Question

Growth of pollen tube towards embryo sac is termed as
A.Geotropism
B.Chemotaxis
C.Phototaxis
D.Thigmotaxis

Answer 1

Hint: Pollen tube is a tubular structure which is produced by the male gametophyte of the seed containing plants when they begin to germinate. Germination of seed and elongation of the pollen grain is an important part of the life cycle of a plant.

Complete answer:
Let us analyze the options to find out the correct option.

Option A: Geotropism is defined as the growth of plant parts in response to the force of gravity. It can be of two types: positive geotropism and negative geotropism. Upward movement of shoots is an example of negative geotropism and downward movement of roots is an example of positive geotropism. Pollen tubes do not show any response to the gravity. Therefore, this is the incorrect option.

Option B: Chemotaxis is the mechanism of growth of plant parts in response to chemical stimulus. In the case of pollen tube development, growth of pollen tube happens towards the embryo sac and this is driven by ion flux (reactive oxygen species) and calcium gradient. Therefore, this is the correct option.

Option C: Phototaxis is defined as the movement of plant parts in response to light. It happens either towards the light or away from the light. Pollen tube development occurs in the direction of embryo sac of the plant not in the response to light. Therefore, this is the incorrect option.

Option D: Thigmotaxis is defined as the motion or development of plant parts in response to touch stimulus. Development of the pollen tube does not show any response upon stimulus. Therefore, this is the incorrect option.

Hence, the correct answer is option (B)

Note: In chemotaxis a chemical gradient influences the growth in a negative or positive way. Positive growth is characterised by the growth of the part towards the stimulus while negative growth is the growth of the part away from the stimulus.