• Reproduction in vertebrates
- External or Internal fertilisation:
➢ Vertebrate animals reproduce sexually, and to do so
successfully fertilisation needs to take place.
➢ Problems of bring the sperm and ova together in terrestrial vertebrates, is that they require a
liquid medium.
➢ Terrestrial vertebrates create their own liquid medium to avoid the drying effects of the outside
environment, this has all led to the development of internal fertilisation.
• External fertilisation:
- Vertebrates living in water make use of external
fertilisation.
- This type of fertilisation takes place outside the body, in
which the female & male gametes are released into the
water.
- The sperm either swim towards the eggs or are swept by currents towards the eggs.
- Physical contact between male and female are not necessary.
- Chances of successful fertilisation increases when the male and female find themselves
in the same intermediate area.
- Courtship is necessary to attract opposite sexes, which would include colour changes,
fertilisation occurring at full moon.
- External fertilisation can be a “hit or miss” affair, as many eggs end up not being
fertilised but a large number of eggs and sperm are produced to compensate for this.
- Frogs:
• Frogs call to attract a female into his territory, in which the female arrives and
he climbs onto her backs and stays there while she releases her eggs and he
releases his sperm over the eggs.
• The eggs are soft and not surrounded by shell, so that sperm can easily
penetrate.
• Eggs require water as they will dry out. [ surrounded by a slimy, jelly-like
substance]
• Jelly protects embryos and allows exchange of gases between water and
embryo.
- External or Internal fertilisation:
➢ Vertebrate animals reproduce sexually, and to do so
successfully fertilisation needs to take place.
➢ Problems of bring the sperm and ova together in terrestrial vertebrates, is that they require a
liquid medium.
➢ Terrestrial vertebrates create their own liquid medium to avoid the drying effects of the outside
environment, this has all led to the development of internal fertilisation.
• External fertilisation:
- Vertebrates living in water make use of external
fertilisation.
- This type of fertilisation takes place outside the body, in
which the female & male gametes are released into the
water.
- The sperm either swim towards the eggs or are swept by currents towards the eggs.
- Physical contact between male and female are not necessary.
- Chances of successful fertilisation increases when the male and female find themselves
in the same intermediate area.
- Courtship is necessary to attract opposite sexes, which would include colour changes,
fertilisation occurring at full moon.
- External fertilisation can be a “hit or miss” affair, as many eggs end up not being
fertilised but a large number of eggs and sperm are produced to compensate for this.
- Frogs:
• Frogs call to attract a female into his territory, in which the female arrives and
he climbs onto her backs and stays there while she releases her eggs and he
releases his sperm over the eggs.
• The eggs are soft and not surrounded by shell, so that sperm can easily
penetrate.
• Eggs require water as they will dry out. [ surrounded by a slimy, jelly-like
substance]
• Jelly protects embryos and allows exchange of gases between water and
embryo.
