Author: Philip Colls
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Cell membranes and transport booklet revision questions  NAME:
Q1.
The diagram shows the structure of the cell-surface membrane of a cell.
 
(a)     Name A and B.
A _________________________________________________________________
B _________________________________________________________________
(2)
(b)     (i)      C is a protein with a carbohydrate attached to it. This carbohydrate is formed by joining monosaccharides together. Name the type of reaction that joins monosaccharides together.
Name the type of reaction that joins monosaccharides together.
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(1)
(ii)     Some cells lining the bronchi of the lungs secrete large amounts of mucus. Mucus contains protein.
Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus.
Organelle______________________________________________________
Description of role _______________________________________________
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(2)
(Total 5 marks)
Q2. (a)     Give two similarities in the movement of substances by diffusion and by osmosis.
1. _________________________________________________________________
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2. _________________________________________________________________
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A scientist measured the rate of uptake of a monoglyceride and a monosaccharide by epithelial cells of the small intestine of mice. A monoglyceride is a molecule of glycerol with one fatty acid attached. She did this for different concentrations of monoglyceride and monosaccharide. Her results are shown in the graph.

(b)     Use your knowledge of transport across membranes to explain the shape of the curve in the graph for uptake of monosaccharides between concentrations:
A and B ____________________________________________________________
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C and D ____________________________________________________________
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(3)
(c)     The graph is evidence for monoglycerides being lipid-soluble molecules.
Suggest how.
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(2)
(Total 7 marks)
Q3.
The diagram shows part of a plasma membrane. The arrows show the path taken by sodium ions and by substance X when they diffuse through the membrane into a cell.

(a)     An optical microscope cannot be used to see a plasma membrane. Explain why.
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(2)
(b)     Give one property of the molecules of substance X which allows them to diffuse through the membrane at the position shown.
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(1)
(c)     The effect of the concentration of sodium ions in the surrounding solution on their rate of diffusion across the membrane was investigated. The graph shows the results.
 
(i)      What limits the diffusion of sodium ions across the membrane between
A and B on the graph? Give the evidence for your answer.
Limiting factor __________________________________________________
Evidence ______________________________________________________
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(2)
(ii)     Explain the shape of the curve between C and D.
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______________________________________________(2)  (Total 7 marks)
Q4. The cells of beetroot contain a red pigment. A student investigated the effect of temperature on the loss of red pigment from beetroot. He put discs cut from beetroot into tubes containing water. He maintained each tube at a different temperature. After 25 minutes, he measured the percentage of light passing through the water in each tube.
(a)     The student put the same volume of water in each tube.
Explain why it was important that he controlled this experimental variable.
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(b)     Describe a method the student could have used to monitor the temperature of the water in each tube.
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The graph shows the student’s results.
 
(c)     Draw a suitable curve on the graph above.
(1)
(d)     The decrease in the percentage of light passing through the water between 25 °C and 60 °C is caused by the release of the red pigment from cells of the beetroot. Suggest how the increase in temperature of the water caused the release of the red pigment.
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_____________________________________________________(2)(Total 6 marks)
Q5. (a)     Describe how you would test a piece of food for the presence of lipid.
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The figure below shows a phospholipid.

X         Y                      
(b)     The part of the phospholipid labelled A is formed from a particular molecule. Name this molecule.
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(1)
(c)     Name the type of bond between A and fatty acid X.
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(1)
(d)     Which of the fatty acids, X or Y, in the figure above is unsaturated? Explain your answer.
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(1)
Scientists investigated the percentages of different types of lipid in plasma membranes from different types of cell. The table shows some of their results.
 
Type of lipid | Percentage of lipid in plasma membrane by mass
| Cell lining ileum of mammal | Red blood cell of mammal | The bacterium Escherichia coli
Cholesterol | 17 | 23 | 0
Glycolipid | 7 | 3 | 0
Phospholipid | 54 | 60 | 70
Others | 22 | 14 | 30
(e)     The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.
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(2)
Cholesterol increases the stability of plasma membranes. Cholesterol does this by making membranes less flexible.

(f)     Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.
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(g)     E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.
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Q6. (a)     Contrast the processes of facilitated diffusion and active transport.
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Students investigated the uptake of chloride ions in barley plants. They divided the plants into two groups and placed their roots in solutions containing radioactive chloride ions.
•        Group A plants had a substance that inhibited respiration added to the solution.
•        Group B plants did not have the substance added to the solution.
The students calculated the total amount of chloride ions absorbed by the plants every 15 minutes. Their results are shown in the figure below.
 
