Life Sciences Term 1

Fertilisation

• Spermatozoa deposited in the vagina move by spiral movements towards the ovum in the fallopian tubes
• The head of one sperm cell penetrates the membranous barrier around the ovum
• Enzymes from the acrosome hydrolyse these barriers
• The spermatozoon loses its tail  
• The yolk membrane becomes impenetrable to other sperm
• The pronuclei of the male and female fuse
• Two sets of chromosomes lie on the equator
• Fertilization occurs in the fallopian tubes forming a zygote
• The zygote undergoes mitosis to form a ball of cells called a blastula
• The blastula moves along the fallopian tube until it reaches the uterus.