• In animals two individuals are involved, a male and a female.
• Special organs known as gonads produce gametes.
• In males testes produce sperms while in females ovaries produce ova.

• The fusion of male gamete and female gamete to form a zygote is called fertilisation.
There are two types of fertilisation. External and internal


Distinguish between external and internal fertilization in animals
• In external fertilization fusion of the male and female gametes takes place outside the body of the female e.g. amphibians and fish
• In internal fertilization union of gametes occurs inside the body of the female


State the advantages and disadvantages of external fertilization
Advantages
• Large numbers produced therefore many offspring per breeding season
• Female does not suffer gestation stress
• Mother does not need to care for the young except in a few species
• The surviving individuals are highly selected for better survival
Disadvantages
• many predators surround the eggs before and after fertilization
• fewer chances of fertilization/a lot of gametes wasted
• embryo development at mercy of environment
• large numbers of female gametes are required therefore female gets much exhausted

State the advantages and disadvantages of internal fertilization
Disadvantages
• number of gametes fewer hence less number of offspring
• less adapted for sudden change of environment after birth
• in mammals females suffer gestation stress
Advantages
• more chances of fertilization
• fewer predators of oval/fertilized egg protected in females body
• stable internal environment
• fewer gametes required

Give a reason why it is necessary for frogs to lay many eggs
• to increase chances of survival/fertilization

Compare external and internal fertilization

External fertilization	Internal fertilization
occurs in water outside the bodies of animals	occurs inside the body of the female animal
many eggs are laid	fewer eggs released from ovary
usually less contact between male and female	very close contact in form of copulation between male and female
both fertilized eggs exposed to danger	Fertilized eggs are enclosed hence highly protected inside females’ body.