1. STIMULI AND RESPONSE IN PLANTS

2. . Two types of responses: tropism and nastic movement Tropism - Growth response in a particular direction - Occurs slowly, not noticeable

3. TROPISM Tropism is the response by plant to stimuli. 2 types of tropism: a. positive tropism -response by plants towards the stimuli b. negative tropism -response by plants away from the stimulus. Plants responds to light, gravity, and water also stimulus of touch.

4. Type of tropism The tropic movement are important to plants because these movements help the plants to get necessities like light, water and minerals. This enable plants to grow healthy. Type of tropism stimulus phototropismlight geotropismgravity Hydrotropismwater Thigmotropismtouch Nastic movement ( seismonasty) touch

5. Responses of different parts of the plant Responsepart of plantDirection of growth advantage Positive phototropism Stem tipGrowth towards light To get maximum light for photosynthesis Negative phototropism Root tipGrowth away from light Less chance of drying out Positive geotropism Root tipTowards gravityMore chance of finding moisture Negative geotropism Stem tipAway from gravity More chance of finding light

6. Phototropism-light -Response of plant towards light - Shoot grow towards light (positive phototropism) while root grow away light (negative phototropism) Advantage: Enables plants to obtain sunlight for photosynthesis

7. Geotropism-gravity -Response of plant towards gravity - Roots grow downwards (positive geotropism) and shoot grow upwards (negative geotropism) -Advantage: Support the plants and enables them to obtain water and minerals

8. Hydrotropism-water Response of plant towards water - Root grow towards water (positive hydrotropism) and shoot grow away from water (negative hydrotropism) -Advantage: Enables plants to obtain water

9. Thigmotropism-touch or contact - Plant response towards touch or contact -Root grow away from solid objects such as stone -- Stem or tendrils grow towards the objects that come into contact such as cucumber and bitter gourd. -Advantage: Support the plants

10. Nastic Movements - Response part of plant towards touch, light and heat - Does not depend on the direction of the stimulus - Movement is reversible - Example: Mimosa pudica, Venus fly trap - Advantage : Acts as defence

11. Importance of plant responses - To ensure plant get their basic need. - Plant depend on phototropism to get sunlight for photosynthesis. - Geotropism and hydrotropism enables the plant to obtain water and minerals salt

12. That’all Thank you. See you in the next chapter 5