Question

The growth of pollen tubes towards ovules is due to
A) Hydrotropism
B) Chemotropism
C) Geotropism
D) Phototropism

Answer 1

A pollen tube is a tubular structure produced when germinating by the male gametophyte of seed plants. In the plant life cycle, pollen tube elongation is an integral stage.

Complete answer:
Chemotropism is the growth from outside the organism or from the part of the organism of organisms such as bacteria and plants, with the help of a chemical stimulus. If the growth is towards the stimulus its negative if the development is away from the stimulus, the organism's response is called 'positive'.
During the growth of the pollen tube, where growth is always towards the ovules, an instance of chemotropic motion can be seen. Fertilization of pollen flowers is achieved because the ovary releases chemicals from the developing pollen tube that generate a positive chemotropic reaction.
Guided root growth is referred to as hydrotropism in relation to a moisture gradient and starts with the sensing of the gradient of moisture in the root cap.
In response to the force of gravity, the growth of the parts of plants. An example of negative geotropism is the upward growth of plant shoots; positive geotropism is the downward growth of roots.
Phototropism is the orientation of a plant or other organism either towards (positive phototropism) or away from the light source (negative phototropism) in reaction to light.
In plant fertilization and pollen tube elongation of angiosperms and flowering plants, one prime example of chemotropism is seen. Plants can not move, unlike animals, and therefore need a delivery mechanism for sexual reproduction. Pollen, which contains the male gametophyte, is transferred via insects or wind to another plant. If it is compatible with the pollen, it will germinate and start developing.
The ovary releases chemicals from the developing pollen tube that stimulates a positive chemotropic response. In response to the calcium gradient, the tube creates a given growth area for the tip that promotes the directional growth and elongation of the pollen tube.
The steep calcium gradient in the tip is localised and promotes elongation and growth orientation.For the occurrence of growth, this calcium gradient is crucial; it has been shown that no growth benefits from inhibiting the gradient formation.
The male sperm remains in the apical region and is carried to the female ovule as the pollen tube continues to grow towards the ovules. The pollen tube elongates at a rate comparable to the development of neurites.

Thus the correct answer is option (B) Chemotropism.

Note: An example of chemotropism is the addition of atmospheric nitrogen, also called nitrogen fixation. An example of positive and negative chemotropism is seen in the roots of a plant. The roots grow towards beneficial minerals that show positive chemotropism and grow away from harmful acids that show negative chemotropism.