Question 1
An artificial surface is designed to exchange and rapidly with surrounding water.
What combination of properties would best increase the rate of diffusion across the surface?
A.
Thin, waterproof, dry and with a large surface area
B.
Thick, dry, permeable and with a small surface area
C.
Thin, moist, permeable and with a large surface area
D.
Thick, moist, impermeable and with a large surface area
Question 2
A haemoglobin molecule is fully saturated with oxygen.
How many oxygen molecules are bound to it?
A.
One, because haemoglobin has one globular protein chain
B.
Eight, because each oxygen molecule contains two oxygen atoms
C.
Two, because oxygen is transported as molecules
D.
Four, because each haem group can bind one molecule
Question 3
A small aquatic organism increases in diameter while keeping the same body shape. Gas exchange across its outer body surface becomes less adequate for supplying all cells.
What explains this effect?
A.
Volume increases faster than surface area as size increases.
B.
Diffusion becomes an active process in larger organisms.
C.
Oxygen molecules become too large to cross membranes.
D.
Surface area increases faster than volume as size increases.
Question 4
The table shows relative gas concentrations at a mammalian alveolus.
| Region | concentration | concentration |
|---|---|---|
| Alveolar air | High | Low |
| Blood arriving at alveolus | Low | High |
What are the net directions of diffusion?
A.
from blood to alveolar air; from alveolar air to blood
B.
Both and from alveolar air to blood
C.
from alveolar air to blood; from blood to alveolar air
D.
Both and from blood to alveolar air
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Question 5
A person carries out forced expiration after taking a deep breath.
What muscle action helps to reduce thoracic volume during forced expiration?
A.
Internal intercostal muscles relax and ribs move upwards.
B.
External intercostal muscles and diaphragm contract.
C.
Diaphragm contracts and abdominal muscles relax.
D.
Internal intercostal muscles and abdominal muscles contract.
Question 6
A spirometer gives the following lung volume measurements for a student at rest.
Tidal volume:
Inspiratory reserve volume:
Expiratory reserve volume:
What is the student’s vital capacity?
A.
B.
C.
D.
Question 7
Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
What is the significance of this in the placenta?
A.
Foetal haemoglobin binds oxygen at partial pressures where adult haemoglobin releases it.
B.
Foetal haemoglobin prevents oxygen from diffusing across placental tissue.
C.
Foetal haemoglobin has a lower maximum oxygen saturation than adult haemoglobin.
D.
Foetal haemoglobin only binds oxygen when maternal and foetal blood mix.
Question 8
In an actively respiring muscle, the concentration of in the blood increases.
What is the effect of the Bohr shift in this tissue?
A.
Haemoglobin affinity for oxygen decreases, increasing oxygen unloading.
B.
Haemoglobin loses all haem groups, preventing oxygen transport.
C.
Haemoglobin affinity for oxygen increases, increasing oxygen loading.
D.
Haemoglobin binds oxygen irreversibly, preventing dissociation.
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Question 9
Unicellular organisms can often exchange gases across their body surface, whereas many larger multicellular organisms have specialized gas-exchange organs.
Define diffusion.
[1]
Explain why larger multicellular organisms need specialized systems for gas exchange.
[2]
Question 10
Haemoglobin in red blood cells transports oxygen using haem groups.
State the maximum number of oxygen molecules that one haemoglobin molecule can bind.
[1]
Explain cooperative binding of oxygen to haemoglobin.
[2]
Question 11
A leaf surface cast is viewed under a microscope. Counts from three fields of view are 22, 18 and 20 stomata. Each field of view has an area of .
What is the mean stomatal density?
A.
B.
C.
D.
Question 12
Carbon dioxide can bind allosterically to haemoglobin.
What does allosteric binding mean in this context?
A.
binds only to haem iron and blocks oxygen permanently.
B.
replaces all four haem groups in the haemoglobin molecule.
C.
binds at a site that changes haemoglobin’s oxygen affinity.
D.
converts haemoglobin into an enzyme for aerobic respiration.
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Question 13
The oxygen dissociation curve for adult haemoglobin is sigmoid rather than linear.
What causes the steep middle section of the curve?
A.
Oxygen is converted into carbon dioxide inside red blood cells.
B.
