(N/A) $\rightarrow$ The respiratory system consists of a network of trachea,which are the main elements of the respiratory system.
$\rightarrow$ Many branches of the trachea are spread throughout the body. Their terminal branches are called tracheoles,which transport $O_{2}$ to all parts of the body.
$\rightarrow$ The trachea maintains direct contact with atmospheric air through openings called spiracles.
$\rightarrow$ There are $10$ pairs of spiracles present on the lateral sides of the body. Among these,$2$ pairs are located in the thorax region and $8$ pairs are located in the abdomen region.
$\rightarrow$ The walls of the spiracles are formed of funnel-like structures.
$\rightarrow$ These funnel-like structures prevent dust and foreign substances from entering the respiratory system. Valves control the opening and closing of the spiracles.
$\rightarrow$ During respiration,oxygen enters the trachea through the spiracles,reaches the tissue fluid via tracheoles,and dissolves in it. Body tissues use this dissolved oxygen to produce energy. Carbon dioxide produced during metabolism also dissolves in the tissue fluid and is expelled during exhalation.