Regulation of Respiration (NCERT) - NEET Free MCQ Test with solutions

Metabolic activities are the sum of physical and chemical processes taking place in the living organisms. Rate of breathing, O₂ intake and CO₂ output and pulse rate slow down indicating that the metabolic needs of the body are at their minimum during rest.

Respiratory rhythm centre is a specialised centre present in the medulla of the brain which is primarily responsible for the regulation of respiration. A chemosensitive area situated adjacent to the rhythm centre is highly sensitive to changes in CO₂ and hydrogen ion concentrations in blood. Increase in CO₂ and H⁺ ions stimulate this centre, which in turn stimulate the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated.

The pneumotaxic centre, also known as the pontine respiratory group (PRG), is a network of neurons in the rostral dorsolateral pons. The PRG regulates the amount of air a person can take into the body in each breath. The absence of the PRG results in an increase in depth of respiration and a decrease in respiratory rate.

Answer: A. Alveoli

Solution: The alveoli are the primary sites for the exchange of gases. They are tiny, balloon-like structures in the lungs where oxygen is absorbed into the blood and carbon dioxide is released from the blood. This process is facilitated by the large surface area and thin walls of the alveoli, making them perfectly suited for gas exchange.

Trachea consists of C-shaped cartilaginous rings that support the walls of the trachea and prevent its collapse during inspiration.
Respiratory centre is located in the medulla oblongata.
Yeast undergoes anaerobic respiration to produce ethanol and CO₂
The type of respiration in insects and fish is tracheal respiration and branchial respiration respectively.
ATP is a biologically useful energy produced during respiration.
The partial pressure of O₂ in alveolar air is approximately 104 mm Hg.
Vocal cords are present inside the larynx.

• Inspired Air: The partial pressure of oxygen in inspired air is approximately 158 mm of Hg.


• Expired Air: The partial pressure of oxygen in expired air is around 40 mm of Hg.

• Inspired Air: When we breathe in, the air we inhale contains a higher concentration of oxygen compared to the air we breathe out. This is why the partial pressure of oxygen in inspired air is higher at around 158 mm of Hg.


• Expired Air: As we exhale, our body utilizes oxygen for various metabolic processes, leading to a decrease in the partial pressure of oxygen in the exhaled air, which is around 40 mm of Hg.

• Therefore, the partial pressure of oxygen in inspired and expired air is approximately 158 mm of Hg and 40 mm of Hg, respectively.

The basic rhythm of respiration is generated mainly in the dorsal respiratory group in the medulla. Changes in blood carbon dioxide is believed to stimulate the neurons in chemosensitive area which affect the rhythm centre. CO₂ acts by forming carbonic acid which dissociates into H⁺ and HCO₃^- H⁺ has direct effect on this. Oxygen does ot have a significant direct effect on rhythm centre.

Corrected statements:
(ii) Lungs do not become empty after a forceful expiration.
(iii) The exchange of gases in the lungs is not interrupted during expiration.

Human beings have a significant ability to maintain and moderate the respiratory rhythm, to suit the demands of the body tissues. This is done by the neural system. A specialised centre present in the medulla region of the brain called (i) Respiratory rhythm centre is primarily responsible for this regulation. Another centre present in the pons region of the brain called the (ii) Pneumotaxic centre can moderate the functions of the respiratory rhythm centre. A neural signal from this centre can reduce the duration of (iii) inspiration and thereby alter the respiratory rate. A chemosensitive (iv) area is situated adjacent to the rhythm centre which is highly sensitive to CO₂ and hydrogen ions.
Correct answer is B.

Rate of breathing is mainly controlled by CO₂ level in the blood.
Excess CO₂ decrease the pH of the blood and it mainly stimulate the respiratory centre of the brain (i.e., Medulla oblongata) and increase the inspiratory and expiratory signals to the respiratory muscles.