                  Time / minutes
(b)     Calculate the ratio of the mean rate of uptake of chloride ions in the first hour to the rate of uptake of chloride ions in the second hour for group B plants.

 
Ratio = ____________________ :1
(2)
(c)     Explain the results shown in the figure above.
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____________________________________________________ (4) (Total 9 marks)
Q7. Read the following passage.

The plasma membrane plays a vital role in microorganisms. It forms a barrier between the cell and its environment, controlling the entry and exit of solutes.
This makes bacteria vulnerable to a range of antiseptics and antibiotics.

When bacteria are treated with antiseptics, the antiseptics bind to the proteins in the membrane and create tiny holes. Bacteria contain potassium ions at a concentration many times that outside the cell. Because of the small size of these ions and their concentration in the cell, the first observable sign of antiseptic damage to the plasma membrane is the leaking of potassium ions from the cell. Some antibiotics damage the plasma membrane in a similar way. One of these is tyrocidin. This is a cyclic polypeptide consisting of a ring of ten amino acids. Tyrocidin and other polypeptide antibiotics are of little use in medicine.

Other antibiotics also increase the rate of potassium movement from cells. It is thought that potassium ions are very important in energy release and protein synthesis, and a loss of potassium ions would lead to cell death. Gramicidin A coils to form a permanent pore passing through the plasma membrane. This pore enables potassium ions to be conducted from the inside of the cell into the surrounding medium. Vanilomycin also facilitates the passage of potassium ions from the cell. 
A molecule of vanilomycin forms a complex with a potassium ion and transports it across the membrane. The potassium ion is released on the outside and the vanilomycin is free to return and pick up another potassium ion. Vanilomycin depends on the fluid nature of the plasma membrane in order to function.

Polyene antibiotics have flattened ring-shaped molecules. The two sides of the ring differ from each other. One side consists of an unsaturated carbon chain. This part is strongly hydrophobic and rigid. The opposite side is a flexible, strongly hydrophilic region. It has been shown that polyene antibiotics bind only to sterols. Sterols are lipids found in the membranes of eukaryotes but not in the membranes of prokaryotic organisms. It is thought that several sterol-polyene complexes come together. The plasma membranes of eukaryotic cells treated with these polyene antibiotics lose the ability to act as selective barriers and small ions and molecules rapidly leak out.

5

 
 
10

 

15

 
 
20

 

25

          Use information in the passage and your own knowledge to answer the questions.
(a)     By what process do potassium ions normally enter a bacterial cell? Explain the evidence for your answer.
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(b)     (i)      Draw a peptide bond showing how the COOH group of one amino acid joins to the NH_2 group of another.

 
 
(1)
(ii)     How many peptide bonds are there in a molecule of tyrocidin (lines 9 - 10)?
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(c)     Experiments have shown that vanilomycin is unable to transport potassium ions across a membrane when it is cooled. Gramicidin A continues to facilitate the movement of potassium ions at these low temperatures. Explain these results.
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(d)     Draw a simple diagram of one of the phospholipid layers to show how polyene antibiotics allow small ions and molecules to leak rapidly through a plasma membrane. Use the following symbols to represent the different molecules. Note that the zigzag line on the symbol for the polyene antibiotic represents its hydrophobic region.

 

 
                            (2)           (Total 9 marks)
Q8. A group of students carried out an investigation to find the water potential of potato tissue. The students were each given a potato and 50 cm^3 of a 1.0 mol dm^−3 solution of sucrose.
•        They used the 1.0 mol dm^−3 solution of sucrose to make a series of different concentrations.
•        They cut and weighed discs of potato tissue and left them in the sucrose solutions for a set time.
•        They then removed the discs of potato tissue and reweighed them.
The table below shows how one student presented his processed results.
 
