Transport of gases Questions in English

(B) In the human body,$97 \%$ of $O_{2}$ is transported by erythrocytes (RBCs) in the form of oxyhemoglobin.
The remaining $3 \%$ of $O_{2}$ is transported in a dissolved state through the blood plasma.

(N/A) $CO_{2}$ is carried by blood in three main forms:
$1$. As Carbamino-haemoglobin: About $20-25$ percent of $CO_{2}$ is carried by haemoglobin. This binding is related to the partial pressure of $CO_{2}$. $pO_{2}$ is a major factor which affects this binding. When $pCO_{2}$ is high and $pO_{2}$ is low (as in tissues),more $CO_{2}$ binds to haemoglobin. Conversely,when $pCO_{2}$ is low and $pO_{2}$ is high (as in alveoli),$CO_{2}$ dissociates from haemoglobin.
$2$. As Bicarbonates: About $70$ percent of $CO_{2}$ is transported as bicarbonates $(HCO_{3}^{-})$. $RBCs$ contain a high concentration of the enzyme carbonic anhydrase,which facilitates the reaction: $CO_{2} + H_{2}O \rightleftharpoons H_{2}CO_{3} \rightleftharpoons HCO_{3}^{-} + H^{+}$. At the tissue site,$CO_{2}$ diffuses into blood and forms $HCO_{3}^{-}$ and $H^{+}$. At the alveolar site,the reaction proceeds in the opposite direction to release $CO_{2}$.
$3$. Dissolved in Plasma: About $7$ percent of $CO_{2}$ is carried in a dissolved state through the blood plasma.

(D) The correct answer is $D$.
In the alveoli,conditions are favourable for the formation of oxyhaemoglobin,which include high $pO_2$,low $pCO_2$,low $H^+$ concentration,and lower temperature.
Conversely,in the tissues,low $pO_2$,high $pCO_2$,high $H^+$ concentration,and higher temperature favour the dissociation of oxygen from oxyhaemoglobin.
Therefore,a higher $H^+$ concentration in the alveoli would actually inhibit the formation of oxyhaemoglobin,making statement $D$ incorrect.

(C) The formation of oxyhemoglobin is favored in the alveoli where there is high $P_{O_2}$,low $P_{CO_2}$,low $H^+$ concentration,and lower temperature.
Conversely,in the tissues,high $P_{CO_2}$,high $H^+$ concentration,and high temperature favor the dissociation of oxyhemoglobin.
Therefore,the statement that 'High concentration of $H^+$ in the alveoli helps in the formation of oxyhemoglobin' is incorrect,as high $H^+$ concentration promotes dissociation,not formation.

(C) Each haemoglobin molecule can carry a maximum of four molecules of $O_{2}$.
The reaction is represented as: $Hb_{4} + 4O_{2} \rightarrow Hb_{4}O_{8}$.
Binding of oxygen with haemoglobin is primarily related to the partial pressure of $O_{2}$,partial pressure of $CO_{2}$,hydrogen ion concentration,and temperature.

(B) The transport of $CO_{2}$ occurs primarily in the form of bicarbonate ions $(HCO_{3}^{-})$.
$1$. At the tissue level, $CO_{2}$ produced by metabolic activities diffuses into the blood and enters the Red Blood Cells $(RBCs)$ $(A = RBC)$.
$2$. Inside the $RBCs$, $CO_{2}$ reacts with water in the presence of the enzyme carbonic anhydrase to form $HCO_{3}^{-}$ and $H^{+}$ $(C = \text{bicarbonate})$.
$3$. This blood is transported to the lungs. At the alveolar site, the partial pressure of $CO_{2}$ $(pCO_{2})$ is low $(B = \text{alveolar})$.
$4$. Due to low $pCO_{2}$, the reaction proceeds in the opposite direction, converting $HCO_{3}^{-}$ back into $CO_{2}$, which is then released into the alveoli and exhaled $(D = CO_{2})$.
Therefore, the correct sequence is $A = RBC, B = \text{alveolar}, C = \text{bicarbonate}, D = CO_{2}$.

