stimuli and response in plants. . two types of responses: tropism and nastic movement tropism -...
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STIMULI AND RESPONSE IN PLANTS
• . Two types of responses: tropism and nastic movement
• Tropism - Growth response in a particular direction - Occurs slowly, not noticeable
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.
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
phototropism light
geotropism gravity
Hydrotropism water
Thigmotropism touch
Nastic movement ( seismonasty)
touch
Responses of different parts of the plant
Response part of plant Direction of growth
advantage
Positive phototropism
Stem tip Growth towards light
To get maximum light for photosynthesis
Negative phototropism
Root tip Growth away from light
Less chance of drying out
Positive geotropism
Root tip Towards gravity More chance of finding moisture
Negative geotropism
Stem tip Away from gravity
More chance of finding light
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
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
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
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
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
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
That’all• Thank you. See you in the next chapter 5