Concentration of sucrose solution / mol dm^−3 | Percentage change in mass of potato tissue
0.15 | +4.7
0.20 | +4.1
0.25 | +3.0
0.30 | +1.9
0.35 | −0.9
0.40 | −3.8
(a)     Explain why the data in the table above are described as processed results.
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(1)
(b)     Describe how you would use a 1.0 mol dm^−3 solution of sucrose to produce 30 cm^3 of a 0.15 mol dm^−3 solution of sucrose.
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(2)
(c)     Explain the change in mass of potato tissue in the 0.40 mol dm^−3 solution of sucrose.
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(2)
(d)     Describe how you would use the student’s results in the table above to find the water potential of the potato tissue.
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(Extra space) _______________________________________________________
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(3)
(Total 8 marks)

Q9. A student investigated the effect of surface area on osmosis in cubes of potato.
•        He cut two cubes of potato tissue, each with sides of 35 mm in length.
•        He put one cube into a concentrated sucrose solution.
•        He cut the other cube into eight equal-sized smaller cubes and put them into a sucrose solution of the same concentration as the solution used for the large cube.
•        He recorded the masses of the cubes at intervals.
His results are shown in the graph.

(a)     Describe the method the student would have used to obtain the results in the graph. Start after all of the cubes of potato have been cut. Also consider variables he should have controlled.
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(b)     The loss in mass shown in the graph is due to osmosis. The rate of osmosis between 0 and 40 minutes is faster in B (the eight small cubes) than in A (single large cube).
Is the rate of osmosis per mm^2 per minute different between A and B during this time?
Use appropriate calculations to support your answer.
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(3)
(Total 6 marks)

