Human Physiology – Breathing and Exchange of Gases Quiz - ICSE Class 11 Biology

Free practice quiz: Human Physiology – Breathing and Exchange of Gases (ICSE Class 11 Biology). 52 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. Which of the following anatomical structures is primarily responsible for the efficient diffusion of gases between the alveoli and the pulmonary capillaries?

   1. The smooth muscle layer in the bronchioles
   2. The squamous epithelial cells forming the alveolar wall
   3. The elastic fibers surrounding the alveoli
   4. The goblet cells lining the trachea
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   Answer: B. The squamous epithelial cells forming the alveolar wall

   The alveolar wall is extremely thin, composed of a single layer of squamous epithelial cells (type I pneumocytes), which minimizes the diffusion distance for oxygen and carbon dioxide between the alveolar air and the blood in the pulmonary capillaries. This thinness is crucial for efficient gas exchange.

2. What is the approximate percentage of oxygen transported in the blood bound to hemoglobin?

   1. 1.5%
   2. 3%
   3. 7%
   4. 98.5%
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   Answer: D. 98.5%

   Oxygen is transported in the blood in two main ways: dissolved in the plasma (about 1.5%) and bound to hemoglobin within red blood cells (about 98.5%).

3. What effect does a decrease in atmospheric pressure at high altitudes have on the partial pressure of oxygen in the alveoli?

   1. Increases alveolar PO2
   2. Decreases alveolar PO2
   3. Has no effect on alveolar PO2
   4. Increases alveolar PCO2
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   Answer: B. Decreases alveolar PO2

   At high altitudes, the total atmospheric pressure is lower. Although the percentage of oxygen in the air remains about 21%, the lower total pressure means that the partial pressure of oxygen (PO2) is also lower. This reduced alveolar PO2 is the primary challenge for gas exchange at high altitudes.

4. The vocal cords, which produce sound, are located in which part of the respiratory tract?

   1. Pharynx
   2. Trachea
   3. Larynx
   4. Bronchi
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   Answer: C. Larynx

   The larynx, commonly known as the voice box, is situated between the pharynx and the trachea. It contains the vocal cords, which vibrate when air passes through them, producing sound.

5. Which nerve carries the primary motor signals from the respiratory center to the diaphragm?

   1. Vagus nerve
   2. Phrenic nerve
   3. Glossopharyngeal nerve
   4. Hypoglossal nerve
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   Answer: B. Phrenic nerve

   The phrenic nerve originates from the cervical spinal cord (C3-C5) and innervates the diaphragm. It transmits motor impulses that cause the diaphragm to contract, initiating inspiration.

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