Question

Assertion (A) A person goes to high altitude and experiences ‘altitude sickness’ with symptoms like breathing difficulty and heart palpitations. Reason (R) Due to low atmospheric pressure at high altitude, the body does not get sufficient oxygen.
In the light of the above statements, choose the correct answer from the options given below. [NEET 2021]
(a) Both $A$ and $R$ are true and $R$ is the correct explanation of $A$

(b) Both $A$ and $R$ are true, but $R$ is not the correct explanation of $A$

(c) A is true, but $R$ is false

(d) A is false, but $R$ is true

Answer/Explanation

Ans. (a)

Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.
A person goes to the high altitude and experiences altitude sickness like heavy breathing and heart palpitation. It is due to low atmospheric pressure at high altitude, the body does not get sufficient oxygen.

Question

Select the favourable conditions required for the formation of oxyhaemoglobin at the alveoli. [NEET 2021]

(a) High $\mathrm{pO}_2$, low $\mathrm{pCO}_2$, less $\mathrm{H}^{+}$, lower temperature

(b) Low $\mathrm{pO}_2$, high $\mathrm{pCO}_2$, more $\mathrm{H}^{+}$, higher temperature

(c) High $\mathrm{pO}_2$, high $\mathrm{pCO}_2$, less $\mathrm{H}^{+}$, higher temperature

(d) Low $\mathrm{pO}_2$, low $\mathrm{pCO}_2$, more $\mathrm{H}^{+}$, higher temperature

Answer/Explanation

Ans. (a)

The favourable conditions for the formation of oxyhaemoglobin is high $\mathrm{pO}_2$, Iesser $\mathrm{H}^{+}$concentration and lower temperature found in alveoli, whereas low $\mathrm{pO}_2$, high $\mathrm{H}^{+}$concentration and high temperature are favourable for dissociation of axygen from the oxyhaemoglobin found in tissues.

Question

 The partial pressures (in $\mathrm{mm} \mathrm{Hg}$ ) of oxygen $\left(\mathrm{O}_2\right)$ and carbon dioxide $\left(\mathrm{CO}_2\right)$ at alveoli (the site of diffusion) are [NEET 2021]

(a) $\mathrm{pO}_2=104$ and $\mathrm{pCO}_2=40$

(b) $\mathrm{pO}_2=40$ and $\mathrm{pCO}_2=45$

(c) $\mathrm{pO}_2=95$ and $p \mathrm{CO}_2=40$

(d) $\mathrm{pO}_2=159$ and $\mathrm{pCO}_2=0.3$

Answer/Explanation

Ans. (a)
Partial pressures of oxygen( in $\mathrm{mm} \mathrm{Hg}$ ) and carbon dioxide at alveoli are $\mathrm{pO}_2$ $=104$ and $p \mathrm{PO}_2=40$.

Question

Match the following columns and select the correct option from the codes given below. [NEET (Oct.) 2020]

  Codes
      A B C D
(a) 1 3 2 4
(b) 2 3 4 1
(c) 3 2 4 1
(d) 4 1 3 2

Answer/Explanation

Ans. (b)

Option (b) is correct match, which is as follows. Pneumotaxic centre is present in the pons region of the brain.
$\mathrm{O}_2$ dissociation curve is useful in studying the effect of factors like $\mathrm{pCO}_2$, $\mathrm{H}^{+}$concentration, etc. on binding $\mathrm{of}_2$ with haemoglobin.
Carbonic anhydrase is an enzyme present on the surface of RBC.
Primary site of exchange of gases is the alveoli of the lungs.

Question

 Identify the wrong statement with reference to transport of oxygen. [NEET (Sep.) 2020]

(a) Partial pressure of $\mathrm{CO}_2$ can interfere with $\mathrm{O}_2$ binding with haemoglobin

(b) Higher $\mathrm{H}^{+}$concentration in alveoli favours the formation of oxyhaemoglobin

(c) Low $\mathrm{pCO}_2$ in alveoli favours the formation of oxyhaemoglobin

(d) Binding of oxygen with haemoglobin is mainly related to partial pressure of $\mathrm{O}_2$

Answer/Explanation

Ans. (b)

Statement in option (b) is incorrect with reference to transport of oxygen. It can be corrected as
In alveoli high $\mathrm{pO}_2$, low $\mathrm{pCO}_2$, low $\mathrm{H}^{+}$ concentration and lower temperature are the factors that favour the formation of oxyhaemoglobin.

