Question

Anthesis is a phenomenon, which refers to
A. Reception of pollen by stigma
B. Formation of pollen
C. Development of anther
D. Opening of flower bud

Answer 1

It is a phenomenon found in the flowering plants which is related to flowers. Anthesis process is caused by the nastic (epinastic) movements. Nastic movements are the non-directional responses to stimuli which are associated with plants.

Complete answer:
Anthesis is a phenomenon in which the opening of the flower bud occurs. It is the flowering period in which the flower bud opens and becomes functional. This process involves extension of style, maturation of stamen and change in colour
There are several types of nastic movements:

Epinasty: It is the downward bending or drooping of flower bud resulting from greater growth of the upper side than the lower side. Due to more growth on the upper side, the flower will open.
Hyponasty: It is the upward bending or uncoiling of leaves due to the greater growth of the lower side.
Photonasty: It is the response to light by the plants.
Chemonasty: It is the response to chemicals by the plants.
Hydronasty: It is the response to water by the plants.
Thermonasty: It is the response to temperature by the plants.
Seismonasty: It is the response to shock by the plants.
Geonasty: It is the response to gravity by the plants.

So the correct answer is option D.

Note: Nastic movements occur due to changes in turgor pressure or changes in structure of the plant. Decrease in turgor pressure causes shrinkage of plant parts and swelling of plant parts occurs when turgor pressure increases.