A single-celled fertilised egg is called a/an:

Correct option is D

The correct answer is (d) zygote.
· A zygote is the initial single-celled stage formed when a sperm cell fertilizes an egg cell.
· This cell undergoes multiple divisions and differentiations, leading to the formation of a blastocyst, then an embryo, and eventually a fetus as it develops.
Information Booster:
· Blastocyst: A blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (which will form the embryo) and an outer layer of cells (which will form part of the placenta).
· Embryo: An embryo is the early stage of development in multicellular organisms. In humans, it is the stage from implantation until the end of the eighth week of gestation, after which it is referred to as a fetus.
· Foetus: A fetus is the stage of development from the end of the eighth week of gestation until birth in humans.