Transport of gases Questions in English

(B) Oxygen is transported in the blood in two forms:
$1$. As oxyhaemoglobin: About $97\%$ of $O_2$ is transported by red blood cells (RBCs) in combination with haemoglobin.
$2$. In dissolved form: About $3\%$ of $O_2$ is carried in a dissolved state through the blood plasma.

(C) Haemoglobin consists of four polypeptide chains ($2 \alpha$ and $2 \beta$) having heme as a prosthetic group.
Heme is an iron $(Fe^{2+})$ containing porphyrin ring.
One haemoglobin molecule binds four oxygen molecules,one per heme group,to form oxyhaemoglobin.
The reaction is: $Hb + 4O_2 \rightleftharpoons Hb(O_2)_4$.

(B) Haemoglobin $(Hb)$ consists of two main parts: the haem group and the globin protein chain.
$CO_2$ does not bind to the iron $(Fe^{2+})$ in the haem group,as that is the site for $O_2$ binding.
Instead,$CO_2$ binds to the amino group of the globin protein chain to form a compound known as carbaminohaemoglobin.
The reaction is represented as: $Hb + CO_2 \rightleftharpoons HbCO_2$ (carbaminohaemoglobin).

(D) The oxygen-hemoglobin dissociation curve shifts to the left under conditions that favor the association of oxygen with hemoglobin,typically found in the alveoli.
These conditions include:
$1$. High $pO_2$
$2$. Low $pCO_2$
$3$. Low $H^+$ ion concentration (high $pH$)
$4$. Low temperature
Conversely,a high $H^+$ ion concentration (low $pH$) shifts the curve to the right,which promotes the dissociation of oxygen from hemoglobin (Bohr effect). Therefore,high $H^+$ ion concentration is not responsible for shifting the curve to the left.

(D) The conditions favourable for the binding of $CO_2$ with $Hb$ (hemoglobin),which also facilitate the dissociation of $O_2$ from $Hb$,are as follows:
$1$. High $pCO_2$ (partial pressure of carbon dioxide).
$2$. Low $pO_2$ (partial pressure of oxygen).
$3$. Higher $H^+$ concentration (lower $pH$).
$4$. High temperature.
These conditions are typically found in the metabolically active tissues,causing the oxygen dissociation curve to shift to the right,a phenomenon known as the Bohr effect.

(D) Under normal physiological conditions, $100 \,ml$ of oxygenated blood delivers $5 \,ml$ of $O_2$ to the tissues.
However, under strenuous exercise conditions, the tissues require more oxygen, and $100 \,ml$ of blood delivers approximately $15 \,ml$ of $O_2$ to the tissues.
Since $1 \,litre = 1000 \,ml$, we calculate the oxygen delivery for $1000 \,ml$ of blood as follows:
If $100 \,ml$ of blood delivers $15 \,ml$ of $O_2$, then $1000 \,ml$ of blood will deliver $(15 \,ml / 100 \,ml) \times 1000 \,ml = 150 \,ml$ of $O_2$.
Therefore, the amount of oxygen transported by one litre of blood under strenuous conditions is approximately $150 \,ml$.

(C) The assertion is incorrect because carbon dioxide is primarily transported in the form of bicarbonate ions $(HCO_3^-)$,not specifically as sodium bicarbonate.
The reason is correct because approximately $7\%$ of $CO_2$ is transported in a dissolved state through the blood plasma,which corresponds to about $0.3 \; ml$ of $CO_2$ per $100 \; ml$ of blood.
Therefore,the correct answer is that the Assertion is incorrect,but the Reason is correct.

(A) The solubility coefficient of $CO_2$ is $20-25$ times higher than that of $O_2$.
Due to this high solubility,$CO_2$ is transported more efficiently in the blood.
In $100 \; ml$ of oxygenated blood,the amount of $O_2$ is approximately $20 \; ml$,whereas the amount of $CO_2$ is approximately $48 \; ml$.
Therefore,human blood always contains a higher amount of $CO_2$ compared to $O_2$,and this is directly due to the higher solubility coefficient of $CO_2$.

