Respiration in human beings - class-X

In the alveoli, O2 is 104 and CO2 is 40. In oxygenated blood, O2 is 95 and CO2 is 40. In tissues, O2 is 40 and CO2 is 45.

Gas exchange occurs across the respiratory membrane, which consists of the alveolar wall and the capillary wall.

Respiratory bronchioles are the final branches of the bronchial tree, which then divide into alveolar ducts that lead to the alveolar sacs.

The alveolus is the functional unit of the lung where the actual exchange of oxygen and carbon dioxide takes place.

Alveolar air contains approximately 13.1% oxygen and 5.3% carbon dioxide, reflecting the exchange that has occurred with the blood.

The total surface area of the alveoli in human lungs is estimated to be between 70 and 100 square meters, facilitating efficient gas exchange.

Alveolar air composition is approximately 14% oxygen, 6% carbon dioxide, and 80% nitrogen. This differs from atmospheric air due to the continuous exchange of gases in the lungs.

Pulmonary ventilation is the total volume of air moved into and out of the lungs per minute. Alveolar ventilation is lower because it excludes the air that remains in the anatomical dead space where no gas exchange occurs.

Oxygen diffuses from the alveoli into the blood because the partial pressure of oxygen in the alveoli (approx. 104 mmHg) is higher than that in the deoxygenated pulmonary capillary blood (approx. 40 mmHg).

The pleura are membranes that secrete a lubricating fluid, which allows free movement of the lungs against the chest wall while breathing. The alveolar sacs are sacs of many alveoli (clusters of chambers), that help exchange oxygen and carbon dioxide in the lungs. The bronchioles are the passageways by which air passes through the nose or mouth to the alveoli (air sacs) of the lungs. Each lobe of the lung has the same physiologic function, bringing oxygen into the bloodstream and removing carbon dioxide. So, the correct option is 'alveolar sacs'.

The air present inside the alveoli or the alveolar air usually has a higher amount of oxygen than carbon dioxide. The approximate composition of alveolar air under normal condition is 14% oxygen, 6% carbon dioxide, and 80% nitrogen.

So, the correct answer is '14% oxygen, 6% carbon dioxide, 80% nitrogen'.

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(b) Activity of respiratory centres is directly proportional to the level of free $CO _2$ in blood.

A normal man, when resting, usually respires about 12-18 times per minute. So, the correct option is 'False'.

The volume of air inspired or expired during normal breath is called tidal volume. It is about 500 mL of air in average young adult man.

Heavy laboured breathing is a sign of abnormal respiration and an increased effort to breathe. Rapid breathing or Tachypnea has seen the breathing rate in adult humans is greater than the normal 20 breaths per minute. This  breathing pattern reduces carbon dioxide in the blood due to increased rate or depth of respiration.