Chapter 14: Breathing and Exchange of Gases Short Questions | biology Class 11 CBSE

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Chapter 14: Breathing and Exchange of Gases Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Define breathing and distinguish it from cellular respiration.

Breathing is the process of exchange of O2 from the atmosphere with CO2 produced by the cells, involving inspiration and expiration.
Cellular respiration refers to the utilisation of O2 by cells for catabolic reactions (breakdown of glucose, amino acids, fatty acids) to derive energy, with resultant release of CO2.
Breathing is a physical/mechanical process involving respiratory organs, whereas cellular respiration is a biochemical process occurring within cells.

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Question 2

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State the role of the epiglottis in the human respiratory system.

The epiglottis is a thin elastic cartilaginous flap located at the larynx.
During swallowing, the glottis is covered by the epiglottis to prevent the entry of food into the larynx.
This prevents food from entering the respiratory tract, ensuring that the airway remains unblocked during eating.

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Question 3

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What is the significance of pleural fluid in the respiratory system?

The lungs are covered by a double-layered pleura with pleural fluid present between the two layers.
The pleural fluid reduces friction on the lung surface during breathing movements.
The outer pleural membrane is in close contact with the thoracic lining, while the inner membrane contacts the lung surface, ensuring tight coupling between thoracic and pulmonary volumes.

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Question 4

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Differentiate between the conducting part and the exchange part of the human respiratory system.

The conducting part extends from the external nostrils up to the terminal bronchioles; it transports atmospheric air to the alveoli, filters foreign particles, humidifies air, and brings it to body temperature.
The exchange part consists of the alveoli and their ducts; it is the actual site of diffusion of O2 and CO2 between blood and atmospheric air.
No gas exchange occurs in the conducting part because the walls there are not thin or vascularised enough for diffusion.

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Question 5

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Why is the thoracic chamber described as an air-tight chamber, and what is its functional importance?

The thoracic chamber is formed by the vertebral column (dorsal), sternum (ventral), ribs (lateral), and the dome-shaped diaphragm (lower side), making it anatomically air-tight.
Because the lungs are situated inside this air-tight thoracic chamber, any change in the volume of the thoracic cavity is directly reflected as a change in pulmonary volume.
This anatomical arrangement is essential for breathing because we cannot directly alter pulmonary volume; changes must be mediated through thoracic volume changes.

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Question 6

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State the pressure conditions required for inspiration and expiration.

Inspiration occurs when intra-pulmonary pressure is less than the atmospheric pressure (negative pressure in the lungs), which forces air to move inward.
Expiration occurs when intra-pulmonary pressure is higher than the atmospheric pressure, which causes expulsion of air from the lungs.
These pressure gradients are generated by the diaphragm and the external and internal intercostal muscles between the ribs.

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Question 7

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Define Tidal Volume and calculate the approximate volume of air a healthy man can inspire or expire per minute.

Tidal Volume (TV) is the volume of air inspired or expired during a normal respiration; it is approximately 500 mL.
A healthy man breathes 12–16 times per minute on average.
Therefore, the approximate volume of air per minute is 500 mL × 12 to 500 mL × 16 = 6000 to 8000 mL per minute.

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Question 8

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What is Residual Volume? Why is it physiologically important?

Residual Volume (RV) is the volume of air remaining in the lungs even after a forcible expiration, averaging 1100–1200 mL.
RV ensures that the alveoli are never completely empty, preventing their collapse and maintaining a continuous surface for gas exchange between breaths.
It also forms part of Functional Residual Capacity (FRC = ERV + RV) and Total Lung Capacity (TLC = VC + RV), both of which are clinically significant.

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Question 9

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Write the formula for Vital Capacity and Total Lung Capacity.

Vital Capacity (VC) = ERV + TV + IRV; it is the maximum volume of air a person can breathe in after a forced expiration (or breathe out after a forced inspiration).
Total Lung Capacity (TLC) = RV + ERV + TV + IRV, or equivalently, TLC = VC + RV.
TLC represents the total volume of air that can be accommodated in the lungs at the end of a forced inspiration.

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Question 10

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What is partial pressure? Give the partial pressure values of O2 and CO2 in the alveoli.

Partial pressure is the pressure contributed by an individual gas in a mixture of gases; it is represented as pO2 for oxygen and pCO2 for carbon dioxide.
In the alveoli, the partial pressure of O2 (pO2) is 104 mm Hg.
In the alveoli, the partial pressure of CO2 (pCO2) is 40 mm Hg.

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Question 11

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Name the three layers that make up the diffusion membrane and state its significance.

The diffusion membrane consists of: (i) the thin squamous epithelium of the alveoli, (ii) the basement substance between them, and (iii) the endothelium of the alveolar capillaries.
Its total thickness is much less than a millimetre, which minimises the distance gases must diffuse, facilitating rapid exchange.
This thin membrane, combined with the large surface area of alveoli, allows efficient diffusion of O2 from alveoli to blood and CO2 in the reverse direction.

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Question 12

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Why does CO2 diffuse faster than O2 across the diffusion membrane despite its larger molecular nature?

The solubility of CO2 is 20–25 times higher than that of O2.
As a result, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to O2.
Therefore, even though the partial pressure gradient for CO2 is smaller (about 5 mm Hg at alveoli) compared to O2 (about 64 mm Hg), CO2 diffuses efficiently due to its high solubility.

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Question 13

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How is oxygen transported in the blood? Give percentage values for each mode.

About 97% of O2 is transported by RBCs bound to haemoglobin as oxyhaemoglobin.
The remaining 3% of O2 is carried in a dissolved state through the plasma.
Each haemoglobin molecule can carry a maximum of four O2 molecules, and O2 binding is primarily related to the partial pressure of O2.

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Chapter 14: Breathing and Exchange of Gases | Short Questions

Define breathing and distinguish it from cellular respiration.

State the role of the epiglottis in the human respiratory system.

What is the significance of pleural fluid in the respiratory system?

Differentiate between the conducting part and the exchange part of the human respiratory system.

Why is the thoracic chamber described as an air-tight chamber, and what is its functional importance?

State the pressure conditions required for inspiration and expiration.

Define Tidal Volume and calculate the approximate volume of air a healthy man can inspire or expire per minute.

What is Residual Volume? Why is it physiologically important?

Write the formula for Vital Capacity and Total Lung Capacity.

What is partial pressure? Give the partial pressure values of O2 and CO2 in the alveoli.

Name the three layers that make up the diffusion membrane and state its significance.

Why does CO2 diffuse faster than O2 across the diffusion membrane despite its larger molecular nature?

How is oxygen transported in the blood? Give percentage values for each mode.

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