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

Q1. Define vital capacity. What is its significance?

Answer:

Vital capacity (VC) refers to the largest volume of air that can be expelled from the lungs following maximum inspiration. It is equal to tidal volume (TV) plus inspiratory reserve volume (IRV) plus expiratory reserve volume (ERV). Vital capacity is a vital measure of lung function and respiratory health.

An increase in VC indicates increased oxygenation and stamina, making it essential for sportspersons and singers. It also helps in the diagnosis of lung diseases such as asthma and COPD. Exercise and breathing exercises can increase VC, whereas aging and respiratory disease can impair it. VC is quantified through the use of a spirometer during pulmonary function tests.

Q2. 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.

Q3. 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.

Q4. What are the major transport mechanisms for CO2? Explain.

Answer:

The major transport mechanisms for CO2 is transported by sodium bicarbonate as well as 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.

Q5. What will be the pO2 and pCO2 in the atmospheric air compared to those in the alveolar air?

(i) $p{O}_2$ lesser, $pC{O}_2$ higher
(ii) $p{O}_2$ higher, $pC{O}_2$ lesser
(iii) $p{O}_2$ higher, $pC{O}_2$ higher
(iv) $p{O}_2$ lesser, $pC{O}_2$ lesser

Answer:

PO2 is higher, pCO2 lesser

The oxygen partial pressure in atmospheric air is greater than in alveolar air. In atmospheric air, ( P{O2}) 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,( P{CO2})is about 0.3 mm Hg, but in alveolar air, it is around 40 mm Hg.

Q6. Explain the process of inspiration under normal conditions.

Answer:

Inspiration is the process during which atmospheric air is drawn inside the body. It can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs concerning 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 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 intra-pulmonary pressure to less than the atmospheric pressure, which forces the air from outside to move into the lungs,

Q7. How is respiration regulated?

Answer:

A center present in the medulla region of the brain is called the respiratory rhythm center, and it is primarily responsible for respiration regulation. Another center, which is present in the pons region of the brain, is called the pneumatic centre. It can moderate the functions of the respiratory rhythm center. 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 center, which is highly sensitive to CO2 and hydrogen ions. An increase in these substances can activate this center, 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 also can 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.

Q8. 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. At 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.

Q9. 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 acclimatizes 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 acclimatization help the body to adapt to lower oxygen levels.

Q10. 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 out through the spiracles.

Q11. 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.

Q12. Have you heard about hypoxia? Try to gather information about it, and discuss it with your friends.

Answer:

Hypoxia is a type of condition characterized 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 generalized, affecting the whole body, or local, affecting a region of the body.

Different types of hypoxia are:

• Anaemic hypoxia
• Hypoxemic hypoxia

Q13. (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 :

• 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.

Q13. (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

Q13. (c). Distinguish between Vital capacity and Total lung capacity.

Answer:

Vital capacity

• It is the maximum volume of air that can be exhaled after a maximum inspiration. It includes IC and ERV.
• It is about 4000 mL in the human lungs.

Total lung capacity

• It is the volume of air in the lungs after maximum inspiration. It includes IC, ERV, and residual volume.
• It is about 5000-6000 mL in the human lungs.

Q14. 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 that is transported into and out of the lungs ( inspired or expired ) with each normal respiratory cycle. Tidal volume is approximately 6000 to 8000 mL of air per minute for a healthy human.

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

If Tidal volume = 6000 to 8000 mL/minute

So, the Tidal volume in an hour will be:

= 6000 to 8000 mL × (60 min)

= 3.6 × 10 5 mL to 4.8 × 10 5 mL

Hence, the hourly tidal volume for a healthy human is approximately 360000 ml-480000 ml.