How is an egg a single cell? And if it is, where is all that mitochondria and stuff.
Well, if you are referring to the eggs you can buy in a shop:
not sure if it is..
An egg starts as an Ovum, which is a single cell with all the organelles floating in the Cytoplasm.
After fertilisation Cleavage starts, i.e. division of the cell into two, then four etc. Cleavage rather than Division, because they stay connected in a clump.
So, during hatching, even though it appears to be a single entity, in reality a multicellular organism grows inside until it breaks the shell and gets out...