(B) During the transport of $CO_2$,bicarbonate ions $(HCO_3^-)$ formed in the erythrocytes diffuse out into the plasma. To maintain the electrical neutrality of the cells,chloride ions $(Cl^-)$ move from the plasma into the erythrocytes. This process is known as the chloride shift or the Hamburger phenomenon.

(A) Under normal physiological conditions,$100\; mL$ of oxygenated blood carries approximately $20\; mL$ of $O_{2}$.
Out of this,it delivers approximately $5\; mL$ of $O_{2}$ to the tissues during each circulatory cycle.
Therefore,the correct answer is $5\; mL$.

(D) About $7 \%$ of carbon dioxide is transported as dissolved in plasma,$23 \%$ as carbaminohaemoglobin,and $70 \%$ as bicarbonates.
Most of the carbon dioxide that dissolves in blood plasma reacts with water to form carbonic acid.
All carbonic acid in $RBCs$ dissociates into hydrogen and bicarbonate ions,and these bicarbonate ions diffuse from $RBCs$ into the blood plasma.

(C) Carbon monoxide $(CO)$ has a very high affinity for haemoglobin,approximately $250$ times greater than that of oxygen $(O_2)$.
When $CO$ binds to haemoglobin,it forms a stable compound called carboxyhaemoglobin.
This binding is essentially irreversible under normal physiological conditions,which prevents haemoglobin from transporting oxygen to the body tissues,leading to carbon monoxide poisoning.

(B) Haemoglobin $(Hb)$ is an iron-containing,deep red-coloured respiratory pigment found in red blood cells.
It plays a crucial role in the transport of oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs.
When it combines with oxygen,it forms oxyhaemoglobin,which gives it a bright red colour.

(B) The transport of $CO_{2}$ by blood is primarily dependent upon the enzyme $\text{Carbonic Anhydrase}$.
About $70\%$ of $CO_{2}$ is transported as bicarbonate ions $(HCO_{3}^{-})$.
In the erythrocytes, $CO_{2}$ reacts with water to form carbonic acid $(H_{2}CO_{3})$ in the presence of the enzyme $\text{Carbonic Anhydrase}$.
This $H_{2}CO_{3}$ then dissociates into $H^{+}$ and $HCO_{3}^{-}$ ions.
The reaction is: $CO_{2} + H_{2}O \xrightarrow{\text{Carbonic Anhydrase}} H_{2}CO_{3} \rightleftharpoons HCO_{3}^{-} + H^{+}$.

(D) Haemoglobin is a respiratory pigment present in red blood cells that plays a crucial role in gas transport.
$I.$ Oxygen binds to haemoglobin to form oxyhaemoglobin,which is the primary method of oxygen transport.
$III.$ Carbon dioxide is also transported by haemoglobin in the form of carbamino-haemoglobin (about $20-25\%$).
Therefore,statements $I$ and $III$ are correct.

(A) Chloride shift,also known as the Hamburger phenomenon,occurs in response to the movement of $HCO_{3}^{-}$ ions.
To maintain the electrostatic neutrality of the plasma,when bicarbonate ions $(HCO_{3}^{-})$ diffuse out of the red blood cells (RBCs) into the plasma,an equivalent number of chloride ions $(Cl^{-})$ diffuse from the plasma into the RBCs.
This exchange ensures that the electrical balance is maintained during the transport of carbon dioxide.
Therefore,the chloride shift is a direct response to the exit of $HCO_{3}^{-}$ ions from the RBCs.

(D) Carbaminohemoglobin dissociates in the alveoli because the partial pressure of oxygen $(pO_{2})$ is high and the partial pressure of carbon dioxide $(pCO_{2})$ is low.
Due to this pressure gradient, $CO_{2}$ is released from the hemoglobin, and $O_{2}$ binds to the hemoglobin to form oxyhemoglobin.

(C) $98.5 \%$ of $O_{2}$ is transported by blood with the help of haemoglobin.
Haemoglobin has $250$ times more affinity for $CO$ compared to $O_{2}$.
When $CO$ is inhaled,it binds with haemoglobin to form carboxyhaemoglobin,which is a stable complex.
This prevents the transport of $O_{2}$ to tissues,leading to hypoxia and eventually death.

