Question

Which among the following is an example of chemotropism?
i)Formation of tendrils
ii)Fertilization of flowers by pollen
iii)Growth of plant roots
iv)Falling of leaves

A)(ii) and (iii)
B)(i) and (iv)
C)(i) and (ii)
D)None of these

Answer 1

Hint: Tropism is the response of a plant towards a stimulus that acts with greater intensity from one direction than the other one. It's achieved by active movement or by structural alteration. Varieties of tropism include phototropism (response to light), geotropism (response to gravity), chemotropism (response to particular substances), hydrotropism (response to water), thigmotropism (response to mechanical stimulation), traumatropism (response to wound lesion), and galvanotropism, or electrotropism (response to electric current). Most tropic movements are orthotropic; i.e., they're directed toward the source of the stimulus. Plagiotropic movements are oblique to the direction of stimulus. Diatropic movements are at right angles to the direction of stimulus.

Complete answer:
 Tropism is an involuntary orienting response of an organism to a stimulus. It involves growth instead of movement of an organism. In tropism, the response of the organism is usually by its growth instead of by its movement. It's going to grow either towards or faraway from the stimulus. There are many sorts of tropisms and one among them is the so-called chemotropism. The expansion or movement of a plant or natural object in response to a chemical stimulus is thought as chemotropism. Organisms like bacteria, plants and fungi, navigated by chemical stimuli from outside of the organism or organism's part. The response is positive if the growth is towards the stimulus and negative if it’s faraway from the stimulus.

One example of chemotropism is observed in plant fertilization and plant structure elongation of angiosperms, phanerogam. Unlike animals, plants cannot move, and thus need a delivery mechanism for reproduction. Pollen, which contains the male gametophyte, is transferred to a different plant via insects or wind. If the pollen is compatible it'll germinate and start to grow. The ovary releases chemicals that stimulate a positive chemotropic response from the developing pollen tube. In response the tube develops an outlined tip growth area that promotes directional growth and elongation of the pollen tube because of a calcium gradient. The steep calcium gradient is localized within the tip and promotes elongation and orientation of the expansion. This calcium gradient is important for the expansion to occur; it's been shown that inhibiting the formation of the gradient ends up in no growth. As the plant continues to grow towards the ovules, the male sperm remains within the apical region and transported to the female ovule. The pollen tube elongates at a rate reminiscent of neurite development.

Examples of positive and negative chemotropism are observed in a plant's roots; the roots grow towards useful minerals displaying positive chemotropism, and grow off from harmful acids displaying negative chemotropism.

Chemotropism is also observed during growth of the plant structure towards the ovules. This is often because of the ovary releasing chemicals that influence the event of pollen tubes. The roots growing towards useful minerals are exhibiting chemotropism, i.e. Positive. There are instances though when the roots grow far from harmful acids and this can be an example of negative chemotropism.

Hence, the correct answer is option (C)

Note: Chemotropism shouldn't be confused with chemotaxis and chemokinesis. Chemotaxis pertains to directional movement of an organism or a living motile cell in response to certain diffusible chemicals within the environment. Chemokinesis may be defined as a behavioral response of a cell or an organism to a soluble chemical that results in random movement.