1. How and why plants respond to the environment Explain why plants need to respond to their environment in terms of the need to avoid predation and abiotic stress. Define the term: tropism.

2. Mimosa pudica

3. Venus fly trap

4. No aluminium Aluminium Hydrangea

5. Etiolated plant grown in limited light Plant grown in normal light

6. Light to left No light Normal light

7. Osteospermum

8. Tropic Responses Tropisms are directional growth responses of plants The direction of the growth is always related to the direction of the stimulus It may be positive or negative

9. 1)Phototropism – shoots grow towards light 2)Geotropism – roots grow towards the pull of gravity 3)Chemotropism – pollen tubes grow down the style attracted by chemicals to the ovary 4)Thigmotropism – shoots of climbing plants wind around other plants or solid structures

10. Longitudinal section showing a pollen tube growing from a pollen grain towards the ovary of a flower

11. Nastic Repsonses These are not directional so the direction of the movement is not determined by the direction of the stimulus, they are temporary changes e.g. Venus fly trap, flowers that open in day and close at night, the sensitive plant Mimosa pudica whose leaves wilt to deter grazers

12. Control of Plant Responses by hormones Recall how a hormone works to produce a response Hormones move around plants by active transport, diffusion and mass flow (check back to AS plant transport)

13. Task Use p221 table 1 and additional sheets to compile a comprehensive table of the functions of different plant hormones

14. Plant growth Plant growth only occurs in meristematic regions: 1)Apical meristem at the tips of roots or shoots where they cause shoot and root growth 2)Lateral Bud Meristem In buds give rise to side shoots 3)Lateral meristems In cylinder near the outside of roots and shoots for increasing root and shoot width 4)Intercalary Meristems (some plants) Between nodes causes shoot to get longer

15. Plant Growth Meristems

16. Auxins and Plant Growth Growth occurs as cell division, followed by elongation and then differentiation Auxins cause cell elongation the more auxins the more elongation Auxins increase cell wall stretchiness by promoting active transport of H + by an ATPase enzyme into the cell wall The low pH activates wall loosening enzymes which break bonds, weakening the cellulose so water can enter.

17. Activity Examine a pre-prepared root tip and shoot tip slide to observe the growth regions