What component of sea water makes it hypertonic compared to body fluids?

Sea water is considered hypertonic compared to body fluids primarily due to its high salt content, specifically sodium chloride (NaCl). When comparing solutions, a hypertonic solution has a higher concentration of solutes than another solution, which in this case refers to body fluids.

In physiological terms, when cells are placed in a hypertonic solution, they tend to lose water due to osmosis, as water moves from an area of lower solute concentration (inside the cells) to an area of higher solute concentration (the surrounding sea water). This can lead to cell shrinkage or dehydration.

The presence of salt in sea water not only impacts osmotic balance but also plays a significant role in marine life and habitats. While chlorine, potassium, and calcium are present in sea water, they do not account for its hypertonic nature to the same extent as salt does. Sodium chloride is the primary contributor to the osmotic properties of sea water, making it effectively hypertonic relative to human body fluids.