IGCSE Biology - Chemical Coordination in Plants
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This document discusses how plants respond to environmental stimuli through a process known as tropism, where growth responses are influenced by factors such as light (phototropism) and gravity (geotropism). It highlights the role of auxin, a plant hormone, in directing these growth responses, with positive tropisms occurring when plants grow towards stimuli. The material serves as an educational resource, protected under copyright and intended for personal or classroom use.
IGCSE Biology - Chemical Coordination in Plants
- 1. IGCSE Biology – 4BI0 MAKING SENSE OF Copyright©2015HenryExham Icons CC – The Pink GroupIcons CC – The Pink Group Copyright©2017HenryExham
- 2. 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 © 2015 Henry Exham Brought to you by MrExham.com TERMS AND CONDITIONS 2
- 3. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Objectives 3 • 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?
- 4. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Plants can respond to their environment 4 • 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
- 5. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Tropisms 5 • 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.
- 6. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Tropisms 6 • 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.
- 7. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Phototropism 7 • 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. Cress seeds grown on a window sill
- 8. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Phototropism 8
- 9. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Geotropism 9 • If there is no light under the soil, how does a germinating seed know which way to grow?
- 10. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Geotropism 10 • 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.
- 11. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms Hydrotropism 11 • The roots of some species show positive hydrotropism.
- 12. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms What causes these responses? 12 • 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.
- 13. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms What causes phototropism? 13 • Auxin is produced at the tip of the shoot and causes it to grow.
- 14. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms What causes phototropism? 14 • When light comes from one direction, the auxins get transported to the shaded side.
- 15. Copyright © 2015 Henry Exham 3.3 Chemical Coordination in Plants - Tropisms What causes phototropism? 15 • The shaded side elongates faster than the illuminated side and the shoot bends towards the light
- 16. 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 © 2015 Henry Exham Brought to you by MrExham.com TERMS AND CONDITIONS 16