Water: Water is a slightly polar molecule: the two hydrogen atoms have a partial positive charge and the oxygen atom a partial negative charge. Sixty to 80% of a cell is water. Water has many important roles in cells: 1. It takes part in some reactions 2. It serves as a medium or solvent for other reactions to occur in 3. It serves as a basis for the transportation of materials 4. It absorbs and releases heat 5. It maintains body temperature 6. It protects the body 7. It is the base for all body lubricants