Answer:
Theres no nucleus and what makes it a nucleus is the nuclear membrane. So the answer is the presence of a nuclear membrane.
Bacteria was the first life form :)
Coin flipping simulates the events of mitosis and the production of sperm. This is because females carry XX chromosomes so all eggs will have a singular X chromosome. It is the sperm that determines the sex of the foetus: males have XY chromosomes and therefore sperm will carry either X or Y chromosomes (a 50/50 chance, just like flipping a coin)
As cells die, and reproduce from time to time, educational references show that every seven years, all cells have been replaced and considered as brand new. This also applies to the skeletal system. However, this statement is still not verified by health researchers.
