Gas Exchange In Humans

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Features of Gas Exchange Surfaces

All gas exchange surfaces share features that maximise the rate of diffusion.
Large surface area – allows faster diffusion of gases across the surface.
Thin walls – ensure short diffusion distances.
Good ventilation – maintains diffusion gradients.
Good blood supply – maintains a steep concentration gradient for faster diffusion.
The alveolus is the gas exchange surface in humans.

Features of gas exchange surfaces

The Breathing System

Air enters through the nose/mouth, passes through the trachea, bronchi, bronchioles, and reaches the alveoli.
The trachea is supported by rings of cartilage to prevent collapse.
The bronchi branch from the trachea into each lung.
Bronchioles are smaller branches leading to alveoli.
Alveoli are tiny air sacs where gas exchange occurs.
The diaphragm is a sheet of muscle separating the thorax from the abdomen.
Intercostal muscles are located between the ribs; external (outside) and internal (inside).

Structures in the human breathing system

Ventilation: Volume & Pressure Changes

Inspiration (inhalation): diaphragm contracts and flattens; external intercostal muscles contract, pulling ribs up and out.
This increases thorax volume, decreases air pressure inside lungs, drawing air in.
Expiration (exhalation): diaphragm relaxes and moves up; external intercostal muscles relax, ribs drop down and in.
This decreases thorax volume, increases air pressure, forcing air out.
Forced exhalation (e.g., during exercise) involves internal intercostal muscles contracting to pull ribs down more forcefully.
Cartilage in trachea and bronchi keeps airways open during pressure changes.

Inhalation and exhalation

Differences Between Inspired and Expired Air

Inspired air: ~21% oxygen, ~0.04% carbon dioxide, variable water vapour.
Expired air: ~16% oxygen, ~4% carbon dioxide, more water vapour.
Nitrogen remains constant at ~78%.
Differences arise because oxygen diffuses into blood and carbon dioxide diffuses out in alveoli.
Limewater test: expired air turns limewater cloudy (milky) due to higher CO₂; inspired air does not.

Effects of Physical Activity on Breathing

Exercise increases both breathing rate (breaths per minute) and depth (tidal volume).
More oxygen is needed for increased aerobic respiration in muscles; more CO₂ is produced.
Increased CO₂ lowers blood pH, detected by chemoreceptors in the medulla oblongata.
The brain sends nerve impulses to diaphragm and intercostal muscles to increase ventilation.
After exercise, breathing remains elevated to repay oxygen debt (remove lactic acid).
Investigation: count breaths per minute and measure chest expansion before and after exercise.

Protecting the Breathing System

Airways are lined with ciliated epithelial cells and goblet cells.
Goblet cells produce mucus that traps dust, bacteria, and particles.
Cilia beat to move mucus upwards towards the throat, where it is swallowed or expelled.
This prevents pathogens and debris from reaching the lungs.

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1.Which of the following is a feature of gas exchange surfaces that maximises the rate of gas exchange?
Easy
- ALarge surface area
- BThick walls
- CPoor blood supply
- DLack of ventilation
2.What is the function of cartilage in the trachea?
Easy
- ATo produce mucus
- BTo support the airways and keep them open
- CTo contract and expand the lungs
- DTo trap dust and bacteria
3.During inhalation, the diaphragm:
Easy
- ARelaxes and moves upwards
- BContracts and flattens
- CRemains stationary
- DContracts and moves upwards
4.Which gas has the same percentage in inspired and expired air?
Easy
- AOxygen
- BCarbon dioxide
- CNitrogen
- DWater vapour
5.What is the approximate percentage of carbon dioxide in exhaled air?
Easy
- A0.04%
- B4%
- C16%
- D21%
6.In an investigation using limewater to compare inhaled and exhaled air, which observation indicates a higher carbon dioxide concentration?
Medium
- ALimewater turns cloudy in the tube receiving exhaled air
- BLimewater turns cloudy in the tube receiving inhaled air
- CLimewater remains clear in both tubes
- DLimewater turns red in the tube receiving exhaled air
7.Which muscles contract during forced exhalation?
Medium
- AExternal intercostal muscles only
- BInternal intercostal muscles only
- CBoth external and internal intercostal muscles
- DDiaphragm only
8.What causes the increase in breathing rate during exercise?
Medium
- AIncreased oxygen levels in the blood
- BDecreased carbon dioxide levels in the blood
- CIncreased carbon dioxide levels detected by chemoreceptors
- DDecreased pH in the muscles

