NCERT Solution for Class 10 Science Chapter 7
Control and Coordination
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-122
Questions No-4
How do auxins promote the growth of a tendril around a support?
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These tendrils are sensitive to touch. When they come in contact with any support, auxin (a growth hormone) diffuses from the part of the tendril in contact with the object to other side, which is not in the contact. Therefore the part of the tendril in the contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.
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When the tip of a tendril touches a support, then the auxins present in its tip move to that side of tip which is away from the support. Auxins promote growth. So, due to more auxins in it, the side of tendril away from the support grows faster (and becomes longer) than the side which is in contact with the support and makes the tendril twirl (or bend) around the support.
Auxin is a plant growth hormone. When the tip of the tendril touches a support, then the auxins present on its tip moves to the side of tip which is away from the support, so, due to more auxins in its tendrils away from the support grows faster.
at the tip of tendrils. When tendrils are attached around any support their growth is
slowed down as auxins are sensitive to touch. This make them move to the other side of
the tip to get support this makes the other side grow faster than the side of tendril in
contact with the support and the tendril bends towards the support.
Auxin increase in concentration in the part of the tendril which is away from the support. This results in increased cell division in that part. The part which is nearer to the support has lesser rate of cell division. As a result, the external part of the tendril grows more than the internal part and the tendril coils around the support.
When tendrils come in contact with any support, the tip of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. this is due to the fast that auxin secreted in the tip diffuses towards the side opposite to the point of contact. So this induces more growth on the side opposite to the point of contact. Thereby causing the tendril to circle around the object.
The growth of a tendril around a support is a process known as thigmotropism, and auxins play a crucial role in this response. Thigmotropism is a type of tropism, which refers to the growth or movement of a plant in response to touch or contact with a solid object. In the case of a tendril, which is a slender, spirally coiling structure, thigmotropism allows it to wrap around a support structure for stability and climbing.
1. Touch Perception:
» When the tendril comes into contact with a solid object, such as a support structure, it perceives the touch or mechanical stimulus.
2. Auxin Redistribution:
» Auxins, particularly indole-3-acetic acid (IAA), are the primary plant hormones involved in tropic responses. Upon sensing touch, there is a redistribution of auxins within the cells of the tendril.
3. Asymmetric Auxin Distribution:
» The contact or touch leads to an asymmetric distribution of auxins, with higher concentrations on the side of the tendril away from the support.
4. Cell Elongation and Curling:
» Higher concentrations of auxins stimulate cell elongation on the side of the tendril facing away from the support. This differential cell elongation causes the tendril to curve and wrap around the support.
5. Coiling and Growth Response:
» The asymmetric growth and elongation of cells result in the tendril coiling around the support. This coiling is a growth response driven by the differential distribution of auxins.
6. Tendril Attachment:
» As the tendril continues to grow and coil, it eventually wraps around the support structure, providing the plant with a means of attachment for climbing.
The process described above allows the plant to efficiently utilize external structures for support and climbing. Thigmotropism, facilitated by auxins, is a mechanism that enhances the plant’s ability to reach sunlight, reduce competition for resources, and optimize its position in the environment.
In summary, auxins promote tendril growth around a support by inducing differential cell elongation in response to touch, leading to the tendril coiling and attaching to the support structure.