The pO₂ difference across the alveolar membrane is about 64 mm Hg, but the pCO₂ difference is only about 5 mm Hg. Even so, CO₂ diffuses adequately because

its solubility is 20-25 times that of oxygen

its molecules diffuse only through the plasma

the membrane is thinner on the side where CO₂ leaves

haemoglobin carries it across the membrane

Breathing and Exchange of Gases

11 NEET-UG practice questions on Breathing and Exchange of Gases, part of Zoology. The first 11 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
Earthworms exchange gases through their
1. Amoist cuticle
2. Blungs
3. Ctracheal tubes
4. Dgills
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Answer: A · moist cuticle
Earthworms use their moist cuticle for gas exchange. Insects use tracheal tubes, and many aquatic animals use gills.
- B: Lungs are used by terrestrial vertebrates.
- C: Tracheal tubes are used by insects.
- D: Gills are used by aquatic arthropods, molluscs and fishes.
Remember this
Earthworm uses moist cuticle; insects use tracheae; fishes use gills; frogs use skin and lungs.
Question 2 · Hard
Read these statements on regulation and disorders: A. Receptors in the aortic arch and carotid artery recognise changes in CO₂ and H⁺ concentration. B. Oxygen has the major role in regulating the respiratory rhythm. C. Emphysema increases the respiratory surface of the lungs. D. A chemosensitive area next to the rhythm centre is highly sensitive to CO₂ and H⁺. Which of these are correct?
1. AB and C only
2. BA and D only
3. CA, B and D only
4. DA, C and D only
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Answer: B · A and D only
A and D are true. The role of oxygen in regulating respiration is quite insignificant, so B fails. Emphysema damages alveolar walls and reduces the respiratory surface, so C fails.
- A: A and D are the true ones, not B and C.
- C: B fails, as oxygen's role is insignificant.
- D: C fails, as emphysema reduces the surface.
Remember this
CO₂ and H⁺ drive rhythm regulation; emphysema is often caused by cigarette smoking.
Question 3 · Easy
Roughly what share of carbon dioxide is carried in blood as bicarbonate?
1. AAbout 97 per cent
2. BAbout 7 per cent
3. CAbout 20-25 per cent
4. DAbout 70 per cent
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Answer: D · About 70 per cent
About 70 per cent of CO₂ goes as bicarbonate, about 20-25 per cent as carbamino-haemoglobin, and about 7 per cent dissolved in plasma.
- A: This is the share of oxygen carried by RBCs.
- B: This is the share dissolved in plasma.
- C: This is the carbamino-haemoglobin share.
Remember this
Oxygen is 97 per cent via RBCs; CO₂ is 70 per cent via bicarbonate.
Question 4 · Hard
The pO₂ difference across the alveolar membrane is about 64 mm Hg, but the pCO₂ difference is only about 5 mm Hg. Even so, CO₂ diffuses adequately because
1. Aits solubility is 20-25 times that of oxygen
2. Bits molecules diffuse only through the plasma
3. Cthe membrane is thinner on the side where CO₂ leaves
4. Dhaemoglobin carries it across the membrane
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Answer: A · its solubility is 20-25 times that of oxygen
The amount that can diffuse depends on solubility as well as the pressure gradient. CO₂ is 20-25 times more soluble than O₂, so more CO₂ can cross per unit difference in partial pressure.
- B: This gives no reason for greater transfer.
- C: The same thin membrane serves both gases.
- D: Haemoglobin does not cross the membrane.
Remember this
Diffusion across the membrane depends on the pressure gradient, solubility and membrane thickness.
Question 5 · Easy
A thin, elastic cartilaginous flap prevents food from entering the larynx during swallowing. This flap is the
1. Aglottis
2. Bepiglottis
3. Cpleura
4. Dtertiary bronchus
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Answer: B · epiglottis
The epiglottis covers the glottis during swallowing, which keeps food out of the larynx.
- A: The glottis is the opening, not the flap.
- C: Pleura is the double membrane around the lungs.
- D: A bronchus is an air passage in the lungs.
Remember this
Glottis is the opening; epiglottis is the flap that closes it during swallowing.
Question 6 · Medium
Given below are two statements: Statement I: Contraction of the diaphragm increases the thoracic volume in the antero-posterior axis. Statement II: The pneumotaxic centre in the pons can reduce the duration of inspiration. Choose the correct answer.
1. AStatement I is correct but Statement II is incorrect
2. BBoth Statement I and Statement II are correct
3. CStatement I is incorrect but Statement II is correct
4. DBoth Statement I and Statement II are incorrect
Answer and explanation in LearnFree account
Question 7 · Medium
Assertion A: Oxygen dissociates from oxyhaemoglobin readily in the tissues. Reason R: Low pO₂, high pCO₂, high H⁺ concentration and higher temperature prevail in the tissues. Choose the correct answer.
1. ABoth A and R are correct and R is the correct explanation of A
2. BA is not correct but R is correct
3. CA is correct but R is not correct
4. DBoth A and R are correct but R is not the correct explanation of A
Answer and explanation in LearnFree account
Question 8 · Medium
Arrange these structures in the order in which inhaled air passes through them. A. Primary bronchi B. Larynx C. Terminal bronchioles D. Nasopharynx
1. AB, D, A, C
2. BD, B, C, A
3. CD, A, B, C
4. DD, B, A, C
Answer and explanation in LearnFree account
Question 9 · Medium
Match List-I with List-II. List-I (site) A. Atmospheric air B. Alveoli C. Oxygenated blood D. Deoxygenated blood List-II (typical pO₂ in mm Hg) I. 95 II. 40 III. 159 IV. 104
1. AA-III, B-I, C-IV, D-II
2. BA-IV, B-III, C-I, D-II
3. CA-III, B-IV, C-I, D-II
4. DA-III, B-IV, C-II, D-I
Answer and explanation in LearnFree account
Question 10 · Medium
The lung volumes of an adult are: tidal volume 500 mL, inspiratory reserve volume 2500 mL, expiratory reserve volume 1000 mL, residual volume 1200 mL. Find the functional residual capacity.
1. A4000 mL
2. B5200 mL
3. C2200 mL
4. D3000 mL
Answer and explanation in LearnFree account
Question 11 · Medium
Under normal conditions, every 100 mL of oxygenated blood delivers about 5 mL of O₂ to the tissues. If a person's cardiac output is 5000 mL/min, about how much O₂ reaches the tissues each minute?
1. A250 mL
2. B2500 mL
3. C25 mL
4. D200 mL
Answer and explanation in LearnFree account

