Week 5 homework (glucose co – transport and gas exchange)
Q1.
The diagram shows one method by which amino acids are absorbed from the small
intestine into the blood. They are co-transported into the epithelial cell with sodium ions
(Na+) at point X on the diagram. Normally, the concentration of sodium ions inside the
epithelial cell is low.
Source: adapted from M. ROWLAND,
Biology (University of Bath Science 16-19) (Nelson Thornes) 1992.
Dinitrophenol (DNP) prevents oxidative phosphorylation. When treated with DNP, the
sodium-potassium pump at Y no longer works. As a result, the concentration of sodium
ions in the cell rises and amino acid absorption stops.
(i) Explain why pump Y will not work in the presence of DNP.
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(2)
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(ii) Explain why sodium ions and amino acids are not absorbed from the lumen of the
small intestine in the presence of DNP.
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(2)
(iii) By what mechanism would amino acids leave the epithelial cell at point Z?
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(1)
(Total 5 marks)
Q2.
(a) Cells lining the ileum of mammals absorb the monosaccharide glucose by co-
transport with sodium ions. Explain how.
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(3)
A student set up the experiment shown in the diagram below.
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The material from which Visking tubing is made is partially permeable.
After 15 minutes, the student removed samples from the liquid in the beaker and from the
liquid inside the Visking tubing. She carried out biochemical tests on these samples. She
drew the table below to record her results.
(b) Complete the table by placing a tick ( ) in each box that you expect to have shown
a positive result.
Liquid from Liquid inside
Biochemical test
beaker Visking tubing
Biuret reagent
Iodine in potassium
iodide
Benedict’s solution
(3)
(c) Justify your answers to part (b).
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(3)
(Total 9 marks)
Q3.
Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of
digestion.
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SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it transports
glucose and sodium ions (Na +) into the cell.
Figure 1
(a) The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP
hydrolase enzyme.
Explain the function of this ATP hydrolase.
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(2)
(b) The movement of Na+ out of the cell allows the absorption of glucose into the cell
lining the ileum.
Explain how.
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(2)
(c) Describe and explain two features you would expect to find in a cell specialised for
absorption.
1 _________________________________________________________________
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2 _________________________________________________________________
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(2)
Figure 2 is a diagram of one SGLT1 carrier protein.
Figure 2
(d) Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit
into the cell-surface membrane.
Do not draw more than eight phospholipids.
(2)
(e) Figure 2 shows the SGLT1 polypeptide with NH2 at one end and COOH at the other
end.
Describe how amino acids join to form a polypeptide so there is always NH 2 at one
end and COOH at the other end.
You may use a diagram in your answer.
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Space for diagram:
(2)
(Total 10 marks)
Q4.
(a) Describe the processes involved in the absorption and transport of digested lipid
molecules from the ileum into lymph vessels.
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(5)
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(b) Describe how the structure of a protein depends on the amino acids it contains.
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(5)
(Total 10 marks)
Q5.
Alpha-1-antitrypsin is a protein that reduces the activity of enzymes that can damage lung
tissue.
Cigarette smoke contains hydrogen peroxide. Hydrogen peroxide reduces the activity of
alpha-1-antitrypsin. Scientists investigated the effect of different concentrations of
hydrogen peroxide on the activity of alpha-1-antitrypsin. The graph shows their results.
(a) (i) Hydrogen peroxide reacts with two amino acids in alpha-1-
antitrypsin. Explain how this reduces activity of the protein.
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(2)
(ii) Explain the results shown in the graph.
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(2)
(b) Long-term smokers are often short of breath. Use this information to explain why.
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(2)
(Total 6 marks)
Q6.
(a) Describe two differences between active transport and facilitated diffusion.
1. _________________________________________________________________
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2. _________________________________________________________________
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(2)
(b) Explain why molecules of oxygen and carbon dioxide are able to diffuse across
membranes.
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(2)
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(c) Explain why ventilation of the lungs increases the efficiency of gas exchange.
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(2)
(Total 6 marks)
Q7.
(a) Describe how air is taken into the lungs.
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(3)
The volume of air breathed in and out of the lungs during each breath is called the tidal
volume. The breathing rate and tidal volume were measured for a cyclist pedalling at
different speeds. The graph shows the results.
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(b) Describe the two curves.
(i) Tidal volume
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(ii) Breathing rate
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(2)
(c) Calculate the total volume of air breathed in and out per minute when the cyclist is
cycling at 20 km h–1. Show your working.
____________________ dm3
(2)
(Total 7 marks)
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Mark schemes
Q1.
(i) Lack of ATP;
Pump = active transport / requires energy / ATP provides energy /
transport is up
concentration gradient;
2
(ii) Concentration of Na+ inside cell no longer less than concentration in
gut lumen / no longer a concentration gradient;
No (facilitated) diffusion of NA+ ions possible / amino acid absorption
requires diffusion of Na+ ions into cell;
2
(iii) Diffusion / facilitated diffusion;
1
[5]
Q2.
(a) 1. Sodium ions actively transported from ileum cell to blood;
2. Maintains / forms diffusion gradient for sodium to enter cells from gut (and
with it, glucose);
3. Glucose enters by facilitated diffusion with sodium ions;
3
(b)
Biochemical Liquid from Liquid inside
test beaker Visking tubing
Biuret reagent
I2/KI or blank
Benedict’s
1 mark for each correct row
3
(c) 1. Biuret: protein molecules too large to pass through tubing;
Neutral: enzyme molecules
2. Iodine in potassium iodide solution: starch molecules too large to pass
through tubing;
If no tick in 04.2, allow no starch hydrolysed
3. Benedict’s: starch hydrolysed to maltose, which is able to pass through tubing.
Reject: glucose
3
[9]
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Q3.
