Gametes and Fertilisation

The diagram below shows a front view of the female reproductive system.

Once a month, an egg is released from one of the ovaries. The egg is transported through the fallopian tube by tiny hair-like structures called cilia.

During sexual intercourse, a man ejaculates and releases millions of sperm into the woman’s vagina. The sperm swim through the cervix and into the uterus, and some even reach the fallopian tubes.

However, not all sperm make it to the right fallopian tube. This is because only one egg is released, so some sperm might end up in a tube without an egg. Out of the millions of sperm, usually only one will penetrate and fertilise the egg.

Fertilisation

Fertilisation is the process of combining the male gamete (sperm) with the female gamete (egg).

When the nuclei of the sperm and egg fuse, the genetic information of the mother (from the egg) combines with the genetic information of the father (from the sperm). This forms the genetic blueprint for the developing embryo and ultimately, the baby.

  • Remember, the genetic information is stored in the nucleus of cells

Gametes

Gametes are the reproductive cells that are responsible for sexual reproduction. In females, the gametes are called egg cells or ova, while in males, the gametes are called sperm.

Gametes have evolved specialised characteristics that increase the chances of fertilisation.

Sperm cell adaptations

Sperm cells have several adaptations that improve their chances of fertilising an egg, including:

  • A tail (flagellum), which allow the sperm to swim
  • A streamlined shape, which allows for faster swimming
  • An acrosome, which is a specialised structure located in the head of the sperm that contains digestive enzymes that can break down the egg’s membrane

The production of millions of sperm cells increases the chances that at least one will successfully reach and fertilise the egg.

Egg cell adaptations

Egg cells, or ova, also have several adaptations that aid in fertilisation and the development of the embryo. These adaptations include:

  • A thick outer layer that hardens after fertilisation to prevent additional sperm from entering
  • A cytoplasm that contains nutrients and other substances necessary for the growth and development of the embryo

Overall, the adaptations of both sperm and egg cells play an important role in fertilisation and the development of a healthy embryo.

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