Osmotic pressure changes the shape of red blood cells in hypertonic, isotonic, and hypotonic solutions. A doctor injects a patient with what the doctor thinks is an isotonic saline solution. The patient dies, and an autopsy reveals that many red blood cells appear swollen and many others have burst. Explain how this observation provides evidence that the solution the doctor used was not an isotonic saline solution.

Figure 5.17 provides a representation of features controlling the dynamic homeostasis of key ions across a cell membrane. Injection of a potassium solution into a person’s blood is lethal; this procedure is used in capital punishment and euthanasia. Describe the gradients across the membrane in terms of the distribution of charge and mass. How does gradient formation explain the lethality of potassium solution injection?