Embryo Development Gizmo

a hollow ball of cells that forms during embryogenesis. o The blastula consists of a single, spherical layer of cells surrounding an open cavity. o A smaller ball of cells, the inner cell mass, is found inside at one end.

a standardized system of 23 stages used to identify the developmental stage of a vertebrate embryo. o The stages are identified by the presence common structures (such as limb buds or a heart), not by size of the embryo or time from conception. o Carnegie stages are most often used to classify human development. o Other organisms may use different systems, such as the Hamburger-Hamilton stages for chick embryos.

the process by which less specialized cells change to become more specialized cells that perform a different function than before. Different cells will turn on or off different subsets of genes to allow them to perform different functions.

one of the three germ layers in the early embryo that will eventually form cells in the skin and nervous system

the unborn offspring of a multicellular organism in the early stages of development. o A human offspring is referred to as an embryo through the 8th week of pregnancy, after which it is referred to as a fetus.

the branch of biology that studies embryo development.

Undifferentiated cells that have the potential to develop into any cell in the adult organism.

one of the three germ layers in the early embryo that will eventually form structures including the lining of the digestive and respiratory tracts.

the unborn offspring of a mammal in the later stages of development. o A human offspring is referred to as a fetus after the 8th week of pregnancy.

a stage in development when the embryo consists of three layers of cells. o The three germ layers (endoderm, mesoderm and ectoderm) will become all of the structures in the adult organism.

group of cells inside the blastula that will eventually become the organism, amniotic cavity, and primitive yolk sac.

one of the three germ layers in the early embryo that will eventually form structures including connective tissue, bones, and muscles

an early-stage embryo consisting of a solid ball of cells.

a stage in development when the three germ layers of the embryo change shape. The ectoderm folds inward creating a neural tube. o The nervous system begins to form at this stage.

an elongated band of cells that forms along the axis of the developing embryo during gastrulation. o Epiblast cells migrate into and down below the primitive streak to establish the three germ layers. o The primitive streak is the precursor to the neural tube and central nervous system.

a structure that consists of three layers of cells in the gastrula. o The three germ layers in the trilaminar disk are the endoderm, mesoderm and ectoderm.

a cell formed after fertilization of an egg cell. o The zygote is the very first structure development. o Two haploid gametes (a sperm and egg) fuse to form the zygote.