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