NCERT Solutions for Class 11 Biology Chapter 14 - Breathing and Exchange of Gases

Question 1. Define vital capacity. What is its significance?

Answer:

Vital capacity (VC) is the maximum volume of air a person can exhale forcefully after a maximum inspiration. It is equal to tidal volume (TV) + inspiratory reserve volume (IRV) + expiratory reserve volume (ERV).

Vital capacity indicates the strength of the respiratory muscles and lung health. It is essential for sports, singing, and physical endurance. A reduced VC may indicate lung disorders such as asthma or COPD. Regular exercise and breathing practices can help improve VC.

Question 2. State the volume of air remaining in the lungs after normal breathing.

Answer:

The volume of air remaining in the lungs after normal breathing is called functional residual capacity (FRC). It combines expiratory reserve volume (ERV) and residual volume (RV). ERV is the maximum volume of air that can be exhaled after a normal expiration, and it is about 1000 mL to 1500 mL. RV, on the other hand, refers to the volume of air remaining in the lungs after maximum expiration and is about 1100 mL to 1500 mL.

Thus, FRC = ERV + RV

1500 + 1500 = 3000 mL

Hence, the functional residual capacity of the human lungs is about 2500 - 3000 mL.

Question 3. Diffusion of gases occurs in the alveolar region only and not in the other parts of the respiratory system. Why?

Answer:

Diffusion of gases can only take place in the alveolar area since alveoli possess thin walls (one-cell thick), a large surface area, and are well-perfused with blood capillaries, thus facilitating efficient gas exchange. The other structures of the respiratory system, i.e., trachea, bronchi, and bronchioles, are only air passageways and devoid of structural modifications to facilitate diffusion.

The alveolar membrane is permeable and wet, permitting oxygen to diffuse into the blood and carbon dioxide to diffuse out. Moreover, the partial pressure gradient between alveolar air and blood propels the movement of gases. These unique properties render the alveoli the sole location for effective gas exchange.

Question 4. What are the major transport mechanisms for CO₂? Explain.

Answer:

The major transport mechanisms for CO₂ are sodium bicarbonate and red blood cells. See, about 70% of carbon dioxide is transported as sodium bicarbonate. As CO₂ diffuses into the blood plasma, a large part of it combines with water to form carbonic acid in the presence of the enzyme carbonic anhydrase.

Carbonic anhydrase is a zinc enzyme that speeds up the formation of carbonic acid. This carbonic acid dissociates into bicarbonate (HCO₃^–) and hydrogen ions (H⁺). About 20 – 25% of CO₂ is transported by the red blood cells as carbaminohaemoglobin. Carbon dioxide binds to the amino groups on the polypeptide chains of haemoglobin and forms a compound known as carbaminohaemoglobin.

Question 5. What will be the pO₂ and pCO₂ in the atmospheric air compared to those in the alveolar air?

(i) pO₂ lesser, pCO₂ higher
(ii) pO₂ higher, pCO₂ lesser
(iii) pO₂ higher, pCO₂ higher
(iv) pO₂ lesser, pCO₂ lesser

Answer:

(ii) PO₂ is higher, pCO₂ lesser

The oxygen partial pressure in atmospheric air is greater than in alveolar air. In atmospheric air, the partial pressure of oxygen is about 159 mm Hg, but in alveolar air, it is around 104 mm Hg. Likewise, the carbon dioxide partial pressure in atmospheric air is less than in alveolar air. In atmospheric air, the partial pressure of carbon dioxide is about 0.3 mm Hg, but in alveolar air, it is around 40 mm Hg.

Question 6. Explain the process of inspiration under normal conditions.

Answer:

Inspiration is the process by which atmospheric air is drawn into the body. It can occur if the pressure within the lungs (intrapulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs compared to atmospheric pressure.

It is initiated by the contraction of the diaphragm, which increases the volume of the thoracic chamber in the anteroposterior axis. The contraction of the external intercostal muscles lifts the ribs and the sternum, causing an increase in the volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intrapulmonary pressure to less than the atmospheric pressure, which forces the air from outside to move into the lungs.

Question 7. How is respiration regulated?

Answer:

A centre present in the medulla region of the brain is called the respiratory rhythm centre, and it is primarily responsible for respiration regulation. Another centre, which is present in the pons region of the brain, is called the pneumatic centre. It can moderate the functions of the respiratory rhythm centre. The neural signal from this centre can reduce the duration of inspiration and thereby alter the respiratory rate.

A chemosensitive area is situated adjacent to the rhythm centre, which is highly sensitive to CO₂ and hydrogen ions. An increase in these substances can activate this centre, which in turn can signal the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated. Receptors associated with the aortic arch and carotid artery can also recognize changes in CO₂ and H⁺ concentration and send necessary signals to the rhythm centre for remedial actions. The role of oxygen in the regulation of respiratory rhythm is quite insignificant.