(A) The oxygen-haemoglobin dissociation curve represents the relationship between the partial pressure of oxygen $(pO_2)$ and the percentage saturation of haemoglobin with oxygen.
Due to the cooperative binding of oxygen molecules to the haemoglobin subunits,the curve takes a characteristic $S$-shaped or sigmoid form.

(B) $CO_{2}$ is transported by haemoglobin in the form of carbaminohaemoglobin (approximately $20-25 \%$ of total $CO_{2}$ transport).
This binding is primarily related to the partial pressure of $CO_{2}$. The partial pressure of oxygen $(pO_{2})$ is also a major factor that influences this binding,as high $pO_{2}$ in the alveoli promotes the dissociation of $CO_{2}$ from carbaminohaemoglobin.

(C) Chloride shift occurs in response to $HCO_{3}^{-}$ diffusion.
To maintain electrostatic neutrality of the plasma,many chloride ions $(Cl^{-})$ diffuse from the plasma into the $RBCs$,and bicarbonate ions $(HCO_{3}^{-})$ pass out into the plasma.
The chloride content of $RBCs$ increases when oxygenated blood becomes deoxygenated.
This phenomenon is known as the chloride shift or Hamburger shift.

(B) $O_2$ binds with $RBC$.
Haemoglobin is a red-coloured,iron-containing pigment present in the $RBCs$ (erythrocytes).
$O_2$ binds with haemoglobin in a reversible manner to form oxyhaemoglobin $(HbO_2)$.

(D) If a person breathes air containing a normal amount of oxygen $(21 \%)$ and a small amount of carbon monoxide,they suffer from suffocation because haemoglobin combines with carbon monoxide to form a stable compound known as carboxyhaemoglobin.
The affinity of haemoglobin for carbon monoxide is about $250$ times greater than its affinity for oxygen.
Even $0.1 \%$ of carbon monoxide can block $50 \%$ of the body's haemoglobin,significantly decreasing the oxygen-carrying capacity of the blood.
This condition,which leads to oxygen deprivation in tissues,is called hypoxia.

(B) Haemoglobin has approximately $250$ times more affinity for carbon monoxide $(CO)$ compared to oxygen $(O_2)$.
When $CO$ binds to haemoglobin,it forms a stable,cherry-red compound known as carboxyhaemoglobin $(HbCO)$.
This binding prevents oxygen from binding to haemoglobin,leading to hypoxia and potentially fatal carbon monoxide poisoning.

(C) Under normal physiological conditions,every $100\; mL$ of deoxygenated blood delivers approximately $4\; mL$ of $CO_2$ to the alveoli for elimination.

(B) The transport of oxygen from the lungs to body tissues and $CO_{2}$ from tissues to the lungs is a vital role of blood.
Transport of carbon dioxide: Most of the $CO_{2}$ that dissolves in blood plasma reacts with water to form carbonic acid:
$CO_{2} + H_{2}O \rightarrow H_{2}CO_{3}$
An enzyme,carbonic anhydrase,is present in RBCs,which accelerates the carbonic acid formation by about $5000$ times. About $70\%$ of the $CO_{2}$ received by blood from the tissues immediately enters into RBCs and is hydrated to carbonic acid. All carbonic acid in RBCs dissociates into hydrogen and bicarbonate ions. The $H^{+}$ ions mostly combine with haemoglobin to maintain the pH of blood $(7.4)$ in a steady state,whereas the bicarbonate ions diffuse from RBCs into the plasma. To maintain the electrostatic neutrality of the plasma,many chloride ions in turn diffuse from the plasma into RBCs. This is termed the chloride shift or Hamburger phenomenon.

(A) The process of $CO_{2}$ transport involves the reaction: $CO_{2} + H_{2}O \xrightarrow{\text{Carbonic Anhydrase}} H_{2}CO_{3} \rightleftharpoons HCO_{3}^{-} + H^{+}$.
To maintain the electrical neutrality of the $RBC$ and plasma,$HCO_{3}^{-}$ ions diffuse out of the $RBC$ into the plasma,and an equivalent amount of $Cl^{-}$ ions move from the plasma into the $RBC$. This phenomenon is known as the Hamburger shift or chloride shift.
As a result,the chloride content of the $RBC$ increases when oxygenated blood becomes deoxygenated (venous blood),making the $Cl^{-}$ concentration in venous $RBC$s significantly higher than in arterial $RBC$s.

