External vs Internal Fertilisation

Question 1

When does external fertilisation take place?

Answer 1

• in water
• occurs in most aquatic vertebrates
• e.g. fish and frogs

Question 2

Why is external fertilisation not an ideal process?

Answer 2

• it is wasteful as huge numbers of eggs are produced and most of the eggs (and many young) are eaten
• fertilisation is not certain

Question 3

What are some strategies that aquatic animals use to maximise external fertilisation?

Answer 3

• huge numbers of eggs and sperm are released into the water to increase the probability of fertilised eggs
• courtship rituals (e.g. many fish swim side by side when releasing their eggs and sperm to ensure that the male and female gametes are close to each other)

Question 4

When does internal fertilisation occur?

Answer 4

• in terrestrial vertebrates
• with no external water for the sperm to swim in, the male gametes are released directly into the body of the female and fertilise the eggs inside the body

Question 5

How do most birds and reptiles mate?

Answer 5

• using a cloaca

Question 6

What is a cloaca?

Answer 6

• a single opening located in the lower abdomen

Question 7

What does the penis ensure?

Answer 7

• that sperm is transferred successfully without being destroyed by any environmental conditions

Question 8

How does internal fertilisation maximise reproduction?

Answer 8

• fertilisation is more certain as the gametes are placed as close together as possible
• fewer gametes are therefore needed
• the energy saved in producing fewer gametes can be used for other purposes to maximise reproduction