Introduction:
In biology, motility refers to the ability of an organism or cell to move or exhibit self-propelled movement. Motility is an important characteristic of many biological processes and is observed in various stages of reproductive cycles in organisms. In the given options, we are asked to identify which one is motile.

Explanation:
1. Male gamete:
The male gamete, also known as sperm, is motile. Sperm cells are specialized reproductive cells produced by males. They have a tail-like structure called a flagellum that allows them to swim towards the female gamete for fertilization. This motility helps in ensuring successful fertilization.

2. Female gamete:
The female gamete, also known as the egg or ovum, is non-motile. Unlike sperm cells, eggs do not possess any means of self-propelled movement. They are larger in size and stationary within the female reproductive system. Eggs rely on external factors such as the movement of the reproductive tract or the assistance of the male gamete for fertilization.

3. Cotyledons:
Cotyledons are embryonic structures found in the seeds of flowering plants. They are responsible for absorbing nutrients from the endosperm or the surrounding soil during germination. Cotyledons are not motile as their primary function is to provide nourishment to the developing plant embryo.

4. Zygote:
A zygote is the initial cell formed when a sperm fertilizes an egg. It is the result of the fusion of male and female gametes. Initially, the zygote is non-motile as it undergoes cell division and develops into an embryo. However, once the embryo reaches a certain stage of development, it may exhibit motility through the movement of specialized structures such as cilia or flagella.

Conclusion:
Among the given options, the male gamete is the only motile structure. Sperm cells possess a flagellum that enables them to swim towards the female gamete for fertilization. The female gamete (egg), cotyledons, and zygote are non-motile structures.