(C) Under normal physiological conditions,$100 \; ml$ of oxygenated (arterial) blood carries approximately $19 \; ml$ of $O_2$.
When this blood passes through the tissues,about $5 \; ml$ of $O_2$ is delivered to the tissues,leaving $14.4 \; ml$ of $O_2$ in the venous blood.
This means that venous blood remains $75\%$ saturated with oxygen at rest.
The Reason statement provided is slightly inaccurate regarding the context of 'exercise' versus 'resting' conditions,as the $25\%$ delivery is the standard value for resting conditions,not exercise (where delivery increases significantly).
Therefore,the Assertion is correct,but the Reason is technically incorrect due to the mention of 'exercise'.

(C) The number of oxygen molecules is equal to the number of haemoglobin molecules. Each haemoglobin molecule can bind up to $4$ oxygen molecules.
Since the binding of oxygen to $Hb$ is cooperative (allosteric) in nature,once the $1^{st}$ oxygen molecule binds to an $Hb$ molecule,the affinity of that $Hb$ molecule for subsequent oxygen molecules increases significantly.
Therefore,if we have $4$ $Hb$ molecules and $4$ oxygen molecules,the $4$ oxygen molecules will preferentially bind to a single $Hb$ molecule until it is saturated $(HbO_8)$,rather than distributing themselves across the other $Hb$ molecules.
As a result,$1/4$ of the total $Hb$ molecules will be fully saturated with $4$ oxygen molecules,while the remaining $3/4$ of the $Hb$ molecules will remain vacant (unbound).
Thus,nearly one-fourth of all the $Hb$ molecules are bound to four oxygen molecules each.

(A) In the human body,$98.5 \%$ of $O_{2}$ is transported by the respiratory pigment haemoglobin,which is present in the erythrocytes of the blood.
One molecule of haemoglobin can carry four molecules of $O_{2}$.

(A) In a healthy human adult, the average concentration of haemoglobin is $12-16$ grams per $100$ mL of blood.
Haemoglobin is a red-coloured iron-containing pigment present in the red blood cells $(RBCs)$.
These molecules play a significant role in the transport of respiratory gases, specifically oxygen $(O_2)$ and carbon dioxide $(CO_2)$.

(B) At high altitudes,the atmospheric oxygen level is low.
To compensate for the reduced partial pressure of oxygen,the body increases the production of $RBCs$ to ensure that sufficient oxygen is transported to the tissues.
Therefore,people living at high altitudes have a higher count of $RBCs$ (around $8 \; million/mm^3$) compared to those living at sea level (around $5 \; million/mm^3$).

(B) The given graph represents the oxygen-haemoglobin dissociation curve.
In the lungs,the partial pressure of $O_{2}$ $(pO_{2})$ is high,which facilitates the binding of $O_{2}$ with haemoglobin,leading to high percentage saturation of haemoglobin. This corresponds to point $A$ on the curve.
In the tissues,the partial pressure of $O_{2}$ $(pO_{2})$ is low due to metabolic activity,which causes the dissociation of $O_{2}$ from oxyhaemoglobin,leading to lower percentage saturation. This corresponds to point $B$ on the curve.
Therefore,$A$ represents lungs and $B$ represents tissues.

(A) Carbonic anhydrase is an enzyme present in high concentrations within the red blood cells (erythrocytes).
It plays a crucial role in the transport of $CO_2$.
Most of the $CO_2$ produced by tissues diffuses into the blood and enters the erythrocytes,where it reacts with water to form carbonic acid $(H_2CO_3)$ in the presence of the enzyme carbonic anhydrase.
This reaction occurs very rapidly inside the erythrocytes,facilitating the conversion of $CO_2$ into bicarbonate ions for transport.
Therefore,statement $I$ is correct and is responsible for the process described in statement $II$.

(D) Haemoglobin is a quaternary protein consisting of four polypeptide chains ($2 \alpha$ and $2 \beta$ chains).
Each polypeptide chain is associated with one heme group.
Therefore,each haemoglobin molecule contains a total of $4$ heme groups.

