NLN PAX Practice Exam 2026 – Complete Study Guide

When a human red blood cell (RBC) is placed in distilled water, it will swell up and eventually burst due to the process of osmosis. In this scenario, the RBC is in a hypotonic solution, meaning the concentration of solutes outside the cell is lower than that inside the cell.

As a result, water moves into the RBC from the surrounding environment in an attempt to equalize the solute concentrations on both sides of the cell membrane. The influx of water causes the cell to swell. Since RBCs lack the structural rigidity of plant cells (which have a cell wall to withstand pressure), the continued influx of water leads to an increase in internal pressure, ultimately resulting in the cell bursting, or undergoing hemolysis.

Understanding this osmotic behavior is fundamental in biology and helps explain various physiological and pathological conditions related to cellular fluid balance.