Transport of gases Questions in English

(D) Carbon dioxide $(CO_2)$ is transported in the blood in three forms:
$1$. As bicarbonates $(HCO_3^-)$: About $70\%$ of $CO_2$ is transported in this form.
$2$. As carbaminohaemoglobin: About $20-25\%$ of $CO_2$ is transported by binding with haemoglobin.
$3$. Dissolved in plasma: About $7\%$ of $CO_2$ is carried in a dissolved state through blood plasma.
Since the majority of $CO_2$ is transported as bicarbonates,the correct answer is $D$.

(A) The dissociation of oxyhaemoglobin into oxygen and deoxyhaemoglobin is primarily determined by the partial pressure of oxygen $(P_{O_2})$.
In metabolically active tissues,the $P_{O_2}$ is significantly lower compared to the blood.
According to the oxygen-haemoglobin dissociation curve,a decrease in $P_{O_2}$ promotes the release of oxygen from haemoglobin.
Therefore,oxyhaemoglobin dissociates into oxygen and deoxyhaemoglobin at low $O_2$ pressure in the tissues.

(A) The oxygen dissociation curve represents the relationship between the partial pressure of oxygen $(pO_2)$ and the percentage saturation of hemoglobin with oxygen.
An increase in the concentration of $CO_2$ (hypercapnia) leads to a decrease in blood $pH$ (Bohr effect).
This shift in $pH$ and the presence of $CO_2$ reduces the affinity of hemoglobin for oxygen.
Consequently,the oxygen dissociation curve shifts to the right,indicating that oxygen is released more easily from hemoglobin to the tissues.

(D) The binding of oxygen with haemoglobin is primarily determined by the partial pressure of oxygen $(pO_2)$.
According to the oxygen-haemoglobin dissociation curve,as the partial pressure of oxygen increases,the percentage saturation of haemoglobin with oxygen (forming oxyhaemoglobin) increases.
Conversely,a decrease in $pO_2$ leads to the dissociation of oxyhaemoglobin into haemoglobin and oxygen.
Therefore,the ratio of oxyhaemoglobin to haemoglobin is directly dependent on the oxygen tension $(pO_2)$.

(A) The ${O_2}$ dissociation curve for haemoglobin is sigmoid in shape.
This $S$-shaped curve is obtained when the percentage saturation of haemoglobin with ${O_2}$ is plotted against the partial pressure of oxygen $({pO_2})$.

(B) Haemoglobin is a respiratory pigment present in red blood cells that binds with gases to facilitate their transport.
$1$. Haemoglobin binds with $O_2$ to form oxyhaemoglobin $(HbO_2)$.
$2$. Haemoglobin also binds with $CO_2$ to form carbaminohaemoglobin $(HbCO_2)$.
Since haemoglobin forms compounds with both $O_2$ and $CO_2$,the correct option is $B$.

(A) Oxygen is primarily transported in the blood by binding with hemoglobin,a red pigment present in the Red Blood Cells $(RBCs)$.
Approximately $97\%$ of oxygen is transported by $RBCs$ in the form of oxyhemoglobin,while the remaining $3\%$ is carried in a dissolved state through the blood plasma.
$WBCs$ (White Blood Cells) are primarily involved in the immune response and do not play a role in the transport of respiratory gases.
Therefore,$RBC$ is the correct medium for oxygen transport.

(D) During respiration,$CO_2$ is transported in the blood in three forms:
$1$. As dissolved gas in plasma (about $7\%$).
$2$. As bicarbonate ions $(HCO_3^-)$ in plasma,combined with sodium $(Na^+)$ and potassium $(K^+)$ ions to form $NaHCO_3$ and $KHCO_3$ (about $70\%$).
$3$. As carbaminohemoglobin (about $23\%$).
Therefore,the correct option is $(d)$ as it covers the dissolved state and the bicarbonate transport mechanism.

(C) Oxyhaemoglobin is an unstable compound because the binding of oxygen with haemoglobin is a reversible chemical process.
Haemoglobin is an iron-containing respiratory pigment found in red blood cells.
It is a tetrameric conjugated protein that binds with four oxygen molecules through coordinate covalent bonds to form oxyhaemoglobin.
Because this bond is reversible,it allows haemoglobin to pick up oxygen in the lungs and release it efficiently in the tissues.

