Transport of gases Questions in English

(A) In the red blood cells $(RBCs)$, carbon dioxide $(CO_2)$ reacts with water $(H_2O)$ to form carbonic acid $(H_2CO_3)$.
This reaction is catalyzed by the enzyme $Carbonic \, anhydrase$.
This enzyme is present in very high concentrations in $RBCs$ and in minute quantities in blood plasma.
It facilitates the hydration of $CO_2$ to form $H_2CO_3$, which then dissociates into bicarbonate $(HCO_3^-)$ and hydrogen ions $(H^+)$.

(D) The $pH$ of human blood is maintained within a narrow range of $7.35$ to $7.45$,which is slightly alkaline.
This slightly alkaline environment is crucial for the efficient transport of respiratory gases.
If the blood becomes too acidic or too alkaline,it interferes with the binding capacity of hemoglobin with $O_2$ and the transport of $CO_2$ as bicarbonate ions.
Therefore,the correct nature of blood for efficient gas exchange is slightly alkaline.

(B) The chloride shift,also known as the Hamburger phenomenon,occurs in the blood to maintain electrical neutrality during the transport of carbon dioxide $(CO_2)$.
As $CO_2$ diffuses into red blood cells,it reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into bicarbonate $(HCO_3^-)$ and hydrogen ions $(H^+)$.
To maintain the ionic balance,bicarbonate ions move out of the red blood cells into the plasma,and chloride ions $(Cl^-)$ move into the red blood cells from the plasma.
Therefore,the chloride shift is a mechanism that facilitates the transport of $CO_2$ in the form of bicarbonate ions.

(C) In human blood,oxygen $(O_2)$ is transported in two ways:
$1$. About $3\%$ of $O_2$ is carried in a dissolved state through the plasma.
$2$. About $97\%$ of $O_2$ is transported by binding with hemoglobin in the red blood cells $(RBCs)$ to form oxyhemoglobin.
Therefore,the correct percentage of $O_2$ transported by hemoglobin is $97\%$.

(C) During the transport of $CO_2$,$HCO_3^-$ ions are formed inside the $RBCs$ due to the action of carbonic anhydrase.
To maintain the ionic balance,$HCO_3^-$ ions diffuse out of the $RBCs$ into the plasma,and in exchange,$Cl^-$ ions move from the plasma into the $RBCs$.
This phenomenon is known as the chloride shift or the Hamburger phenomenon.

(C) The formation of oxyhemoglobin occurs in the alveoli where oxygen binds to hemoglobin.
This process is favored by high partial pressure of oxygen $(PO_2)$,low partial pressure of carbon dioxide $(PCO_2)$,low hydrogen ion concentration $(H^+)$,and low temperature.
These conditions shift the oxygen-hemoglobin dissociation curve to the left,promoting the binding of $O_2$ to hemoglobin.
Conversely,high $PCO_2$,high $H^+$ concentration,and high temperature favor the dissociation of oxyhemoglobin in the tissues.

(B) The oxygen dissociation curve shifts to the right under conditions that promote the release of oxygen from hemoglobin to the tissues. This phenomenon is known as the Bohr effect.
Factors that cause a rightward shift include:
$1$. Increased $CO_2$ concentration (partial pressure of $CO_2$).
$2$. Decreased $pH$ (increased $H^+$ concentration/acidity).
$3$. Increased temperature.
$4$. Increased $2,3-BPG$ levels.
Among the given options,an increase in $CO_2$ concentration promotes the dissociation of oxyhemoglobin,shifting the curve to the right.

(A) In the human body,$CO_2$ is transported in the blood in three forms:
$1$. As dissolved gas in plasma $(7\%)$.
$2$. As carbaminohemoglobin bound to hemoglobin $(20-25\%)$.
$3$. As bicarbonates $(HCO_3^-)$ in plasma $(70\%)$.
Since the majority of $CO_2$ is transported as bicarbonates,the correct option is $A$.

