Cell biology is built on the premise of aqueous solution behavior, or how things work in normal water with water being a neutral carrier. If that s wrong, then many of the constructs will have to be re-evaluated. Traditionally, biologists have accepted the idea that cells are surrounded by a relatively impermeable lipid membrane. According to that theory, essential substances enter the cell via selective channels. To maintain the proper chemical balance, dissolved substances, or solutes, are passed out of the cell via an assortment of pumps.
Problems quickly arise with such a scenario, however.
And pumps require energy. Sodium concentrations are lower inside cells than outside, for instance, and scientists have proposed a sodium pump to help maintain that equilibrium. But the sodium pump alone has been estimated to consume as much as 35 percent of a cell s energy. You get into negative numbers real fast, Pollack said. As a result, sodium is kept outside, with or without a membrane.