(C) The dissociation of oxyhaemoglobin into haemoglobin and oxygen occurs primarily in the body tissues.
This process is facilitated by the Bohr effect,where the partial pressure of oxygen $(pO_2)$ is low and the partial pressure of carbon dioxide $(pCO_2)$ is high in the tissues compared to the lungs.
Additionally,factors like increased hydrogen ion concentration (lower pH) and higher temperature in the tissues further promote the release of oxygen from oxyhaemoglobin.
Therefore,the correct condition for dissociation is low ${O_2}$ and high $CO_2$ concentration.

(B) The process is known as the $Chloride \ shift$ or $Hamburger \ phenomenon$.
To maintain the electrostatic neutrality of the plasma,chloride ions $(Cl^-)$ diffuse from the plasma into the $R.B.C.s$ in exchange for bicarbonate ions $(HCO_3^-)$ that move out into the plasma.
This exchange occurs primarily when oxygenated blood becomes deoxygenated at the tissue level,facilitating the transport of carbon dioxide.

(C) The transport of $CO_2$ in the blood occurs in three forms:
$1$. About $7\%$ of $CO_2$ is transported in a dissolved state through the blood plasma.
$2$. About $20-25\%$ of $CO_2$ is transported as carbaminohaemoglobin bound to haemoglobin.
$3$. About $70\%$ of $CO_2$ is transported as bicarbonates (mainly sodium and potassium bicarbonates) in the blood plasma.
Therefore,the correct percentage range is $70-72\%$.

(C) Approximately $70\%$ of $CO_2$ is transported from tissues to the lungs in the form of bicarbonates $(HCO_3^-)$.
In the blood plasma,these bicarbonate ions are primarily carried as sodium bicarbonate $(NaHCO_3)$.
Carbon dioxide reacts with water in the presence of the enzyme carbonic anhydrase to form carbonic acid,which then dissociates into hydrogen ions and bicarbonate ions. These ions then combine with sodium ions in the plasma to form sodium bicarbonate.

(C) The dissociation of oxyhaemoglobin into haemoglobin and ${O_2}$ depends on the partial pressure gradient of ${O_2}$ between the blood and the tissues.
In normal physiological conditions,the partial pressure of ${O_2}$ $(pO_2)$ is high in the alveoli (respiratory surface) and low in the tissues,which facilitates the release of ${O_2}$ from oxyhaemoglobin to the tissues.
If the ${O_2}$ concentration (and thus $pO_2$) in the tissue were as high as at the respiratory surface,there would be no partial pressure gradient.
Without this gradient,oxyhaemoglobin would not dissociate,and ${O_2}$ would not be released to the tissues.

(B) Under normal physiological conditions,arterial blood contains approximately $19 \text{ ml}$ of $O_2$ per $100 \text{ ml}$ of blood.
Venous blood returning from the tissues contains approximately $14 \text{ ml}$ of $O_2$ per $100 \text{ ml}$ of blood.
This indicates that $5 \text{ ml}$ of $O_2$ is delivered to the tissues for every $100 \text{ ml}$ of blood.
The percentage of oxygen released by haemoglobin is calculated as: $(5 \text{ ml} / 19 \text{ ml}) \times 100 \approx 26.3 \%$.
Therefore,the closest standard value accepted in biological contexts for this exchange is $25 \%$.

(C) The chloride shift,also known as the $Hamburger$ phenomenon,is a process that occurs in the blood to facilitate the transport of $CO_2$.
When $CO_2$ enters the 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 electrical neutrality as bicarbonate ions diffuse out of the red blood cells into the plasma,chloride ions $(Cl^-)$ move from the plasma into the red blood cells.
This exchange is essential for the efficient transport of $CO_2$ from the tissues to the lungs in the form of bicarbonate ions.

