Final answer:
Humans start life as a single cell called a zygote, which undergoes cleavage to form a blastula, and then a blastocyst in mammals.
Step-by-step explanation:
The single cell that humans begin life is called a zygote. This zygote then undergoes rapid cell division, known as cleavage, and forms a hollow ball of cells called a blastula. In mammals, including humans, the blastula develops into a structure called a blastocyst, which is characterized by an inner cell mass.
Humans begin life as a single cell that divides repeatedly. This cell is known as a zygote. A zygote is a fertilized egg that undergoes trillions of cell divisions, which enable the development of a complex, multicellular organism. Post fertilization, the zygote undergoes a process of division known as cleavage, resulting in a hollow ball of cells called a blastula. As these cells continue to divide and grow, mammals, including humans, will develop a structure called a blastocyst, which features an inner cell mass distinct from the surrounding blastoderm.