igcse biology - chemical coordination in plants
DESCRIPTION
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.TRANSCRIPT
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MAKING SENSE OF TROPISMS
IGCSE Biology3.3 Chemical Coordination in
Plants
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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
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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?
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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
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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.
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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.
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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
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Geotropism• If there is no light under the soil, how does a
germinating seed know which way to grow?
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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.
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Hydrotropism• The roots of some species show positive
hydrotropism.
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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.
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What causes phototropism?• Auxin is produced at the tip of the shoot and
causes it to grow.
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What causes phototropism?• When light comes from one direction, the
auxins get transported to the shaded side.
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What causes phototropism?• The shaded side elongates faster than the
illuminated side and the shoot bends towards the light
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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