Mechanism of Breathing Questions in English

(A) The movement of guard cells is primarily driven by changes in their turgor pressure. When water enters the guard cells,they become turgid and the stomatal pore opens. When water leaves,they become flaccid and the pore closes. This type of plant movement,which is caused by changes in turgor pressure,is known as turgor movement.

(A) According to the starch-sugar interconversion theory proposed by Sayre,the opening and closing of stomata are regulated by the $pH$ of guard cells.
When the $pH$ of guard cells increases (becomes more alkaline),the enzyme phosphorylase converts glucose$-1-$phosphate into starch,which is insoluble and leads to the closing of stomata.
An increase in $pH$ corresponds to a decrease in the concentration of $H^+$ ions in the guard cells.
Therefore,sugar is converted into starch when the $H^+$ ion concentration decreases.

(C) During normal breathing,expiration is a passive process. However,during forced expiration,the process becomes active. This involves the contraction of the internal intercostal muscles and the abdominal muscles. These muscles work to increase the pressure within the thoracic cavity by reducing its volume,thereby pushing air out of the lungs more forcefully. Therefore,the correct option is $C$.

(B) The diaphragm is a primary muscle of respiration that separates the thoracic cavity from the abdominal cavity. In its relaxed state,the diaphragm is dome-shaped,with the convex side facing the thoracic cavity. During inhalation,it contracts and flattens,which increases the volume of the thoracic cavity and facilitates air intake.

(D) The diaphragm is a dome-shaped muscular partition that separates the thoracic cavity from the abdominal cavity.
Its primary and most critical function is to facilitate the process of breathing (ventilation).
When the diaphragm contracts,it flattens,increasing the volume of the thoracic cavity,which decreases the pressure inside the lungs,allowing air to flow in (inhalation).
When it relaxes,it returns to its dome shape,decreasing the thoracic volume and forcing air out (exhalation).
Therefore,it is the primary muscle responsible for pulmonary ventilation.

(D) The breathing process, or pulmonary ventilation, involves the movement of air into and out of the lungs.
This process is primarily driven by changes in the volume of the thoracic cavity.
The $2$ main structures responsible for creating these pressure gradients are the $intercostal muscles$ (located between the ribs) and the $diaphragm$ (a dome-shaped muscle at the base of the thoracic cavity).
Contraction and relaxation of these muscles alter the thoracic volume, which in turn changes the intrapulmonary pressure, allowing air to flow in or out.

(A) The ventilation of the lungs (breathing) is primarily driven by changes in the volume of the thoracic cavity.
This process is facilitated by the contraction and relaxation of the diaphragm and the external and internal intercostal muscles (costal muscles).
The diaphragm moves downward during inspiration to increase the thoracic volume,while the costal muscles move the ribs and sternum to further expand the thoracic cavity.
Therefore,both the diaphragm and costal muscles are essential for lung ventilation.

(C) The bucket-handle movement refers to the elevation of the ribs during inspiration.
This movement occurs in the $6^{th}$ to $10^{th}$ ribs.
These ribs move along an oblique anteroposterior axis,which results in an increase in the transverse diameter of the thoracic cavity.

(B) During expiration,the diaphragm relaxes and returns to its original dome-shaped position. This relaxation reduces the intrathoracic volume,which increases the pressure inside the thoracic cavity,forcing the air to move out of the lungs.

(C) Pulmonary respiration in amphibians like frogs involves a buccal pump mechanism. During this process,the mouth remains closed at all times. The external nostrils open and close in a coordinated manner to allow air intake and expulsion. Specifically,the buccal cavity moves,and the sternohyal and pterohyal muscles contract and relax to change the volume of the buccal cavity. Therefore,the activity of 'successive opening and closing of the mouth' does not occur because the mouth remains closed throughout the process.

(B) The average respiratory rate in a healthy adult human at rest is approximately $12$ to $16$ times per minute. Therefore, $16$ times is the standard value considered for a normal adult.

(B) Air moves into the lungs during inspiration (inhalation).
Inspiration occurs when the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure.
This pressure gradient is created by the contraction of the diaphragm and external intercostal muscles,which increases the volume of the thoracic cavity.
According to Boyle's Law,an increase in volume leads to a decrease in pressure,causing air to flow from the high-pressure atmosphere into the low-pressure lungs.