(A) In the alveoli,the partial pressure of oxygen $(pO_{2})$ is high and the partial pressure of carbon dioxide $(pCO_{2})$ is low.
These conditions are ideal for the binding of oxygen with haemoglobin to form oxyhaemoglobin.
Additionally,lower concentrations of $H^{+}$ ions (higher $pH$) and lower temperatures further promote the association of oxygen with haemoglobin.
Therefore,the conditions at the alveoli are high $pO_{2}$,low $pCO_{2}$,less $H^{+}$,and lower temperature.

(A) In human beings,oxygenated blood leaves the lungs with an oxygen saturation of approximately $97\%$ to $98\%$.
Every $100 \ ml$ of oxygenated blood contains about $20 \ ml$ of $O_2$.
Under normal physiological conditions,when this blood reaches the systemic tissues,it releases approximately $5 \ ml$ of $O_2$ to the tissues for every $100 \ ml$ of blood.
Therefore,the correct answer is $5 \ ml$.

(A) The transport of oxygen $(O_2)$ in the human body occurs primarily through two methods:
$1$. About $97\%$ of $O_2$ is transported by red blood cells $(RBCs)$ in the blood,where it binds with hemoglobin to form oxyhemoglobin.
$2$. The remaining $3\%$ of $O_2$ is carried in a dissolved state through the blood plasma.
Therefore,the ratio of transport via plasma to transport via $RBCs$ is $3\% : 97\%$.

(D) The transport of $CO_2$ in the blood occurs in three forms:
$1$. As Bicarbonate ions $(HCO_3^-)$: About $70\%$ of $CO_2$ is transported in this form.
$2$. As Carbaminohemoglobin: About $20-25\%$ of $CO_2$ is transported bound to hemoglobin in $RBCs$.
$3$. Dissolved in Plasma: About $7\%$ of $CO_2$ is carried in a dissolved state through blood plasma.
Therefore,the correct sequence for $RBCs$,$Plasma$,and $Bicarbonate$ is $20-25\%$,$7\%$,and $70\%$ respectively.

(C) Hemoglobin is a red-colored iron-containing pigment present in the red blood cells $(RBCs)$.
Each hemoglobin molecule can carry a maximum of four molecules of $O_2$.
The binding of $O_2$ with hemoglobin is primarily related to the partial pressure of $O_2$ $(pO_2)$.
However,the binding of $O_2$ with hemoglobin is a reversible process,not an irreversible one. This reversibility is essential for the transport and release of oxygen to the tissues. Therefore,the statement that $O_2$ binds with hemoglobin in an irreversible manner is incorrect.

(B) The curve plotted between the percentage saturation of hemoglobin with oxygen and the partial pressure of oxygen $(pO_2)$ is known as the oxygen dissociation curve.
This curve is typically sigmoid ($S$-shaped) in nature.
It represents the relationship between the affinity of hemoglobin for oxygen and the partial pressure of oxygen in the blood.
Therefore,the correct option is $B$.

(B) The relationship between the partial pressure of oxygen $(PO_2)$ and the percentage saturation of hemoglobin with oxygen is represented by the oxygen-hemoglobin dissociation curve.
This curve is sigmoid or $S$-shaped in nature.
This $S$-shaped curve indicates that as the partial pressure of oxygen increases,the binding of oxygen to hemoglobin increases rapidly until it reaches a plateau,reflecting the cooperative binding of oxygen to the four heme groups of the hemoglobin molecule.

(B) The formation of oxyhemoglobin occurs in the alveoli where oxygen binds to hemoglobin.
This process is favored by conditions that increase the affinity of hemoglobin for oxygen.
These conditions include:
$1$. High partial pressure of oxygen $(pO_2)$.
$2$. Low partial pressure of carbon dioxide $(pCO_2)$.
$3$. Low concentration of hydrogen ions $(H^+)$ (i.e.,higher pH).
$4$. Lower temperature.
These factors shift the oxygen-hemoglobin dissociation curve to the left,promoting oxygen binding.

