Question 1
A selectively permeable membrane separates a sucrose solution from a sucrose solution. Sucrose cannot cross the membrane. What is the net movement of water?
A.
From the solution to the solution
B.
Equally in both directions because sucrose is too large to cross the membrane
C.
No movement because water cannot cross a selectively permeable membrane
D.
From the solution to the solution
Question 2
Normal saline used for intravenous infusion is approximately isotonic with human blood plasma. Why is isotonicity important?
A.
It prevents net osmotic gain or loss of water by blood cells.
B.
It prevents oxygen from binding reversibly to haemoglobin.
C.
It makes all dissolved ions diffuse rapidly through blood cell membranes.
D.
It causes red blood cells to swell so that more oxygen can be carried.
Question 3
Sodium chloride dissolves in water. What interaction explains the solvation of the separated chloride ions?
A.
Water molecules form covalent bonds with chloride ions in the solution.
B.
The partial negative oxygen atoms of water molecules are attracted to chloride ions.
C.
Water molecules become non-polar when they surround chloride ions.
D.
The partial positive hydrogen atoms of water molecules are attracted to chloride ions.
Question 4
An animal cell is placed in an isotonic solution. What occurs at dynamic equilibrium?
A.
The plasma membrane uses ATP to pump water out of the cell.
B.
Water molecules stop crossing the plasma membrane because the cell is isotonic.
C.
Solute molecules cross the plasma membrane until both sides have no solute.
D.
Water molecules cross the plasma membrane in both directions at equal rates.
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Question 5
A freshwater unicellular organism has a cytoplasm that is more concentrated than the surrounding water. What is the role of its contractile vacuole?
A.
It collects excess water entering by osmosis and expels it from the cell.
B.
It prevents all water molecules from crossing the plasma membrane.
C.
It digests solute molecules so that osmosis can no longer occur.
D.
It pumps dissolved salts out of the cell to make the cytoplasm hypotonic.
Question 6
A plant epidermal cell is placed in a hypertonic solution for several minutes. What change is most likely to be observed?
A.
The vacuole expands and presses the plasma membrane against the cell wall.
B.
The cell bursts because turgor pressure rises above the wall strength.
C.
The plasma membrane and cytoplasm pull away from the cell wall.
D.
The cell wall becomes selectively permeable and stops osmosis.
Question 7
Water potential values in biology are measured relative to pure water under standard reference conditions. What value is assigned to pure water at atmospheric pressure and ?
A.
B.
C.
D.
Question 8
Two plant cells are connected by plasmodesmata that allow water movement. Cell X has a water potential of and cell Y has a water potential of . What is the direction of net water movement?
A.
There is no net movement because both water potentials are negative
B.
From cell X to cell Y only if ATP is supplied to the cells
C.
From cell X to cell Y because is a higher water potential
D.
From cell Y to cell X because has the larger magnitude
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Question 9
A small crystal of sodium chloride is added to water and dissolves.
State the property of water molecules that allows them to interact with ions.
[1]
Outline how water solvates sodium chloride.
[2]
Question 10
An animal cell is placed in an isotonic solution.
Explain why the volume of the cell remains approximately constant.
[2]
Question 11
The graph shows the mean percentage change in mass of potato cylinders after immersion in sucrose solutions of different concentrations. What is the best estimate of the isotonic sucrose concentration for the potato tissue?
A.
B.
C.
D.
Question 12
A turgid plant cell has a solute potential of and a pressure potential of . What is its water potential?
A.
B.
C.
D.
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Question 13
In which situation is pressure potential most likely to be negative?
A.
Cell sap in a fully turgid leaf mesophyll cell
B.
Water in a xylem vessel being pulled upwards under tension
C.
Pure water in an open beaker at atmospheric pressure
D.
A plant cell vacuole pressing strongly against the cell wall
Question 14
Two solutions are separated by a selectively permeable membrane that allows water, but not sucrose, to pass through. Side A contains a lower sucrose concentration than side B.
Identify the side towards which there will be a net movement of water.
[1]
Explain this movement using the terms hypotonic and hypertonic.
