Question

A dioecious flowering plant prevents both
(A)Cleistogamy and xenogamy
(B)Autogamy and xenogamy
(C)Autogamy and geitonogamy
(D) Geitonogamy and xenogamy

Answer 1

Various types of pollination are seen in nature depending on the environment and requirements of the plant. Dioecious plants possess their male and female flowers on different plants and therefore, require cross-pollination for reproduction.

Complete answer:
Dioecious plants prevent both autogamy and geitonogamy.
Autogamy is the process of fusion of two gametes that belongs to the same flower i.e. self-pollination. It is seen in many flowering plants especially in Monoecious plants. However, dioecious plants possess male and female organs in two different flowers of two different plants, and therefore, they prevent autogamy.
On the other hand, geitonogamy refers to the type of pollination that occurs between two different flowers but on the same plant. It is also a type of self-pollination like autogamy. Dioecious plants possess their gametes in different plants and hence can prevent geitonogamy as well.

Additional Information: Cleistogamy and xenogamy are also types of Pollination.
Cleistogamy occurs in certain plants and propagates by using non-opening flowers. It is really efficient and therefore very few plant resources are required for this type of pollination to occur. Therefore, it is perfect for unfavorable sites and adverse conditions.
Xenogamy refers to the type of pollination that occurs from the anther of a plant to the stigma of a different plant. This occurs in the dioecious plants and is responsible for bringing genetic differences in offsprings.
So, the correct answer is option ‘C’.

Note: Each type of pollination has its own benefits in their environment. For example, autogamy helps the plant to reproduce even without the help of pollinating agents, Cleistogamy helps in efficient pollination in unfavorable conditions and last but not least xenogamy brings about variations in the offspring which is helpful for evolution.