Question

The growth of pollen tube toward the ovule is an example of
А. Phototropism
B. Hydrotropism
C. Thigmotropism
D. Chemotropism

Answer 1

Hint: Plants show certain types of movements. The movement occurs in response to external or internal stimulus. When movements are induced by external stimulus they are called as autonomic movements and when movements are induced by external stimulus they are termed as paratonic movements.

Complete Answer:
Tropism is generally defined as a biological phenomenon that indicates the growth or turning movements in the plants in response to environmental stimulus. Growth can be positive growth or negative growth. Positive growth: It means the growth of an organism in the direction of the stimulus. Negative growth: It means the growth of an organism that occurs away from the direction of the stimulus.

Now let us find out the solution from the given,
- Phototropism: It is defined as the movement of plant parts Towards the light. The shoot shows positive phototropism This shows that shoot bends towards the direction of light while root bends away from the direction of light, so are negatively phototropic.
- Hydrotropism: It is defined as the movement of plant parts Towards the water. The shoot is negatively hydrotropic that is bent away from the direction of water but roots show positive hydrotropism.
- Thigmotropism: It is defined as the movement of the plant part towards touch. Leaves of touch me not plant or Mimosa podia show folding when touched by external stimuli.
- Chemotropism: It is defined as movement of plant parts toward the response of chemical stimuli. The growth and movement of pollen tubes towards the embryo sac is the most common example of chemotropism.

Hence the correct answer is option D.

Note: Embryo sac allows the pollen to enter the ovule from the micropylar end. Due to the presence of filiform apparatus, the pollen tube passes either between the egg cells and the synergrid part that is present in it. Misogamy is the process in which pollen tubes enter in the ovule through the integuments and commonly seen in the plants such as Populous and Cucurbita.