Final answer:
In biology, a solution's osmolality must exceed the normal range of 280 to 300 mOsm/kg to be considered hypertonic. Urine osmolality, for example, is expected to be greater than 800 mOsm/kg after fluid intake is restricted, indicating a hypertonic condition for urine.
Step-by-step explanation:
Osmolality is a measure of the solute concentration per kilogram of solvent and is related to the osmotic pressure of a solution. When the osmolality is above a certain threshold, it makes the solution hypertonic in comparison to body fluids. Body fluids typically have an osmolality of 280 to 300 mOsm/kg. Therefore, to be considered hypertonic, a solution's osmolality would need to be higher than this range. With excessive osmolality, water leaves the cells to balance the concentrations, which is why drinking seawater, with its high osmolality, can lead to further dehydration.
An example of how the human body reacts to such conditions is when urine osmolality is measured. Kidneys adjust the concentration of urine based on fluid intake. In a concentrated state after restricted fluid intake, urine's osmolality should be greater than 800 mOsm/kg. This value indicates the kidneys' ability to concentrate solutes when necessary and gives a benchmark as to what is considered a high osmolality value.