(A) The oxygen dissociation curve of hemoglobin is $S$-shaped,which is technically referred to as a $Sigmoid$ curve.
This shape occurs because the binding of one molecule of $O_2$ to hemoglobin increases the affinity of the remaining heme groups for $O_2$,a phenomenon known as cooperative binding.
As the partial pressure of oxygen $(pO_2)$ increases,the percentage saturation of hemoglobin with oxygen increases,resulting in this characteristic $Sigmoid$ pattern.

(B) The enzyme $Carbonic \text{ } Anhydrase$ is present in very high concentrations within the $RBCs$ (Red Blood Cells).
It is also present in minute quantities in the blood plasma.
This enzyme plays a crucial role in the transport of $CO_2$ by catalyzing the reaction: $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$.
Due to its high concentration in $RBCs$, the reaction proceeds rapidly, facilitating the efficient exchange of gases.

(A) The oxygen-hemoglobin dissociation curve is a sigmoid curve.
Factors that shift the curve to the right include increased $PCO_2$,increased $H^+$ concentration (decreased $pH$),and increased temperature.
Conversely,factors that shift the curve to the left include decreased $PCO_2$,decreased $H^+$ concentration (increased $pH$),and decreased temperature.
Therefore,when the temperature decreases,the affinity of hemoglobin for oxygen increases,causing the curve to shift to the left.

(A) Hemoglobin is a quaternary protein found in red blood cells that is responsible for oxygen transport.
Each hemoglobin molecule consists of $4$ polypeptide subunits (two alpha and two beta chains).
Each subunit contains a heme group with a central iron atom $(Fe^{2+})$.
Since each heme group can bind to one molecule of $O_2$,a single hemoglobin molecule can carry a maximum of $4$ molecules of $O_2$ to form oxyhemoglobin.

(D) The oxygen-hemoglobin dissociation curve shifts to the right (Bohr effect) under conditions that favor the release of oxygen from hemoglobin.
These conditions include increased $PCO_2$,increased hydrogen ion concentration (increased acidity),increased temperature,and increased $2,3-BPG$.
Since an increase in hydrogen ion concentration corresponds to a decrease in $pH$,a decrease in $pH$ causes a rightward shift.
Conversely,a decrease in acidity (or an increase in $pH$) or a decrease in $CO_2$ concentration would shift the curve to the left.
Therefore,the curve shifts to the right when $pH$ decreases.

(B) The $Hamburger$ shift is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate $(HCO_3^-)$ and chloride $(Cl^-)$ across the membrane of red blood cells $(RBCs)$.
As bicarbonate ions diffuse out of the $RBCs$ into the blood plasma,chloride ions diffuse into the $RBCs$ to maintain the electrical neutrality of the cell.
This phenomenon is widely known as the $Chloride$ shift.

(B) Carbon dioxide $(CO_2)$ is transported in the blood in three forms:
$1$. As bicarbonates: About $70\%$ of $CO_2$ is transported as bicarbonates in the plasma and erythrocytes.
$2$. As carbamino-hemoglobin: About $20-25\%$ of $CO_2$ is transported by binding with hemoglobin.
$3$. Dissolved in plasma: About $7\%$ of $CO_2$ is carried in a dissolved state through the plasma.
Therefore,the majority of $CO_2$ released from tissues is transported as bicarbonates.

(C) The chloride shift,also known as the Hamburger phenomenon,occurs in the red blood cells (RBCs) to maintain electrical neutrality during the transport of carbon dioxide.
As $CO_2$ diffuses into the RBCs,it reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into hydrogen ions $(H^+)$ and bicarbonate ions $(HCO_3^-)$.
To maintain the ionic balance,the $HCO_3^-$ ions diffuse out of the RBCs into the blood plasma,and in exchange,chloride ions $(Cl^-)$ move from the plasma into the RBCs.
Therefore,the chloride shift is specifically associated with the movement of $HCO_3^-$ ions.