[2]
Question 15
A freshwater unicellular organism has a cytoplasm that is more concentrated than the pond water around it. It contains contractile vacuoles.
Explain the role of contractile vacuoles in this organism.
[3]
Question 16
Water movement affects cells differently depending on whether a cell wall is present. Isotonic solutions are also used in medical treatment.
Outline why plant cells in a hypotonic medium become turgid but usually do not burst.
[2]
State what happens to a plant cell in a hypertonic medium if water loss is severe.
[1]
State one medical use of an isotonic solution.
[1]
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Question 17
Water potential is used to compare the tendency of water to move in biological systems.
Define water potential.
[2]
State the water potential of pure water at atmospheric pressure and .
[1]
Question 18
Two plant cells are connected by plasmodesmata through which water can move. Cell X has a water potential of and cell Y has a water potential of .
Identify the direction of net water movement.
[1]
Explain the reason for this movement in terms of potential energy.
[2]
Question 19
The diagram shows solvation of three solutes in water. The same number of particles of each solute was added to equal volumes of water and stirred for the same time.
Identify the type of attraction shown between water molecules and glucose.
[1]
Describe how water molecules are oriented around the sodium ions and chloride ions shown.
[2]
Explain why the hydrocarbon is least likely to affect the net movement of water across a membrane.
[1]
Question 20
Two aqueous solutions were separated by a membrane permeable to water but not to the dissolved solute. The diagram shows the initial solute concentrations.
Compartment | Initial solute concentration / mol dm |
|---|---|
Left-hand solution | 0.20 |
Right-hand solution | 0.60 |
State which solution is hypertonic compared with the other.
[1]
Predict the direction of net water movement, using solute concentration in your answer.
[1]
Suggest why the rate of net water movement decreases as the experiment continues.
[2]
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Question 21
A flaccid plant cell with and is placed in pure water. What changes are expected as the cell approaches equilibrium?
A.
Water enters; remains zero and becomes more negative.
B.
There is no net water movement because the pressure potential is initially zero.
C.
Water leaves; becomes more positive and becomes more negative.
D.
Water enters; becomes more positive and becomes less negative.
Question 22
A student placed equal-sized potato cylinders in sucrose solutions of different concentrations. Mean percentage changes in mass and length were plotted with standard error bars.
Sucrose concentration / mol | Mean percentage change in mass / % | SE mass / % | Mean percentage change in length / % | SE length / % |
|---|---|---|---|---|
0.00 | +20 | 0.8 | +14 | 2.1 |
0.10 | +12 | 0.8 | +8 | 2.0 |
0.20 | +4 | 0.7 | +3 | 1.9 |
0.40 | -4 | 0.7 | -3 | 2.0 |
0.50 | -12 | 0.8 | -8 | 2.2 |
Estimate the isotonic sucrose concentration for the potato tissue.
[1]
Explain why there is no percentage change in mass at the isotonic concentration.
[2]
Compare the reliability of the mass and length measurements using the standard error bars.
[1]
Question 23
A turgid epidermal plant cell has a solute potential, , of and a pressure potential, , of . It is transferred to a solution with a water potential of .
Calculate the water potential, , of the plant cell before transfer.
[1]
Predict the initial direction of net water movement after transfer.
[1]
Suggest how the pressure potential changes as this net movement occurs.
[1]
Question 24
In a transpiring leaf, xylem sap may be under tension. This can affect pressure potential.
State the possible range of solute potential values in a solution.
[1]
Explain how tension in xylem affects water potential.
[2]
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Question 25
Animal cells were placed in three media with different concentrations of osmotically active solutes. Cell volume was recorded over ten minutes.
Identify the medium in which the cells were closest to dynamic equilibrium.
[1]
Explain why dynamic equilibrium does not mean that water movement has stopped.
[2]
Predict the consequence for cells left for longer in the medium causing the greatest increase in volume.
[1]
Question 26
Red blood cells were incubated in saline solutions of different concentrations. The percentage of cells showing normal shape, crenation or lysis was recorded.
