produced at the tip of the shoot and

causes it to grow.

Copyright © 2014 Henry Exham

Page 14: IGCSE Biology - Chemical Coordination in Plants

What causes phototropism?• When light comes from one direction, the

auxins get transported to the shaded side.

Copyright © 2014 Henry Exham

Page 15: IGCSE Biology - Chemical Coordination in Plants

What causes phototropism?• The shaded side elongates faster than the

illuminated side and the shoot bends towards the light

Copyright © 2014 Henry Exham

Page 16: IGCSE Biology - Chemical Coordination in Plants

Terms and Conditions

This PowerPoint is protected under copyright.It is designed for educational use. Either personal study or to be presented to a class. It may be edited or duplicated for these purposes only.It must not be shared or distributed online in any format.Some images used are under a separate creative commons license, these are clearly marked.

Copyright © 2014 Henry Exham

Brought to you by MrExham.com