All haem groups bind oxygen independently with constant affinity.
C.
Haemoglobin becomes saturated only when concentration is highest.
D.
Binding of one molecule increases the affinity of remaining haem groups.
Question 14
Gas-exchange surfaces in different organisms show similar structural features.
Outline two properties of an effective gas-exchange surface.
[2]
Explain how ventilation and blood flow maintain concentration gradients at mammalian alveoli.
[2]
Question 15
The diagram shows an alveolus and an adjacent blood capillary in a mammalian lung.
State the role of surfactant in alveoli.
[1]
Explain how alveoli and their capillaries are adapted for rapid gas exchange.
[3]
Question 16
Ventilation of the lungs depends on changes in thoracic volume and pressure.
State why air enters the lungs during inspiration.
[1]
Describe the roles of the diaphragm, intercostal muscles and abdominal muscles during forced expiration.
[3]
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Question 17
The graph shows the oxygen dissociation curve of adult haemoglobin.
Describe the change in haemoglobin saturation as partial pressure of oxygen increases.
[2]
Explain the S-shaped form of the curve in terms of cooperative binding.
[2]
Question 18
Carbon dioxide can interact with haemoglobin as well as being transported in the plasma.
Define allosteric binding.
[1]
Explain how allosteric binding of carbon dioxide to haemoglobin links oxygen transport to tissue respiration.
[2]
Question 19
A student modelled organisms using agar cubes containing an indicator. The cubes were placed in an oxygen-sensitive solution for the same length of time. The graph shows how the percentage of each cube reached by diffusion changed with cube side length.
Cube side length / cm | Percentage of cube reached by diffusion / % | Surface area-to-volume ratio / |
|---|---|---|
1.0 | 100 | 6.0 |
2.0 | 88 | 3.0 |
3.0 | 70 | 2.0 |
4.0 | 58 | 1.5 |
Describe the relationship shown between cube side length and the percentage of the cube reached by diffusion.
[1]
Calculate the percentage decrease in surface area-to-volume ratio from the smallest cube to the largest cube.
[2]
Explain why larger multicellular animals need specialized gas-exchange surfaces rather than relying only on diffusion across the body surface.
[1]
Question 20
The graph shows oxygen dissociation curves for haemoglobin. Curve P represents adult haemoglobin under standard conditions. Curve Q is shifted to the left of P. Curve R is shifted to the right of P.
What identifies curves Q and R?
A.
Q: foetal haemoglobin; R: adult haemoglobin at high
B.
Q: adult haemoglobin after Bohr shift; R: haemoglobin with higher oxygen affinity
C.
Q: adult haemoglobin at high ; R: foetal haemoglobin
D.
Q: haemoglobin with lower oxygen affinity; R: foetal haemoglobin
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Question 21
A spirometer trace was recorded for a healthy student. The trace includes several normal breaths followed by a maximum inhalation and a maximum exhalation.
Determine the tidal volume from the normal breaths on the trace.
[1]
Calculate the vital capacity from the maximum and minimum lung volumes on the trace.
[1]
Suggest why carbon dioxide must be absorbed if a closed spirometer is used for repeated breaths.
[2]
Question 22
A leaf surface cast was made using clear nail varnish and observed with a microscope. In one field of view, 42 stomata were counted in an area of .
Calculate the stomatal density in .
[2]
Outline why several fields of view should be counted when estimating stomatal density.
[1]
State why opening stomata increases transpiration.
[1]
Question 23
The graph shows oxygen dissociation curves for adult haemoglobin and foetal haemoglobin at the same carbon dioxide concentration.
Identify which curve represents foetal haemoglobin.
[1]
Explain how the difference between the curves enables oxygen transfer in the placenta.
[2]
State why maternal and foetal blood do not need to mix for oxygen transfer to occur.
[1]
Question 24
During intense exercise, the carbon dioxide concentration in an active muscle increases.
State the effect of increased carbon dioxide on pH in red blood cells.
[1]
Explain how the Bohr shift benefits actively respiring tissues.
[3]
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Question 25
The diagram shows an alveolus and a surrounding blood capillary. The partial pressures of oxygen and carbon dioxide are shown for alveolar air, blood entering the capillary and blood leaving the capillary.