Plus de questions

9.What is the role of cilia in the breathing system?
Easy
- ATo produce mucus
- BTo trap pathogens
- CTo beat and push mucus towards the throat
- DTo support the trachea
10.Which structure is the gas exchange surface in humans?
Easy
- ABronchus
- BTrachea
- CAlveolus
- DBronchiole
11.Which of the following is NOT a feature that makes alveoli efficient gas exchange surfaces?
Easy
- AThin walls
- BLarge surface area
- CThick layer of mucus
- DGood blood supply
12.The diagram shows the human breathing system. Which structure is the trachea?
Easy
- ATrachea
- BBronchus
- CBronchiole
- DPleural cavity
13.In an investigation, a student breathes in and out through the apparatus shown. Boiling tube A contains limewater through which air is drawn during inhalation. Boiling tube B contains limewater through which exhaled air is blown. What is the expected result after several breaths?
Medium
- ALimewater in both tubes remains clear.
- BLimewater in both tubes turns cloudy.
- CLimewater in tube A turns cloudy, tube B remains clear.
- DLimewater in tube A remains clear, tube B turns cloudy.
14.The table shows the composition of inspired and expired air. | Gas | Inspired air / % | Expired air / % | |---|---|---| | Oxygen | 21 | 16 | | Carbon dioxide | 0.04 | 4 | | Water vapour | 0.2–4 | 1–5 | | Nitrogen | 78 | 78 | Which gas shows the largest percentage decrease from inspired to expired air?
Medium
- AOxygen
- BCarbon dioxide
- CWater vapour
- DNitrogen
15.During exercise, the depth of breathing increases. What is the most likely reason for this?
Medium
- ATo increase the rate of carbon dioxide removal from the blood
- BTo decrease the heart rate
- CTo reduce the oxygen concentration in the alveoli
- DTo increase the amount of nitrogen exhaled
16.A student counts their breaths per minute at rest and then after 5 minutes of exercise. The results are shown in the graph. What is the percentage increase in breathing rate from rest to immediately after exercise? (Rest: 12 breaths/min, After exercise: 24 breaths/min)
Medium
- A50%
- B100%
- C200%
- D12%
17.Which of the following is a correct description of the action of the diaphragm during inhalation?
Medium
- AIt relaxes and moves upwards, decreasing the volume of the thorax.
- BIt contracts and flattens, increasing the volume of the thorax.
- CIt contracts and moves upwards, decreasing the volume of the thorax.
- DIt relaxes and flattens, increasing the volume of the thorax.
18.What is the function of the rings of cartilage in the trachea?
Easy
- ATo produce mucus
- BTo trap dust particles
- CTo keep the trachea open during breathing
- DTo increase the surface area for gas exchange
19.In a study, the number of people with COPD in cities and villages was compared. The data showed that 15% of city dwellers and 8% of village dwellers had COPD. What is the ratio of city to village COPD prevalence?
Medium
- A15:8
- B8:15
- C1.875:1
- D1:1.875
20.Which of the following is a feature of alveoli that makes them efficient for gas exchange?
Easy
- AThick walls
- BSmall surface area
- CRich blood supply
- DPoor ventilation
21.The diagram shows a section through an alveolus and a surrounding capillary. Which structure is the site of gas exchange?
Medium
- AWall of the alveolus
- BThe tube supplying air to the alveolus
- CDeoxygenated red blood cell
- DAir space inside the alveolus
22.Which cells produce mucus in the breathing system?
Easy
- ACiliated epithelial cells
- BGoblet cells
- CAlveolar cells
- DRed blood cells
23.A student measures chest expansion at rest and after exercise. At rest, the chest circumference increases by 2 cm during inhalation. After exercise, it increases by 4 cm. What does this indicate?
Medium
- ABreathing rate has increased.
- BDepth of breathing has increased.
- CTidal volume has decreased.
- DThe student is hyperventilating.