(C) The dissociation of oxygen from oxyhaemoglobin is influenced by several factors in the tissues,known as the Bohr effect.
In the tissues,the partial pressure of oxygen $(pO_2)$ is low,while the partial pressure of carbon dioxide $(pCO_2)$ is high due to cellular respiration.
Additionally,the metabolic activity in tissues increases the concentration of $H^+$ ions (lowering the $pH$) and increases the local temperature.
These conditions—low $pO_2$,high $pCO_2$,high $H^+$ concentration,and high temperature—shift the oxygen-haemoglobin dissociation curve to the right,thereby facilitating the release of oxygen from oxyhaemoglobin to the tissues.

(C) In a healthy individual,every $100 \,mL$ of oxygenated blood contains approximately $20 \,mL$ of $O_2$.
Under normal physiological conditions,this blood delivers approximately $5 \,mL$ of $O_2$ to the tissues during each circulatory cycle.
Therefore,the correct answer is $5 \,mL$.

(B) The transport of $CO_2$ in the blood occurs in three forms:
$1$. As dissolved gas in plasma: About $7\, \%$ of $CO_2$ is transported in a dissolved state through the plasma.
$2$. As carbaminohemoglobin: About $20-25\, \%$ of $CO_2$ binds with hemoglobin to form carbaminohemoglobin.
$3$. As bicarbonate ions: About $70\, \%$ of $CO_2$ is transported as bicarbonate ions $(HCO_3^-)$ in the plasma.
Therefore,the correct percentage of $CO_2$ transported as carbaminohemoglobin is $20-25\, \%$.

(C) The formation of carbaminohemoglobin is primarily dependent on the partial pressure of carbon dioxide $(pCO_2)$ and oxygen $(pO_2)$.
In the tissues,metabolic activities result in a high concentration of $CO_2$ and a low concentration of $O_2$.
$A$ high $pCO_2$ promotes the binding of $CO_2$ with hemoglobin to form carbaminohemoglobin.
Conversely,a low $pO_2$ reduces the affinity of hemoglobin for oxygen,facilitating the release of $O_2$ to the tissues and allowing hemoglobin to bind more readily with $CO_2$.

(D) In the alveoli,the partial pressure of oxygen $(pO_2)$ is high and the partial pressure of carbon dioxide $(pCO_2)$ is low.
According to the Haldane effect,the binding of oxygen to hemoglobin in the lungs promotes the dissociation of $CO_2$ from carbaminohemoglobin.
High $pO_2$ facilitates the oxygenation of hemoglobin,which displaces $CO_2$ from the carbamino compounds.
Low $pCO_2$ in the alveoli creates a concentration gradient that allows $CO_2$ to diffuse out of the blood and into the alveoli for exhalation.
Therefore,the conditions $pCO_2$ low and $pO_2$ high are necessary for the dissociation of $CO_2$ from carbaminohemoglobin.

(A) The reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons HCO_3^- + H^+$ occurs in the red blood cells $(RBCs)$.
This reaction is catalyzed by the enzyme Carbonic anhydrase.
Carbonic anhydrase is a zinc-containing enzyme that facilitates the hydration of $CO_2$ to form carbonic acid $(H_2CO_3)$ and its subsequent dissociation into bicarbonate $(HCO_3^-)$ and hydrogen ions $(H^+)$.
Both steps of this reversible reaction are catalyzed by the same enzyme,Carbonic anhydrase.
Therefore,both $P$ and $Q$ represent Carbonic anhydrase.

(C) The reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$ is catalyzed by the enzyme carbonic anhydrase.
At the tissue level,high $pCO_2$ facilitates the formation of $HCO_3^-$ and $H^+$ ions,which are then transported to the lungs.
At the pulmonary (alveolar) level,the reaction proceeds in the reverse direction due to low $pCO_2$,leading to the formation of $CO_2$ and $H_2O$,which is then exhaled.
Therefore,this reaction occurs at both the tissue and pulmonary levels.

(B) The reaction $H^+ + HCO_3^- \rightarrow H_2CO_3 \rightarrow H_2O + CO_2$ represents the conversion of bicarbonate ions back into carbon dioxide.
This process occurs at the pulmonary level (in the lungs) where $CO_2$ is released from the blood into the alveoli to be exhaled.
At the tissue level,the reaction proceeds in the opposite direction $(CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow H^+ + HCO_3^-)$ to transport $CO_2$ in the form of bicarbonate ions.

