embryo

Early developmental stage of an animal or a plant following fertilization of an ovum (egg cell), or activation of an ovum by parthenogenesis. In humans, the term embryo describes the fertilized egg during its first seven weeks of existence; from the eighth week onwards it is referred to as a fetus.

In animals the embryo exists either within an egg (where it is nourished by food contained in the yolk), or in mammals, in the uterus of the mother. In mammals (except marsupials) the embryo is fed through the placenta. The plant embryo is found within the seed in higher plants. It sometimes consists of only a few cells, but usually includes a root, a shoot (or primary bud), and one or two cotyledons, which nourish the growing seedling.