Human Respiratory System Questions in English

(A) In cockroaches,spiracles are small openings on the lateral side of the body that allow for the exchange of gases by connecting the internal tracheal system to the external environment.
In humans,the nostrils (external nares) serve as the primary openings that connect the internal respiratory tract to the external environment,facilitating the intake and outflow of air.
Therefore,the spiracle of a cockroach is functionally analogous to the nostril in humans.

(B) The diaphragm is a characteristic feature of mammals. However,among non-mammalian vertebrates,crocodiles are unique because they possess a muscular diaphragm that separates the thoracic cavity (containing the lungs) from the abdominal cavity. This structure assists in their respiration.

(B) The diaphragm is a characteristic muscular partition that separates the thoracic cavity from the abdominal cavity. It is a unique feature found exclusively in mammals. Among the given options,the kangaroo is a mammal,whereas crocodiles are reptiles,ostriches are birds,and snakes are reptiles. Therefore,the diaphragm is present in the kangaroo.

(D) The presence of a $diaphragm$ is a unique characteristic of mammals. It is a muscular partition that separates the thoracic cavity from the abdominal cavity and plays a crucial role in the mechanism of breathing. While other vertebrates may have a four-chambered heart (like birds) or exhibit homeothermy (like birds), the $diaphragm$ is exclusively found in mammals.

(D) The bronchioles are the smaller airways of the lungs.
As the bronchioles branch into smaller segments,the epithelium changes from ciliated pseudostratified columnar epithelium (found in the trachea and bronchi) to ciliated simple columnar epithelium,and finally to ciliated simple cuboidal epithelium in the terminal bronchioles.
Therefore,the epithelium in the bronchioles is primarily characterized as cuboidal and columnar.

(A) Ciliated epithelium consists of cells that bear cilia on their free surface.
These cilia move particles or mucus in a specific direction over the epithelium.
In the human body,ciliated epithelium is primarily found in the inner surface of hollow organs like the bronchioles and fallopian tubes.
Among the given options,the bronchus is lined with ciliated epithelium,which helps in trapping and moving foreign particles out of the respiratory tract.

(C) Stomata are microscopic pores found on the epidermis of leaves,primarily involved in gas exchange ($CO_2$ and $O_2$) and transpiration.
If a tiny particle is placed within the stomatal pore,it will enter the sub-stomatal cavity (also known as the respiratory cavity).
From the sub-stomatal cavity,the particle will be accommodated within the intercellular spaces of the mesophyll cells,as these spaces are directly connected to the stomatal pore to facilitate gas diffusion.

(B) The lymphatic tissue located at the sides of the root of the tongue is known as the palatine tonsils.
These are a pair of soft tissue masses that form part of the immune system and help in defending the body against infections entering through the mouth or nose.
Therefore,the correct option is $B$.

(A) Kupffer cells are specialized macrophages located in the liver sinusoids that perform phagocytosis to remove debris and pathogens.
Dust cells (also known as alveolar macrophages) are found in the lungs and perform a similar phagocytic function by engulfing inhaled particles and microorganisms.
Therefore,Kupffer cells and dust cells are functionally similar as both are phagocytic cells.

(C) The $Taeniae$ $coli$ are three distinct longitudinal bands of smooth muscle found on the outer surface of the large intestine (specifically the $caecum$ and $colon$).
These bands are formed by the thickening of the longitudinal muscle layer of the muscularis externa.
Therefore,the correct option is $C$.

(D) The human respiratory system consists of a series of branching tubes that transport air into the lungs.
Air enters through the nose or mouth,passes through the pharynx,larynx,and trachea,and then travels through the bronchi and bronchioles.
The final destination for the inspired air is the $Alveoli$,which are tiny,thin-walled,balloon-like structures.
It is at the level of the $Alveoli$ that the actual exchange of gases ($O_2$ and $CO_2$) occurs between the air and the blood capillaries.