(B) Expiration in mammals,including rabbits,is a passive process during quiet breathing.
It occurs primarily due to the relaxation of the diaphragm muscles (which return to their dome-shaped position) and the external intercostal muscles.
However,during forced expiration,the internal intercostal muscles contract to pull the rib cage downward and inward,further decreasing the thoracic volume and increasing thoracic pressure to expel air.

(A) During inspiration,the diaphragm and external intercostal muscles contract simultaneously.
This contraction increases the volume of the thoracic cavity in the anteroposterior and dorsoventral axes.
The diaphragm contraction flattens it,while the external intercostal muscles lift the ribs and sternum,moving the thoracic walls outward and upward.
This creates a negative pressure in the lungs,causing air to rush in.

(D) The ventilation of lungs in mammals is a mechanical process that involves the movement of air into and out of the lungs. This process is primarily driven by changes in the volume of the thoracic cavity.
These volume changes are brought about by the coordinated contraction and relaxation of the diaphragm and the external and internal intercostal muscles (costal muscles) attached to the ribs.
The diaphragm,a dome-shaped muscular partition,flattens during contraction to increase the thoracic volume vertically,while the costal muscles move the rib cage upward and outward to increase the thoracic volume in the dorso-ventral and lateral axes.
Therefore,both the diaphragm and the costal muscles are essential for pulmonary ventilation.

(C) The process of breathing involves the movement of air into and out of the lungs,which is primarily driven by changes in the volume of the thoracic cavity.
These volume changes are created by the contraction and relaxation of the diaphragm and the external and internal intercostal muscles associated with the ribs.
When the diaphragm and external intercostal muscles contract,the thoracic volume increases,leading to inspiration.
When these muscles relax,the thoracic volume decreases,leading to expiration.

(B) During inspiration,the diaphragm contracts and flattens,which increases the volume of the thoracic cavity in the antero-posterior axis. This contraction creates a negative pressure in the lungs,allowing air to flow in.

(A) During respiration,the volume of the thoracic cavity increases during inspiration due to the contraction of the diaphragm and external intercostal muscles.
When the thoracic volume reaches its maximum,the lungs are fully inflated with air.
At this point,the process of inspiration is complete,and the next phase,which is expiration,is about to begin.
Therefore,at the moment of maximum thoracic volume,further inspiration is not possible because the lungs have reached their maximum capacity.

(A) When a person attempts to inhale with maximal effort while the nose and mouth are closed,the thoracic cavity expands,which significantly increases the volume of the alveoli.
According to Boyle's Law,for a fixed amount of gas at a constant temperature,pressure is inversely proportional to volume $(P \propto 1/V)$.
As the volume of the alveoli increases rapidly due to the strong contraction of the respiratory muscles (diaphragm and external intercostals),the pressure inside the alveoli drops significantly below atmospheric pressure.
In such a forced maneuver,the alveolar pressure can decrease to as low as $-80\;\text{mm Hg}$ relative to atmospheric pressure.

(B) The breathing rate is lowered during eating because swallowing and breathing cannot occur simultaneously. During the process of swallowing (deglutition),the epiglottis closes the glottis to prevent food from entering the trachea,which temporarily inhibits the intake of air.

(C) The diaphragm is the primary muscle of respiration. It plays a crucial role in the process of breathing by creating a pressure gradient between the lungs and the atmosphere.
If the diaphragm is punctured,the thoracic cavity loses its ability to maintain the negative pressure required for inspiration.
This leads to immediate respiratory failure,preventing the exchange of gases,which results in rapid death due to asphyxiation,even if other vital organs remain intact.

(B) During the later part of inspiration,the thoracic cavity volume reaches its maximum,which leads to a decrease in intrathoracic pressure. This pressure change facilitates increased venous return to the heart. According to the Frank-Starling law,increased venous return leads to an increased stroke volume,which subsequently causes a transient increase in systolic blood pressure.

(B) Expiration (exhalation) is the process of moving air out of the lungs.
This process occurs when the intra-pulmonary pressure (pressure inside the lungs) becomes higher than the atmospheric pressure.
When the diaphragm and external intercostal muscles relax,the thoracic volume decreases,which increases the pressure inside the lungs relative to the outside atmosphere,forcing air to move out.

(A) During the process of inspiration (inhalation),the diaphragm muscles contract.
This contraction causes the diaphragm to flatten and move downwards,which increases the volume of the thoracic cavity in the antero-posterior axis.
This increase in volume leads to a decrease in intrapulmonary pressure,causing air to rush into the lungs from the atmosphere.

