Which organism first dominated Earth?

Which material is commonly used as a culture medium for living cells

What determines whether a particular cell is able to respond to a hormone?

Hydrogen has only one electron in its only (and outer) electron shell. if a hydrogen atom were to absorb a small amount of energy, where would bohr say the electron would go? a. fly off the atom b. nowhere, it would just speed up. c. spiral inwards towards the nucleus d. move up to another shell that would form