NaCl concentration / % | Normal cells / % | Crenated cells / % | Lysed cells / % |
|---|---|---|---|
0.30 | 1 | 0 | 99 |
0.60 | 25 | 5 | 70 |
0.90 | 90 | 7 | 3 |
1.20 | 35 | 60 | 5 |
1.50 | 5 | 92 | 3 |
Identify the sodium chloride concentration that is closest to isotonic for the red blood cells.
[1]
Explain the high percentage of lysed cells in the most dilute saline solution.
[2]
Suggest why multicellular animals regulate the solute concentration of tissue fluid.
[1]
Question 27
Epidermal strips from onion were placed in solutions of different sucrose concentration. The percentage of cells showing plasmolysis was counted using a light microscope.
Describe the relationship between sucrose concentration and the percentage of plasmolysed cells.
[1]
Explain why plasmolysis occurs at high sucrose concentration.
[2]
Discuss why the cells do not usually burst in the lowest sucrose concentration.
[2]
Question 28
Water potential was measured for several solutions at atmospheric pressure and . Pure water under the same conditions was used as the reference.
State the water potential assigned to pure water at atmospheric pressure and .
[1]
Describe the effect of increasing solute concentration on water potential.
[1]
Explain why water potential values are given relative to pure water rather than as absolute potential energy values.
[2]
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Question 29
Three plant cells were connected by plasmodesmata that allowed water movement between them. Water potential was measured in each cell before net movement began.
Identify the cell with the highest water potential.
[1]
Predict the direction of net water movement between cell A and cell C.
[1]
Explain the prediction in terms of potential energy.
[2]
Question 30
A piece of flaccid plant tissue is placed in pure water at atmospheric pressure.
State the water potential of the external solution.
[1]
Explain the changes in solute potential and pressure potential as water enters the cells.
[2]
Explain why net water entry eventually stops.
[1]
Question 31
Cells from onion epidermis are placed in a concentrated sucrose solution. After equilibration, the cytoplasm has pulled away from the cell wall. The solute potential of the cell contents is and the pressure potential is . The bathing solution has a water potential of .
Calculate the water potential of the cell contents after equilibration.
[1]
State whether there is net water movement between the cell contents and the bathing solution after equilibration.
[1]
Explain why the pressure potential is zero in these plasmolysed cells.
[2]
Question 32
Cylinders of beetroot tissue were placed in sucrose solutions for one hour. Mean percentage changes in mass and length were calculated from repeated samples.
Sucrose concentration / mol dm | Mean % change in mass / % | Mass SE / % | Mean % change in length / % | Length SE / % |
|---|---|---|---|---|
0.0 | 18.2 | 0.5 | 8.4 | 1.8 |
0.1 | 13.5 | 0.5 | 6.1 | 1.7 |
0.2 | 8.7 | 0.4 | 3.3 | 1.8 |
0.3 | 4.0 | 0.5 | 0.8 | 1.9 |
0.4 | -5.8 | 0.5 | -2.2 | 2.0 |
0.5 | -10.9 | 0.6 | -4.8 | 2.1 |
Estimate the isotonic sucrose concentration from the mass data.
[1]
Describe the effect of increasing sucrose concentration on percentage change in mass.
[1]
Evaluate which measurement, mass or length, gives the more reliable estimate of the isotonic concentration.
[2]
Suggest one controlled variable needed to make this investigation valid.
[1]
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Question 33
Solute potential and pressure potential were measured in cells from three regions of a celery petiole.
Cell region | Solute potential / kPa | Pressure potential / kPa |
|---|---|---|
Turgid cortical cell | -720 | 520 |
Flaccid cortical cell | -760 | 0 |
Xylem vessel | 0 | -150 |
Calculate the water potential of the turgid cortical cell using .
[1]
Identify the cell region with a negative pressure potential.
[1]
Explain why solute potential values in the table are zero or negative, but not positive.
[2]
Suggest why pressure potential is positive in the turgid cortical cell.
[1]
Question 34
Sections of carrot tissue were transferred from an isotonic solution into distilled water. Water potential components were measured at intervals.
State the initial direction of net water movement.
[1]
Explain the change in pressure potential shown by the data.
[2]
Explain why net water entry stops even though the cells contain dissolved solutes.