(D) The correct sequence of air passage in the human respiratory system is as follows:
$1$. Air enters through the external nostrils into the nasal cavity.
$2$. From the nasal cavity, it passes into the pharynx, which is a common passage for food and air.
$3$. From the pharynx, air enters the larynx (voice box) through the glottis.
$4$. The larynx leads into the trachea (windpipe).
$5$. The trachea divides into two primary bronchi (left and right).
$6$. Each bronchus undergoes repeated divisions to form secondary and tertiary bronchi and bronchioles.
$7$. Finally, the bronchioles terminate into thin-walled, vascularized bag-like structures called alveoli, where gas exchange occurs.
Therefore, the correct sequence is: Nasal cavity $\rightarrow$ Pharynx $\rightarrow$ Larynx $\rightarrow$ Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli.

(B) The vocal cords are located inside the $Larynx$ (voice box).
They consist of two pairs of mucous membrane folds that extend from the sides into the lumen of the $Larynx$.
When air passes through these cords,they vibrate to produce sound.

(D) The $Pharynx$ is a funnel-shaped muscular tube that serves as a common passage for both air (respiratory system) and food (digestive system).
It connects the oral and nasal cavities to the larynx and esophagus,respectively.
Therefore,the correct option is $D$.

(D) The terminal bronchioles are the smallest airways of the conducting zone.
They are lined by ciliated cuboidal epithelium.
Unlike larger bronchi,they lack cartilage,goblet cells,and submucosal glands.
The wall of the terminal bronchiole is primarily composed of smooth muscle and connective tissue,which contains both elastic and reticular fibres to provide structural support and elasticity for the respiratory process.

(A) In human beings,the right lung is divided into three lobes: superior,middle,and inferior lobes. The left lung is smaller and is divided into two lobes: superior and inferior lobes,to accommodate the heart.

(A) The $Thyroid$ cartilage is the largest cartilage of the larynx. It is shield-shaped and forms the anterior and lateral walls of the larynx. However,the description of a 'broad ring' that is 'incomplete posteriorly' specifically refers to the $Thyroid$ cartilage's structure in some contexts,though the $Cricoid$ is a complete ring. Given the standard biological classification,the $Thyroid$ cartilage is the largest. Note: The $Cricoid$ cartilage is a complete ring,while the $Thyroid$ is incomplete posteriorly.

(B) The larynx contains two pairs of folds: the upper pair is called the false vocal cords (vestibular folds),and the lower pair is the true vocal cords. The space or recess located between these two sets of folds is known as the laryngeal ventricle (or sinus of Morgagni). Therefore,the correct option is $B$.

(A) The trachea is a tube approximately $10 \, cm$ long in humans.
It is supported by $C$-shaped rings of hyaline cartilage in its wall.
These rings prevent the trachea from collapsing and keep the airway open for the passage of air.

(A) The larynx,also known as the voice box,is a cartilaginous structure located at the top of the trachea.
It is present in all mammals,including the rabbit,to facilitate sound production and protect the airway.
In amphibians like the frog,a structure called the larynx is also present,which serves as the voice box for vocalization.
Therefore,the larynx is found in both frogs and rabbits.

(D) The trachea (windpipe) is a tube that extends through the neck and into the thorax.
In rabbits,as in other mammals,the trachea is supported by $C$-shaped rings of hyaline cartilage.
These cartilaginous rings are incomplete dorsally,meaning they do not form a complete circle.
This structure allows the esophagus,which lies behind the trachea,to expand during the passage of food.

(C) In a rabbit,the left lung is divided into two lobes: the left anterior and the left posterior.
In contrast,the right lung is divided into four lobes: the anterior azygous,the right anterior,the right posterior,and the posterior azygous lobe.
Therefore,the correct option is $C$.

(B) Each lung is enclosed in two membranes called pleurae. The outer membrane is attached to the chest wall and diaphragm and is called the parietal pleura. The inner membrane,which closely covers the lung surface,is called the visceral pleura.

(A) In mammals,including rabbits,the lungs are situated within the thoracic cavity.
Specifically,they are enclosed by the pleural membranes,which define the pleural cavities,but the entire respiratory apparatus is housed within the thoracic cavity,which is protected by the rib cage,vertebral column,and sternum.

(C) The respiratory tract is lined by different types of epithelium depending on the location.
Terminal bronchioles are the final part of the conducting zone.
They are lined by a simple cuboidal epithelium,which is often ciliated.
Therefore,the correct description for the lining of the terminal bronchiole is ciliated columnar or cuboidal epithelium.

