Breathing and Exchange of GasesClass 11 Biology NCERT Solutions

Definition of Vital Capacity (VC): Vital Capacity is the maximum volume of air a person can breathe in after a forced expiration, or the maximum volume of air a person can breathe out after a forced inspiration. It includes the Expiratory Reserve Volume (ERV), Tidal Volume (TV), and Inspiratory Reserve Volume (IRV).

Significance: Vital capacity is a measure of the strength of respiratory muscles and the overall health of the lungs. It is of great clinical significance as any deviation from the normal value can indicate a pulmonary disorder. Measuring vital capacity helps in the clinical assessment of pulmonary functions and diagnosis of respiratory diseases.

The volume of air remaining in the lungs after a normal expiration (normal breathing) is called the Functional Residual Capacity (FRC). It is the sum of the Expiratory Reserve Volume (ERV) and the Residual Volume (RV).

Using the approximate values from the textbook:

Therefore, the Functional Residual Capacity (FRC) is approximately: $\text{FRC} = (1000 \text{ to } 1100 \text{ mL}) + (1100 \text{ to } 1200 \text{ mL}) = 2100 \text{ to } 2300 \text{ mL}$

The diffusion of gases occurs in the alveolar region only because the structure of the alveoli is specifically adapted for efficient gas exchange, while the other parts of the respiratory system are not.

The human respiratory system is divided into two main parts:

These structural adaptations in the alveolar region facilitate rapid and efficient exchange of O2 and CO2, which is not possible in the thicker-walled conducting parts of the respiratory system.

Carbon dioxide ($CO_2$) is transported from the tissues to the alveoli by the blood through three major mechanisms:

The correct option is (ii) $pO_2$ higher, $pCO_2$ lesser.

Explanation: According to Table 14.1 in the textbook, the partial pressures are as follows:

Comparing these values:

This is because as atmospheric air enters the lungs, it mixes with the air already present (residual volume), and oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli. This process lowers the $pO_2$ and raises the $pCO_2$ in the alveolar air compared to the inhaled atmospheric air.

Inspiration, or inhalation, is the process by which atmospheric air is drawn into the lungs. Under normal conditions, it is an active process involving the contraction of specific muscles to create a pressure gradient between the atmosphere and the lungs.

The steps involved are as follows:

Respiration is regulated by the neural system to maintain and moderate the respiratory rhythm according to the demands of the body. The key components of this regulation are:

The role of oxygen in the regulation of respiratory rhythm is considered quite insignificant under normal physiological conditions.

The partial pressure of carbon dioxide ($pCO_2$) has a significant effect on oxygen transport by influencing the binding affinity of haemoglobin for oxygen ($O_2$). This relationship is illustrated by the oxygen dissociation curve.

Oxygen binds with haemoglobin to form oxyhaemoglobin. The efficiency of this binding and its subsequent dissociation is affected by factors like $pCO_2$, hydrogen ion concentration ($H^+$), and temperature.

In summary, a high $pCO_2$ promotes the release of oxygen from haemoglobin, which is crucial for delivering oxygen to the body's tissues. A low $pCO_2$ promotes the uptake of oxygen by haemoglobin in the lungs.

When a person goes up a hill, they move to a higher altitude. At higher altitudes, the atmospheric pressure is lower, and consequently, the partial pressure of oxygen ($pO_2$) in the atmospheric air is also lower. This reduction in available oxygen can lead to a condition known as hypoxia (oxygen deficiency at the tissue level).

To compensate for the lower oxygen availability, the body makes several physiological adjustments to the respiratory process:

These immediate responses help the body to cope with the reduced oxygen supply and maintain adequate oxygenation of tissues. Over a longer period of acclimatization, the body would also increase the production of red blood cells to enhance the oxygen-carrying capacity of the blood.

In insects, the respiratory system consists of a network of tubes called tracheal tubes. The site of gaseous exchange is this tracheal system. Atmospheric air enters the body through small openings called spiracles and flows into the network of tracheal tubes. These tubes branch into finer tubules called tracheoles, which reach every cell and tissue in the insect's body. The exchange of gases ($O_2$ and $CO_2$) occurs by simple diffusion directly between the tracheoles and the body cells. This system allows for direct transport of atmospheric air to the cells without the involvement of blood.

Definition: The oxygen dissociation curve is a graph that plots the percentage saturation of haemoglobin with oxygen against the partial pressure of oxygen ($pO_2$).

Reason for its Sigmoidal (S-shaped) Pattern: The sigmoidal pattern of the curve is due to the property of cooperative binding of oxygen to the haemoglobin molecule. A haemoglobin molecule is made of four subunits, each containing a heme group that can bind one molecule of oxygen.

This cooperative binding mechanism allows haemoglobin to be highly efficient in both picking up oxygen in the lungs (where $pO_2$ is high) and releasing it in the tissues (where $pO_2$ is low).

Yes, hypoxia is a physiological condition where the body as a whole (generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of an adequate oxygen supply at the tissue level.

Definition of Tidal Volume (TV): Tidal Volume is the volume of air inspired or expired during a normal, quiet respiration. For a healthy adult, it is approximately 500 mL.

Formula: Total Volume per hour = (TV per breath) $\times$ (Breaths per minute) $\times$ (60 minutes per hour)

Calculation: First, we calculate the volume of air breathed per minute:

Next, we calculate the volume per hour:

Final Answer: The approximate tidal volume for a healthy human in an hour ranges from 360,000 mL to 480,000 mL (or 360 to 480 Litres).