Tonicity
Solutions may be loosely categorised as hypertonic, hypotonic or isotonic according to their relative solute concentrations
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Solutions with relatively higher solute concentrations are categorised as hypertonic (high solute ⇒ gains water)
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Solutions with relatively lower solute concentrations are categorised as hypotonic (low solute ⇒ loses water)
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Solutions that have equivalent solute concentrations are categorised as isotonic (same solute ⇒ no net water flow)
Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)
The osmolarity of a tissue may be interpolated by bathing the sample in solutions with established solute concentrations
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The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
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Water loss or gain may be determined by weighing the sample before and after bathing in solution
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Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)
Osmosis in Onion Cells
Adapted from: https://www.youtube.com/watch?v=Iv7eGCPVaAk
