Q. 244.5( 4 Votes )
What is meant by the following: (a) Feedback mechanism (b) Geotropism (c) Thigmotropism?
(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.
Rate this question :
How does phototropism occur in plants?NCERT - Science Exemplar
When the leaves of a sensitive plant are touched with a finger, they fold up and when light fades at dusk, the petals of a dandelion flower close.
(a) State one way in which the above two processes are similar.
(b) State two ways in which the above two processes differ.Lakhmir Singh & Manjit Kaur- Biology
Which of the following is not associated with growth of plant?NCERT - Science Exemplar
The chemical substance P is made and secreted by the meristematic tissue at the tip of stem (or shoot) of a plant. The chemical substance P is responsible for a phenomenon Q in plants in which the stem bends towards a source of light. The same chemical substance P has an opposite effect on the root of a plant. It causes the root of a plant to bend away from the source of light in a process called R.
(a) What is the chemical substance P?
(b) State whether P prefers to remains in the sunlight side of a stem or in shade.
(c) What is the effect of substance P on the rate of growth of (i) a root, and (ii) a stem?
(d) What is the name of process (i) Q, and (ii) R?
(e) What is the general name of chemical substances like P? Name another substance which belongs to this class of chemical substances.Lakhmir Singh & Manjit Kaur- Biology
The main function of abscissic acid in plants is toNCERT - Science Exemplar
The bending of the root of a plant away from a source of light is caused by a plant hormone called:Lakhmir Singh & Manjit Kaur- Biology
Which of the following are not tropisms?
(i) growing of pollen tube in response to a sugary substance
(ii) folding up of leaves of sensitive plant in response to touch
(iii) winding of tendril around a support in response to touch
(iv) opening up of the leaves of a daisy flower in response to lightLakhmir Singh & Manjit Kaur- Biology
The movement of sunflower in accordance with the path of sun is due toNCERT - Science Exemplar
The growth of pollen tubes towards ovules is due toNCERT - Science Exemplar
Most of the plant hormones promote plant growth. A plant hormone which inhibits growth is:Lakhmir Singh & Manjit Kaur- Biology