(a) 1. (ATP to ADP + Pi ) Releases energy;
Reject ‘produces/makes/creates energy’.
2. (energy) allows ions to be moved against a concentration gradient
OR
(energy) allows active transport of ions;
For ‘ions’ accept Na+ or K+.
Do not accept if this movement is of glucose not ions.
2
(b) 1. (Maintains/generates) a concentration/diffusion gradient for Na +
(from ileum into cell);
Accept '(Maintains/generates) a lower concentration of Na +
inside the cell compared with outside the cell’.
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
OR
Na+ moving (in) by co-transport, brings glucose with it;
Accept ‘co-transporter’ for ‘co-transport’.
2
(c) 1. Folded membrane/microvilli so large surface area (for absorption);
Reject references to ‘villi’.
Accept ‘brush border’ for ‘microvilli’.
2. Large number of co-transport/carrier/channel proteins so fast rate
(of absorption)
OR
Large number of co-transport/carrier proteins for active transport
OR
Large number of co-transport/carrier/channel proteins for facilitated diffusion;
3. Large number of mitochondria so make (more) ATP (by respiration)
OR
Large number of mitochondria for aerobic respiration
OR
Large number of mitochondria to release energy for active transport;
4. Membrane-bound (digestive) enzymes so maintains concentration
gradient (for fast absorption);
Accept named examples of digestive enzymes.
2 max
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(d) 1. Phospholipids drawn with head and two tails;
2. Correctly positioned as a bilayer on either side of SGLT1;
Some of every ‘head’ must extend into the hydrophilic region
and some of every ‘tail’ must extend into the hydrophobic
region.
Reject phospholipids drawn within the protein.
2
(e) 1. One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond;
Accept on diagram, for example (at least) two amino acids
joining by a correctly drawn peptide bond (MP1) with NH 2 at
one end and COOH at the other (MP2).
Ignore incorrect names of NH2 and COOH groups.
2. (So in chain) there is a free amine/NH 2 group at one end and a
free carboxyl/COOH group at the other
OR
Each amino acid is orientated in the same direction in the chain;
Allow ECF for incorrect naming of groups.
2
[10]
Q4.
(a) 1. Micelles contain bile salts and fatty acids/monoglycerides;
Ignore other correct components of micelles
2. Make fatty acids/monoglycerides (more) soluble (in water)
OR
Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem)
OR
Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of
the ileum);
Accept lipid/fat for fatty acid/ monoglyceride
3. Fatty acids/monoglycerides absorbed by diffusion;
Reject if absorbed by facilitated diffusion
Ignore if micelles themselves are being absorbed
4. Triglycerides (re)formed (in cells);
Accept chylomicrons form
5. Vesicles move to cell membrane;
Accept exocytosis for ‘vesicles move’
5
(b) 1. Structure is determined by (relative) position of amino acid/R
group/interactions;
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Accept for 'interactions', hydrogen bonds / disulfide bridges /
ionic bonds / hydrophobichydrophilic interactions
2. Primary structure is sequence/order of amino acids;
3. Secondary structure formed by hydrogen bonding (between amino acids);
Accept alpha helix/β-pleated sheet for ‘secondary structure’
4. Tertiary structure formed by interactions (between R groups);
Accept for 'interactions', hydrogen bonds / disulfide bridges /
ionic bonds / hydrophobichydrophilic interactions
5. Creates active site in enzymes
OR
Creates complementary/specific shapes in antibodies/carrier proteins/receptor
(molecules);
6. Quaternary structure contains >1 polypeptide chain
OR
Quaternary structure formed by interactions/bonds between polypeptides;
Accept for ‘intereactions’, hydrogen bonds/ disulfide
bridges/ionic bonds/hydrophobichydrophilic interactions
Accept prosthetic (group)
5 max
[10]
Q5.
(a) (i) Changes shape of antitrypsin;
Reference to hydrogen/ionic/disulfide bonds;
No longer attaches to/interacts/ reacts with trypsin;
Accept protease
2
(ii) Higher the concentration of hydrogen peroxide, more amino acids/
proteins affected;
More antitrypsin molecules change shape;
2
(b) (Longterm smokers) inhale a lot of hydrogen peroxide;
Smokers have more active enzyme that damages lung tissue;
Reducing gas exchange surface;
2 max
[6]
Q6.
(a) Active transport against / facilitated down with concentration gradient;
Accept answers in terms of water potentials
Active transport uses ATP/energy, /facilitated doesn’t;
Reject along/across gradient
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Active uses carrier (proteins), / facilitated (often) uses channel (proteins);
2 max
(b) Lipid/fatty acid part of membrane is non-polar/hydrophobic;
Accept lipid/fatty acid bilayer
Oxygen and carbon dioxide small/ non-polar (molecules);
Oxygen/carbon dioxide can diffuse through/dissolve in/
get between molecules in this layer;
Down a concentration gradient;
2 max
(c) Brings more oxygen/removes carbon dioxide;
Maintains diffusion/concentration gradients;
Between alveoli and blood/capillaries;
Reject references to surface area
2 max
[6]
Q7.
(a) contraction of (diaphragm) muscles flattens diaphragm;
contraction of intercostal muscles raises ribcage;
increase in volume decreases pressure;
3
(b) (i) tidal volume increases steeply, then increase slows down after
10 to 15 km h-1;
1
(ii) breathing rate increases slowly then steeply after 10 to 15 km h -1;
(max 1 if no reference to speed where change occurs in
either (i) or (ii))
1
(c) 20 × 2.75 = 55 dm2;
(award 1 mark for correct method i.e. tidal volume × rate);
2
[7]
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