(D) Normal expiration is a passive process in humans. During normal breathing,the diaphragm and external intercostal muscles $(EICM)$ relax,which causes the thoracic volume to decrease and leads to the expulsion of air from the lungs. No active muscle contraction is required for normal expiration. Therefore,the correct answer is that no muscles contract during normal expiration.

(A) Breathing involves two stages: inspiration and expiration.
These processes are facilitated by the creation of pressure gradients between the lungs and the atmosphere.
The diaphragm and a specialized set of muscles,known as external and internal intercostal muscles between the ribs,help generate these pressure gradients.
Contraction of the diaphragm increases the volume of the thoracic chamber in the antero-posterior axis,while the contraction of external intercostal muscles lifts up the ribs and the sternum,increasing the volume in the dorso-ventral axis.
Therefore,the coordinated action of the diaphragm and intercostal muscles is responsible for the movement of air in and out of the lungs.

(C) Hiccups occur due to involuntary, spasmodic contractions of the $Diaphragm$.
These contractions are followed by the rapid closure of the vocal cords, which produces the characteristic '$hic$' sound.
Therefore, the correct option is $C$.

(A) Expiration occurs when the diaphragm and external intercostal muscles relax.
$1$. During expiration,the diaphragm and the external intercostal muscles return to their resting positions.
$2$. This movement reduces the volume of the thoracic cavity.
$3$. The decrease in thoracic volume leads to an increase in pulmonary pressure relative to atmospheric pressure.
$4$. Consequently,air is expelled from the lungs to the outside environment.

(D) In humans, the $diaphragm$ is a dome-shaped muscular structure that separates the thoracic cavity from the abdominal cavity.
It plays a crucial role in the mechanism of breathing by contracting and flattening, which increases the volume of the thoracic cavity, thereby facilitating inspiration.
While reptiles and birds also possess ribs and intercostal muscles for breathing, the presence of a well-developed $diaphragm$ in mammals significantly enhances the efficiency of pulmonary ventilation compared to other vertebrates.

(B) The process of breathing involves two stages: inspiration and expiration.
During inspiration,the diaphragm contracts,which flattens its dome-shaped structure.
This contraction increases the volume of the thoracic cavity in the $Antero-posterior$ axis.
Simultaneously,the contraction of external intercostal muscles lifts the ribs and the sternum,causing an increase in the volume of the thoracic cavity in the $Dorso-ventral$ axis.
Therefore,the contraction of the diaphragm specifically increases the thoracic volume along the $Antero-posterior$ axis.

(A) In humans,the diaphragm and ribs play a crucial role in the mechanism of breathing by changing the volume of the thoracic cavity,which creates a pressure gradient.
In frogs,the diaphragm is absent,and they use a buccal pump mechanism to force air into the lungs.
Therefore,the participation of the diaphragm and ribs in respiration is a key difference between the two.

(C) The diaphragm is a dome-shaped muscular partition that separates the thoracic cavity from the abdominal cavity in mammals. Its primary and most important function is to facilitate breathing. During inhalation,the diaphragm contracts and flattens,increasing the volume of the thoracic cavity,which creates negative pressure and draws air into the lungs. During exhalation,it relaxes and moves upward,decreasing the thoracic volume and forcing air out of the lungs. Thus,it is essential for the mechanism of breathing.

(D) The thoracic cavity is a closed,airtight chamber. The lungs are kept inflated by the negative intrapleural pressure (pressure lower than atmospheric pressure) within the pleural cavity. If a puncture occurs in the thoracic wall (thoracic cavity) without damaging the lungs,air enters the pleural space from the outside. This leads to the loss of the negative pressure,causing the lungs to collapse (a condition known as pneumothorax). As the lungs collapse,the body attempts to compensate for the reduced gas exchange by increasing the breathing rate to maintain oxygen levels. Therefore,the breathing rate increases.

(B) Respiration is primarily of two types: diaphragmatic (abdominal) and costal (thoracic/rib-based).
In males,diaphragmatic breathing is more dominant,where the diaphragm plays a major role in changing the thoracic volume.
In females,especially during pregnancy,the movement of the diaphragm is restricted due to the pressure exerted by the growing fetus in the abdominal cavity.
Therefore,to compensate for the limited diaphragmatic movement,females rely more on the movement of the rib cage (costal respiration) to facilitate breathing.