(D) The trachea is supported by $C$-shaped cartilaginous rings. These rings provide structural support and prevent the trachea from collapsing when the air pressure inside it decreases,ensuring that the airway remains open for the passage of air.

(D) The respiratory system consists of a branching network of tubes. The trachea divides into primary bronchi,which further branch into secondary and tertiary bronchi,and finally into smaller bronchioles. The bronchioles are the narrowest and most numerous tubes within the lungs,which eventually lead to the alveolar sacs. Therefore,the correct option is $D$.

(B) The thyroid cartilage is a large,shield-shaped structure that forms part of the larynx (voice box) in mammals,including the rabbit. It provides structural support to the larynx and protects the vocal cords.

(D) The presence of a diaphragm is a characteristic feature of mammals.
It is a dome-shaped muscular partition that separates the thoracic cavity from the abdominal cavity.
This structure plays a crucial role in the process of breathing by changing the volume of the thoracic cavity.

(D) When air passes through the nasal cavity,it undergoes three primary processes:
$1$. Warming: The blood vessels in the nasal mucosa warm the incoming air to body temperature.
$2$. Humidification: Mucus secreted by the nasal lining adds moisture to the air,preventing the respiratory tract from drying out.
$3$. Filtration: Nasal hairs (vibrissae) and mucus trap dust,pollen,and other foreign particles,ensuring that only clean air reaches the lungs.
Therefore,all the given options are correct.

(C) The trachea is supported by $C$-shaped cartilaginous rings. These rings are incomplete on the dorsal side to allow the esophagus to expand during the passage of food. Therefore,the tracheal rings are incomplete dorsally.

(A) The alveoli are the primary sites for gaseous exchange in the lungs of mammals,including rabbits.
They are thin-walled,sac-like structures that provide a very large surface area for the diffusion of gases ($O_2$ and $CO_2$) between the air and the blood.
Similar to the villi in the intestine,the alveoli significantly increase the total surface area available for respiration.

(D) Bronchi are the primary,secondary,and tertiary airways that contain cartilaginous rings to prevent collapse.
Bronchioles are the smaller branches of the respiratory tree with a diameter of less than $1\,mm$.
Unlike bronchi,bronchioles lack cartilaginous support in their walls.
Instead,larger bronchioles are supported by connective tissue that extends from the interlobular septa.
Therefore,both statements $(a)$ and $(c)$ correctly distinguish bronchioles from bronchi.

(A) The pharynx is divided into three parts: nasopharynx,oropharynx,and laryngopharynx.
The laryngopharynx is the lowest part of the pharynx.
It serves as a common pathway for both air and food.
From the laryngopharynx,the air passes into the larynx (voice box) through the glottis,while food passes into the oesophagus.

(A) The trachea is lined with a pseudostratified ciliated columnar epithelium containing goblet cells that secrete mucus.
The cilia present on these epithelial cells beat in a coordinated manner to move the mucus,along with trapped dust particles and pathogens,upwards towards the pharynx.
Once the mucus reaches the pharynx,it is either swallowed or coughed out,thereby protecting the lungs from infection and obstruction.

(D) In the respiratory system of mammals like rabbits,the conducting zone ends at the terminal bronchioles.
These lead into the respiratory zone,which begins with the respiratory bronchioles.
The respiratory bronchioles further divide and open into the alveolar ducts,which eventually lead to the alveolar sacs and alveoli.
Therefore,alveolar ducts originate from the respiratory bronchioles.

(A) The larynx,also known as the voice box,is a cartilaginous structure in the respiratory tract. In mammals like rabbits,the larynx is supported by several cartilages. The primary cartilages include the thyroid cartilage,the cricoid cartilage,and the paired arytenoid cartilages. These structures provide structural support to the airway and facilitate the movement of vocal cords.

(C) The nasal cavity is divided into two nasal passages by the nasal septum.
Within the nasal cavity,there are three scroll-shaped bony structures known as nasal conchae or turbinates.
These structures increase the surface area of the nasal cavity,which helps in warming,humidifying,and filtering the inhaled air before it reaches the lungs.
Therefore,the correct answer is $C$ (Turbinates).

