A phosphite is a compound that contains the ion $PO_3^{3-}$, whereas a phosphate contains the ion $PO_4^{3-}$.

Both phosphites and phosphates play crucial roles in biological systems. Phosphites are frequently utilized as fertilizers and can be absorbed by plants and microorganisms as a source of phosphorus. However, they are generally less effective than phosphates, which represent the primary form of phosphorus utilized by plants. Additionally, phosphates are essential components of vital biological molecules, including DNA, RNA, and ATP—the energy currency of cells.

The key distinction between phosphites and phosphates lies in the number of oxygen atoms present in their molecular structures. Phosphites contain three oxygen atoms, while phosphates contain four. This difference influences their chemical and biological properties. For instance, phosphates are more stable and less reactive than phosphites, which have the potential to be oxidized to phosphates when exposed to oxygen.

In summary, both phosphites and phosphates are significant compounds in biological systems. However, phosphates are more commonly utilized by plants and exhibit greater stability and reactivity due to the presence of an additional oxygen atom.