FSc Part 1 Biology chapter 13: Gaseous exchange MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

20 exam-style questions on Gaseous exchange, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

20 questions · 2 topics · 10 per test

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What chapter 13 covers

Ten Gaseous exchange questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. In bright light, a leaf makes 18 mL of oxygen per hour by photosynthesis and uses 6 mL of oxygen per hour in respiration. What is its net release of oxygen?

  1. A
    3 mL per hour
  2. B
    12 mL per hour
  3. C
    18 mL per hour
  4. D
    24 mL per hour
Show answer

Answer: B. Net release = oxygen made − oxygen used = 18 − 6 = 12 mL per hour. The leaf releases oxygen overall because photosynthesis is faster than respiration in bright light.

2. During an asthma attack, a person wheezes and finds it hard to breathe because

  1. A
    the alveoli fill with fluid and pus after bacterial infection
  2. B
    the smooth muscle of the bronchioles contracts, narrowing the airways
  3. C
    the alveolar walls break down and lose their elasticity
  4. D
    the red blood cells lose their ability to carry oxygen
Show answer

Answer: B. Asthma is usually an allergic reaction: bronchioles constrict and secrete mucus, narrowing the airways.

3. A person has a tidal volume of 500 mL, an inspiratory reserve volume of 3000 mL and an expiratory reserve volume of 1100 mL. What is the vital capacity?

  1. A
    3500 mL
  2. B
    4100 mL
  3. C
    4600 mL
  4. D
    5800 mL
Show answer

Answer: C. Vital capacity = tidal volume + IRV + ERV = 500 + 3000 + 1100 = 4600 mL. Residual volume is not included.

4. A patient has had a persistent cough with blood-stained sputum, night sweats and weight loss for several weeks. A chest X-ray shows cavities in the upper lungs. Which pathogen is the most likely cause?

  1. A
    Corynebacterium diphtheriae
  2. B
    Mycobacterium tuberculosis
  3. C
    Bordetella pertussis
  4. D
    Streptococcus pneumoniae
Show answer

Answer: B. A long-lasting cough with blood-stained sputum, night sweats, weight loss and cavities in the upper lungs is typical of tuberculosis, caused by Mycobacterium tuberculosis. Pneumococcal pneumonia comes on suddenly and pertussis causes whooping cough.

5. In woody stems, gases are exchanged through loosely arranged cells in pores of the bark called

  1. A
    lenticels
  2. B
    hydathodes
  3. C
    spiracles
  4. D
    stomata
Show answer

Answer: A. Lenticels in the bark allow gases to diffuse into and out of the stem. Stomata are on leaves and young stems.

6. The flap that closes the entrance to the larynx during swallowing is the

  1. A
    uvula
  2. B
    glottis
  3. C
    vocal cord
  4. D
    epiglottis
Show answer

Answer: D. The epiglottis covers the glottis during swallowing so food goes into the oesophagus, not the trachea.

7. During inspiration the diaphragm contracts and flattens while the external intercostal muscles raise the ribs. What happens to the volume of the chest cavity and to the air pressure in the lungs?

  1. A
    the volume decreases and the pressure rises, so air is pushed out
  2. B
    the volume increases and the pressure falls below that outside, so air flows in
  3. C
    the volume increases and the pressure rises above that outside, so air flows in
  4. D
    the volume stays the same and the pressure falls, so air is drawn in
Show answer

Answer: B. Flattening of the diaphragm and raising of the ribs enlarge the chest cavity, so the air in the lungs has more space and its pressure falls below atmospheric pressure. Air always moves from higher to lower pressure, so it flows into the lungs.

8. Which property is NOT an advantage of a good respiratory surface?

  1. A
    large surface area
  2. B
    thick and dry
  3. C
    thin
  4. D
    moist
Show answer

Answer: B. Gas exchange by diffusion needs a large, thin, moist surface, usually with a good blood supply.

9. In emphysema, breathing becomes difficult because

  1. A
    the bronchioles are blocked by thick mucus and infected alveoli fill with pus
  2. B
    the diaphragm is paralysed so the chest cannot expand
  3. C
    alveolar walls break down, reducing the surface area for gas exchange
  4. D
    the trachea collapses because its cartilage rings break down
Show answer

Answer: C. Alveolar walls lose elasticity and rupture, forming larger air spaces with less surface area. Smoking is the main cause.

10. In the cockroach, air enters the tracheal system through openings on the body called

  1. A
    gill slits
  2. B
    lenticels
  3. C
    stomata
  4. D
    spiracles
Show answer

Answer: D. Air passes through spiracles into tracheae and fine tracheoles that carry oxygen directly to the tissues.

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Ways to practise this chapter

Gaseous exchange: questions students ask

How many Gaseous exchange MCQs are there?

20, each with the answer and a short explanation, across 2 topics: Gaseous exchange in plants and animals, Human respiratory system. Every chapter test draws ten of them, so you can take it many times.

Is the FSc Part 1 Biology chapter 13 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

Can I read the explanations in Urdu?

Yes. In practice mode and on your results you can switch the explanations to Urdu.

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