(C) During the transport of $CO_2$,it reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into $H^+$ and $HCO_3^-$ ions.
If these $H^+$ ions were to accumulate,the blood pH would drop significantly,making it acidic.
However,blood contains efficient buffer systems,primarily the hemoglobin buffer and the bicarbonate buffer system.
These buffers neutralize the excess $H^+$ ions,thereby maintaining the blood pH within a narrow physiological range (approximately $7.4$).
Therefore,the presence of blood buffers prevents the blood from becoming acidic.

(D) The Haldane effect describes how the oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin,which increases the removal of $CO_2$. Conversely,in the tissues,the deoxygenation of blood increases its ability to carry $CO_2$. This phenomenon is primarily driven by the state of hemoglobin. When hemoglobin is oxygenated (forming oxyhemoglobin),it becomes a stronger acid,which promotes the release of $CO_2$ and hydrogen ions. Therefore,the Haldane effect is caused by the presence or absence of oxyhemoglobin.

(C) When blood becomes acidic (due to an increase in $H^+$ concentration or $PCO_2$),the $pH$ of the blood decreases.
According to the Bohr effect,a decrease in $pH$ shifts the oxygen-hemoglobin dissociation curve to the right.
This shift indicates that the affinity of hemoglobin for oxygen decreases,facilitating the release of oxygen to the tissues.

(A) In the human body,oxygen $(O_2)$ is transported in the blood in two forms:
$1$. Bound to hemoglobin in red blood cells $(RBCs)$: About $97\%$ of $O_2$ is transported this way as oxyhemoglobin.
$2$. Dissolved in blood plasma: The remaining $3\%$ of $O_2$ is carried in a dissolved state through the blood plasma.
Therefore,the correct option is $A$.

(A) The Bohr effect describes the phenomenon where an increase in $CO_2$ concentration or a decrease in $pH$ (increased acidity) shifts the oxygen-hemoglobin dissociation curve to the right.
This shift indicates a decreased affinity of hemoglobin for oxygen,facilitating the release of oxygen into the tissues.
Conversely,the Haldane effect describes how the oxygenation of blood in the lungs displaces $CO_2$ from hemoglobin,which is the opposite process occurring in the tissues.
Therefore,the effect of $CO_2$ concentration on the dissociation of oxyhemoglobin is known as the Bohr effect.

(B) The dissociation of oxyhemoglobin is primarily influenced by the partial pressure of oxygen $(PO_2)$.
In the tissues,the $PO_2$ is low compared to the alveoli.
When blood reaches the tissues,the low $PO_2$ environment promotes the release of oxygen from hemoglobin,leading to the dissociation of oxyhemoglobin into hemoglobin and oxygen.
Other factors like high $PCO_2$,high $H^+$ concentration (low $pH$),and high temperature also facilitate this dissociation,a phenomenon known as the Bohr effect.

(D) The binding of oxygen with hemoglobin is primarily a function of the partial pressure of oxygen $(pO_2)$.
However,other factors such as the partial pressure of carbon dioxide $(pCO_2)$,hydrogen ion concentration $(pH)$,and temperature also interfere with this binding.
An increase in $pCO_2$,a decrease in $pH$ (higher acidity),and an increase in temperature shift the oxygen-hemoglobin dissociation curve to the right,facilitating the dissociation of oxygen from hemoglobin.
Therefore,all the listed factors affect the binding of oxygen with hemoglobin.

(A) Hemoglobin has a significantly higher affinity for carbon monoxide $(CO)$ compared to oxygen $(O_2)$.
Specifically,the affinity of hemoglobin for $CO$ is approximately $200$ to $250$ times greater than its affinity for $O_2$.
When $CO$ is inhaled,it binds to hemoglobin to form carboxyhemoglobin,which prevents oxygen from binding to the hemoglobin,leading to tissue hypoxia and potentially fatal poisoning.