(B) The exchange of gases occurs between the blood and the alveoli.
Deoxygenated blood,which reaches the alveoli,contains $CO_2$ that needs to be exhaled.
Every $100$ $mL$ of deoxygenated blood delivers approximately $4$ $mL$ of $CO_2$ to the alveoli for elimination.
Therefore,the correct option is $B$.

(A) The formation of oxyhaemoglobin in the alveoli is primarily determined by the partial pressure of oxygen $(pO_2)$.
In the alveoli,the conditions are high $pO_2$,low $pCO_2$,low $H^{+}$ concentration,and lower temperature.
These conditions shift the oxygen-haemoglobin dissociation curve to the left,promoting the binding of oxygen to haemoglobin.
Therefore,high $pO_2$ and lesser $H^{+}$ concentration are the favourable factors for the formation of oxyhaemoglobin.

(C) In the alveoli,the conditions are favourable for the formation of oxyhaemoglobin.
These conditions include high $pO_2$,low $pCO_2$,lower $H^+$ concentration,and lower temperature.
High $pO_2$ promotes the binding of oxygen with haemoglobin.
Conversely,high $pCO_2$,high $H^+$ concentration,and higher temperature are favourable for the dissociation of oxyhaemoglobin in the tissues.

(C) The reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons HCO_3^- + H^+$ is catalyzed by the enzyme Carbonic anhydrase.
This enzyme is present in high concentrations in red blood cells $(RBCs)$.
It facilitates the hydration of $CO_2$ to form carbonic acid $(H_2CO_3)$ and its subsequent dissociation into bicarbonate $(HCO_3^-)$ and hydrogen ions $(H^+)$.
Since the enzyme Carbonic anhydrase catalyzes both steps of this reversible reaction,both $A$ and $B$ are Carbonic anhydrase.

(C) Carbonic anhydrase is a zinc-containing enzyme that catalyzes the reversible reaction between carbon dioxide $(CO_2)$ and water $(H_2O)$ to form carbonic acid $(H_2CO_3)$.
This enzyme is found in high concentrations within red blood cells $(RBCs)$,also known as erythrocytes.
It plays a crucial role in the transport of $CO_2$ from tissues to the lungs by facilitating the conversion of $CO_2$ into bicarbonate ions $(HCO_3^-)$ in the $RBCs$ and vice versa.

$(D)$ Let us analyze each statement:
$(i)$ Incorrect: $100 \ ml$ of oxygenated blood carries about $20 \ ml$ of oxygen. Therefore, $1 \ litre$ $(1000 \ ml)$ of blood carries $200 \ ml$ of oxygen, not $20 \ ml$.
$(ii)$ Incorrect: According to the Bohr effect, when $PCO_2$ rises, the affinity of haemoglobin for oxygen decreases, shifting the dissociation curve to the right.
$(iii)$ Incorrect: $100 \ ml$ of arterial blood carries about $4 \ ml$ of $CO_2$. Therefore, $1 \ litre$ of arterial blood carries about $40 \ ml$ of $CO_2$, not $4 \ ml$.
$(iv)$ Incorrect: The role of oxygen in the regulation of respiratory rhythm is considered insignificant compared to the role of $CO_2$ and $H^+$ ions.
Since all four statements are incorrect, the correct option is $(d)$.

(B) Deoxygenated blood carries $CO_2$ from the tissues to the lungs for expiration.
In the human body,every $100 \ ml$ of deoxygenated blood contains approximately $4 \ ml$ of $CO_2$ that is delivered to the alveoli for exchange.
Therefore,the correct option is $B$.

(B) Under normal physiological conditions,every $100 \ ml$ of oxygenated blood contains approximately $20 \ ml$ of $O_2$.
However,it delivers only about $5 \ ml$ of $O_2$ to the tissues during one complete circulation.
Therefore,the correct answer is $5 \ ml$.

(C) Hamburger's phenomenon,also known as the chloride shift,is the process where chloride ions $(Cl^-)$ move from the plasma into the $RBCs$ to maintain electrical neutrality when bicarbonate ions $(HCO_3^-)$ diffuse out of the $RBCs$ into the plasma during $CO_2$ transport.

