1.4.S1

Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions.

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Osmolarity is:

• the concentration of solutes in a solution.
• the number of particles of solute per liter of solution
• = moles of solute

liters of solvent

It is important to know the osmolarity of tissues because tissues or organs used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis (1.4.A2)

Osmolarity of a tissue can be determined experimentally.

1. Mass samples of tissues.
2. Place samples of a tissue in solutions of known osmolarity
3. Let the samples sit for a set amount of time.
4. Re-mass the tissue samples.

When measuring the mass of the tissue samples, it is important to make accurate quantitative measurements (1.4.NOS)

Osmolarity of a tissue can be determined experimentally.

5. Calculate the percent change in mass of each tissue sample.

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• the pieces of tissue will not all be the same mass as the were at the beginning of the experiment
• the change in mass indicates whether the tissue has gained or lost water
• using percent change allows you to compare the relative changes in mass, since the initial samples were likely not all the identical starting mass

Due to osmosis (1.4.U1) …

• Samples will gain mass when placed in a hypotonic solution (as water moves into the sample).
• Samples will lose mass when placed in a hypertonic solution (as water moves out of the sample).
• There will be zero change in mass when the sample is placed in an isotonic solution.

Hypotonic Solution

Hypertonic Solution

Isotonic Solution

By plotting the percent change in mass of the tissue sample in the different solutions, the osmolarity of the tissue can be determined.

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The osmolarity of a tissue is the point at which there is no change in mass. On the graph, this is the osmolarity extrapolated from the point at which a best fit line through the points crosses the 0% change line.

Tissues will have different osmolarities because they:

• Have different dissolved solutes (sugars, salts, proteins)
• May have been grown in different soils giving their tissues different contents
• May have been stored under different conditions
• May be more or less dehydrated
• May be different ages
• May be different tissue types