Question

During respiration, exchange of gases takes place in
(a) Trachea and larynx
(b) Alveoli of lungs
(c) Alveoli and throat
(d) Throat and larynx

Answer 1

Hint: Gaseous exchange occurs when oxygen and carbon dioxide diffuse along the gradient. This occurs in sacs with thin membranes that are the structural and functional unit of the respiratory system.

Complete answer:
Alveoli are tiny sacs emerging from the bronchiolar extensions within the lungs that allow for the movement of oxygen and carbon dioxide between the lungs and bloodstream. They have thin walls that are surrounded by blood capillaries which also have simple squamous epithelium, thus forming a very thin membrane.
The gaseous exchange occurs in the alveolar sacs. During inhalation, oxygen has a higher concentration in the alveoli as compared to the blood and hence it diffuses into the blood through the thin layer of cells. During exhalation, carbon dioxide is in a higher concentration in the blood than the alveoli and so it diffuses into the alveoli from the capillaries, again through this thin layer of cells.

So, the answer is, “Alveoli of lungs.”

Note: Though alveoli are the structures that facilitate the gaseous exchange, the actual gaseous exchange occurs through a layer called the respiratory membrane. The membrane has several layers which include – a layer of lining fluid that is formed of surfactant molecules, the epithelial layer, and the basement membrane; a very thin interstitial space present between the epithelial lining and the capillary membrane; a capillary basement membrane that sometimes fuses with the alveolar basement membrane, and the capillary endothelium.