Question

 Reduction in $\mathrm{pH}$ of blood will [NEET 2016, Phase I]

(a) reduce the blood supply to the brain

(b) decrease the affinity of haemoglobin with oxygen

(c) release bicarbonate ions by the liver

(d) reduce the rate of heartbeat

Answer/Explanation

Ans. (b)

Reduction in $\mathrm{pH}$ of blood, i.e. increase in acidity favours the dissociation of axyhaemoglobin thereby giving upmore $\mathrm{O}_2$. When this phenomenon occurs due to increase in $\mathrm{CO}_2$ concentration then it is called Bohr effect.

Question

 The partial pressure of oxygen in the alveoli of the lungs is [NEET 2016, Phase II]

(a) equal to that in the blood

(b) more than that in the blood

(c) less than that in the blood

(d) less than that of carbon dioxide

Answer/Explanation

Ans. (b)

The partial pressure of oxygen $\left(\mathrm{pO}_2\right)$ in alveoli of lungs is $104 \mathrm{~mm} \mathrm{Hg}$, which is more than that of blood in the blood capillaries of lung alveoli $(40 \mathrm{~mm} \mathrm{Hg})$. This difference allows passive diffusion of $\mathrm{O}_2$ from air filled in the lungs to the bload vessels of lung alveoli.

Question

Approximately seventy percent of carbon dioxide absorbed by the blood will be transported to the lungs [CBSE AIPMT 2014]

(a) as bicarbonate ions

(b) in the form of dissolved gas molecules

(c) by binding to RBC

(d) as carbaminohaemoglobin

Answer/Explanation

Ans. (a)

The largest fraction of carbon dioxide, i.e. about $70 \%$ is converted to bicarbonates ( $\left.\mathrm{HCO}_1^{-}\right)$and transported in the plasma.
$
\begin{aligned}
& \mathrm{HCO}_2^{-}+\mathrm{H}^{+} \\
&
\end{aligned}
$
About $-23 \%$ of $\mathrm{CO}_2$ is carried by haemoglabin as carbaminahaemoglobin $\mathrm{CO}_2+\mathrm{Hb}$ (haemoglobin) $\rightleftharpoons \mathrm{HbCO}_2$ Carbo amino haemoglobin

Question

 People who have migrated from the planes to an area adjoining Rohtang Pass about six months back [CBSE AIPMT 2012]

(a) have more RBCs and their haemoglobin has a lower binding affinity to $\mathrm{O}_2$

(b) are not physically fit to play games like football

(c) suffer from altitude sickness with symptoms like nausea, fatigue, etc.

(d) have the usual RBC count but their haemoglobin has very high binding affinity $\mathrm{to}_2$

Answer/Explanation

Ans. (a)

As a person moves up a hill the $\mathrm{pO}_2$ and total atmospheric pressure decreases. Decrease in $\mathrm{pO}_2$ due to the increasing altitude, stimulates the Juxtaglomerular cells of kidney to secrete erythropoietin hormone which increases the number of RBCs(polycythemia) to compensate the supply of $\mathrm{O}_2$. At higher altitude, haemoglobin has lower binding affinity to $\mathrm{O}_2$ because the primary factor responsible for binding is $\mathrm{pO}_2$ which decreases at higher altitude.

Question

 Which two of the following changes (1-4) usually tend to occur in the plain dwellers when they move to high altitudes $(3,500 \mathrm{~m}$ or more)? [CBSE AIPMT 2010]

1. Increase in red blood cell size

2. Increase in red blood cell production

3. Increased breathing rate

4. Increase in thrombocyte count Changes occurring are [CBSE AIPMT 2010]

(a) 2 and 3

(b) 3 and 4

(c) 1 and 4

(d) 1 and 2

Answer/Explanation

Ans. (a)
When a person moves to higher altitudes, the $\mathrm{pO}_2$ and total atmospheric pressure decrease. Hypoxia stimulates the Juxtaglomerular cells of the kidney to release erythropoietin hormone which stimulates erythropoesis in bone marrow causing polycythemia (increase in RBCs production). Hypoxia will also increase breathing rate. Initially the size af RBCs will also increase but with increase in number of $\mathrm{RBCs}$, the size of RBCs becomes normal.

