# Class 11 Biology MCQ – Breathing and Exchange of Gases

This set of Class 11 Biology Chapter 17 Multiple Choice Questions & Answers (MCQs) focuses on “Breathing and Exchange of Gases”. These MCQs are created based on the latest CBSE syllabus and the NCERT curriculum, offering valuable assistance for exam preparation.

1. Gaseous exchange is held by ________
a) osmosis
b) simple diffusion
c) facilitated diffusion
d) co-transport

Explanation: Gaseous exchange is a passive process. It is held by simple diffusion. Diffusion pressure for every gas is called partial pressure. At the time of diffusion, gases move from high partial pressure to low partial pressure.

2. What is the primary site for exchange of gases in lungs?
a) Larynx
b) Trachea
c) Alveoli
d) Bronchi

Explanation: Alveoli are the primary site for exchange of gases in lungs. Exchange of gases is found only in respiratory zone of the lungs, as they are covered by simple squamous epithelium.

3. Solubility of carbon dioxide is ________ than oxygen.
a) more
b) less
c) 50 times more
d) equal

Explanation: The solubility of carbon dioxide is 20-25 times higher than that of oxygen, therefore the amount of carbon dioxide that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of oxygen.

4. What is the concentration of oxygen in expired air?
a) 19%
b) 4%
c) 10%
d) 16%

Explanation: Inspired air contains 19.6% oxygen and expired air has 15.7% oxygen. So approximately 4% oxygen goes to blood from air. In the same way inspired air contains carbon dioxide 0.04% and expired air has 3.6% carbon dioxide so approximately 3.56% carbon dioxide goes to air from blood.

5. Partial pressure of oxygen in alveolar air is ________
a) 159 mm Hg
b) 90 mm Hg
c) 104 mm Hg
d) 45 mm Hg

Explanation: The Partial pressure of oxygen in alveolar air is 104 mm Hg, its value in arterial blood is 40 mm Hg. So, oxygen goes from alveolar air to arterial air. At the time of diffusion, gases move from high partial pressure to low partial pressure.
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6. On which of the following factors diffusion does not depend?
a) Solubility of gases
b) Thickness of the respiratory membrane
c) Partial pressure difference
d) Molecular weight of gases

Explanation: Diffusing capacity depends on solubility of gases, thickness of the respiratory membrane, partial pressure difference. These all factors play an important role in the exchange of gases through the process of simple diffusion.

7. Which one of the following does not consist diffusion membrane?
a) Thin squamous epithelium of alveoli
b) Cuboidal epithelium of alveoli
c) Basement membrane
d) Endothelium of blood capillaries

Explanation: Alveoli is made up of simple squamous epithelium. Diffusion membrane is made up of three major layers: Thin squamous epithelium of alveoli, endothelium of blood capillaries, basement substances in between them.

8. Carbon dioxide is _______ times more soluble than oxygen.
a) 20-25
b) 5-10
c) 15-20
d) 25-30

Explanation: The solubility of carbon dioxide is 20-25 times higher than that of oxygen, therefore the amount of carbon dioxide that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of oxygen.

9. What is the partial pressure of carbon dioxide in alveolar air and in deoxygenated blood respectively?
a) 50 mm Hg, 45 mm Hg
b) 104 mm Hg, 45 mm Hg
c) 45 mm Hg, 40 mm Hg
d) 40 mm Hg, 45 mm Hg

Explanation: In alveolar air, partial pressure of carbon dioxide is 40 mm Hg and its value in deoxygenated blood is 45 mm Hg. So, carbon dioxide moves from arterial blood to alveoli. In this way, according to partial pressure exchange of gases takes place.

10. Right comparison of partial pressure of oxygen and partial pressure of carbon dioxide in the atmospheric air than in alveolar air is _________
a) partial pressure of oxygen lesser, partial pressure of carbon dioxide higher
b) partial pressure of oxygen higher, partial pressure of carbon dioxide lesser
c) partial pressure of oxygen lesser, partial pressure of carbon dioxide higher
d) partial pressure of oxygen lesser, partial pressure of carbon dioxide lesser

Explanation: Partial pressure of oxygen in atmospheric air is 159 mm Hg and in alveoli is 104 mm Hg. Partial pressure of carbon dioxide in atmospheric air is 0.3 mm Hg and in alveoli is 40 mm Hg.

More MCQs on Class 11 Biology Chapter 17

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