(A) $I$. $100\%$ saturation of haemoglobin is very rare under physiological conditions because the partial pressure of oxygen in the blood rarely reaches levels that would cause complete saturation.
$II$. In the alveoli,the $ppO_2$ is approximately $100 \text{ mm Hg}$,which results in $95-97\%$ saturation of haemoglobin,which is a correct statement.
$III$. At a $ppO_2$ of $30 \text{ mm Hg}$,the saturation of haemoglobin is approximately $50\%$,which is a correct statement.
$IV$. The oxyhaemoglobin dissociation curve is sigmoidal ($S$-shaped),not $J$-shaped.
Therefore,statements $I$ and $IV$ are incorrect.

(C) Blood transports oxygen from the lungs to the tissues.
Oxygen is transported in the blood in two forms:
$1$. Bound to hemoglobin in red blood cells (about $97\%$).
$2$. Dissolved in the blood plasma (about $3\%$ or $0.03$).
Therefore,the plasma carries $0.03$ of the total oxygen in a dissolved state.

(B) When $ppCO_2$ is high and pH is low (acidic conditions),the affinity of haemoglobin for $O_2$ decreases. This phenomenon is known as the Bohr effect.
As a result,the oxygen dissociation curve shifts to the right.
This decrease in affinity facilitates the release of $O_2$ from oxyhaemoglobin,allowing $O_2$ to diffuse into the tissue cells where it is needed for cellular respiration.
Therefore,statements $ii$ and $iv$ are correct.

(A) Statement $I$ is correct because the oxygen-dissociation curve represents the relationship between the percentage saturation of hemoglobin with oxygen $(HbO_2)$ and the partial pressure of oxygen $(pO_2)$.
Statement $II$ is incorrect because the oxygen dissociation curve shifts towards the right (Bohr effect) due to an increase in $ppCO_2$,an increase in hydrogen ion concentration (decrease in $pH$),and an increase in temperature. $A$ decrease in $ppCO_2$ and temperature would cause a leftward shift.

$(A)$ 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 $RBCs$ (erythrocytes) and is present in minute quantities in blood plasma.
Statement $I$ is correct because the enzyme is primarily localized within $RBCs$ and is considered absent or negligible in plasma for physiological purposes.
Statement $II$ is correct because the high concentration of carbonic anhydrase in $RBCs$ accelerates the reaction rate significantly compared to plasma, where the enzyme concentration is extremely low.

(C) The oxygen dissociation curve is a sigmoid-shaped curve.
It shifts towards the left due to an increase in pH,a decrease in $ppCO_2$,a decrease in temperature,and a decrease in $DPG$ levels.
Since an increase in pH corresponds to a decrease in hydrogen ion concentration (alkalinity),it facilitates the binding of oxygen to hemoglobin,causing a leftward shift.

(D) The correct $ppCO_2$ of alveolar air is $40 \ mm \ Hg$,not $45 \ mm \ Hg$. Therefore,option $D$ is the incorrect statement. Oxygen and carbon dioxide diffuse across the alveolar membrane based on partial pressure gradients,and the membrane is highly permeable to both gases.

(C) Carbon monoxide $(CO)$ has a very high affinity for haemoglobin,approximately $200-250$ times greater than that of oxygen $(O_2)$.
When $CO$ binds to haemoglobin,it forms a stable compound known as carboxyhaemoglobin.
This binding prevents haemoglobin from transporting oxygen to the tissues,leading to hypoxia and potentially fatal carbon monoxide poisoning.
Therefore,the correct option is $C$.

(B) The correct answer is $B$.
In the alveoli,the conditions are high $pO_2$,low $pCO_2$,lower $H^+$ concentration,and lower temperature.
These factors are favourable for the binding of oxygen with haemoglobin to form oxyhaemoglobin.
Conversely,in the tissues,low $pO_2$,high $pCO_2$,high $H^+$ concentration,and higher temperature promote the dissociation of oxygen from oxyhaemoglobin.
Therefore,$O_2$ binds to haemoglobin in the lungs and dissociates in the tissues.