1. Water: Water is the most abundant substance in a cell, making up about 70% of its total mass. It serves as a solvent, allowing for chemical reactions to occur, and plays a crucial role in transporting nutrients and removing waste products.

2. Salts: Salts are inorganic compounds that dissolve into ions in water. They are essential for maintaining the cell's osmotic balance, nerve impulse transmission, and muscle contraction.

3. Lipids: Lipids, including fats and oils, are organic molecules that are mostly hydrophobic (water-repelling). They form the structural basis of cell membranes, store energy, and serve as insulation.