Breathing and Exchange of Gases

Earthworms exchange gases through their

Roughly what share of carbon dioxide is carried in blood as bicarbonate?

The pO₂ difference across the alveolar membrane is about 64 mm Hg, but the pCO₂ difference is only about 5 mm Hg. Even so, CO₂ diffuses adequately because

A thin, elastic cartilaginous flap prevents food from entering the larynx during swallowing. This flap is the

Given below are two statements: Statement I: Contraction of the diaphragm increases the thoracic volume in the antero-posterior axis. Statement II: The pneumotaxic centre in the pons can reduce the duration of inspiration. Choose the correct answer.

Assertion A: Oxygen dissociates from oxyhaemoglobin readily in the tissues. Reason R: Low pO₂, high pCO₂, high H⁺ concentration and higher temperature prevail in the tissues. Choose the correct answer.

Arrange these structures in the order in which inhaled air passes through them. A. Primary bronchi B. Larynx C. Terminal bronchioles D. Nasopharynx

Match List-I with List-II. List-I (site) A. Atmospheric air B. Alveoli C. Oxygenated blood D. Deoxygenated blood List-II (typical pO₂ in mm Hg) I. 95 II. 40 III. 159 IV. 104

The lung volumes of an adult are: tidal volume 500 mL, inspiratory reserve volume 2500 mL, expiratory reserve volume 1000 mL, residual volume 1200 mL. Find the functional residual capacity.

Under normal conditions, every 100 mL of oxygenated blood delivers about 5 mL of O₂ to the tissues. If a person's cardiac output is 5000 mL/min, about how much O₂ reaches the tissues each minute?