union of gametes of opposite sexes during the process of sexual reproduction to form a zygote

Fertilization (British English spelling: fertilisation) is when a male's sperm enters a female's ovum (or "egg"). Fertilization is also called conception. Biologists call a fertilized egg a zygote. A zygote grows into an embryo.

Human sperm arrives at the egg cell.
Liverworts are a kind of small plant with a complex life cycle that includes fertilization. The sperm and the egg come together to make a zygote. The zygote grows into an embryo.

Fertilization occurs in animals, including humans and birds, in plants, fungi, protists, in fact all eukaryotes. Fertilization makes a cell with twice as many chromosomes. The eukaryote life cycle includes meiosis which divides the chromosome number in half.

In animals


In animals, there are two types of fertilization, internal and external. Internal fertilization happens in the female body. External fertilization happens outside of the body. Mammals, birds, and reptiles use internal fertilization.[1] Amphibians and most fish use external fertilization. Some animals with internal fertilization give birth to live offspring. Others such as birds, most reptiles, and some mammals such as the Platypus, lay eggs.

Internal fertilization happens during mating (sexual intercourse in humans). Sperm cells travel from the male testicles to the female uterus. One sperm attaches to the egg in the uterus. Together, they become a zygote.



  1. Pradhan, Sarala; Bespalova, Ioulia (2019-07-16). "Internal Fertilization". askabiologist.asu.edu. Retrieved 2021-01-15.