Question

Thigmotropism is best exhibited by
A. Tendrils
B. Stem apex
C. Root apex
D. Leaf apex

Answer 1

Hint: Thigmotropism is the directional reaction of a plant to some contact. Some plants are very sensitive to touch than humans. Tendrils of some plants climb by this phenomenon.

Complete answer: Thigmotropism is the directional reaction of a plant organ to contact or some physical contact with the strong article. Example- the climbing tendrils of some plants such as sweet pea. The tendril feels the solid object and this results in coiling.
-Some plants are more sensitive to touch than humans. A feeding tentacle of the insectivorous sundew plant responds to a thread of 0.0008mg, which is nearly ten times as sensitive as humans.
-Roots likewise rely upon contact affectability to explore their way through the soil. The general touch response in root is negative. That is, when a root feels an object, the root grows away from the object, whereas tendrils grow towards the touch stimulus and wrap around it.
-Tendrils can bend by a process known as differential growth. This process involves the stimulation of growth in particular regions of the tendrils. In positive thigmotropism, for example, the side of the tendril which is opposite to the side of contact will grow at a faster rate than the contact side. Along these lines, the non-contact side starts to stretch quicker than the remainder of the tendril, while the contact side packs. This causes the tendril to curve towards the site of contact.
So, the correct answer is option A-Tendrils.

Note: Tendril is a green thread-like structure, which helps in coiling around the support. Tendrils can be a modification of stem (in cucurbits) or leaf (in pea). The tendril feels the solid object and this results in coiling.