Multiple - choice Test
1 The diagram shows a small part of a cell surface membrane.
Answers for Multiple - choice Test
1 D 2 C 3 D 4 C 5 A 6 B 7 A 8 B 9 C 10 A
End-of-chapter questions
1 Whatare the most abundant molecules in the cell surface membranes of plant cells?
A cholesterol
B glycolipids
C phospholipids
D proteins
2 Whereare the carbohydrate portions of glycolipids and glycoproteins located in cell surface membranes?
A the inside and outside surfaces of the membrane
B theinside surface of the membrane
C the interior of the membrane
D the outside surface of the membrane
3 The cells of the myelin sheath are wrapped in layers around nerve cell axons. Freeze-fractured preparations of themyelin sheath cell surface membranes show very few particles. This indicates that myelin membranes contain relativelfyew of which type of molecule?
A cholesterol
B glycolipids
C polysaccharides
D proteins
4 Prepare a table to summarise briefly the major functions of phospholipids, cholesterol, glycolipids, glycoproteins and proteins in cell surface membranes.
5 a Describe fully what will occur if a plant cell is placed in a solution that has a higher water potential than the cell. Use the following terms in your answer.
cell wall, freely permeable, partially permeable, cell surface membrane, vacuole, tonoplast, cytoplasm, solute potential, pressure potential, water potential, turgid, osmosis, protoplast, equilibriumb Describe fully what will occur if a plant cell is placedin a solution that has a lower water potential than the cell. Use the following terms in your answer.
cell wall, freely permeable, partially permeable, cell surface membrane, vacuole, tonoplast, cytoplasm, solute potential, pressure potential, water potential, incipient plasmolysis, plasmolysed, osmosis, protoplast, equilibrium6 The diagram shows part of a membrane containing a channel protein. Part of the protein molecule is shaded.
b For each of the following, state whether the component is hydrophilic or hydrophobic:
i A
ii B
iii darkly shaded part of protein
iv lightly shaded part of protein.
c Explain how ions would move through the channel protein.
d State two features that the channel proteins and carrier proteins of membranes have in common. e State one structural difference between channel and carrier proteins.
f Calculate the magnification of the drawing. Show your working. 7 Copy the table below and place a tick or cross in each box as appropriate.
9 A cell with a water potential of -300 kPa was placed in pure water at time zero. The rate of entry of water into the cell was measured as the change in water potential with time. The graph shows the results of this investigation. Describe and explain the results obtained. [8]
10 The rate of movement of molecules or ions across a cell surface membrane is affected by the relative concentrations of themolecules or ions on either side of the membrane. The graphs below show the effect of concentration difference (the steepness of the concentration gradient) on three transport processes, namely diffusion, facilitated diffusion and activetransport.
a With reference to the graphs, state what the three transport processes have in common.[1]
b Explain the rates of transport observed when the concentration difference is zero. [3]
c i Which one of the processes would stop if a respiratory inhibitor were added?[1]
ii Explain your answer.[2]
d Explain the difference between the graphs for diffusion and facilitated diffusion.[5]
[Total: 12]
11 When a cell gains or loses water, its volume changes. The graphs overleaf show changes in the water potential (Ψ), pressure potential (Ψ) and solute potential (Ψ) of a plant cell as its volume changes as a result of gaining or losing water. (Note that 80% relative cell volume means the cell or protoplast has shrunk to 80% of the volume it was at 100% relative cell volume.)
a What is a protoplast? [1]
b What is the pressure potential at 90%, 95% and 100% relative cell volume? [1]
ii Calculate the change in pressure potential between 90% and 95% relative cell volume and between 95% and 100% relative cell volume,[2]
iii Explain why the pressure potential curve is not linear.[2]
iv State the water potential when the cell reaches maximum turgidity.[1]
The graph shows that as the cell loses water, pressure potential falls and the relative cell volume decreases (the cell shrinks),
c i What is the minimum value of the pressure potential? [1]
ii In a shrinking cell, what is the relative cell volume when the minimum value of the pressure potential is reached? [1]
iii What is the term used to describe the state of the cell at this point? [1]
iv What happens to the values of water potential and solute potential at this point? [1]
v State the equation which links Ψ p, Ψs and Ψ.[1]
vi Describe what is happening to the cell between the point identified in c ii and c iii above and 80% relative cell volume.[5]
d As the cell changes volume, the change in solute potential is much less than the change in pressure potential. Suggest an explanation for this.[3]
[Total: 20]
12 Thediagram shows the concentration in mmol dm-3 of two different ions inside a human red blood cell and in the plasmaoutside the cell.
a Explain why these concentrations could not have occurred as a result of diffusion.[1]
b Explain how these concentrations could have been achieved.[2]
c If respiration of red blood cells is inhibited, the concentrations of potassium and sodium ions inside the cells gradually change until they come into equilibrium with the plasma. Explain this observation.[4]
[Total: 7]
End-of-chapter answers
1 C
2 D
3 D
4 Information for constructing this table can be found on pages 72–73.
5 a Information for answering this question can be found on page 77 and in the answer to SAQ 4.5.
b Information for answering this question can be found on page 77 and in the answer to SAQ 4.5.
