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Tropisms
Tropisms is a term used for a plants responses to the enviroment it is in. The three main changes in enviroment that effect tropisms in a plant are moisture, light and gravity.
Tropisms, the responses to enviroment changes are controlled by hormones in the plant called Auxins.
Auxins control the palnts growth, making it grow faster in some areas than in others, to move towards or away from the stimulus.
Negative tropism - Away rom the stimulus
Positive tropism - Towards the stimulus
Tropism examples
Negative geotropism - A plants shoot grows upwards, away from gravity
Positive phototropism - A plants leaves and shoots grow towards the light.
Positive hydrotropism - Plants roots grow towards a source of water.
Explanation of positive phototropism
Auxins in the leaves and shoots are destroyed when that part of the plant is in the light. The auxins in the part of the plant that are in the shade cause that part of the plant to grow quicker. This causes the leave to turn towards the light to maximise photosynthesis.
Explanation of Etiolation
When a plant is left in the dark, it puts it's energy into growing to reach the light. Little chlorophyll is made, therefore the plant becomes very pale, and straggly. The term for this is etiolated. when the plant eventually reaches the light it will turn green by making chlorophyll for photostnthesis.
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