Fertilisation inside

The idea

In internal fertilisation, found in reptiles, birds and mammals, fertilisation takes place inside the female's body; the fertilised egg or embryo is better protected, so the young generally survive better.

A bird's nest

A bird lays a few eggs in a nest. A frog lays thousands of eggs in a pond.

Which do you think has a better chance for its young to survive?

• The bird, whose eggs were fertilised inside its body
• The frog, because it lays more
• Both are exactly the same

Inside or outside?

Sort each animal by where fertilisation takes place.

Better protected

Reptiles, birds and mammals were all in the inside group. A fertilised egg or embryo inside the mother is better protected, so the young ones generally survive better.

In internal fertilisation, found in reptiles, birds and mammals, fertilisation takes place inside the female's body. The fertilised egg or embryo is better protected, so the young generally survive better.

• Animal | Fertilisation | Survival of young ones
• Fish | External | Low
• Frog | External | Low
• Lizard | Internal | Moderate
• Bird | Internal | Moderate to High

Notes

Internal fertilisation (reptiles, birds, mammals) takes place inside the female's body; the embryo is better protected, so the young generally survive better.

Check yourself

Where does fertilisation take place in internal fertilisation?

Why do the young ones of internally fertilising animals generally survive better?

Which of these animals has internal fertilisation?

According to Table 11.4, the estimated survival of young frogs is…

• In the water outside the body. That is external fertilisation.
• Inside the egg shell after it is laid. In internal fertilisation the fertilisation takes place inside the female's body.
• Inside the body of the female — correct. Yes!
• The fertilised egg or embryo is protected more — correct. Yes!
• They lay more eggs at a time. Table 11.4 shows lizards and birds lay fewer eggs than fish and frogs.
• Water currents carry them to safety. In internal fertilisation the egg is not released into water to be carried by currents.
• Frog. The frog has external fertilisation, in water.
• Bird — correct. Yes!
• Fish. Fish have external fertilisation, in water.
• moderate to high. That is the estimate given for birds.
• moderate. That is the estimate given for lizards.
• low — correct. Yes!