Density is the amount of mass in a certain .

Air
results from a column of air pushing on an area.

A measure of how tightly air molecules are packed together is called

They both determine the exact age of rocks.

Cell division is important to single celled organisms because it allows the cells to reproduce. through cell division, cells make exact copies of themselves. when single celled organisms go through cell division, they make exact copies of themselves which is how they reproduce.