Tropism
Tropism is the directional growth movement of a plant part in response to a stimulus.
Practice This ConceptMain explanation
Teacher explanation
Tropism happens when a plant grows towards or away from a stimulus. The movement is directional, so the direction of the stimulus matters. Plant parts can show positive tropism when they grow towards the stimulus, or negative tropism when they grow away from it. This is different from fast movement in animals because it is mainly a growth response in plants.
Example
A shoot growing towards light shows positive phototropism, and roots growing downward show positive geotropism.
Simple analogy
Tropism means growth turned by a stimulus.
Common confusion
Students often call every plant movement tropism. Not every movement is tropic; tropism specifically involves directional growth.
Exam tip
In exam answers, always mention the stimulus and the direction of growth. That is the heart of tropism.
Answer writing and exam use
1-mark use
Write the exact meaning of tropism in one clean line.
2-mark use
Define tropism and add one example or condition.
3-mark use
Explain tropism, show the method or example, and mention the common mistake.
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