(C) The $Diaphragm$ is a dome-shaped muscular structure that separates the thoracic cavity from the abdominal cavity in mammals,including rabbits.
It plays the most critical role in the mechanism of breathing by contracting and flattening to increase the volume of the thoracic cavity,thereby facilitating inspiration.
Therefore,the correct option is $C$.

(B) The process of breathing involves the movement of air into and out of the lungs,which is driven by pressure gradients created by the thoracic cavity.
$1$. The thoracic cavity is an airtight chamber.
$2$. The diaphragm is a dome-shaped muscular partition that separates the thorax from the abdomen.
$3$. During inspiration,the contraction of the diaphragm muscle flattens it,which increases the volume of the thoracic cavity in the antero-posterior axis.
$4$. This increase in volume leads to a decrease in pressure within the lungs,causing air to flow in.
$5$. While external intercostal muscles also assist by lifting the ribs and sternum,the primary increase in thoracic volume is attributed to the contraction of the diaphragm.

(D) During expiration,the diaphragm and the external intercostal muscles relax. As the diaphragm relaxes,it moves upward and returns to its original dome-shaped position. This decreases the thoracic volume and increases the thoracic pressure,causing air to be expelled from the lungs.

(C) Normal breathing and normal expiration are passive processes that rely on the elastic recoil of the lungs and the relaxation of the diaphragm and external intercostal muscles. However,forced expiration is an active process that requires the contraction of expiratory muscles,specifically the internal intercostal muscles and abdominal muscles,to decrease the thoracic volume rapidly.

(B) : Intrapleural pressure is the pressure within the pleural cavity.
Intrapleural pressure is always negative,which acts like a suction to keep the lungs inflated and prevent them from collapsing.
The negative intrapleural pressure is due to three main factors: surface tension of the alveolar fluid,elasticity of the lungs,and elasticity of the thoracic wall.
Normally,there is a difference between intrapleural and intrapulmonary pressure,which is called transpulmonary pressure.
This transpulmonary pressure creates the suction to keep the lungs inflated.
If there is no pressure difference,there is no suction and the lungs will collapse.

(C) The correct answer is $C$.
Breathing is primarily an involuntary process controlled by the respiratory rhythm center in the medulla oblongata. However,we can exert conscious control over our breathing to a limited extent.
It is possible to consciously breathe by using the diaphragm as the primary muscle of respiration while keeping the rib cage relatively still.
Option $A$ is incorrect because we cannot remove all oxygen from the lungs.
Option $B$ is incorrect as the Eustachian tube connects the middle ear to the pharynx and is not involved in breathing.
Option $D$ is incorrect because even after forceful expiration,some air remains in the lungs,known as residual volume $(RV)$.

(C) The process of breathing involves two stages: Inspiration and Expiration.
$1$. Inspiration (Inhalation) occurs when the intra-pulmonary pressure is less than the atmospheric pressure.
$2$. This pressure gradient is created by an increase in the pulmonary volume (thoracic cavity volume),which is primarily achieved by the contraction of the diaphragm and external intercostal muscles.
$3$. Because the pressure inside the lungs is lower than the outside atmospheric pressure,air rushes into the lungs.
$4$. Therefore,the described mechanism corresponds to Inspiration.

(C) healthy human adult breathes at an average rate of $12$ to $16$ times per minute.
This rate is known as the respiratory rate or breathing rate.
It is regulated by the respiratory center located in the medulla oblongata of the brain.

(B) Inspiration is the process by which atmospheric air is drawn into the lungs.
For air to move into the lungs,the pressure inside the lungs (intra-pulmonary pressure) must be less than the atmospheric pressure,creating a negative pressure gradient.
Option $A$ is true because inspiration requires lower intra-pulmonary pressure.
Option $C$ is true as it describes the same condition as $A$.
Option $D$ is true because the contraction of the diaphragm increases the volume of the thoracic cavity,which decreases the intra-pulmonary pressure.
Option $B$ is false because if there were positive pressure in the lungs relative to the atmosphere,air would move out of the lungs (expiration) rather than into them.

(D) The lungs do not collapse even after forceful expiration because of the presence of negative intrapleural pressure.
This negative pressure is generated by the pleural membranes,which act as a suction force that keeps the lungs expanded against the chest wall.
Because of this constant negative pressure,the lungs are held in a stretched state,preventing them from collapsing completely.
Consequently,a certain volume of air,known as the $Residual Volume$ $(RV)$,always remains in the lungs and cannot be expelled.