Question

 The haemoglobin of a human foetus [CBSE AIPMT 2008]

(a) has a lower affinity for oxygen than that of the adult

(b) its affinity for axygen is the same as that of an adult

(c) has only 2 protein sub-units instead of 4

(d) has a higher affinity for oxygen than that of an adult

Answer/Explanation

Ans. (d)

Haemoglobin is the protein that makes red blood corpuscles appear red, binds easily and reversibly with oxygen. Normal values for haemoglobin are $14-20 \mathrm{~g} / 100$ $\mathrm{mL}$ af blood in infants, $13-18 \mathrm{~g} / 100 \mathrm{~mL}$ in adult male and $12-16 \mathrm{~g} / 100 \mathrm{~mL}$ in adult females. Foetal red blood cells are not sickle-shaped even in that destined to have sickle-cell anaemia, i.e. haemoglobin of foetus has higher affinity of oxygen than that an adult.

Question

People living at sea level have around 5 million RBC per cubic millimeter of their blood whereas those living at an altitude of 5400 metre have around 8 million. This is because at high altitude [CBSE AIPMT 2006]

(a) atmospheric $\mathrm{O}_2$ level is less and hence, more RBCs are needed to absorb the required amount of $\mathrm{O}_2$ to survive

(b) there is more UV radiation which enhances RBC production

(c) people eat more nutritive food, therefore, more RBCs are formed

(d) people get pollution-free air to breathe and more axygen is available

Answer/Explanation

Ans. (a)

At high altitudes, the atmospheric $\mathrm{O}_2$ level is less and hence, more RBCs are needed to absorb the required amount of $\mathrm{O}_2$ to survive. That is why, the people living at sea level have around 5 million $\mathrm{RBC} / \mathrm{mm}^3$ of their blood whereas, those living at an altitude of 5400 meter have around 8 million $\mathrm{RBC} / \mathrm{mm}^3$ of their blood.

Question

Blood analysis of a patient reveals an unusually high quantity of carboxyhaemoglobin content. Which of the following conclusions is most likely to be correct? [CBSE AIPMT 2004]

(a) The patient has been inhaling polluted air containing unusually high content of carbon disulphide

(b) The patient has been inhaling polluted air containing unusually high content of chloraform

(c) The patient has been inhaling polluted air containing unusually high content of carbon dioxide

(d) The patient has been inhaling polluted air containing unusually high content of carbon monaxide

Answer/Explanation

Ans. (d)

Inhalation of polluted air causes increase in $\mathrm{CO}$ in the bload of a person. Carbon monoxide forms a stable compound with haemoglobin called carboxyhaemoglobin as affinity of $\mathrm{Hb}$ for $\mathrm{CO}$ is 210 times greater than its affinity for $\mathrm{O}_2$. In this form haemoglobin does not carry oxygen resulting in death due to hypoxia.

Question

 When $\mathrm{CO}_2$ concentration in blood increases, breathing becomes [CBSE AIPMT 2004]

(a) shallower and slow

(b) there is no effect on breathing

(c) slow and deep

(d) faster and deeper

Answer/Explanation

Ans. (d)

When $\mathrm{CO}_2$ concentration in blood increases breathing becomes faster and deeper. The effect of increased $\mathrm{CO}_2$ is to decrease the affinity of haemoglobin for $0_2$.
Thus, due to Bohr’s effect the $\mathrm{CO}_2$ released in respiring tissue accelerates the delivery of oxygen by faster and deeper breathing.

Question

 The process of migration of chloride ions from plasma to $\mathrm{RBC}$ and of carbonate ions from RBC to plasma is [CBSE AIPMT 1999]

(a) chloride shift

(b) ionic shift.

