Why do cells need some things to go in and others out

Why do cells need to regulate what goes in and out of them?

The plasma membrane is selectively permeable; it regulates what passes from one side to the other.

A selectively permeable membrane will allow water to flow freely while limiting the passage of molecules, especially large molecules or those with a charge.

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.