Mark schemes
Q1.
(a)     1.       A: phospholipid (layer);
1. Reject hydrophobic / hydrophilic phospholipid
2.      B: pore / channel / pump / carrier / transmembrane / intrinsic / transport protein;
2. Ignore unqualified reference to protein
2
(b)     (i)      Condensation (reaction);
1
(ii)     Organelle named; Function in protein production / secretion;
Function must be for organelle named 
Incorrect organelle = 0
eg
1.      Golgi (apparatus);
1. Accept smooth endoplasmic reticulum
2.      Package / process proteins;
OR
3.      Rough endoplasmic reticulum / ribosomes;
3. Accept alternative correct functions of rough endoplasmic reticulum. ER / RER is insufficient
3. Accept folding polypeptide / protein
4.      Make polypeptide / protein / forming peptide bonds;
OR
5.      Mitochondria;
6.      Release of energy / make ATP;
6. Reject produce / make energy
6. Accept produce energy in the form of ATP
OR
7.      Vesicles;
8.      Secretion / transport of protein;
2
[5]
Q2.
(a)     1.      (Movement) down a gradient / from high concentration to low concentration;
Ignore along / across gradient
Reject movement from gradient to gradient
2.      Passive / not active processes;
OR
Do not use energy from respiration / from ATP / from metabolism;
OR
Use energy from the solution;
Reject do not use energy unqualified
2
(b)     1.      Movement through carrier proteins;
OR
Facilitated diffusion;
Between A and B
Accept MP1 in either section
Ignore co-transport / active transport
Accept channel proteins
2.      Rate of uptake proportional to (external) concentration;
Between C and D
Accept description of proportional
3.      All channel / carrier proteins in use / saturated / limiting;
Accept used up
Accept transport proteins
3
(c)     1.      Rate of uptake is proportional / does not level off (so diffusion occurring);
Accept as one increases the other increases
2.      (Lipid-soluble molecules) diffuse through / are soluble in phospholipid (bilayer);
2
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Q3.
(a)     Does not have the resolution / cannot distinguish between points this close together;
As light has longer wavelength;
The key ideas in marking this part of the question are resolution and wavelength.
2
(b)     Lipid soluble / small / non-polar / not charged;
1
(c)     (i)      Concentration of sodium ions (outside cell);
As concentration / independent variable increases so does
the rate of diffusion;
2
(ii)     Sodium ions are passing through the channels / pores at their maximum rate;
Rate is limited by the number of sodium channels / another limiting factor;
2
[7]
Q4.
(a)     1.      (If) too much water the concentration of pigment (in solution) will be lower / solution will appear lighter / more light passes through (than expected);
OR
(If) too little water the concentration of pigment (in solution) will be greater / solution will appear darker / less light passes through (than expected);
2.      So results (from different temperatures) are comparable;
1.      Ignore reference to too much water so red pigment / solution too weak to measure
2
(b)     (Take) readings (during the experiment) using a (digital) thermometer / temperature sensor;
1
(c)     Point-to-point line drawn between co-ordinates (with a ruler);
OR
Smooth s-shaped line of best fit;
Reject any extrapolations below 20 °C or above 80 °C
Any line should look smooth (not ‘sketchy’)
1
(d)     1.      Damage to (cell surface) membrane;
2.      (membrane) proteins denature;
3.      Increased fluidity / damage to the phospholipid bilayer;
2 max
[6]
Q5.
(a)     1.      Dissolve in alcohol, then add water;
2.      White emulsion shows presence of lipid.
2
(b)     Glycerol.
1
(c)     Ester.
1
(d)     Y (no mark)
Contains double bond between (adjacent) carbon atoms in hydrocarbon chain.
1
(e)     1.      Divide mass of each lipid by total mass of all lipids (in that type of cell);
2.      Multiply answer by 100.
2
(f)     Red blood cells free in blood / not supported by other cells so cholesterol helps to maintain shape;
Allow converse for cell from ileum – cell supported by others in endothelium so cholesterol has less effect on maintaining shape.
1
(g)     1.      Cell unable to change shape;
2.      (Because) cell has a cell wall;
3.      (Wall is) rigid / made of peptidoglycan / murein.
2 max
[10]
Q6.
(a)     1.      Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;
2.      Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP;
3.      Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.
Since ‘contrast’, both sides of the differences needed
3
(b)     3.3:1.
Correct answer = 2 marks
If incorrect, allow 1 mark for 470–360 / 60 for rate in second hour
2
(c)     1.      Group A – initial uptake slower because by diffusion (only);
2.      Group A – levels off because same concentrations inside cells and outside cells / reached equilibrium;
3.      Group B – uptake faster because by diffusion plus active transport;
4.      Group B fails to level off because uptake against gradient / no equilibrium to be reached;
5.      Group B – rate slows because few / fewer chloride ions in external solution / respiratory substrate used up.
4 max
[9]
Q7.
(a)    Rate of movement / diffusion proportional to concentration gradient / 
difference in concentration;
High concentration of potassium ions inside cell compared to outside;
Must mention high concentration. Ignore reference to other factors if
reasoning is appropriate.
2
(b)     (i)      O
 ||
 C – N
         |
        H;
1
(ii)     10;
1
(c)     Action of vanilomycin depends on fluidity of membrane;
Fluidity reduced / not fluid at low temperatures;
Pore formed by gramicidin A remains in place / permanent;
3
(d)     Pore between sterol molecules lined with polyene antibiotic;
Hydrophobic region next to sterol;
2
[9]
Q8.
(a)     Calculations made (from raw data) / raw data would have recorded initial and final masses.
1
(b)     Add 4.5 cm^3 of (1.0 mol dm^–3) solution to 25.5 cm^3 (distilled) water.
If incorrect, allow 1 mark for solution to water in a proportion of 0.15:0.85
2
(c)     1.      Water potential of solution is less than / more negative than that of potato tissue;
Allow Ψ as equivalent to water potential
2.      Tissue loses water by osmosis.
2
(d)     1.      Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
2.      Find concentration where curve crosses the x-axis / where percentage change is zero;
3.      Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis).
3
[8]
Q9.
(a)     1.      Method to ensure all cut surfaces of the eight cubes are exposed to the sucrose solution;
Credit valid method descriptions to fulfil mp1, 2 and 3 (no explanation is required).
2.      Method of controlling temperature;
Accept ‘at room temperature’ for method
3.      Method of drying cubes before measuring;
4.      Measure mass of cubes at stated time intervals;
Accept time intervals between every 5 minutes with maximum of every 40 minutes.
Accept ‘weigh the cubes at stated time intervals’
3 max
(b)     Yes or No (no mark)
Calculation of rate per mm^2 for both sets of data, accept answers in the range
1.6 × 10^–5 to 1.8 × 10^–5 and
1.5 × 10^–5 to 1.6 × 10^–5;;; Both correct = 3
One correct = 2
Neither correct – look below for max 2
Allow 1 mark for calculation of surface area of two (sets of) cubes 7350 (mm^2) and 14700 (mm^2)
Allow 1 mark for calculation of both rates of osmosis shown in first 40 minutes – between 0.12 and 0.13 and between 0.22 and 0.23
If surface area and/or rate of osmosis is incorrect then, allow 1 mark for (their) calculated rate divided by (their) calculated surface area
Accept answers not given in standard form or to any number of significant figures ≥2sf as long as rounding correct.
3 max
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