(D) The binding of $O_2$ with hemoglobin is primarily determined by the partial pressure of oxygen $(P_{O_2})$.
However,other factors such as partial pressure of carbon dioxide $(P_{CO_2})$,hydrogen ion concentration ($H^+$ concentration),and temperature also significantly influence this binding affinity.
According to the oxygen dissociation curve,high $P_{O_2}$,low $P_{CO_2}$,low $H^+$ concentration (high $pH$),and lower temperature favor the formation of oxyhemoglobin in the alveoli.
Conversely,low $P_{O_2}$,high $P_{CO_2}$,high $H^+$ concentration,and higher temperature favor the dissociation of oxygen from oxyhemoglobin in the tissues.
Therefore,all four factors $(a, b, c, d)$ contribute to the binding and dissociation process of $O_2$ with hemoglobin.

(B) Carbon monoxide $(CO)$ has a much higher affinity for hemoglobin than oxygen $(O_2)$.
When $CO$ is inhaled,it binds with hemoglobin to form carboxyhemoglobin $(HbCO)$.
This binding is very stable and prevents hemoglobin from binding with oxygen.
As a result,the oxygen-carrying capacity of the blood is significantly reduced,leading to a decrease in oxygen availability to the body tissues,which causes hypoxia and can be fatal.

(D) In vertebrates,$Hemoglobin$ is the primary respiratory pigment found in red blood cells $(RBCs)$.
It is a conjugated protein consisting of a protein part called $Globin$ and a non-protein part called $Heme$.
$Hemoglobin$ has a high affinity for oxygen and forms $Oxyhemoglobin$ in the lungs,which then transports oxygen to the tissues where it dissociates to release oxygen for cellular respiration.

(A) Carbon monoxide $(CO)$ has a very high affinity for hemoglobin,approximately $200$ to $250$ times greater than that of oxygen $(O_2)$.
When $CO$ enters the bloodstream,it binds with hemoglobin to form a stable compound called carboxyhemoglobin $(HbCO)$.
Because this bond is much stronger than the bond between hemoglobin and oxygen,it prevents hemoglobin from binding with oxygen.
Consequently,the oxygen-carrying capacity of the blood is significantly reduced,leading to tissue hypoxia.

(C) Hemoglobin has a very high affinity for carbon monoxide $(CO)$ compared to oxygen $(O_2)$.
When $CO$ binds with hemoglobin,it forms a stable compound called carboxyhemoglobin.
This compound is approximately $200$ to $300$ times more stable than oxyhemoglobin.
Because of this high stability,$CO$ prevents oxygen from binding to hemoglobin,which can lead to suffocation and death.

(C) Under normal physiological conditions,every $100 \ ml$ of oxygenated blood can deliver around $5 \ ml$ of $O_2$ to the tissues.
Since $100 \ ml$ of arterial blood carries approximately $20 \ ml$ of $O_2$,the amount delivered is $5 \ ml / 20 \ ml = 0.25$ or $25\%$ of the total oxygen carried by the blood.
Therefore,during one circulation,blood delivers $25\%$ of its oxygen content to the tissues.

(B) The transport of oxygen in the blood is primarily carried out by hemoglobin $(Hb)$.
$CO$ (Carbon monoxide) has a very high affinity for hemoglobin (about $200-250$ times more than $O_2$),forming carboxyhemoglobin,which prevents oxygen transport.
$NO$ (Nitric oxide) also binds to hemoglobin and can interfere with oxygen transport.
$SO_2$ (Sulfur dioxide) and $SO_3$ (Sulfur trioxide) are respiratory irritants that can cause inflammation in the respiratory tract,but they do not directly bind to hemoglobin to inhibit oxygen transport in the same manner as $CO$ or $NO$.
Among the given options,$SO_3$ is the substance that does not directly inhibit the transport of oxygen by binding to hemoglobin.

(D) Carbon monoxide $(CO)$ binds to hemoglobin to form carboxyhemoglobin.
Its affinity for hemoglobin is approximately $200$ to $250$ times greater than that of oxygen $(O_2)$.
Because of this high affinity, $CO$ effectively displaces oxygen from hemoglobin, leading to tissue hypoxia and potential fatality.