(B) In the lungs,the partial pressure of $CO_2$ $(pCO_2)$ is low,which triggers the reversal of the chloride shift (Hamburger phenomenon).
$HCO_3^-$ ions move from the plasma into the $RBC$ in exchange for $Cl^-$ ions moving out of the $RBC$ into the plasma.
Inside the $RBC$,$HCO_3^-$ combines with $H^+$ to form $H_2CO_3$,which is then converted into $H_2O$ and $CO_2$ by the enzyme carbonic anhydrase.
This $CO_2$ then diffuses out of the $RBC$ and into the alveoli to be exhaled.
Therefore,the removal of $CO_2$ involves the influx of $HCO_3^-$ ions into the $RBC$.

(D) Respiratory pigments are specialized molecules that facilitate the transport of respiratory gases like $O_2$ and $CO_2$ in the blood.
$1$. They are indeed coloured pigments (e.g.,hemoglobin is red).
$2$. They possess a high affinity for binding with respiratory gases.
$3$. They are conjugated proteins containing a metal ion (e.g.,$Fe^{2+}$ in hemoglobin,$Cu^{2+}$ in hemocyanin).
Since all the provided statements ($A$,$B$,and $C$) are scientifically correct,the correct choice is $D$.

(A) The dissociation of oxyhaemoglobin is governed by the Bohr effect.
According to the Bohr effect,an increase in $CO_2$ concentration,an increase in $H^+$ ion concentration (which leads to a decrease in $pH$),and an increase in temperature shift the oxygen-haemoglobin dissociation curve to the right.
This shift indicates a decrease in the affinity of haemoglobin for oxygen,thereby promoting the dissociation of oxyhaemoglobin.
Therefore,if the $pH$ of the blood falls (becomes more acidic),the dissociation of oxyhaemoglobin increases to release oxygen into the tissues.

(D) The $Bohr$ effect describes the phenomenon where an increase in $CO_2$ concentration or a decrease in $pH$ (increased acidity) reduces the affinity of haemoglobin for oxygen.
This shift in the oxygen-haemoglobin dissociation curve to the right facilitates the release of oxygen to the tissues where metabolic activity is high.
Therefore,the $Bohr$ effect is essentially the effect of $CO_2$ and $H^+$ ions on the oxygen-binding capacity of haemoglobin.

(D) During cellular respiration,$CO_2$ is produced as a metabolic waste product. It is transported in the blood in three forms:
$1$. Dissolved in plasma $(7\%)$.
$2$. Bound to haemoglobin as carbaminohaemoglobin $(20-25\%)$.
$3$. As bicarbonate ions $(HCO_3^-)$ in plasma $(70\%)$.
Therefore,the major fraction of $CO_2$ is transported in the form of bicarbonate ions.

(A) In the lungs,the process is the reverse of the chloride shift (Hamburger phenomenon) that occurs in the tissues.
At the level of the lungs,the partial pressure of $CO_2$ is low.
$HCO_3^-$ ions move from the plasma into the $RBC$ to combine with $H^+$ ions to form $H_2CO_3$,which then dissociates into $H_2O$ and $CO_2$ to be exhaled.
To maintain electrical neutrality,$Cl^-$ ions move from the $RBC$ back into the plasma.
Therefore,the movement involves chloride ions moving from $RBC$ to plasma.

(D) $CO_2$ is transported in the blood in three main forms:
$1$. As bicarbonate ions $(HCO_3^-)$,primarily as sodium bicarbonate $(NaHCO_3)$ in the plasma,which accounts for about $70\%$ of $CO_2$ transport.
$2$. As carbaminohemoglobin $(Hb-CO_2)$,where $CO_2$ binds to the amino group of hemoglobin,accounting for about $20-25\%$ of transport.
$3$. Dissolved in plasma as carbonic acid $(H_2CO_3)$ or dissolved $CO_2$,accounting for about $7\%$ of transport.
Since all these forms are involved in the transport of $CO_2$,the correct answer is $D$.

(B) Carbon dioxide $(CO_2)$ is transported in the blood in three forms:
$1$. As dissolved gas in plasma (about $7\%$).
$2$. As carbaminohaemoglobin,where $CO_2$ binds to the amino groups of haemoglobin (about $20-25\%$).
$3$. As bicarbonates $(HCO_3^-)$,which is the primary mode of transport (about $70\%$). The enzyme carbonic anhydrase in red blood cells facilitates the conversion of $CO_2$ and $H_2O$ into $HCO_3^-$ and $H^+$ ions.