(D) The correct answer is $D$. The larynx is primarily known as the sound-producing organ (voice box) in mammals. While it is a part of the respiratory tract,it does not play an active role in the mechanical process of breathing (ventilation). Ribs,abdominal muscles,and the diaphragm are all directly involved in changing the volume of the thoracic cavity to facilitate inhalation and exhalation.

(C) The human respiratory system consists of a branching network of bronchi,bronchioles,and alveoli.
Alveoli are the primary sites of gaseous exchange.
An adult human has approximately $750$ million alveoli in both lungs.
These numerous alveoli provide a massive surface area for the diffusion of gases,which is estimated to be about $100 \, m^2$.

(D) The presence of a very large number of tiny alveoli significantly increases the surface area available for the exchange of gases ($O_2$ and $CO_2$).
This structural adaptation allows for a more efficient diffusion process.
While the lungs do contain residual air (the volume of air remaining in the lungs after a forced expiration),the branching structure ensures that the ventilation process remains highly efficient for gas exchange.

(C) The trachea, also known as the windpipe, is a tube that connects the larynx to the bronchi of the lungs.
It is supported by $C$-shaped rings of hyaline cartilage.
These cartilaginous rings provide structural support and prevent the trachea from collapsing when the air pressure inside it decreases during inhalation or when it is empty of air.
Therefore, the correct option is $C$.

(A) The human respiratory system is divided into two parts: the conducting zone and the respiratory zone.
$(1)$ The conducting zone includes the nose,pharynx,larynx,trachea,bronchi,and bronchioles. Its primary function is to transport,filter,warm,and humidify the air. No gaseous exchange occurs in this zone.
$(2)$ The respiratory zone,which includes the respiratory bronchioles,alveolar ducts,and alveoli,is the actual site of gaseous exchange between blood and air.
$(3)$ Therefore,the gaseous exchange does not occur in the conducting zone.

(C) The respiratory system,including the lining of the trachea,bronchi,and lungs,is primarily derived from the endoderm germ layer during embryonic development.

(A) The trachea is lined with ciliated pseudostratified columnar epithelium. The cilia (tracheal hair) beat in a rhythmic,coordinated manner to move mucus,along with trapped dust particles and pathogens,upwards towards the pharynx. This process,known as the mucociliary escalator,helps in clearing the respiratory tract and preventing infections.

(B) The trachea and bronchi are supported by $C$-shaped cartilaginous rings.
These rings provide structural support to the airway walls.
Their primary function is to prevent the trachea and bronchi from collapsing during inhalation when negative pressure is generated within the thoracic cavity.

(D) Surfactant is a lipoprotein secreted by specialized cells within the alveolar epithelium.
Its primary function is to reduce the surface tension of the fluid lining the alveoli.
By reducing surface tension,it prevents the collapse of alveoli during expiration,thereby maintaining their stable size.
Additionally,it decreases the effort required to inflate the lungs,thus facilitating lung expansion during inspiration.
Therefore,all the mentioned options are correct.

(C) Alveolar surfactant is a complex mixture of lipids and proteins that lines the inner surface of the alveoli in the lungs.
Its primary function is to reduce the surface tension of the fluid lining the alveoli,which prevents the collapse of the alveoli during expiration.
The most significant component of pulmonary surfactant is dipalmitoylphosphatidylcholine $(DPPC)$,a phospholipid,along with specific surfactant proteins ($SP$-$A$,$SP$-$B$,$SP$-$C$,and $SP$-$D$).
Therefore,it is classified as a lipoprotein complex.

(D) The correct answer is $D$. The total number of alveoli in both human lungs is estimated to be approximately $750$ million. These alveoli provide a massive surface area for the exchange of gases,which is estimated to be nearly $100 \; m^2$.

(D) The correct answer is $D$. Both the alveolar sacs in the lungs and the villi in the small intestine are structural adaptations designed to significantly increase the surface area available for physiological processes. In the lungs,the alveoli increase the surface area for efficient gaseous exchange,while in the intestine,the villi increase the surface area for the absorption of digested food nutrients.