Diversity of Reproductive Strategies-Reproduction in Vertebrates

Question 1

External fertilization

Answer 1

During external fertilization, the sperm cell fertilizes the egg cell outside the body of the female. During external fertilization, it is not necessary for the two parents to make physical contact
Water is always required for external fertilization for two reasons. Firstly, it prevents the egg from drying out. Secondly, water must be present to allow the sperms to swim towards the eggs
Frogs, Starfish and Trout are examples of animals that undergo external fertilization
The disadvantage of external fertilization is that a large amount of sperms may not reach the egg cell. To compensate for this, organisms with external fertilization produce a large number of sperms to ensure that at least some do reach the egg cells

Question 2

Internal Fertilization

Answer 2

During internal fertilization, the male deposits its sperm cells inside the reproductive organs of the female and fertilization occurs inside the female’s reproductive organs. Internal fertilization is an adaption that allows terrestrial animals to reproduce in a dry environment
Birds and mammals are examples that undergo internal fertilization
Because internal fertilization is more certain than external fertilization, organisms with internal fertilization produce a smaller quantity of sperm

Question 3

Ovipary

Answer 3

This refers to a method of reproduction in which eggs are laid development of these eggs takes place outside the mother’s body. Most invertebrates (e.g. snails) and many vertebrates (e.g. frogs) reproduce in this way
The disadvantage of Ovipary is that the eggs may be preyed upon by predators. The chances of this happening are reduced if the eggs are protected by the parents

Question 4

Vivipary

Answer 4

A method of reproduction in which the young develop inside the uterus of the mother after the eggs are fertilized internally, receiving nutrients from the mother’s blood through a placenta. Mammals are vivipary
The advantage of vivipary is that fertilization is internal that increasing the chances of offspring being produced. The young are already well developed when born

Question 5

Ovovipary

Answer 5

This refers to a method of reproduction in which young develop from eggs that are fertilized internally and retained within the mother’s body after fertilization but obtain their nutrients from the egg yolk and not from the mother
Because of internal fertilization there is a greater chance of offspring being produced

Question 6

Amniotic Egg

Answer 6

The Amniotic Egg is characteristics of reptiles and birds
The Amniotic Egg contains four membranes, called extra-embryonic membranes (‘extra’ means outside). These four membranes are: The Amnion, The Chorion, The Allantois, The Yolk Sac

Question 7

The Amnion

Answer 7

It encloses an amniotic cavity containing amniotic fluid which cushions the embryo against mechanical shock

Question 8

The Chorion

Answer 8

It allows oxygen which enters through the shell to pass through to the embryo, and carbon dioxide to pass from the embryo through the shell to the air outside

Question 9

The Allantois

Answer 9

It stores waste produced by the embryo. It also functions in gaseous exchange, just like the chorion

Question 10

The Yolk Sac

Answer 10

The Yolk Sac contains yolk which serves as food for the embryo

Question 11

The Egg Shell

Answer 11

The shells of the eggs of birds and reptiles reduce dehydration. This allows birds and reptiles to occupy a wider rage of terrestrial habitats with amphibians