24.In an investigation to compare the carbon dioxide content of inhaled and exhaled air, a student uses the apparatus shown. Air is drawn through boiling tube A during inhalation and blown into boiling tube B during exhalation. Both tubes contain limewater. After several breaths, the limewater in tube B turns cloudy, while tube A remains clear. What is the correct conclusion?
Medium
- AExhaled air contains more carbon dioxide than inhaled air.
- BInhaled air contains more carbon dioxide than exhaled air.
- CBoth tubes contain the same amount of carbon dioxide.
- DThe limewater in tube A is faulty.
25.A student investigates the effect of exercise on breathing rate. They count breaths per minute at rest (12 breaths/min) and after 5 minutes of exercise (30 breaths/min). What is the percentage increase in breathing rate?
Easy
- A150%
- B60%
- C250%
- D18%
26.In an experiment to investigate the effect of physical activity on breathing, which two measurements should be taken before and after exercise?
Easy
- ABreathing rate and chest expansion
- BHeart rate and blood pressure
- CBody temperature and pulse rate
- DLung volume and oxygen saturation
27.A student uses a tape measure to measure chest expansion at rest and after exercise. At rest, the chest circumference increases by 3 cm during deep inhalation. After running for 5 minutes, the chest expansion is 5 cm. Which conclusion is most valid?
Medium
- AExercise increases the depth of breathing.
- BExercise increases the rate of breathing only.
- CExercise has no effect on chest expansion.
- DThe tape measure reading is unreliable.
28.Which of the following is a limitation of using chest expansion as a measure of breathing depth?
Medium
- AIt does not account for differences in body size and lung capacity.
- BIt directly measures the volume of air in the lungs.
- CIt is more accurate than a spirometer.
- DIt requires expensive equipment.
29.During forced exhalation, which muscles contract to pull the ribs down and in?
Easy
- AInternal intercostal muscles
- BExternal intercostal muscles
- CDiaphragm
- DAbdominal muscles
30.During inhalation, which of the following occurs?
Easy
- AThe diaphragm contracts and flattens.
- BThe diaphragm relaxes and moves upwards.
- CThe external intercostal muscles relax.
- DThe volume of the thorax decreases.
31.In an experiment, a student uses a spirometer to measure lung volumes. The trace shows a tidal volume of 0.5 L and a vital capacity of 4.5 L. What is the inspiratory reserve volume if the expiratory reserve volume is 1.5 L?
Medium
- A2.5 L
- B3.0 L
- C4.0 L
- D1.0 L
32.Which of the following best explains why breathing rate increases during exercise?
Medium
- AIncreased carbon dioxide levels in the blood are detected by chemoreceptors, which signal the brain to increase breathing rate.
- BMuscles directly stimulate the diaphragm to contract faster.
- CThe heart pumps more blood to the lungs, forcing faster breathing.
- DOxygen levels in the blood increase, triggering a reflex.
33.A student measures chest expansion at rest and after exercise. At rest, the chest circumference increases by 2 cm during deep inhalation. After exercise, it increases by 4 cm. What is the percentage increase in chest expansion?
Easy
- A50%
- B100%
- C200%
34.The table shows the composition of inspired and expired air. | Gas | Inspired air / % | Expired air / % | |---|---|---| | Oxygen | 21 | 16 | | Carbon dioxide | 0.04 | 4 | | Water vapour | 0.2–4 | 1–5 | | Nitrogen | 78 | 78 | Which gas shows the largest percentage increase from inspired to expired air?
Medium
- AOxygen
- BCarbon dioxide
- CWater vapour
- DNitrogen
35.During exercise, a person's breathing rate increases from 12 breaths per minute to 30 breaths per minute, and tidal volume increases from 500 cm³ to 1500 cm³. What is the total volume of air breathed in per minute after exercise?
Medium
- A18 000 cm³
- B45 000 cm³
- C36 000 cm³