(B) The oxygen-haemoglobin dissociation curve is a sigmoid curve that represents the relationship between the partial pressure of oxygen $(pO_2)$ and the percentage saturation of haemoglobin with oxygen.
This curve illustrates how the affinity of haemoglobin for oxygen changes under different physiological conditions,such as changes in $pH$,temperature,and $pCO_2$.
Therefore,the dissociation curve is specifically associated with the binding and release of oxygen from oxyhaemoglobin.

(A) Carbon dioxide $(CO_2)$ is transported in the blood in three forms:
$1$. Dissolved in plasma: Approximately $7\%$ of $CO_2$ is carried in a dissolved state through the plasma.
$2$. As carbaminohemoglobin: About $20-25\%$ of $CO_2$ binds with hemoglobin to form carbaminohemoglobin.
$3$. As bicarbonates: The majority of $CO_2$ (approximately $70-75\%$) is transported as bicarbonates $(HCO_3^-)$ in the plasma and $RBCs$.
Therefore,the correct option is $75\%$.

(B) Haemoglobin has a significantly higher affinity for $CO_2$ compared to $O_2$.
In fact,the affinity of haemoglobin for $CO_2$ is approximately $20$ to $25$ times greater than its affinity for $O_2$.
This property is crucial for the transport of $CO_2$ from tissues to the lungs.

(C) Carbon monoxide $(CO)$ is a poisonous gas that binds to haemoglobin to form carboxyhaemoglobin.
Haemoglobin has a significantly higher affinity for $CO$ than for oxygen $(O_2)$.
This affinity is approximately $200$ to $210$ times greater for $CO$ than for $O_2$.
Because of this, even small concentrations of $CO$ can effectively block oxygen transport in the blood, leading to tissue hypoxia and potential death.

(B) Carboxyhaemoglobin is formed when haemoglobin binds with carbon monoxide $(CO)$.
Carbon monoxide has an affinity for haemoglobin that is approximately $200$ to $250$ times higher than that of oxygen.
When $CO$ binds to haemoglobin,it forms a stable compound called carboxyhaemoglobin,which prevents oxygen from binding to the haemoglobin,leading to hypoxia and potentially fatal conditions.
Therefore,the presence of high levels of carboxyhaemoglobin indicates carbon monoxide poisoning.

(B) The blood arriving at the tissues is oxygenated and contains approximately $48\,ml$ of $CO_2$ per $100\,ml$ of blood.
As blood passes through the tissues,it picks up $CO_2$ produced by cellular respiration.
On average,every $100\,ml$ of blood receives $3.7\,ml$ of $CO_2$ from the tissues,resulting in venous blood containing approximately $51.7\,ml$ of $CO_2$ per $100\,ml$ of blood.
Therefore,the amount of $CO_2$ added to the blood by the tissues is $3.7\,ml$ per $100\,ml$.

(D) Haemoglobin $(Hb)$ is a respiratory pigment that carries gases in the blood.
It binds with oxygen to form oxyhaemoglobin.
However,the affinity of haemoglobin for carbon monoxide $(CO)$ is approximately $200$ to $250$ times greater than its affinity for oxygen $(O_2)$.
When $CO$ is inhaled,it binds firmly with haemoglobin to form carboxyhaemoglobin,which is a very stable compound.
This prevents haemoglobin from binding with oxygen,leading to tissue hypoxia and potentially fatal carbon monoxide poisoning.

(A) $CO_2$ is transported by blood in three forms:
$1$. Approximately $7\%$ is dissolved in plasma.
$2$. Approximately $23\%$ is transported as carbaminohaemoglobin.
$3$. Approximately $70\%$ is transported as bicarbonate ions.
Therefore,the majority of $CO_2$ is carried in the form of bicarbonate ions.

(B) The Hamburger phenomenon is also known as the chloride shift.
To maintain the electrostatic neutrality of the plasma,chloride ions $(Cl^-)$ diffuse from the plasma into the $RBCs$ in exchange for bicarbonate ions $(HCO_3^-)$ that pass out of the $RBCs$ into the plasma.
This process occurs when oxygenated blood becomes deoxygenated,leading to an increase in the chloride content of the $RBCs$.

