Breathing and Exchange of Gases

$\bullet$ In water, frogs respire through skin and not through buccal cavity i.e., undergo cutaneous respiration only.

$\bullet$ On land, the buccal cavity, skin and lungs act as respiratory organs i.e., undergo buccopharyngeal, cutaneous and pulmonary respiration.

To solve this question, we need to match the terms in List-I with their appropriate definitions in List-II:

(A) Residual Volume: This is the volume of air remaining in the lungs after forcible expiration.

(B) Vital Capacity: This is the maximum volume of air that can be breathed in after forced expiration.

(C) Expiratory Capacity: This is the total volume of air expired after normal inspiration.

(D) Tidal Volume: This is the volume of air inspired or expired during normal respiration.

Now match each item:

• (A) Residual Volume matches with (III) Volume of air remaining in lungs after forcible expiration.
• (B) Vital Capacity matches with (I) Maximum volume of air that can be breathed in after forced expiration.
• (C) Expiratory Capacity matches with (IV) Total volume of air expired after normal inspiration.
• (D) Tidal Volume matches with (II) Volume of air inspired or expired during normal respiration.

Hence, the correct matching is:

(A) - III, (B) - I, (C) - IV, (D) - II

The correct answer is:

Option C: A-III, B-I, C-IV, D-II

Let's analyze the given statements:

Assertion A: During the transportation of gases, about 20-25 percent of CO$_2$ is carried by Haemoglobin as carbamino-haemoglobin.

Reason R: This binding is related to high pCO$_2$ and low pO$_2$ in tissues.

Explanation:

1. Assertion A: It is true that during the transportation of gases in the blood, around 20-25% of carbon dioxide (CO$_2$) is indeed carried by hemoglobin in the form of carbamino-haemoglobin. Hemoglobin not only carries oxygen (O$_2$) but also plays a role in transporting CO$_2$ from the tissues back to the lungs.

2. Reason R: This is also true. The binding of CO$_2$ to hemoglobin to form carbamino-haemoglobin is influenced by the partial pressures of CO$_2$ (pCO$_2$) and O$_2$ (pO$_2$). In tissues where cellular respiration is occurring, the pCO$_2$ is high, and the pO$_2$ is low. This environment favors the formation of carbamino-haemoglobin, as hemoglobin has a higher affinity for CO$_2$ under these conditions.

Therefore, both Assertion A and Reason R are true. Additionally, Reason R correctly explains why Assertion A is true, as the conditions in the tissues (high pCO$_2$ and low pO$_2$) directly promote the formation of carbamino-haemoglobin.

Correct Answer: Option C - Both A and R are true and R is the correct explanation of A.

First, let's define each term listed in List I and match them with their appropriate descriptions in List II.

List I:

• Expiratory Capacity (EC): This is the maximum volume of air that a person can expel from the lungs after a normal tidal expiration. It is composed of the expiratory reserve volume (ERV) and tidal volume (TV).
• Functional Residual Capacity (FRC): This represents the volume of air present in the lungs at the end of a passive expiration. It is the sum of the residual volume (RV) and the expiratory reserve volume (ERV).
• Vital Capacity (VC): This includes the total volume of air that can be expelled from the lungs after taking as deep an inhalation as possible. Hence, this comprises the tidal volume (TV), inspiratory reserve volume (IRV), and the expiratory reserve volume (ERV).
• Inspiratory Capacity (IC): It refers to the volume of air that can be inhaled after a normal expiration. This combines tidal volume (TV) and inspiratory reserve volume (IRV).

List II:

• I. Expiratory reserve volume + Tidal volume + Inspiratory reserve volume = Vital Capacity (VC).
• II. Tidal volume + Expiratory reserve volume = Expiratory Capacity (EC).
• III. Tidal volume + Inspiratory reserve volume = Inspiratory Capacity (IC).
• IV. Expiratory reserve volume + Residual volume = Functional Residual Capacity (FRC).

Now, let's match the terms:

• A (Expiratory Capacity) matches with II.
• B (Functional Residual Capacity) matches with IV.
• C (Vital Capacity) matches with I.
• D (Inspiratory Capacity) matches with III.

The correct option that pairs these correctly is:

Option A: A-II, B-IV, C-I, D-III.

The formation of oxyhemoglobin in the alveoli is primarily influenced by the partial pressure of oxygen ($\mathrm{pO}_2$), partial pressure of carbon dioxide ($\mathrm{pCO}_2$), hydrogen ion concentration ($\mathrm{H}^{+}$), and temperature. Understanding these factors will help in selecting the right option that describes the conditions favorable for maximizing the binding of oxygen to hemoglobin in the lungs.

1. Oxygen Partial Pressure ($\mathrm{pO}_2$): High $\mathrm{pO}_2$ enhances the formation of oxyhemoglobin. In the alveoli, where gas exchange occurs, the $\mathrm{pO}_2$ is relatively high, making it a favorable condition for oxyhemoglobin formation as oxygen molecules bind readily to hemoglobin.

2. Carbon Dioxide Partial Pressure ($\mathrm{pCO}_2$): Lower $\mathrm{pCO}_2$ is favorable in the alveoli for oxyhemoglobin formation. High $\mathrm{pCO}_2$ leads to a lower pH (due to formation of carbonic acid), which can cause the release of O₂ from hemoglobin (Bohr effect), reducing hemoglobin's affinity for oxygen.