[2]
Question 35
A solid crystal of sodium chloride and a small amount of glucose are added to water before the solution is used in a cell culture medium.
I.
Explain why water molecules can form attractions with both ions and polar molecules.
[2]
II.
Explain the process by which sodium chloride becomes solvated in water.
[3]
Compare the significance of water solubility for glucose and for non-polar lipid molecules in cells.
[2]
Question 36
A model cell is made by filling dialysis tubing with a sucrose solution and placing it in a beaker containing a different sucrose solution. The tubing is permeable to water but not to sucrose.
I.
Solution A contains a higher concentration of sucrose than solution B. State the relative tonicity of solution B compared with solution A.
[1]
II.
Explain the predicted net movement of water in this model.
[2]
Explain why there is no net change in mass if the two sucrose solutions are isotonic.
[2]
Suggest why the model would be less useful if the membrane were permeable to sucrose.
[2]
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Question 37
Epidermal strips from a plant leaf were placed in two unlabelled solutions. In solution X most cells appeared firm with the plasma membrane pressed against the cell wall. In solution Y many cells showed separation of the cytoplasm from the cell wall.
I.
Deduce which solution was hypotonic to the cell contents and which was hypertonic.
[2]
II.
Explain the appearance of the cells in solution Y.
[2]
Compare the response of plant cells and animal cells when placed in a hypotonic medium.
[3]
Question 38
Water potential is used to predict water movement in cells and tissues. Pure water at atmospheric pressure and is assigned a water potential of .
I.
Explain what is meant by water potential.
[2]
II.
Explain why water potential values are given relative to pure water rather than as absolute values.
[2]
Compare water movement between a solution with water potential and a solution with water potential if they are separated by a membrane permeable to water.
[2]
Explain briefly why water tends to move from higher to lower water potential.
[1]
Question 39
Leaf epidermal cells were placed in external solutions with different water potentials. The proportion of plasmolysed cells and the mean pressure potential were measured after equilibrium.
External water potential / kPa | Plasmolysed cells / % | Mean pressure potential / kPa |
|---|---|---|
-300 | 0 | |
-500 | 0 | |
-650 | 5 | |
-720 | 35 | |
-800 | 80 | |
-950 | 95 |
Identify the range of external water potential over which mean pressure potential falls to zero.
[1]
Explain why plasmolysis becomes more frequent as external water potential becomes more negative.
[2]
Evaluate the use of pressure potential data for estimating the onset of plasmolysis.
[2]
Question 40
A shoot was exposed to increasing light intensity. Measurements were made of water potential components in mesophyll cells and xylem vessels.
Light intensity / a.u. | Mesophyll solute potential / kPa | Mesophyll pressure potential / kPa | Xylem pressure potential / kPa |
|---|---|---|---|
0 | |||
20 | |||
40 | |||
60 |
Calculate the mesophyll water potential at the highest light intensity.
[1]
Compare pressure potential in mesophyll cells and xylem vessels at high light intensity.
[2]
Discuss how the water potential gradient would affect water movement from mesophyll cells to xylem vessels.
[2]
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Question 41
Students investigated osmosis in potato cylinders by placing equal lengths of tissue in sucrose solutions for one hour. They measured percentage change in mass and percentage change in length, with standard error shown for each mean.
Sucrose conc. / mol dm | Mean % change in mass | SE mass / % | Mean % change in length | SE length / % |
|---|---|---|---|---|
0.00 | 13.0 | 0.5 | 10.0 | 1.1 |
0.10 | 8.5 | 0.4 | 6.3 | 1.0 |
0.20 | 4.0 | 0.4 | 3.6 | 1.0 |
0.30 | -1.0 | 0.4 | -0.9 | 0.9 |
0.40 | -5.2 | 0.5 | -4.0 | 1.0 |
0.50 | -9.4 | 0.6 | -7.3 | 1.1 |
I.
Explain how the isotonic solute concentration can be deduced from the graph.
[2]
II.
Explain how standard error bars can be used to judge which dependent variable gave the more reliable estimate of the mean.
[2]
Explain the changes in mass expected for potato tissue in hypotonic and hypertonic sucrose solutions.