(C) Carbon monoxide $(CO)$ binds to haemoglobin to form a stable compound called carboxyhaemoglobin $(COHb)$.
$CO$ has an affinity for haemoglobin that is approximately $200-250$ times greater than that of oxygen.
Because of this high affinity,$CO$ binds to haemoglobin more readily than oxygen,effectively blocking oxygen binding sites.
This prevents the formation of oxyhaemoglobin,thereby reducing the oxygen-carrying capacity of the blood and leading to tissue hypoxia and death.

(B) Carbon monoxide $(CO)$ has approximately $210$ times more affinity for haemoglobin compared to oxygen $({O_2})$.
When $CO$ is inhaled,it binds with haemoglobin to form a very stable compound called carboxyhaemoglobin.
Because this bond is much stronger than the oxyhaemoglobin bond,the haemoglobin is unable to transport oxygen to the body tissues effectively.
This leads to cellular hypoxia,which the body perceives as suffocation.

(B) Carbon dioxide $(CO_2)$ reacts with water $(H_2O)$ in the presence of the enzyme carbonic anhydrase to form carbonic acid $(H_2CO_3)$.
This reaction is reversible: $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$.
In the blood, hemoglobin acts as a buffer. When $H^+$ ions are produced, they are buffered by hemoglobin, preventing a significant rise in acidity.
However, the question refers to the specific role of ions in maintaining acid-base balance. Potassium ions $(K^+)$ play a crucial role in the chloride shift (Hamburger phenomenon) and the exchange of ions across the erythrocyte membrane to maintain electrical neutrality, which helps in regulating the $pH$ and preventing the accumulation of excess carbonic acid in the plasma.

(A) The affinity of haemoglobin for oxygen is influenced by the $pH$ of the blood,a phenomenon known as the Bohr effect.
An increase in $pH$ (alkalinity) shifts the oxygen-haemoglobin dissociation curve to the left,which increases the affinity of haemoglobin for oxygen.
At a $pH$ of $8$,the blood becomes more alkaline than the normal physiological $pH$ $(7.4)$.
This increased affinity makes it difficult for oxyhaemoglobin to release oxygen at the tissue level.
Therefore,the tissues will not receive sufficient oxygen because oxyhaemoglobin will not dissociate efficiently into oxygen and haemoglobin.

(B) Oxygen is primarily transported in the blood by binding to hemoglobin,a respiratory pigment present in the $RBCs$ (Red Blood Cells).
Approximately $97\%$ of oxygen is transported by $RBCs$ in the form of oxyhemoglobin,while the remaining $3\%$ is carried in a dissolved state through the blood plasma.

(D) Carbon dioxide $(CO_2)$ is transported in the blood in three forms:
$1$. As dissolved gas in plasma $(7\%)$.
$2$. As carbamino-haemoglobin bound to haemoglobin $(20-25\%)$.
$3$. As bicarbonate ions $(HCO_3^-)$ in plasma $(70\%)$.
Since the majority of $CO_2$ is transported as bicarbonate ions dissolved in the plasma,the correct answer is plasma.

(A) Haemoglobin contains an iron-based pigment called haem,which has a high affinity for oxygen,allowing it to easily bind and transport oxygen in the blood.
In contrast,haemocyanin is a copper-containing respiratory pigment.
Copper-based pigments generally have a lower affinity for oxygen compared to iron-based haemoglobin.
Therefore,if haemoglobin is replaced by haemocyanin,the oxygen-carrying capacity of the blood would decrease,meaning it will carry less oxygen.

(A) Blood contains various buffer systems,primarily the bicarbonate buffer system $(HCO_3^-/H_2CO_3)$ and hemoglobin,which help maintain the $pH$ of the blood within a narrow range $(7.35-7.45)$.
When $CO_2$ enters the blood,it reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into $H^+$ and $HCO_3^-$.
The buffer systems neutralize the excess $H^+$ ions,preventing a significant drop in $pH$ and keeping the blood from becoming acidic.

