(a) Feedback mechanism- This mechanism is for the regulation of the hormone secretion as we require hormones to be secreted in précised quantities. So, what happens is whenever we require the hormone to be secreted in our body there is an activator which activates the particular gland and hormone is secreted. Whenever we don’t require there is an inhibitor which inhibits the release of hormone according to requirement of body. This process is called feedback mechanism.
For example- When blood sugar levels start rising pancreas cells start secreting insulin and as the levels are normal they do not secrete insulin.
(b) Geotropism- This refers to the directional movement that takes place in plants due to gravitational pull. As we know that stems of a plant always move toward upwards i.e. away from earth and opposite to gravitational pull and roots moves downwards inside the earth according to the gravitational pull. This upward movement of stem and downward movement of root is due to geotropism.
(c) Thigmotropism- This refers to the directional movement that takes place due to touch as some plants are mechanosensitive. For example- Tendrils are very much sensitive to touch. As they come in contact with any kind of support in that particular part growth rate is retarded while in parts away from it there is higher growth due to rapid cell division in that part.
Due to this reason, only the tendrils get circled around the object. So, this directional movement that the plant exhibit due to touch is termed as thigmotropism.
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