(C) $RBCs$ contain a very high concentration of the enzyme carbonic anhydrase,and minute quantities of the same are also present in the blood plasma.
This enzyme facilitates the following reaction in both directions:
$CO _2+ H _2 O \underset{\text { Carbonic anhydrase }}{\text { Carbonic anhydrase }} H _2 CO _3 \underset{\text { Carbonic anhydrase }}{\stackrel{\text { Carbonic anhydrase }}{\rightleftharpoons}} HCO _3^{-}+ H ^{+}$
Therefore,both enzymes $A$ and $B$ are carbonic anhydrase.

(A) The oxygen-haemoglobin dissociation curve is sigmoid in shape,representing the relationship between the partial pressure of oxygen $(pO_2)$ and the percentage saturation of haemoglobin with oxygen.
Factors like an increase in temperature,decrease in $pH$,or increase in $pCO_2$ shift the curve to the right (Bohr effect),indicating a lower affinity of haemoglobin for oxygen.
Conversely,when the temperature decreases or $pH$ increases,the affinity of haemoglobin for oxygen increases,causing the curve to shift to the left and become more steep.

(C) At the tissue level,the partial pressure of oxygen $(pO_2)$ is low due to continuous metabolic consumption of oxygen by the cells.
Conversely,the partial pressure of carbon dioxide $(pCO_2)$ is high due to cellular respiration.
According to the oxygen-haemoglobin dissociation curve,a low $pO_2$ and high $pCO_2$ (Bohr effect) facilitate the dissociation of oxygen from oxyhaemoglobin.
Therefore,oxyhaemoglobin releases oxygen to the tissues where it is needed for metabolic processes.

(C) Blood does not become acidic because of the presence of blood buffers.
Carbon dioxide reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into hydrogen ions $(H^+)$ and bicarbonate ions $(HCO_3^-)$.
The blood contains buffer systems,primarily the bicarbonate buffer system,which neutralizes the excess $H^+$ ions,thereby maintaining the $pH$ of the blood within a narrow range (approximately $7.4$).

(A) Nearly $20-25 \%$ of carbon dioxide is transported by $RBCs$. It is carried by haemoglobin as carbaminohaemoglobin.
$70 \%$ of carbon dioxide is carried as bicarbonates.
About $97 \%$ of oxygen is transported by $RBCs$ in the blood.
The remaining $3 \%$ of oxygen is carried in a dissolved state through the plasma.

(B) In the human body,blood acts as the primary medium for the transport of respiratory gases.
$O_{2}$ is transported in the blood primarily by binding with hemoglobin present in the Red Blood Cells $(RBCs)$.
Approximately $97\%$ of $O_{2}$ is transported by $RBCs$ in the blood in the form of oxyhemoglobin.
The remaining $3\%$ of $O_{2}$ is carried in a dissolved state through the blood plasma.
Therefore,the correct values are $A=97, B=RBC, C=3, D=plasma$.

(C) Carbonic anhydrase is a zinc-containing enzyme that catalyzes the reversible reaction between carbon dioxide and water to form carbonic acid. It is found in very high concentrations within the $RBCs$ (erythrocytes) and in smaller quantities in the blood plasma.

(B) $2,3-DPG$ $(2,3-diphosphoglycerate)$ is an organic phosphate found in human red blood cells.
Its concentration increases in response to low oxygen levels,such as at high altitudes.
$2,3-DPG$ binds to the deoxygenated haemoglobin,which stabilizes the $T$ (tense) state of the molecule.
This binding decreases the affinity of haemoglobin for $O_2$,thereby shifting the oxygen-haemoglobin dissociation curve to the right.
This mechanism facilitates the unloading of $O_2$ from the blood to the peripheral tissues where it is needed most.

(D) In the tissues,the following conditions exist:
$(a)$ Low $pO_{2}$
$(b)$ High $pCO_{2}$
$(c)$ High $H^{+}$ concentration
$(d)$ High temperature
All these conditions shift the oxygen-haemoglobin dissociation curve to the right,which is favourable for the dissociation of oxygen from oxyhaemoglobin.

