| 1.3 |
Plant Stimulus and Response |
| Definition |
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Plants respond to touch, water, light, and gravity which are divided into two, namely the tropism response and the nastic response.
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Types of tropism and reactions:
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Type of tropism
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Example
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Phototropism
Growth of plant parts towards the light
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The growth of sunflower shoots in the direction of sunlight
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Geotropism
Growth of plant parts towards gravity
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Root growth of red chili tree according to the direction of gravity
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Hydrotropism
Growth of plant parts towards the water
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Growth of pandan tree roots in the direction of water
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Tigmotropism
The movement of plant growth against touch or when in contact with an object
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Cucumbers have suckers that twist an object that touches them
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Nastic response:
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Plants respond to touch, light, and heat
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The direction of the response does not depend on the direction of the stimulus
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For example, the leaves of a semalu tree (Mimosa pudica) are covered when touched
The importance of each response:
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Response
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Importance
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Phototropism
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Helps shoots get sunlight for photosynthesis
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Geotropism
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Helps the roots penetrate the soil to obtain water and the roots can grip the soil firmly
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Hydrotropism
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Helps plant roots absorb water and mineral salts from the soil
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Tigmotropism
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Helps plants reach the highest position to get sunlight and maintain an upright position
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Nastic movement
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Protects leaves from injury
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