State the direction of diffusion of oxygen across the alveolar wall.
[1]
Using the data, explain how continuous blood flow maintains the oxygen concentration gradient at the alveolus.
[2]
Suggest one structural feature of the alveolus, visible or indicated in the diagram, that increases the rate of gas exchange.
[1]
Question 26
The graph shows changes in thoracic volume and pressure inside the lungs during one normal breathing cycle. The points labelled P, Q and R mark different stages of the cycle.
Point | Time / s | Thoracic volume / L | Pressure inside lungs / kPa relative to atmospheric |
|---|---|---|---|
P | 0.0 | 4.6 | 0.0 |
Q | 1.5 | 5.2 | -0.1 |
R | 3.0 | 4.7 | +0.1 |
Identify the stage of ventilation occurring between P and Q.
[1]
Explain how contraction of the diaphragm causes the pressure change between P and Q.
[2]
Suggest how muscle activity would differ during forced expiration at R compared with quiet expiration.
[1]
Question 27
The diagram shows a transverse section of a dicotyledonous leaf with tissues labelled A to F.
Identify the labelled tissue that provides the largest internal air spaces for gas diffusion.
[1]
Explain how stomata and guard cells contribute to gas exchange in the leaf.
[2]
Suggest why the waxy cuticle is not the main gas-exchange surface of the leaf.
[1]
Question 28
The graph shows oxygen dissociation curves for adult haemoglobin and foetal haemoglobin at normal carbon dioxide concentration.
Compare the affinity of foetal haemoglobin and adult haemoglobin for oxygen using the curves.
[1]
Determine the difference in percentage saturation between foetal and adult haemoglobin at the placental partial pressure indicated.
[1]
Explain how the difference shown in the graph enables oxygen transfer in the placenta.
[2]
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Question 29
The graph shows three oxygen dissociation curves: adult haemoglobin at normal carbon dioxide concentration, adult haemoglobin at high carbon dioxide concentration, and foetal haemoglobin.
Distinguish between a left shift and a right shift of an oxygen dissociation curve.
[2]
Identify the curve most likely to represent foetal haemoglobin.
[1]
Suggest why high carbon dioxide concentration in pulmonary capillaries would reduce oxygen loading by adult haemoglobin.
[1]
Question 30
A spirometer trace was recorded for a student at rest. The student then made a maximum inhalation followed by a maximum exhalation before returning to normal breathing.
Determine the tidal volume from the resting breaths shown in the trace.
[1]
Calculate the vital capacity of the student.
[2]
Calculate the ventilation rate at rest using the resting breaths during the first minute of the trace.
[1]
Suggest why a closed spirometer used for repeated breaths must contain a chemical that absorbs carbon dioxide.
[1]
Question 31
A student made clear nail-varnish casts from the lower epidermis of leaves of the same plant species. The table shows counts of stomata in five microscope fields. Each field of view had an area of .
Field of view | Number of stomata |
|---|---|
1 | 16 |
2 | 17 |
3 | 17.5 |
4 | 18 |
5 | 19 |
Calculate the mean number of stomata per field of view.
[1]
Calculate the stomatal density in .
[2]
Explain why several fields of view were counted rather than only one.
[1]
Suggest one environmental condition that could increase the rate of transpiration through these stomata.
[1]
Question 32
Oxygen dissociation curves for adult haemoglobin were measured at low and high carbon dioxide concentrations. The high carbon dioxide curve represents conditions in actively respiring muscle.
State the name given to the shift in the oxygen dissociation curve caused by increased carbon dioxide concentration.
[1]
Calculate the additional percentage of oxygen unloaded at the tissue partial pressure when carbon dioxide concentration is high rather than low.
[2]
Explain the benefit of this shift for actively respiring tissues.
[2]
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Question 33
The table shows the percentage saturation of adult haemoglobin with oxygen at increasing partial pressures of oxygen under constant carbon dioxide concentration.
Identify the range of partial pressures over which haemoglobin saturation increases most steeply.
[1]
Explain the S-shaped pattern that would be produced if these data were plotted as an oxygen dissociation curve.
[2]
State the maximum number of oxygen molecules that can be carried by one haemoglobin molecule.