Question 8. What is the effect of pCO₂ on oxygen transport?

Answer:

The pCO₂ plays an important role in the transportation of oxygen. The low pCO₂ and high pO₂ favour the formation of oxyhaemoglobin that takes place at the alveolus. In the tissues, the high pCO₂ and low pO₂ favour the dissociation of oxygen from oxyhaemoglobin. So, the affinity of haemoglobin for oxygen is enhanced by the decrease of pCO₂ in blood. Therefore, oxygen is transported in the blood as oxyhaemoglobin and oxygen dissociates from it at the tissues.

Question 9. What happens to the respiratory process in a man going up a hill?

Answer:

If a man goes uphill, he breathes in less oxygen per inhalation since the oxygen content in the air declines with rising elevation. At the same time, the oxygen level in the blood falls, leading to an acceleration of the rate of breathing to balance the lower level of oxygen. At the same time, the rate of the heart increases to facilitate higher oxygen delivery to tissues and uphold normal body operations.

At greater heights, repeated exposure can result in altitude sickness with symptoms of dizziness, headache, and breathlessness. The body slowly acclimatises by increasing the number of red blood cells to enhance oxygen-carrying capacity. Individuals dwelling at high altitudes naturally have increased haemoglobin levels for more efficient oxygen use. Gradual ascent and hydration through acclimatisation help the body to adapt to lower oxygen levels.

Question 10. What is the site of gaseous exchange in an insect?

Answer:

In insects, gaseous exchange occurs through a system of tubes referred to as the tracheal system. The minute openings on the sides of an insect's body are referred to as spiracles, where oxygen-rich air enters. The spiracles lead to a system of tubes. Oxygen from the spiracles passes into the tracheae and then diffuses into the cells of the body. The movement of carbon dioxide is the opposite, in which CO₂ from the body cells initially passes through the tracheae and then leaves through the spiracles.

Question 11. Define the oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?

Answer:

The oxygen dissociation curve is a plot of the percentage of saturation of oxyhaemoglobin for different partial pressures of oxygen. It portrays the equilibrium of oxyhaemoglobin and haemoglobin at different levels of oxygen. In the lungs, where the partial pressure of oxygen is high, haemoglobin combines with oxygen to produce oxyhaemoglobin.

Question 12. Have you heard about hypoxia? Try to gather information about it, and discuss it with your friends.

Answer:

Hypoxia is a type of condition characterised by an inadequate or decreased supply of oxygen to the lungs. It is caused by several extrinsic factors, such as a reduction in pO₂, inadequate oxygen, etc. It can also be classified as either generalised, affecting the whole body, or local, affecting a region of the body.

Different types of hypoxia are:

• Anaemic hypoxia
• Hypoxemic hypoxia

Question 13. (a) Distinguish between IRV and ERV

Answer:

The differences between the IRV and ERV are given below:

IRV :

• Total lung capacity minus the volume of air in the lung at the end of a normal inspiration. This means that we have a reserve volume that we can tap into as tidal volume increases with exercise or activity.
• IRV is about 2500 – 3500 mL in the human lungs.

ERV :

• The difference between the volume of air left in the lung after normal expiration versus after maximal expiration. That means that we have a "reserve" volume that we can tap into when our tidal volume increases with exercise or activity.
• ERV is about 1000 – 1500 mL in the human lungs.

Question 13. (b) Distinguish between inspiratory capacity and Expiratory capacity.

Answer:

Difference between Inspiratory capacity and Expiratory capacity:

Inspiratory capacity:

• It is the volume of air that can be inhaled after a normal expiration.
• IC = TV + IRV

Expiratory capacity:

• It is the volume of air that can be exhaled after a normal inspiration.
• EC = TV + ERV

Question 13. (c). Distinguish between Vital capacity and Total lung capacity.

Answer:

Vital capacity

a. It is the maximum volume of air that can be exhaled after a maximum inspiration.
b. It includes TV + IRV + ERV.
c. It is about 4000 mL to 4800 mL in healthy adults.

Total lung capacity

a. It is the maximum volume of air the lungs can hold after a maximum inspiration.
b. It includes VC + Residual Volume (RV).
c. It is about 5000 – 6000 mL in healthy adults.

Question 14. What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.

Answer:

Tidal volume is the volume of air inspired or expired in a single normal breath, about 500 mL per breath in a healthy adult.

We can calculate the hourly tidal volume for a healthy human.

If minute ventilation = 6000 to 8000 mL/minute

So, the Tidal volume in an hour will be:

= 6000 to 8000 mL × (60 min)

= 3.6 × 10⁵ mL to 4.8 × 10⁵ mL

Hence, the hourly tidal volume for a healthy human is approximately 3,60,000 ml- 4,80,000 ml.