Final answer:
K+ is the major intracellular cation, maintained at high levels inside cells by the sodium-potassium pump. Chloride, on the other hand, is the predominant extracellular anion, contributing to the osmotic pressure gradient and hydration of cells.
Step-by-step explanation:
K+ (potassium) is the major intracellular cation. It is crucial for various cellular functions, including the establishment of the resting membrane potential in neurons and muscle fibers, and it operates after membrane depolarization and action potentials. Potassium's role is largely intracellular, meaning it is found predominantly inside cells. The high levels of potassium inside cells as compared to low levels in the extracellular fluid are actively maintained by the sodium-potassium pump, which moves potassium into the cell against its concentration gradient by using ATP for energy.
Conversely, chloride (Cl-) is the predominant extracellular anion, playing a key role in the osmotic pressure gradient between the intra- and extracellular fluid compartments and in maintaining cellular hydration. As such, we see a balance of ions, with sodium (Na+) and chloride ions being concentrated in the extracellular fluid, and potassium ions concentrated within the cellular space. This dynamic ion distribution is essential for various physiological processes, including regulation of fluid balance and nerve impulse transmission.