Question

Stigma is sticky
a) To produce scents to attract birds and insects
b) To hold pollen grain strongly
c) There is no known function
d) None of the above

Answer 1

Hint: Stigma is a part of a plant's reproductive system. It is that part of the pistil where pollen germinates. Here in the question they are asking about the reason behind the stickiness of the stigma. Stigma also has various modifications, it all depends on the nature and demand of the pollinators.

Complete answer:
Stigma is a part of the female flower that particularly forms a special adapted part of the pistil and it is also modified for receiving pollen grains. Stigma is also known as landing zones or landing stages as it acts as a stage where pollen falls or lands. They tend to trap the pollen for the process of fertilization.
Stigma has various adapted structures or they are modified to trap pollen grains like presence of hairs, flaps, sticky surface, waxy surface etc.
Sticky surface of stigma helps in the exudation of complex substances that facilitates easy trapping of the pollen grain to prepare the plant for the process of fertilization.
So, basically they are sticky to hold the pollen grain strongly. Imagine if pollen falls on the stigma and its surface is non-sticky, that means due to air or anything, they have the tendency to fall off from the stigma. So in order to hold them strong, stickiness is present.

Therefore, the correct answer is option (b).

Note:
Stigma is the one thing that decides the compatibility of pollen grain with the plant. Number of lobes in the stigma represents the number of carpels, and depending on that stigma may be unified, bifid, trifid, tetrafid, pentafid or multifid. Fertilization in the plant occurs in the embryo sac. The oval structure present in the ovule of the flowering plant is called the embryo sac.