(A) Carbon monoxide $(CO)$ binds to haemoglobin to form carboxyhaemoglobin $(HbCO)$.
The affinity of haemoglobin for $CO$ is approximately $200$ to $250$ times greater than its affinity for oxygen $(O_2)$.
Due to this high affinity, $CO$ effectively displaces oxygen from haemoglobin, leading to hypoxia and tissue damage.

(C) $CO$ (Carbon monoxide) is significantly more toxic than $CO_2$ (Carbon dioxide) because it has a much higher affinity for hemoglobin than oxygen does.
When $CO$ is inhaled,it binds to hemoglobin to form carboxyhemoglobin.
This binding is much stronger and more stable than the binding of oxygen to hemoglobin.
As a result,the amount of hemoglobin available to transport oxygen to the body's tissues is drastically reduced,leading to tissue hypoxia and potentially fatal consequences.

(C) Carbon monoxide $(CO)$ has a much higher affinity for haemoglobin than oxygen. When inhaled,it binds with haemoglobin to form a very stable compound called carboxyhaemoglobin. This process prevents haemoglobin from binding with oxygen,thereby blocking oxygen transport to the body tissues. Prolonged inhalation of $CO$ can lead to severe hypoxia and even death.

(D) Hemoglobin is a complex protein found in red blood cells $(RBCs)$.
It contains iron and acts as a respiratory pigment because it binds with oxygen to form oxyhemoglobin,facilitating the transport of oxygen from the lungs to various tissues in the body.
Therefore,it is classified as a respiratory pigment.

(D) Carbon monoxide $(CO)$ has a very high affinity for hemoglobin,approximately $200$ to $250$ times greater than that of oxygen $(O_2)$.
When $CO$ is inhaled,it binds with hemoglobin to form carboxyhemoglobin $(HbCO)$.
This binding is much more stable than oxyhemoglobin $(HbO_2)$,meaning the $CO$ does not easily dissociate from the hemoglobin.
As a result,the oxygen-carrying capacity of the blood is significantly reduced,leading to tissue hypoxia and potentially death.

(A) The binding of oxygen with hemoglobin is primarily related to the partial pressure of $O_2$.
According to the oxygen dissociation curve,the affinity of hemoglobin for oxygen increases as the partial pressure of $O_2$ $(pO_2)$ increases.
Other factors like $pCO_2$,$H^+$ ion concentration,and temperature also affect this binding (as seen in the Bohr effect),but the primary factor determining the formation of oxyhemoglobin is the partial pressure of $O_2$.

(D) In the human body,carbon dioxide $(CO_2)$ is transported in the blood in three forms:
$1$. Dissolved in plasma: Approximately $7\%$ of $CO_2$ is carried in a dissolved state.
$2$. As carbaminohemoglobin: About $20-25\%$ of $CO_2$ binds with hemoglobin to form carbaminohemoglobin.
$3$. As bicarbonate ions $(HCO_3^-)$: The majority of $CO_2$,approximately $70\%$,is transported in the form of bicarbonate ions in the plasma.
Therefore,the correct percentage is $70\%$.

(C) The oxygen-hemoglobin dissociation curve shifts to the right under conditions that promote the release of oxygen from hemoglobin,a phenomenon known as the $Bohr$ effect.
Factors that shift the curve to the right include:
$1$. Increase in $PCO_2$ (partial pressure of carbon dioxide).
$2$. Increase in $H^+$ concentration (which corresponds to a decrease in $pH$).
$3$. Increase in temperature.
$4$. Increase in $2,3-DPG$ (diphosphoglyceric acid).
Therefore,factors $(a)$ and $(c)$ are correct,while $(b)$ and $(d)$ would shift the curve to the left.

(A) The chloride shift,also known as the $Hamburger$ phenomenon,occurs in the blood to maintain electrical neutrality during the transport of $CO_2$.
When $CO_2$ enters $RBCs$,it reacts with water to form carbonic acid $(H_2CO_3)$,which dissociates into $H^+$ and $HCO_3^-$.
To maintain the ionic balance,$HCO_3^-$ ions diffuse out of the $RBC$ into the plasma,and an equivalent number of $Cl^-$ ions move from the plasma into the $RBC$ to maintain electrical neutrality.
Therefore,the chloride shift refers to the movement of $Cl^-$ from plasma to $RBC$.