How do sperm cells and egg cells differ in size and movement?

In biological terms, the differences between sperm and egg cells are defined by a process called oogamy, which is a form of heterogamy found in animals and higher plants.1

Size and Nutritional Reserves

• Sperm: These are extremely small cells produced in enormous numbers. Their compact size is primarily due to the head, which consists mostly of a nucleus containing chromosomes.23
• Eggs (Ova): These are large cells that contain stored nutritional reserves. This size is essential because the stored material supports the early stages of embryonic development before the new organism must fend for itself.2

Movement

• Sperm: These cells are highly motile. Most possess a flagellum—a whiplike tail—that undulates to propel the cell toward the egg.23
• Eggs: In contrast, egg cells are nonmotile. They rely on the motility of the sperm to bring the two gametes together for fertilization.12

This division of labor ensures that the sperm can efficiently locate the egg, while the egg provides the necessary resources for the development of the zygote.2