Is the human zygote which is formed by fusion of sperm and egg a unicellular structure? Bcz at some places the 2 celled stage which is formed due to cleavage has been labelled as the zygote. So is the zygote 2 celled stage or the unicellular structure which is formed initially.
A zygote is produced when the gametes, a sperm and egg cell, combine with each other. This is unicellular. That one cell then duplicates into two cells, and then four cells. People don't really have a need to name this stage, but anyone would understand it if you just called it two-cell or four-cell within the context of zygotic development. As more cells are created (16+), the solid mass of undifferentiated cells is called a morula. This occurs around 3-5 days after fertilization. This then becomes a sort of hollow sphere of cells. These cells are now called blastomeres and the whole structure is called a blastula. When you hear a cell name with "blast" in it, it typically means it is a precursor to some other type of cell. In this case, those 16 or so cells are the precursor to a future human's entire body.