(D) Inspiration is an active process that occurs due to the contraction of muscles.
The diaphragm and external intercostal muscles contract simultaneously during inspiration.
This contraction increases the volume of the thoracic cavity in the antero-posterior and dorso-ventral axes,leading to a decrease in intrapulmonary pressure,which allows air to flow into the lungs.
Since the assertion states that inspiration occurs due to muscular relaxation,it is incorrect.
However,the reason correctly states that the diaphragm and external intercostal muscles contract during inspiration.
Therefore,the assertion is incorrect,but the reason is correct.

(B) The process of breathing involves two main phases: inspiration and expiration.
$1$. Inspiration occurs when the intrapulmonary pressure is less than the atmospheric pressure,creating a negative pressure in the lungs with respect to the atmosphere,which forces air into the lungs.
$2$. Expiration takes place when the intrapulmonary pressure is higher than the atmospheric pressure.
$3$. During inspiration,the diaphragm and external intercostal muscles contract,increasing the volume of the thoracic cavity.
$4$. During expiration,the diaphragm and external intercostal muscles relax,decreasing the thoracic volume and increasing intrapulmonary pressure,which pushes air out.
Therefore,option $B$ is the correct statement.

(N/A) Inspiration or inhalation is the process by which atmospheric air is drawn into the lungs.
It is initiated by the contraction of the diaphragm,which increases the volume of the thoracic chamber in the anteroposterior axis.
The contraction of external intercostal muscles lifts up the ribs and the sternum,causing an increase in the volume of the thoracic chamber in the dorsoventral axis.
The overall increase in thoracic volume leads to a corresponding increase in pulmonary volume.
An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure,which forces the air from outside to move into the lungs,i.e.,inspiration.

(N/A) Breathing involves two stages:
$(1)$ Inspiration: The process during which atmospheric air is drawn into the lungs.
$(2)$ Expiration: The process by which the alveolar air is released out into the atmosphere.
The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere.
- Inspiration occurs if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure,i.e.,there is a negative pressure in the lungs with respect to atmospheric pressure.
- Expiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure.
The diaphragm and a specialised set of muscles—external and internal intercostals between the ribs—help in the generation of these pressure gradients.
Inspiration is initiated by the contraction of the diaphragm,which increases the volume of the thoracic chamber in the antero-posterior axis.
The contraction of external intercostal muscles lifts up the ribs and the sternum,causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.
The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra-pulmonary pressure to a level lower than the atmospheric pressure,which forces air from outside to move into the lungs (inspiration).
Relaxation of the diaphragm and the intercostal muscles returns the diaphragm and sternum to their normal positions and reduces the thoracic volume,and thereby the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure,causing the expulsion of air from the lungs (expiration).
We have the ability to increase the strength of inspiration and expiration with the help of additional muscles in the abdomen.
On an average,a healthy human breathes $12-16$ times/minute.
The volume of air involved in breathing movements can be estimated by using a spirometer,which helps in the clinical assessment of pulmonary functions.

(N/A) $(1)$ Inspiration: The process during which atmospheric air is drawn into the lungs is called inspiration.
$(2)$ Expiration: The process by which the alveolar air is released out into the atmosphere is called expiration.

(N/A) Breathing involves two stages:
$(1)$ Inspiration: During which atmospheric air is drawn in.
$(2)$ Expiration: By which the alveolar air is released out.
The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere.
- Inspiration occurs if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure,i.e.,there is a negative pressure in the lungs with respect to atmospheric pressure.
- Similarly,expiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure.
The diaphragm and a specialised set of muscles - external and internal intercostals between the ribs,help in the generation of such gradients.
Inspiration is initiated by the contraction of the diaphragm,which increases the volume of the thoracic chamber in the antero-posterior axis.
The contraction of external inter-costal muscles lifts up the ribs and the sternum,causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.
The overall increase in the thoracic volume causes a similar increase in pulmonary volume.
An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure,which forces the air from outside to move into the lungs,i.e.,inspiration.
Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduces the thoracic volume and thereby the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure,causing the expulsion of air from the lungs,i.e.,expiration.
We have the ability to increase the strength of inspiration and expiration with the help of additional muscles in the abdomen.
On an average,a healthy human breathes $12-16$ times/minute.
The volume of air involved in breathing movements can be estimated by using a spirometer,which helps in the clinical assessment of pulmonary functions.