Question | Answer |
Embryo Formation | After fertilization, the embryo divides repeatedly by mitotic division |
Development | Growth and differentiation that produce a fully formed embryo |
Cleavage | repeated cell division of the zygote; produces a hollow ball with a single layer of cells called the blastula; cells do not grow so the blastula stays the same size as the zygote |
Gastrulation | one side of the blastula becomes indented, forming the gastrula; 3 layers form; ectoderm, endoderm, and mesoderm |
Ectoderm | The outer layer; nervous system; epidermis of skin |
Endoderm | The inner layer; lining of the digestive and respiratory tract; liver and pancreas |
Mesoderm | The middle layer; muscles and skeleton; circulatory, excretory, and reproductive system, |
Growth | Results from an increase in the number of cells as well as an increase in cell size |
External Development | Development that occurs outside the female's body |
Internal Development | the embryo develops inside a female organ called the uterus |
Umbilical Cord | Developing embryo obtains nutrients and oxygen and releases wastes through a structure, which is attached to the wall of the uterus |
Placenta | Region of attachment of the umbilical cord; rich in blood vessels of mother and embryo; no direct connection between the two circulatory systems |
Exchange in the Placenta | by diffusion and active transport |
Exchange of gas in the Placenta | only by diffusion |
In water external development | the eggs of most fish and amphibians are fertilized externally and develop externally in an aquatic environment |
Yolk stored in the egg | the source of food for the developing embryo; develops to an advanced stage of development before emerging into the environment |
on land external development | the eggs of birds, many reptiles, and some mammals develop externally in a land environment after internal fertilization; these eggs have special adaptations to insure survival under the conditions of a land environment |
Shell | hard provides protection for the embryo |
Chorion | lines the shell |
Allantois | functions in the exchange of respiratory gases and excretion of wastes |
Amnion | contains amniotic fluid provides watery environment, protects against shock |
Yolk sac | surrounds the yolk and is penetrated by blood vessels, which transports food to the developing embryo |
Pouched Mammals | some internal development but no attachment to the uterus; called non-placental mammals; born before fully developed; climbs to a pouch on mother's outside and obtains nutrients from the mammary glands in the pouch |