Question

During respiration, exchange of gases takes place in
A. Trachea and larynx
B. Alveoli of lungs
C. Alveoli and throat
D. Throat and lungs

Answer 1

Hint: Hormones are chemical messengers which are secreted by the ductless glands called endocrine glands. Hormones coordinate different physical and mental activities of the body and maintain a steady-state. Thyroxine, insulin, adrenalin are some of the examples of hormones.

Complete answer:
To understand this question, we have to visualize the structure of the respiratory system of the body and all the organs situated at different places in the system. All the different organs are responsible for carrying out specific functions.
The lungs are the main area where the exchange of the gases takes place but the lungs itself do not exchange the gases and instead, they have special structure which helps in the respiration and exchange of gases. These special functional structures of the lungs are called Alveoli, they are thin layered.
Now as we know that the exchange of gases takes place in lungs, we now have to analyze our answer by considering the placement of other structures inside the body. Trachea is the passage present in the throat along with the esophagus from which the oxygen reaches the lungs and larynx is present above the trachea which is the voice box of the humans and does not play any role in exchange of gases.
Throat has both the passages for food as well as the oxygen and if exchange is supposed to happen there then it will lead to the mixing of food with air and causing complications.

So, from the above made discussion, we can say that Option (B) is the correct answer.

Additional Information:
The exchange of gases takes place by the process of diffusion, that is the substance moves from a higher concentration to the lower concentration. The concentration of oxygen in the blood reaching lungs is low and the concentration of the carbon dioxide is high, when the oxygen is inhaled and it reaches the alveoli of lungs, the concentration of oxygen is high and the concentration of carbon dioxide is low. So, the exchange of gases takes place along the concentration gradient leading to movement of oxygen to blood and carbon dioxide to alveoli.

Note:
We know that the blood which needs to be oxygenated is sent to the lungs as a part of a double circulation process and the oxygen is supplied to the blood in lungs only. So, by remembering the concept of double circulation we can also find the answer to this question.