Question

Read the following statements about human respiration

(i) Trachea divides at the level of the $6^{\text{th}}$ thoracic vertebra.
(ii) Terminal bronchioles, alveoli and their ducts form the respiratory part of this system.
(iii) Contraction of the diaphragm increases volume of thoracic chamber dorsoventrally.
(iv) The internal intercostals help in inspiration.

• A. Only (i) is true
• B. None is true
• C. Only (iii) and (iv) are false
• D. All except (iv) are true

Answer 1

The correct option is B None is true

Breathing involves inspiration and expiration.

• Inspiration is a process that involves the intake of air into the lungs.
• Exhalation is a process that involves leaving air from the lungs.

Statement (i): Trachea divides at the level of the 6th thoracic vertebra.
Elaboration: The trachea is a long tube that connects the larynx to the bronchi. It is divided into two primary or main bronchi (the left and the right bronchi). The division of the trachea is called carina which is situated at the level of the 5th thoracic vertebra. Hence, the given statement (i) is false.
Statement (ii): Terminal bronchioles, alveoli and their ducts form the respiratory part of this system.
Elaboration: The respiratory system is divided into two parts as follows:
Conducting part: The part that helps in the conduction of air from the atmosphere towards the respiratory part. It consists of the mouth, trachea, primary bronchi, secondary bronchi, tertiary bronchi and the terminal bronchi.
Statement (iV): The internal intercostals help in inspiration.
Elaboration: The internal intercostal muscle is present in the backside of the ribs and helps in the movement of the ribs. The internal intercostals pull down on the rib cage and push air out of the lungs. Thus they help in expiration. Hence, the given statement (iv) is false.
Hence, option D is correct.