IB BIOLOGY
CELL TRANSPORT KEY
PART A: TERMINOLOGY
1. Tonicity: a relative measurement of one solution compared to another solution in terms
of solute concentration
2. Isotonic: a term describing two solutions that have the same solute concentration
3. Hypertonic: a term describing a solution that has a higher solute concentration than
another
4. Hypotonic: a term describing a solution that has a lower solute concentration than
another
5. Plasmolysis: the process where the plant cell membrane pulls away from the cell wall
as a result of water loss
6. Lysis: the process of a cell bursting, often due to too much water
7. Crenation: the shrinking of a red blood cell due to water loss resulting in a wavy
scalloped appearance
8. Osmotic pressure: Pressure generated by the osmotic flow of water through a semipermeable membrane into an aqueous compartment containing solute at a higher
concentration from
(http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/DefO/osmotic_pressure.html)
OR The pressure required to stop osmosis through a semipermeable membrane
between a solution and pure solvent (simplified from
http://www.ndif.org/public/terms/13656-osmotic_pressure)
-solutions with a higher solute concentration have a higher osmotic pressure.
8.1 osmolarity: a measure of the number of dissolved particles per litre of water in osmol
or milliosmols per litre
8.2 osmolality: a measure of the number of dissolved particles per kilogram of water in
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osmos or milliosmols per kilogram
9. Turgor pressure: the pressure of the plant cell's contents against the cell wall caused
by the central vacuole (mainly filled with water) which pushes the cytoplasm towards
the cell membrane and the cell wall
10. In your own words, write the relationship between tonicity and osmotic pressure. You
may want to use other vocabulary words as well. Now go back to the above diagrams
and put labels for areas of higher, lower, or equal osmotic pressures.
The more hypertonic one solution is relative to another, the greater its osmotic
pressure. Conversely, the more hypotonic one solution is relative to another, the lower
its osmotic pressure.
The following diagrams show what happens to cells when placed in solutions with the
relative tonicities specified. The diagram can be found at:
http://kentsimmons.uwinnipeg.ca/cm1504/membranefunction.htm
PART B: IDENTIFY THE TRANSPORTATION PROCESS AND EXPLAIN HOW YOU
KNOW WHICH PROCESS IS INVOLVED.
1. Freshwater moves into a single-celled organism.
OSMOSIS: the molecule that is moving is water and the
inside of the cell is hypertonic
to freshwater
2. Pockets of the cell membrane fill with water and pinch off to become vacuoles inside
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the cell.
PINOCYTOSIS: a liquid is being brought into the cell and sequestered in vacuoles
3. Oxygen molecules (O2) move from the lungs into the bloodstream.
DIFFUSION: oxygen is moving from an area of higher concentration (100 units) to an
area of lower concentration (40 units)
4. An amoeba engulfs a large particle of food.
PHAGOCYTOSIS: a solid is being brought into the cell and sequestered in a vacuole
5. Carrier proteins transport glucose into a muscle cell.
FACIILITATED DIFFUSION: glucose is being transported down its concentration
gradient (from 0.3% to 0%) with the help of a carrier
protein
6. Sodium ions (Na+) are pumped out of a red blood cell.
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ACTIVE TRANSPORT: sodium ions are being moved against their concentration gradient
(from 19 units to 155 units)
PART C: DIFFUSION AND OSMOSIS PROBLEMS. LABEL THE SOLUTIONS AS
ISOTONIC, HYPOTONIC OR HYPERTONIC. DESCRIBE THE NET
MOVEMENT OF WATER AND OTHER NAMED MOLECULES.
1. A bag made of a selectively permeable membrane (dialysis tubing) contains a solution
of 20% protein in water. This bag is placed in a solution of 5% sugar in water. What
will happen to the concentrations of the two solutions? Dialysis tubing is permeable to
water but not to sugar or protein.
-the protein solution in the bag is hypertonic to the outside sugar solution
-water will move into the bag from the outside solution
-the protein solution in the bag will get less concentrated and the outside sugar solution
will get more concentrated
2. What will happen to the protein solution in the left side of the u-tube pictured in the
diagram below? The left side has 20% large protein molecules in 80% water. The right
side has 100% water. The sides are separated by a membrane that simulates a cell
membrane.
-water passes from the right side to the left side as the right side is hypotonic to the
left side
-the solution becomes less concentrated
3. A u-tube like the one pictured below has a semipermeable membrane separating its
two sides. The left side contains a solution of 20% glucose, 1% copper sulphate and
water. The right side contains a solution of 10% glucose, 2% copper sulphate and
water. The membrane is permeable to copper sulphate and water but impermeable to
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glucose.
a) Describe what happens to the concentration of the glucose solution on the left side.
Explain your answer.
-[glucose] decreases as water
-moves from the right side to the left side
b) Describe what happens to the concentration of the copper sulphate solution on the
left side. Explain.
-copper sulphate diffuses from the right side to the left side
-[copper sulphate] is likely to increase but since water is also moving to the left side,
the increase in concentration may not occur; it depends on the amount of water and
copper sulphate that actually crosses the semi-permeable membrane
c) Describe two ways to increase the rate of diffusion across the membrane.
-increase the permeability of the membrane
-heat the solutions
-increase the concentrations of the solutes on the left side of the u-tube
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