EMBRYONIC DEVELOPMENT UNIT 4 The reproduction function Natural Science 2. Secondary Education

Embryonic development OVIPAROUSVIVIPAROUS OVOVIVIPAROUS Click on each box to find out more EMBRYONIC DEVELOPMENT There are three types, depending on where it takes place UNIT 4 Natural Science 2. Secondary Education

These animals hatch from an egg which the mother lays in the environment. The embryo feeds on the nutritive stores contained in the yolk of the egg. Once it has developed, it hatches, which is when the new individual breaks the shell and emerges from the egg. There are two types of eggs: Eggs without a shell: these are found in aquatic animals and must be laid in a wet environment or they will dry up. Eggs with a shell: they are laid on land so they do not dry up. Oviparous animals Toads are oviparous: they lay their eggs in the water, as their eggs do not have shells and would dry up on land. Embryonic development UNIT 4 Natural Science 2. Secondary Education

The structure of the egg Embryo Vitelline membrane: this encloses the yolk, which the embryo feeds on. Amnion: this forms the amniotic sac, which holds the amniotic fluid where the embryo floats. Membranes: they serve as the egg’s excretory system, collecting waste, and the respiratory system, letting CO 2 out and O 2 in. Shell: keeps the embryo from drying out but allows O 2 and CO 2 to pass through. Go back to the Start menu Embryonic development UNIT 4 Natural Science 2. Secondary Education Yolk

The embryos of these animals develop inside the mother’s uterus. The embryo feeds on nutrients that pass from the mother through the placenta. When the new individual has developed, it comes out of the mother’s body: this is called birth. All mammals, with the exception of monotremes (the platypus and the echidna) and some sharks, are viviparous. Viviparous animals Boars are viviparous animals. Embryonic development UNIT 4 Natural Science 2. Secondary Education

The embryo in viviparous animals Embryo Placenta: extracts nutrients and oxygen for the embryo from the mother’s blood. Umbilical cord: connects the embryo to the placenta. Amnion: forms the amniotic sac, which holds the amniotic fluid where the embryo floats. Embryonic development UNIT 4 Go back to the Start menu Natural Science 2. Secondary Education

These animals develop inside an egg, but the mother keeps the egg inside her body until it hatches. The embryo feeds on the food reserves contained in the egg. When the embryos are fully developed, hatching takes place, just as it does in oviparous animals. The young are alive when they come out of the mother. Certain sharks, vipers and some insects are ovoviviparous. Ovoviviparous animals Many sharks are ovoviviparous. Embryonic development UNIT 4 Go back to the Start menu Natural Science 2. Secondary Education