[3]
Evaluate the importance of blotting all potato cylinders in the same way before weighing.
[1]
Question 42
A freshwater unicellular organism such as Paramecium lives in pond water. Its cytoplasm contains more dissolved solutes than the surrounding water, and it has contractile vacuoles.
I.
Explain why water tends to enter the organism continuously.
[2]
II.
Explain the role of contractile vacuoles in this organism.
[2]
Compare the effects of hypotonic and hypertonic media on cells that lack a cell wall.
[3]
Question 43
A patient receives an intravenous fluid after blood loss. Another patient has a donor kidney stored in a preservation fluid before transplantation. Both fluids are designed to be approximately isotonic with human tissue fluid.
Fluid type | Solute conc. vs tissue fluid | Water movement | Cell outcome |
|---|---|---|---|
IV fluid after blood loss | approximately the same | water enters and leaves at equal rates | red blood cells keep normal volume |
Donor kidney preservation fluid | approximately the same | water enters and leaves at equal rates | organ cells stay structurally intact |
Strongly hypotonic IV fluid | lower | water enters faster than it leaves | cells swell and may rupture |
I.
Explain why an isotonic intravenous fluid helps maintain normal red blood cell volume.
[3]
II.
Explain why isotonicity is also important when organs are bathed before transplantation.
[2]
Evaluate the risk of accidentally giving a strongly hypotonic intravenous fluid.
[2]
State why isotonic does not mean that water movement across the membrane has stopped.
[1]
Question 44
The water potential of plant cells with walls can be analysed using the equation . A mesophyll cell has solute potential and pressure potential before it is placed in a bathing solution.
Sample | / kPa | / kPa | / kPa |
|---|---|---|---|
Mesophyll cell | -900 | +500 | -400 |
Bathing solution | -250 | 0 | -250 |
Pure water | 0 | 0 | 0 |
I.
Calculate the water potential of the mesophyll cell.
[2]
II.
A bathing solution has water potential . Predict the initial direction of net water movement and justify your answer.
[2]
Explain how solute potential and pressure potential change as water enters a plant cell in a hypotonic solution.
[3]
State why solute potential cannot be positive.
[1]
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Question 45
A strip of plant tissue is transferred from a concentrated sucrose solution into pure water. Changes in solute potential and pressure potential are recorded over time.
I.
Using , explain how the water potential of the cells changes after transfer to pure water.
[3]
II.
Explain why net water entry eventually stops although water molecules are still able to cross membranes.
[2]
Discuss how the cell wall contributes to the final water potential of the tissue in pure water.
[3]
Question 46
Plant cells from a storage organ are transferred to a strongly hypertonic solution. Xylem vessels in the same plant are transporting sap under tension.
I.
Explain the changes in solute potential and pressure potential as the storage cells lose water.
[3]
II.
Explain why plasmolysis may occur if water loss continues.
[2]
Compare pressure potential in plasmolysed storage cells and in xylem vessels transporting sap under tension.
[2]
Question 47
Two adjacent plant cells have the same water potential but different solute potentials and pressure potentials. Cell A has a more negative solute potential than cell B, but cell A also has a higher positive pressure potential.
Cell | Solute potential, / MPa | Pressure potential, / MPa | Water potential, / MPa |
|---|---|---|---|
A | -1.2 | +0.7 | -0.5 |
B | -0.7 | +0.2 | -0.5 |
I.
Explain how two cells can have the same water potential despite different solute potentials.
[2]
II.
Predict whether there will be net water movement between cell A and cell B at this instant.
[2]
Evaluate the statement: “Water movement in plant tissue can be predicted from solute concentration alone.”
[4]
Question 48
A preserving fluid for plant tissue culture is formulated to avoid rapid water gain or loss by cells. Researchers can alter the concentration of dissolved solutes and can also apply mild external pressure to the tissue chamber.
I.
Discuss how changing dissolved solute concentration in the preserving fluid can alter water movement into or out of the tissue.
[3]
II.
Discuss how pressure potential can influence water movement in cells with walls.
[2]
Evaluate why using water potential is more informative than using the terms hypotonic and hypertonic alone in this situation.
[2]
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