Question

Growth of pollen tube towards embryo sac is?
A. Chemotropic
B. Thigmotaxis
C. Geotropic
D. None of these

Answer 1

The fertilization in plants occurs within the embryo sac present within the ovary of the pistil. It occurs when the pollen reaches the ovary from the stigma. It is done by the growth of the pollen tube which moves towards the embryo sac due to its affinity towards various chemicals such as calcium and or auxin.

Complete answer:
Fertilization is the process of fusion of male and female gametes in both plants and animals. In the case of plants, the male gamete is present within the pollen of the anther and the female gamete is present within the ovary of the pistil. Unlike animals, plants do not possess ancillary appendages to deposit gametes and require the help of various chemical and natural processes. One such process would be chemotropism. Chemotaxis is the phenomenon where one biotic entity is attracted to a particular direction based on the chemical gradient. This phenomenon is seen in the case of microorganisms. In the case of plants, it is known as chemotropism. The major difference between chemotaxis and chemotropism is that chemotaxis is concerned with the movement, whereas chemotropism is concerned with growth. Once the pollen lands on the stigma of the plant, a pollen tube grows towards the ovary of the plant. This growth is guided by the presence of chemicals released by the ovary of the plant such as hormones and mainly calcium. Calcium is crucial to induce the growth of the pollen tube.
Thus, the correct answer is option A.

Note: Thigmotaxis is the movement towards or away from touch, and thigmotropism is the growth towards or away from touch. The touch me not plant is an example of thigmotaxis, and climbers are examples of thigmotropism. Geotropic or geotropism is the growth of plant parts according to the gravitational force of the earth. A common example would be the downwards growth of plant roots irrespective of plant orientation.