(B) The Hamburger phenomenon,also known as the chloride shift,describes the exchange of ions between red blood cells and blood plasma.
As carbon dioxide $(CO_2)$ enters the red blood cells,it reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into hydrogen ions $(H^+)$ and bicarbonate ions $(HCO_3^-)$.
To maintain electrical neutrality,the bicarbonate ions diffuse out of the red blood cells into the plasma,while chloride ions $(Cl^-)$ diffuse from the plasma into the red blood cells.
This movement of chloride ions to balance the exit of bicarbonate ions is known as the chloride shift or Hamburger phenomenon.

(B) Oxyhemoglobin $(HbO_2)$ is a stronger acid than deoxyhemoglobin $(Hb)$.
When oxygen binds to hemoglobin in the lungs,it promotes the release of hydrogen ions $(H^+)$ from the hemoglobin molecule.
Because it is a stronger acid,it dissociates more readily,releasing $H^+$ ions into the blood,which helps in the transport of carbon dioxide via the chloride shift mechanism.
Therefore,oxyhemoglobin functions as an acid in the physiological system.

(B) Carbon monoxide $(CO)$ binds to hemoglobin $(Hb)$ to form carboxyhemoglobin $(COHb)$.
The affinity of hemoglobin for carbon monoxide is approximately $200$ to $250$ times greater than its affinity for oxygen $(O_2)$.
Due to this high affinity, even small concentrations of $CO$ can significantly reduce the oxygen-carrying capacity of blood, leading to carbon monoxide poisoning.

(B) In frogs,like in most vertebrates,the respiratory pigment responsible for oxygen transport is $Hemoglobin$.
$Hemoglobin$ is an iron-containing protein present in the red blood cells $(RBCs)$ that binds with oxygen to form oxyhemoglobin,facilitating its transport from the lungs to the body tissues.

(B) The oxygen-hemoglobin dissociation curve is a plot showing the relationship between the partial pressure of oxygen $(pO_2)$ and the percentage saturation of hemoglobin with oxygen.
This curve is $S$-shaped,which is technically referred to as a sigmoid curve.
The sigmoid shape is due to the cooperative binding of oxygen to hemoglobin,where the binding of one oxygen molecule increases the affinity of the remaining heme groups for oxygen.

(A) Carbonic anhydrase is a zinc-containing enzyme that catalyzes the reversible reaction: $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$. This enzyme is present in very high concentrations within the $RBC$ (Red Blood Cells). It facilitates the rapid conversion of $CO_2$ into bicarbonate ions for transport in the blood and vice versa in the lungs. While small amounts exist in the plasma,its primary and most significant activity occurs inside the $RBC$.

(A) In body tissues,cellular respiration produces $CO_2$,leading to a high partial pressure of $CO_2$ $(pCO_2)$ and a low partial pressure of $O_2$ $(pO_2)$.
This phenomenon is known as the 'Bohr effect'.
High $pCO_2$,low $pO_2$,and low $pH$ (acidic environment) decrease the affinity of hemoglobin for $O_2$.
Consequently,oxyhemoglobin dissociates,releasing $O_2$ to the tissues.
Therefore,the correct condition is low $O_2$ concentration and high $CO_2$ concentration.

(D) $CO$ (Carbon monoxide) is more toxic than $CO_2$ because it binds to hemoglobin with an affinity about $200-250$ times greater than that of oxygen.
This binding forms carboxyhemoglobin,which is a stable compound.
As a result,the oxygen-carrying capacity of the blood is significantly reduced,leading to hypoxia (oxygen deficiency in tissues) and potentially death.

(B) The Hamburger phenomenon,also known as the $Chloride \ shift$,is a process that occurs in the cardiovascular system.
It refers to the exchange of bicarbonate $(HCO_3^-)$ and chloride $(Cl^-)$ ions across the membrane of red blood cells $(RBCs)$.
When carbon dioxide $(CO_2)$ enters the blood,it reacts with water to form carbonic acid,which dissociates into $H^+$ and $HCO_3^-$.
To maintain electrical neutrality,$Cl^-$ ions move into the $RBC$ from the plasma in exchange for $HCO_3^-$ ions moving out of the $RBC$ into the plasma.

