Fertilisation (SQA National 5 Biology): Revision Note

Fetilisation

• Fertilisation can be defined as:

the fusion of a male gamete and female gamete to produce a zygote

• Note that the gametes are haploid and fuse to create a diploid zygote

• The zygote then develops into an embryo

• Cells start to become specialised to perform specific functions, forming all the body tissues of the offspring

Fertilisation in humans

• During sexual intercourse, semen is ejaculated into the female's vagina near the cervix, and sperm travel through the cervix into the uterus

• Fertilisation occurs in the oviduct if a sperm meets an egg, typically 1-2 days after ovulation

• A human zygote contains the full 46 chromosomes (23 pairs of chromosomes) and is therefore diploid

  • Half of the chromosomes in a zygote come from the father (from a haploid sperm cell) and the other half from the mother (from a haploid egg cell)

Fertilisation in plants

• In plants, fertilisation occurs when a pollen tube grows down from a pollen grain to deliver the male nucleus into the ovary

• Here, the male and female gametes fuse to form the embryo