Flashcards in 1: Osmosis Deck (23):
Are plasma membranes usually freely permeable to water?
Why is the passive movement of water across membranes (ie. osmosis) different from diffusion?
because direction of movement of water depends on concentration of solute, rather than the concentration of water molecules
What is a solvent?
a liquid* in which particles dissolve
*true for osmosis, but a solvent is not always a liquid
What are dissolved particles in liquid called?
What does the direction in which water moves depend on?
depends on the solute, not the concentration of water molecules. It is therefore called osmosis, rather than diffusion.
is the passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration, across a partially permeable membrane
Why does water move to regions with a higher solute concentration?
attractions between solute particles and water molecules
What does the osmolarity of a solution tell us?
the number of moles of solute particles per unit volume of solution
What is the osmolarity of pure water?
0 (moles/unit volume)
What does a higher osmolarity tell us?
the solution has a higher concentration of solutes
What will happen if two solutions at equal pressure but different osmolarity are separated by a partially permeable membrane?
water will move by osmosis from the solution with the lower osmolarity to the solution of higher osmolarity
When do plant cells absorb water from their surroundings? What is the name for the conditions for this to happen?
- gain: if their osmolarity is higher than that of the solution
- hypotonic: "surrounding solution has lower osmolarity than that of plant cell"
When do plant cells lose water? What is the name for the conditions for this to happen?
- lose: if their osmolarity is lower than that of the solution
- hypertonic: "surrounding solution has higher osmolarity than that of plant cell"
What is the principle of osmolarity? What can this principle be used to estimate?
- assuming pressure equal: water will move by osmosis from the solution with the lower osmolarity to the solution of higher osmolarity
- used to estimate the osmolarity of a type of plant tissue, e.g potato
Describe the method for estimating the osmolarity of plant tissue. (look at p11)
1. prepare a series of solutions with a suitable range of solute concentrations, such as 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 moles/litre
2. Cut the plant tissue into samples of equal size and shape
3. Find the mass of each sample using an electronic balance
4. Bathe tissue samples in each of the range of solutions for long enough to get measurable mass changes, usually between 10 and 60 mins.
5. Remove the tissue samples from the bathing solutions, dry them and find their mass again
6. Calculate % mass change using the formula (another card).
7. Plot results on a graph.
8. Read off the solute concentration which would give no mass change.
- osmolarity of a glucose solution is equal to its molarity because glucose remains as a single molecules when it dissolves
- osmolarity of a sodium chloride solution is double its molarity because one mole of NaCl gives two moles of ions when it dissolves - one mole of Na+ and one mole of Cl- .
Quote the formula for calculating the percentage mass change of tissue samples in an osmolarity experiment.
% change = (final mass - initial mass)/ initial mass x100%
Practice reading osmolarity results from a graph.
How accurate can estimates from osmolarity experiments be?
only as accurate as the quantitative measurements
The estimates from osmolarity experiments are only as accurate as the quantitative measurements. Which measurements is it important to get right? How should these quantities be measured?
- volume of water used for making solutions should be measured with a volumetric flask
- initial and final mass of tissue samples should be measured with the same electronic balance that is accurate to 0.01g (10mg)
What can gaining/losing too much water in human tissue cause organs to do?
- gaining too much: swell up and burst
- losing too much: shrink
How can shrinking/swelling of human tissue be prevented in organ donations?
(fyi organ is outside body, body not alive)
- organ must be bathed in a solution with the same osmolarity as human cytoplasm
In organ donations, an organ must be bathed in a solution with the same osmolarity as human cytoplasm otherwise it will shrink/swell. What is the solution?
solution of salts called isotonic saline used for some procedures