6 a A phosphate head (of phospholipid);
B fatty acid tail(s) (of phospholipid);
C phospholipid bilayer/membrane;
b i hydrophilic
ii hydrophobic
iii hydrophobic
iv hydrophilic
c ions move by diff usion; channel has shape which is specifi c for particular ion; channel is hydrophilic/water-fi lled/allows movement of polar substance; ions move down concentration gradient;
d both intrinsic proteins;
both have specifi c shape;e channel proteins have a fi xed shape/carrier proteins have a variable shape;
f width of C measured in mm; mm converted to μm and μm converted to nm; correct formula used magnifi cation: M = I/A = width of C ÷ 7; accept mm, μm or nm; correct answer in nm;
Exam-style questions
9 Description rate of entry of water is rapid at fi rst but slows down gradually; until rate is zero/no further entry of water or water enters until water potential of cell = water potential of pure water = 0 (= equilibrium); exponential/not linear; rate depends on/proportional to, diff erence in water potential between cell and external solution; [max. 3]
Explanation
water (always) moves from a region of higher water potential to a region of lower water potential; (in this case) by osmosis; through partially permeable cell surface membrane of cell; as cell fi lls with water, cell/protoplast expands and pressure (potential) increases; until water potential of cell = zero/water potential of pure water; cell wall rigid/will not stretch (far), and prevents entry of more water; cell is turgid; [max. 5]
[Total: 8]
10 a the greater the concentration diff erence, the greater the rate of transport; [1]
b (net) diff usion and facilitated diff usion only occur if there is a concentration, diff erence/gradient, across the membrane
or at equilibrium/if no concentration diff erence, there is no, net exchange/transport across membrane/rate of transport, is same in both directions; AW active transport can occur even if no concentration diff erence; because molecules/ions are being pumped; AW [3]
c i active transport; [1]
ii active transport depends on a supply of ATP; provided by respiration; [2]
d graph for diff usion is linear/straight line (with no maximum rate);
purely physical process/not dependent on transport proteins/channel or carrier proteins; graph for facilitated diff usion is a curve with a maximum rate; AW facilitated diff usion depends on presence of, transport proteins/channel or carrier proteins; as concentration increases, the receptor sites of these proteins become more and more saturated/ the more saturated these become, the less the eff ect of increasing concentration; rate reaches a maximum when all, transport/channel or carrier proteins, are working at full capacity/when all receptor sites are, full/saturated; N.B. Th is is similar to the eff ect of substrate concentration on rate of enzyme activity. [max. 5][Total: 12]
11 a the living contents of a plant cell; [1]b i at 90% = 22 kPa (accept 21 or 23 kPa), at 95% = 100 kPa, at 100% = 350 kPa; [1]
ii change 90–95 % = 78 kPa (accept 77 or 79 kPa); change 95–100% = 250 kPa; [2]
iii as water enters the cell, the cell wall is stretched/protoplast pushes against cell wall; cell wall is (relatively) rigid; water cannot be compressed; therefore pressure builds up more and more rapidly (for given volume of water)/small increase in amount of water has large eff ect on pressure; AW [max. 2] (This could be compared with pumping up a bicycle tyre – pressure increases much more rapidly for a given amount of air towards the end due to the elastic limit of the tyre being reached.)
iv 350 kPa; [1]
c i zero (kPa); [1]
ii 86%; [1]
iii incipient plasmolysis; [1]
iv water potential = solute potential; [1]
v ψ = ψs + ψp ; [1]
vi the cell continues to lose water/protoplast continues to shrink; protoplast pulls away from cell wall = plasmolysis; shrinks until equilibrium is reached; when water potential of cell = water potential of outside solution; solute potential gets lower/more negative; because cell contents becoming more concentrated; [max. 5]
d only a small amount of water is needed to bring about a large change in pressure;
because the cell wall is (relatively) rigid; this is not enough to signifi cantly change the concentration of the cell contents; AW [3][Total: 20]
12 a if it were diff usion, there would be (net) movement of ions from a region of higher concentration to a region of lower concentration until equilibrium is reached when concentration inside = concentration outside; AW [1] R because concentrations diff erent inside and outside
b active transport;
active transport involves pumping ions against a concentration gradient; [2]c if respiration is inhibited, no ATP is produced;
active transport uses ATP as energy source; active transport stops; diff usion continues; ions move down concentration gradients by diff usion until equilibrium reached; [max. 4][Total: 7]