(B) The dissociation of $CO_{2}$ from carbamino haemoglobin occurs when $pCO_{2}$ is low and $pO_{2}$ is high in the alveoli.
In the tissues,where $pCO_{2}$ is high and $pO_{2}$ is low,$CO_{2}$ binds with haemoglobin to form carbamino haemoglobin.
Conversely,in the alveoli,where $pCO_{2}$ is low and $pO_{2}$ is high,the conditions favour the dissociation of $CO_{2}$ from carbamino haemoglobin,allowing $CO_{2}$ to be released into the alveoli for expiration.

(A) Bohr's effect is the phenomenon where a rise in $pCO_2$ or a fall in $pH$ decreases the oxygen affinity of haemoglobin.
This increase in $pCO_2$ and acidity (lower $pH$) promotes the dissociation of oxygen from oxyhaemoglobin,which is represented by a rightward shift of the oxygen-haemoglobin dissociation curve.
This effect facilitates the delivery of oxygen to tissues where metabolic activity is high.
Conversely,a fall in $pCO_2$ and a rise in $pH$ increase the oxygen affinity of haemoglobin.

(D) The transport of oxygen involves the reversible binding of oxygen with haemoglobin $(Hb)$ to form oxyhaemoglobin $(HbO_{2})$.
In the lungs,the high partial pressure of oxygen $(pO_{2})$ and low partial pressure of carbon dioxide $(pCO_{2})$ favor the association of oxygen with haemoglobin: $Hb + O_{2} \rightarrow HbO_{2}$.
In the tissues,the low partial pressure of oxygen $(pO_{2})$ and high partial pressure of carbon dioxide $(pCO_{2})$ favor the dissociation of oxyhaemoglobin to release oxygen: $HbO_{2} \rightarrow Hb + O_{2}$.
Therefore,the correct reversible equation is $Hb + O_{2} \rightleftharpoons HbO_{2}$,where association occurs in the lungs and dissociation occurs in the tissues. Option $D$ correctly represents this process.

(D) The binding of $O_{2}$ with haemoglobin is a complex process influenced by several factors.
Each haemoglobin molecule can carry a maximum of four molecules of $O_{2}$ as shown by the reaction: $Hb_{4} + 4O_{2} \rightarrow Hb_{4}O_{8}$.
The dissociation of oxygen from oxyhaemoglobin is primarily related to the partial pressure of $O_{2}$ $(pO_{2})$,partial pressure of $CO_{2}$ $(pCO_{2})$,hydrogen ion concentration $(pH)$,and temperature.
High $pO_{2}$,low $pCO_{2}$,low $H^{+}$ concentration,and lower temperature favor the formation of oxyhaemoglobin,whereas opposite conditions favor the dissociation of oxygen from the oxyhaemoglobin.
Therefore,all four factors ($I, II, III,$ and $IV$) play a critical role in the binding and dissociation of oxygen with haemoglobin.

(D) The dissociation of oxyhaemoglobin is favoured by conditions such as low partial pressure of $O_{2}$,high partial pressure of $CO_{2}$,high concentration of $H^{+}$ ions (low $pH$),and high temperature.
$I.$ Increased partial pressure of $O_{2}$ promotes the binding of oxygen to haemoglobin (formation of oxyhaemoglobin),not its dissociation.
$II.$ Increased partial pressure of $CO_{2}$ promotes dissociation (Bohr effect).
$III.$ Increased partial pressure of $H^{+}$ (lower $pH$) promotes dissociation.
$IV.$ Decreased partial pressure of $O_{2}$ promotes dissociation.
Therefore,only situation $I$ does not favour the dissociation of oxyhaemoglobin.

(B) The oxyhaemoglobin dissociation curve shifts to the right due to factors like increased temperature,decreased $pH$ (increased $H^+$ concentration),and increased $pCO_2$,which facilitate the release of oxygen to tissues.
Conversely,a left shift of the oxyhaemoglobin dissociation curve occurs under conditions of low temperature,high $pH$ (low $H^+$ concentration),and low $pCO_2$. These conditions increase the affinity of haemoglobin for oxygen,making it harder for oxygen to dissociate.

