Course Content
Biology Form 3
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External fertilization

The fusion of the nuclei of male and female gametes occurs outside the body of the female. e.g. amphibians and fish.

It is only possible in water.

In frogs, the female lays eggs in water and the male sheds sperm cells over these eggs to fertilize them, resulting in fertilization outside the body.

Eggs are laid in strands of slippery jelly-like substance which;

  • Protects the eggs against predation and harsh conditions.
  • Separates eggs from each other allowing for good aeration.
  • Attaches the eggs to the water plants.
  • Makes the eggs to be buoyant.


Advantages of External Fertilization

  • More number of offspring since many eggs are laid to increase the chances of survival.
  • The female do not suffer gestation stress and care-giving of the young.


Disadvantages of External fertilization

  • Requires large number of female gametes hence the female gets much exhausted.
  • There is lower chances of fertilization.
  • Most eggs/embryos are eaten by predator hence low chance of survival.


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