[1]
Question 34
Purified adult haemoglobin was exposed to increasing carbon dioxide concentrations while the partial pressure of oxygen was kept constant. The graph shows the percentage saturation of haemoglobin with oxygen.
Describe the effect of increasing carbon dioxide concentration on oxygen saturation of haemoglobin in this experiment.
[1]
Calculate the change in haemoglobin saturation between the lowest and highest carbon dioxide concentrations shown.
[1]
Suggest two molecular explanations for the effect of carbon dioxide on oxygen saturation.
[2]
Question 35
Two aquatic invertebrates are shown. Organism A is microscopic and approximately spherical. Organism B is much larger and has internal tissues several millimetres from the external surface.
I.
Explain why organism A may be able to exchange gases across its whole body surface.
[2]
II.
State one gas that must be exchanged by animal cells during aerobic respiration.
[1]
Explain why organism B requires specialized gas-exchange surfaces and a transport system.
[3]
Discuss one trade-off faced by organisms with moist gas-exchange surfaces on land.
[1]
Question 36
Researchers compared oxygen transport in three mammals. The graph shows oxygen dissociation curves for haemoglobin from an adult human at sea level, an adult human acclimatized to high altitude and a small burrowing mammal whose tissues often experience high carbon dioxide concentrations.
Identify which curve represents the haemoglobin with the highest affinity for oxygen.
[1]
Calculate the difference in percentage saturation between the left-shifted and reference curves at the alveolar partial pressure indicated.
[1]
Evaluate whether a left-shifted curve is always advantageous for oxygen transport.
[3]
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Question 37
The graph compares oxygen unloading from adult haemoglobin in resting muscle and during intense exercise. The curves represent blood entering and leaving the muscle under different carbon dioxide concentrations.
Condition | level | entering / kPa | Hb saturation entering / % | leaving / kPa | Hb saturation leaving / % |
|---|---|---|---|---|---|
Resting muscle | normal | 13.3 | 98 | 5.3 | 73 |
Intense exercise | high | 13.3 | 95 | 2.7 | 40 |
Determine the percentage of oxygen unloaded from haemoglobin in resting muscle.
[1]
Determine the percentage of oxygen unloaded from haemoglobin in intensely exercising muscle.
[1]
Discuss how the data show a link between gas exchange and metabolic activity in muscle.
[3]
Question 38
A premature infant has reduced secretion of surfactant in the alveoli. A simplified section through several alveoli and surrounding capillaries is shown.
I.
Identify two features of alveoli shown in the diagram that increase the rate of gas exchange.
[2]
II.
State the direction of diffusion of carbon dioxide at the alveolar surface.
[1]
Explain how surfactant contributes to effective gas exchange in alveoli.
[2]
Evaluate how reduced surfactant secretion would affect oxygen uptake in the infant.
[3]
Question 39
A student records breathing movements during rest and immediately after vigorous exercise. The diagram shows the positions of the diaphragm and ribs during two phases of ventilation.
I.
Identify which phase represents inspiration and give one reason.
[2]
II.
State the pressure change in the lungs during inspiration.
[1]
Explain the roles of the diaphragm and external intercostal muscles during normal inspiration.
[3]
Compare quiet expiration with forced expiration after exercise.
[2]
Question 40
A spirometer trace was obtained from a healthy adult before and after a maximal inhalation and maximal exhalation. Carbon dioxide absorbent was present in the spirometer chamber.
I.
Describe how tidal volume would be determined from the trace.
[1]
II.
Describe how vital capacity would be determined from the trace.
[2]
Explain why a carbon dioxide absorbent is needed when a closed spirometer is used for repeated breaths.
[2]
Evaluate one limitation of using a simple water-displacement apparatus rather than a spirometer for measuring lung volumes.
[3]
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Question 41
A transverse section of a dicotyledonous leaf is observed using a low-power microscope. The leaf is from a plant growing in a dry, sunny habitat.
I.
Draw a labelled plan diagram to show the distribution of tissues in the leaf section.
[2]
II.
State the tissue in which large internal air spaces are normally found.
[1]
Explain how stomata and guard cells adapt the leaf for gas exchange.
[2]
Discuss how the waxy cuticle and spongy mesophyll represent different solutions to the requirements of a leaf.