(B) When oxygen binds with hemoglobin $(Hb)$ in the blood,it forms oxyhemoglobin $(HbO_2)$. This process is specifically referred to as oxygenation. Oxidation involves the loss of electrons,whereas oxygenation is a reversible physical-chemical binding process between oxygen and the iron atom in the heme group of hemoglobin.

(A) $CO_2$ is transported from tissues to the respiratory surface primarily in three forms:
$1$. As bicarbonate ions $(HCO_3^-)$ dissolved in the plasma (about $70\%$).
$2$. Bound to hemoglobin as carbaminohemoglobin in $RBCs$ (about $20-25\%$).
$3$. Dissolved in the plasma (about $7\%$).
Since both plasma and $RBCs$ are involved in the transport of $CO_2$,the correct answer is plasma and $RBCs$.

(C) In the human body, $CO_2$ is transported by blood in three forms:
$1$. Dissolved in plasma (about $7\%$).
$2$. As carbaminohemoglobin bound to hemoglobin (about $20-25\%$).
$3$. As bicarbonates $(HCO_3^-)$ in plasma (about $70\%$).
Therefore, the primary mode of $CO_2$ transport is in the form of bicarbonates.

(B) $Methemoglobin$ is a form of hemoglobin in which the iron in the heme group is in the $Fe^{3+}$ (ferric) state rather than the normal $Fe^{2+}$ (ferrous) state.
This state is known as oxidized hemoglobin.
$Methemoglobin$ cannot bind oxygen effectively,which can lead to tissue hypoxia.

(B) In humans,$CO_2$ is transported in the blood in three forms:
$1$. As bicarbonate ions in plasma $(70\%)$.
$2$. Bound to hemoglobin as carbaminohemoglobin in $RBCs$ $(20-25\%)$.
$3$. Dissolved in plasma $(7\%)$.
Therefore,$RBCs$ are responsible for transporting approximately $20-25\%$ of the total $CO_2$ in the form of carbaminohemoglobin.

(A) The $O_2$ dissociation curve,also known as the oxygen-hemoglobin dissociation curve,plots the proportion of hemoglobin in its saturated form on the vertical axis against the prevailing oxygen tension on the horizontal axis.
This curve is $S$-shaped,which is technically referred to as a sigmoid curve.
This shape reflects the cooperative binding of oxygen to hemoglobin,where the binding of one $O_2$ molecule increases the affinity of the remaining heme groups for oxygen.

(B) Under normal physiological conditions,each gram of hemoglobin can bind approximately $1.34 \, ml$ of oxygen. This value is a standard physiological constant used to calculate the oxygen-carrying capacity of blood. Therefore,$1 \, g$ of hemoglobin carries $1.34 \, ml$ of $O_2$.

(B) Each hemoglobin molecule is a protein complex consisting of $4$ polypeptide subunits (two alpha and two beta chains). Each subunit contains a heme group with a central iron atom $(Fe^{2+})$. Since each heme group can bind to one molecule of oxygen $(O_2)$,a single hemoglobin molecule can bind to a maximum of $4$ oxygen molecules to form oxyhemoglobin.

(A) The binding of oxygen with hemoglobin is primarily a function of the partial pressure of oxygen $(pO_2)$.
This relationship is represented by the oxygen-hemoglobin dissociation curve.
As the partial pressure of oxygen $(pO_2)$ increases,the amount of oxyhemoglobin formed increases,thereby increasing the ratio of oxyhemoglobin to hemoglobin.
Conversely,a decrease in $pO_2$ leads to the dissociation of oxyhemoglobin,releasing oxygen to the tissues.
Therefore,the ratio of oxyhemoglobin to hemoglobin is directly dependent on the oxygen tension $(pO_2)$.