| A | B |
|---|
| zygote | a fertilized egg, formed from the fusion of an egg cell with a sperm cell |
| embryo | a multicellular organism that is in the early stages of development |
| embryology | the study of the development of embryos |
| cleavage | an early series of cell divisions that occur without growth |
| morula | solid ball of cells |
| blastula | hollow ball of cells with fluid-filled center |
| blastocoel | the fluid-filled center of the blastula |
| gastrulation | process in which cells on one side of blastula move inward to form two-layered embryo called the gastrula |
| gastrula | two, or three-layered embryo |
| germ layers | cell layers of the gastrula, which give rise to all tissues and organs |
| ectoderm | outer layer of gastrula-forms nervous system and skin |
| mesoderm | middle layer of gastrula-forms muscle,bone,blood vessels,blood,heart,reproductive system |
| endoderm | inner layer of gastrula-forms digestive, respiratory systems, liver, pancreas |
| cytoplasm | plays a role in differentiation/turns genes on or off |
| organizers | parts of the embryo that affect development of neighboring cells |
| embryonic induction | process by which organizers influence other cells of embryo |
| development | the change of unspecialized cells into specialized cells, tissues, and organs |
| primitive gut | cavity within the gastrula/becomes digestive tract |
| neural plate | flattened area of ectoderm on upper surface of gastrula |
| neural folds | two raised edges of neural plate |
| neural tube | forms when neural folds come together;becomes spinal cord and brain |
| external development | development of embryo outside mother's body |
| internal development | development of embryo inside mother's body |
| external development in water | no hard shell/little or no care of young/many eggs produced/nourishment from yolk |
| external development on land | hard shell/fewer eggs/nourishment from yolk |
| chorion | outermost membrane in chicken egg/aids in gas exchange |
| allantois | sac-like membrane/exchanges gases and wastes |
| amnion | filled with amniotic fluid which cushions embryo |
| yolk sac | surrounds yolk/carries food to embryo |
| mammals | feed young milk from mammary glands |
| placental mammals | embryo develops in uterus/nourishment from mother's bloodstream through placenta |
| nonplacental mammals | no placenta forms during development |
| egg-laying and pouched | two types of nonplacental mammals |
| kangaroo | a pouched mammal/embryo is nourished by yolk, born immature, develops further in pouch which contains mammary glands |
| duck-billed platypus | lays eggs/feeds hatchlings milk from mammary glands |