[2]
Question 42
Mammals and bony fish both maintain concentration gradients at gas-exchange surfaces, but they ventilate different external media.
I.
State the process by which oxygen crosses a gas-exchange surface.
[1]
II.
State one property shared by effective gas-exchange surfaces.
[1]
Compare how lungs and gills maintain concentration gradients for oxygen uptake.
[3]
Suggest why gas exchange would slow if blood flow over the exchange surface stopped, even if ventilation continued.
[1]
Question 43
The oxygen saturation of adult haemoglobin and foetal haemoglobin was measured at different partial pressures of oxygen.
I.
Identify which curve represents foetal haemoglobin and give the evidence from the graph.
[2]
II.
State the maximum number of oxygen molecules that one haemoglobin molecule can bind.
[1]
Explain the S-shaped form of the adult haemoglobin dissociation curve.
[3]
Explain the advantage of foetal haemoglobin having a higher oxygen affinity in the placenta.
[2]
Question 44
During intense exercise, carbon dioxide concentration increases in active skeletal muscle. The oxygen dissociation curve for haemoglobin changes under these conditions.
I.
Identify the name of the shift shown by the curve at high carbon dioxide concentration.
[1]
II.
State what the right shift indicates about haemoglobin affinity for oxygen.
[1]
Explain how increased carbon dioxide causes increased oxygen dissociation from haemoglobin.
[3]
Discuss the benefit of this response for active muscle tissue.
[2]
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Question 45
Adult haemoglobin and foetal haemoglobin are both oxygen-transport proteins, but they are adapted for different environments.
I.
Outline the role of haem groups in haemoglobin.
[1]
II.
State why haemoglobin transports more oxygen than blood plasma alone.
[1]
Compare and contrast adult and foetal haemoglobin in relation to oxygen transport.
[3]
Explain how allosteric binding of carbon dioxide links oxygen transport to metabolism in tissues.
[2]
Question 46
Two tissues receive the same blood flow. Tissue X is resting, while tissue Y is undergoing rapid aerobic respiration. Measurements show higher carbon dioxide concentration in tissue Y.
I.
Predict which tissue will receive more oxygen unloaded from haemoglobin.
[1]
II.
State the evidence in the stem that supports this prediction.
[1]
Explain the mechanism by which carbon dioxide affects oxygen unloading from haemoglobin in tissue Y.
[3]
Evaluate why this mechanism is an efficient adaptation rather than a failure of oxygen transport.
[2]
Question 47
Students used clear nail varnish to make leaf surface casts from the lower epidermis of two plant species. They counted stomata in several microscope fields of view for each species.
Field of view | Species A stomata count | Species B stomata count | Area of field of view / mm |
|---|---|---|---|
1 | 19 | 15 | 0.20 |
2 | 21 | 14 | 0.20 |
3 | 20 | 13 | 0.20 |
4 | 18 | 16 | 0.20 |
5 | 22 | 12 | 0.20 |
I.
Outline how stomatal density is calculated from the counts and the field of view area.
[2]
II.
State the formula for stomatal density.
[1]
Explain why repeated counts from different fields of view increase reliability.
[2]
Evaluate the conclusion that the species with the higher stomatal density will always have the higher rate of transpiration.
[3]
Question 48
A researcher compares oxygen transport in blood passing through alveolar capillaries and through capillaries in a respiring tissue. The graph shows adult haemoglobin saturation under two carbon dioxide conditions.
I.
Predict which carbon dioxide condition favours oxygen loading in the alveolar capillaries.
[1]
II.
Explain the prediction in part (i) using the graph.
[2]
Explain why haemoglobin does not release all its oxygen in respiring tissues.
[2]
Evaluate the statement: “A right-shifted oxygen dissociation curve is always disadvantageous.”
[3]
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Question 49
Three oxygen dissociation curves are shown for adult haemoglobin under normal conditions, adult haemoglobin in high carbon dioxide and foetal haemoglobin.
I.
State what is represented by the y-axis of an oxygen dissociation curve.
[1]
II.
Explain how curve position indicates haemoglobin affinity for oxygen.
[2]
Discuss how the three curves illustrate adaptations for gas exchange in different tissues.
[3]
Explain why cooperative binding is necessary for the adult haemoglobin curve to be useful in oxygen transport.
[2]
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