3. Hydrogen Ion Concentration ($\mathrm{H}^{+}$): Lesser $\mathrm{H}^{+}$ concentration, or higher pH, increases the affinity of hemoglobin for oxygen. In alkaline conditions (higher pH), hemoglobin is more likely to bind oxygen, thus forming oxyhemoglobin.

4. Temperature: Temperature also affects oxygen binding. Lower temperatures generally enhance the uptake of oxygen by hemoglobin. However, since the lung environment maintains a stable temperature, significant fluctuations in temperature are less of a consideration in this context compared to $\mathrm{pO}_2$, $\mathrm{pCO}_2$, and $\mathrm{H}^{+}$ concentration.

Given these points, Option B - High $\mathrm{pO}_2$ and Lesser $\mathrm{H}^{+}$ concentration - best describes the conditions that are favorable for the formation of oxyhemoglobin in the alveoli. High $\mathrm{pO}_2$ ensures that more oxygen molecules are available to bind with hemoglobin, and a lower $\mathrm{H}^{+}$ concentration (higher pH) reduces the release of oxygen from hemoglobin, thereby increasing oxygen uptake.

The correct answer is Option A : (D), (A), (C), (B), (E).

Here's the reasoning behind this order :

(D) Pulmonary ventilation by which atmospheric air is drawn in and CO₂ rich alveolar air is released out.

Respiration begins with pulmonary ventilation (breathing), which allows the atmospheric air to enter the lungs and CO₂-rich air to be exhaled.

(A) Diffusion of gases (O₂ and CO₂) across the alveolar membrane.

Inside the lungs, oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli across the alveolar membrane.

(C) Transport of gases by the blood.

Once in the bloodstream, oxygen and carbon dioxide are transported to and from the body's tissues.

(B) Diffusion of O₂ and CO₂ between blood and tissues.

Oxygen diffuses from the blood into the body's tissues, and carbon dioxide diffuses from the tissues into the blood.

(E) Utilisation of O₂ by the cells for catabolic reactions and resultant release of CO₂.

Finally, oxygen is used by cells for metabolic processes, creating carbon dioxide as a byproduct.

Therefore, the sequence is (D), (A), (C), (B), (E).

The correct option is :

Option C : Both (A) and (R) are true and (R) is the correct explanation of (A).

Explanation :

At higher altitudes, the air pressure is lower than at sea level. This means there is less atmospheric pressure to push oxygen into the lungs, which can make it more difficult for the body to get the oxygen it needs. This condition can lead to altitude sickness, which can cause symptoms such as difficulty breathing and heart palpitations, among others. This is the basis for the statement (A) and the reason given in statement (R) accurately explains this situation.

Option (c) is the correct answer as pneumotaxic centre is present in the pons region of the brain, that can moderate the functions of the respiratory rhythm centre.

Option (b) is incorrect as medulla oblongata possesses respiratory rhythm centre and a chemosensitive area.

Option (a) and (d) are incorrect as cerebrum and thalamus does not possess any specialised centre to moderate the respiratory rhythm to suit the demands of the body tissues.

Option (d) is the correct answer because statements (a), (c) and (e) are correct.

Vital capacity includes ERV, TV and IRV.

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.

Statement (b) is incorrect as total volume of air a person can inspire after a normal expiration is termed as inspiratory capacity (IC).

Statement (d) is incorrect as ERV, RV, IRV and TV comprise total lung capacity.

Option (b) is the correct answer because every 100 ml of oxygenated blood can deliver around 5 ml of O₂ to the tissues under normal physiological conditions.

Option (c), (d) and (a) are incorrect because every 100 ml of deoxygenated blood delivers approximately 4 ml of CO₂ to the alveoli.

Option (d) is correct because the part starting with the external nostrils upto the terminal bronchioles constitute the conducting part; whereas the alveoli and their ducts form the respiratory or exchange part of the respiratory system.

The conducting part transports the atmospheric air to the alveoli, clears it from foreign particles, humidifies and also bring the air to body temperature. Exchange part is the site of actual diffusion of O₂/CO₂ between blood and atmospheric air.

Option A: The principle of countercurrent flow facilitates efficient respiration in the gills of fishes.

This statement is correct. In fish, water flows over the gills in one direction while blood flows in the opposite direction. This countercurrent flow mechanism maximizes oxygen uptake and carbon dioxide removal, making respiration more efficient.

Option B: The residual air in lungs slightly decreases the efficiency of respiration in mammals.

This statement is also correct. In mammals, some air always remains in the lungs after exhalation (residual volume). This air is less oxygenated compared to fresh air, which slightly decreases the overall efficiency of gas exchange in the lungs.

Option C: The presence of non-respiratory air sacs increases the efficiency of respiration in birds.

This statement is correct as well. Birds have a unique respiratory system that includes air sacs in addition to lungs. These air sacs do not participate directly in gas exchange but help to ensure a continuous flow of air through the lungs, leading to highly efficient respiration.

Option D: In insects, circulating body fluids serve to distribute oxygen to tissues.

This statement is incorrect. In insects, oxygen is distributed directly to tissues through a network of small tubes called tracheae. The tracheae deliver oxygen directly to the cells, and the circulatory system (haemolymph) does not play a significant role in oxygen transport.

Therefore, the incorrect statement is Option D.