- D15 000 cm³
36.A student investigates the effect of exercise on breathing by counting breaths per minute at rest (12 breaths/min) and after 5 minutes of exercise (30 breaths/min). They also measure chest expansion. Which of the following is a limitation of using chest expansion as a measure of breathing depth?
Medium
- AChest expansion is not related to the volume of air inhaled
- BChest expansion may be affected by the tightness of the tape measure and body position
- CChest expansion always decreases after exercise
- DChest expansion is a measure of heart rate, not breathing
37.Which of the following is the gas exchange surface in humans?
Easy
- AAlveolus
- BTrachea
- CBronchus
- DDiaphragm
38.The percentage of carbon dioxide in expired air is higher than in inspired air.
Easy
True or false?
39.Which of the following are features of all gas exchange surfaces? (Select all that apply)
Medium
- ALarge surface area
- BThick walls
- CGood ventilation
- DGood blood supply
- EContains cartilage
40.Arrange the following events during inhalation in the correct order: 1. Air rushes into lungs 2. Volume of thorax increases 3. External intercostal muscles contract 4. Pressure in thorax decreases 5. Diaphragm contracts and flattens
Medium
- External intercostal muscles contract
- Diaphragm contracts and flattens
- Volume of thorax increases
- Pressure in thorax decreases
- Air rushes into lungs
41.Match each structure with its function.
Medium
- Alveolus
- Cilia
- Goblet cells
- Cartilage
- Gas exchange
- Push mucus upwards
- Produce mucus
- Support airway
42.Match each structure of the breathing system with its correct function.
Medium
- Trachea
- Alveoli
- Diaphragm
- Ribs
- Gas exchange surface
- Separates chest from abdomen
- Supported by rings of cartilage
- Move up and out during inhalation
43.Arrange the following events during inhalation in the correct order starting with the first event.
Medium
- External intercostal muscles contract
- Volume of thorax increases
- Air rushes into lungs
- Pressure in thorax decreases
- Diaphragm flattens and ribs move up and out
44.The percentage of nitrogen in expired air is the same as in inspired air.
Easy
True or false?
45.During forced exhalation, which muscles contract?
Medium
- AExternal intercostal muscles
- BInternal intercostal muscles
- CDiaphragm
- DBoth external and internal intercostal muscles
46.A student breathes into a bag and then tests the air in the bag with limewater. The limewater turns cloudy. Which gas is present in higher concentration in the bag compared to atmospheric air?
Easy
- Aoxygen
- Bcarbon dioxide
- Cnitrogen
- Dwater vapour
47.Complete the sentence about the composition of inspired and expired air.
Easy
Inspired air contains about ____% oxygen and expired air contains about ____% oxygen.
48.A person at rest breathes 12 times per minute with a tidal volume of 500 cm³. What is the total volume of air breathed in per minute in cm³?
Easy
49.State two ways in which the composition of expired air differs from inspired air.
Easy
50.Complete the sentence about the composition of air.
Easy
Inspired air contains about ____ % oxygen, while expired air contains about ____ % oxygen.
51.A person at rest breathes 15 times per minute with a tidal volume of 400 cm³. What is the total volume of air breathed in per minute? Give your answer in cm³.
Easy
52.Explain how the breathing rate increases during exercise.
Hard
53.A person at rest breathes 12 times per minute with a tidal volume of 500 cm³. What is the total volume of air breathed in per minute in cm³?
Easy
- A6000 cm³
- B6600 cm³
- C7200 cm³
- D5400 cm³
54.A person at rest breathes 15 times per minute with a tidal volume of 400 cm³. What is the total volume of air breathed in per minute? Give your answer in cm³.
Easy
- A5400 cm³
- B6000 cm³
- C6600 cm³
- D7200 cm³

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