In Biology the cell is typically thought of as the smallest functional unit that all tissues and organs are made of.
Covalent Bonds
If you look inside of any cell you will see they are made of water, proteins, fatty acids, sugars, and nucleic acids (DNA). These macromolecules allows cells to make energy, reproduce themselves, and communicate with other cells. All life on earth uses these macromolecules to survive!
From Atoms To Cells to Ecosystems of the World
If you look closer at these macromolecule you will see they are mostly held together by Covalent Bonds.
[easytable] Macromolecule,Bond,Bond TypeSugars,Glycosidic Bond,Covalent
Proteins,Peptide Bond,Covalent
Fatty Acids,Many Bonds,Covalent
Nucleotides,Phosphodiester,Covalent
[/easytable]
Ionic Bonds
Ionic bonds are formed due to the attraction between an atom that has lost one or more electrons (known as a cation) and an atom that has gained one or more electrons (known as an anion). The cation(+) is usually a metal atom and the anion(-) is a nonmetal atom.
Ionic bods are not common in living cells. Since cells are about 70% water (a polar molecule), water will compete for and split ionic bonds.