How are atoms in molecules held together? A) neutron sharing
B) ionic bonds
C) proton sharing
D) covalent bonds

The bonds that hold atoms together are called covalent bonds. Covalent bonds are made by atoms sharing their valence electrons.

Ions are held together by ionic bonds, which are formed by ions donating their valence electrons to other ions.

Your body has many different kinds of cells. Though they might look different under a microscope, most cells have chemical and structural features in common. In humans, there are about 200 different types of cells, and within these cells there are about 20 different types of structures or organelles.