INTERNAL VS EXTERNAL Fertilization and Development IIntroduction Embryonic

INTERNAL VS. EXTERNAL Fertilization and Development

IIntroduction: Embryonic development may take place inside or outside the mother’s body, depending on the type of organism developing.

To survive, a developing embryo needs: • 1. • 2. • 3. • 4. • 5. Nourishment Protection Oxygen Waste Removal Proper Temperature

EXTERNAL DEVELOPMENT IN WATER (H 20) In most Aquatic animals fertilization and development both occur outside of the mother’s body. • NOURISHMENT: the yolk is stored in the egg

EXTERNAL DEVELOPMENT IN WATER (H 20) • ENVIRONMENTAL CONDITIONS: Are favorable due to time of year/season, know as “Mating Season”. • OXYGEN: Diffuses in from the surrounding water • WASTE REMOVAL: CO 2 diffuses out of embryo into the surrounding water.

EXTERNAL DEVELOPMENT IN WATER (H 20) • PROTECTION: Little or no protection, or care given by the parents to the offspring. FISH EGGS

EXCEPTIONS TO THE RULE 1. STICKLEBACK: The males of this species will guard the nest and fan the embryos with his tail to move water across the nest to provide more oxygen 2. “MOUTHBREEDER”: fish that keeps the fertilized eggs in its mouth until they hatch, this provides protection from predators.

MALE STICKLEBACK

TYPE OF MOUTHBREEDER: Arowana Fish can carry hundreds of eggs in its mouth. Even after they hatch the little fish stay in the mother’s mouth until they are ready to survive on their own.

EXTERNAL DEVELOPMENT ON LAND Fertilization takes place INSIDE the mother’s body, while development takes place OUTSIDE the body in an egg. • NOURISHMENT: yolk = inside of egg • ENV. CONDITIONS: self contained watery environment inside of shell.

CONTINUED • OXYGEN: the shell is porous which allows oxygen to diffuse IN. • WASTE REMOVAL: shell is porous to allow CO 2 to diffuse OUT. • PROTECTION: hard outer shell provides some protection from environment, (helps keep bacteria out), and keeps inside of egg moist.

EXAMPLES • Survival rate is higher for embryos hatching from a shelled egg that those from an egg with no shell • Reptiles usually leave their eggs, while most birds will carefully tend to their eggs. • Birds have a higher survival rate than do reptiles.

Honduran Milk Snake

INTERNAL DEVELOPMENT In mammals fertilization takes place INSIDE the mother’s body, and development occurs INSIDE the uterus. • 2 KINDS OF MAMMALS – A) Placental Mammals – B) Nonplacental Mammals

PLACENTAL ANIMALS • The blood vessels of the embryo’s circulatory system is in close contact with the mother’s circulatory system. • Placenta = temporary organ. Allows for diffusion of respiratory gases and nutrients from mother to embryo

ALL MAMMALS!!! Exc ept

NONPLACENTAL ANIMALS • There are 2 kinds: 1) Pouched mammals, like the kangaroo and the opossum 2) Egg-laying mammals like the duck billed platypus and the spiny anteater Both types have all characteristics of mammals, except the use of a placenta.

POUCHED MAMMALS

EGG-LAYING MAMMALS

The End of the Notes for this section