(D) Under normal physiological conditions,our body tissues utilize only about $25 \%$ of the $O_{2}$ carried by arterial blood.
Consequently,the venous blood remains approximately $75 \%$ saturated with $O_{2}$.
This remaining oxygen serves as a vital reserve,which can be utilized by the body during periods of increased metabolic demand,such as intense muscular exercise.

(A) The oxygen-carrying capacity of whole blood is significantly higher than that of plasma alone. Because the oxygen content of blood leaving the lungs is much greater than that of blood entering the lungs,it indicates that the majority of oxygen is transported in combination with haemoglobin $(HbO_2)$ rather than being dissolved in the blood plasma.

(B) Haemoglobin $(Hb)$ is a red-coloured iron-containing pigment present in the $RBC$s.
$O_2$ can bind with haemoglobin in a reversible manner to form oxyhaemoglobin $(HbO_2)$.
This binding is primarily related to the partial pressure of $O_2$.
In the lungs,high $pO_2$ favours the formation of oxyhaemoglobin,while in the tissues,low $pO_2$ facilitates its dissociation.
Other combinations include:
$1$. $Hb + CO_2 \rightleftharpoons HbCO_2$ (Carbaminohaemoglobin)
$2$. $Hb + CO \rightleftharpoons HbCO$ (Carboxyhaemoglobin)

(A) Haemoglobin $(Hb)$ is a conjugated protein consisting of a protein part called globin and a non-protein part called haem.
The haem group contains an iron atom in the ferrous state $(Fe^{2+})$.
This $Fe^{2+}$ ion has a specific affinity for oxygen,allowing $O_2$ molecules to bind directly to the haem group to form oxyhaemoglobin.

(D) In the lungs,the partial pressure of oxygen $(pO_2)$ is high,and the partial pressure of carbon dioxide $(pCO_2)$ is low,which favors the formation of oxyhaemoglobin $(HbO_2)$. Thus,the forward reaction occurs in the lungs.
In the tissues,the partial pressure of oxygen $(pO_2)$ is low,and the partial pressure of carbon dioxide $(pCO_2)$ is high,which favors the dissociation of oxyhaemoglobin into haemoglobin $(Hb)$ and oxygen $(O_2)$. Thus,the backward reaction occurs in the tissues.

(C) graphical representation of the relationship between $pO_{2}$ and the percentage saturation of haemoglobin with $O_{2}$ is known as the oxygen dissociation curve or oxygen-haemoglobin dissociation curve.
It is a sigmoid or $S$-shaped curve.

(A) The dissociation of oxygen from hemoglobin $(Hb)$ is primarily influenced by conditions in the body tissues where oxygen is released. These factors include:
$1$. Low partial pressure of oxygen $(pO_{2})$.
$2$. High partial pressure of carbon dioxide $(pCO_{2})$.
$3$. Low $pH$ (high concentration of $H^{+}$ ions).
$4$. High temperature.
These conditions shift the oxygen-hemoglobin dissociation curve to the right,facilitating the release of $O_{2}$ to the tissues.

(B) The solubility of $CO_{2}$ in blood plasma is significantly higher than that of $O_{2}$.
The ratio of the solubility of $CO_{2}$ to $O_{2}$ in plasma is approximately $20-25:1$.
Due to this high solubility,a larger percentage of $CO_{2}$ is transported in a dissolved state in the plasma compared to $O_{2}$.

(C) In the tissues,metabolic activities produce $CO_{2}$,which diffuses into the blood.
This leads to a high partial pressure of carbon dioxide $(pCO_{2})$ in the tissues.
The enzyme carbonic anhydrase,present in red blood cells,catalyzes the reaction: $CO_{2} + H_{2}O \rightleftharpoons H_{2}CO_{3} \rightleftharpoons H^{+} + HCO_{3}^{-}$.
According to Le Chatelier's principle,an increase in the concentration of reactants $(CO_{2})$ shifts the equilibrium to the right,thereby favoring the formation of $H^{+}$ and $HCO_{3}^{-}$ ions.

(A) The reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$ is catalyzed by the enzyme carbonic anhydrase.
This enzyme is present in very high concentrations within $RBC$s and in smaller quantities in the blood plasma.
It facilitates the rapid conversion of carbon dioxide into bicarbonate ions, which is essential for the transport of $CO_2$ in the blood.