(c) atomic shift

(d) $\mathrm{Na}^{+}$pump

Answer/Explanation

Ans. (a)

To maintain electrostatic neutrality of plasma, many chloride ions diffuse from plasma into RBCs and bicarbonate ions pass out. The chlaride content of RBCs increases when oxygenated blood becomes deoxygenated. This is termed as chloride shift or Hamburger shift.

Question

 The exchange of gases in the alveoli of the lungs takes place by [CBSE AIPMT 1998]

(a) simple diffusion

(b) osmosis

(c) active transport

(d) passive transport

Answer/Explanation

Ans. (a)

Oxygen diffuses from alveoli to deoxygenated blood and $\mathrm{CO}_2$ diffuses from deoxygenated blood to alveoli by simple diffusion. Diffusion is defined as, the flow of the substance(gases) from a region of their higher concentration to a region of lower concentration.

Question

 Which one of the following statements about blood constituents and transport of respiratory gases is most accurate? [CBSE AIPMT 1996]

(a) RBCs transport axygen whereas WBCs transport $\mathrm{CO}_2$

(b) RBCs transport axygen whereas plasma transports anly $\mathrm{CO}_2$

(c) RBCs as well as WBCs transport both axygen and $\mathrm{CO}_2$

(d) RBCs as well as plasma transport both oxygen and $\mathrm{CO}_2$

Answer/Explanation

Ans. (d)

RBCs and plasma both transport $\mathrm{D}_2$ and $\mathrm{CO}_2$ either in chemically bonded state or in dissolved state.

Question

 At high altitude, the RBCs in the human blood will [CBSE AIPMT 1995]

(a) increase in size

(b) decrease in size

(c) increase in number

(d) decrease in number

Answer/Explanation

Ans. (c)

At high altitude there is low $\mathrm{O}_2$ concentration, so RBCs increase in number, i.e. $0_2$ supply can be maintained to organs.

Question

 The carbon dioxide is transported via blood to lungs as [CBSE AIPMT 1995]

(a) dissolved in blood plasma

(b) in the form of carbonic acid only

(c) in combination with haemoglobin only

(d) carbaminahaemoglobin and as carbonic acid

Answer/Explanation

Ans. (d)
Most of the $\mathrm{CO}_2(70 \%)$ that dissolves in plasma reacts with water forming carbonic acid. This reaction occurs rapidly inside RBCs because of the presence of an enzyme carbonic anhydrase. Moreover, above $23 \%$ of total bloodCO $\mathrm{C}_2$ is transported by loosely binding with haemoglobin forming an unstable compound called carbaminohaemoglobin.

Question

 Although much $\mathrm{CO}_2$ is carried in blood, yet blood does not become acidic, because [CBSE AIPMT 1995]

(a) it is absorbed by the leucocytes

(b) blood buffers play an important role in $\mathrm{CO}_2$ transport

(c) it cambines with water to form $\mathrm{H}_2 \mathrm{CO}_3$ which is neutralised by $\mathrm{Na}_2 \mathrm{CO}_3$

(d) it is continuously diffused through tissues and is not allowed to accumulate

Answer/Explanation

Ans. (b)

Buffer of the blood is sodium bicarbonate which play an important role in $\mathrm{CO}_2$ transport. During $\mathrm{CO}_2$
transportation, carbonic acid dissociates into $\mathrm{H}^{+}$and $\mathrm{HCO}_3^{-}$ (bicarbonate ions). This bicarbonate combines with sodium forming sodium bicarbonate. Thus, concentration of carbonic acid does not increase in blood due to the presence of sodium and thus blood does not become acidic. About $70 \%$ of $\mathrm{CO}_2$ released during cellular respiration is transported by blood in the form of sodium bicarbonate in plasma.

Question

 Oxygen dissociation curve of haemoglobin is [CBSE AIPMT 1994]

(a)  sigmoid

(b) hyperbolic

(c) linear

(d) hypobolic

Answer/Explanation

Ans. (a)
Oxygen haemaglobin dissociation curve gives the relationship between the saturation of haemoglobin and oxygen tension. The curve obtained by plotting the percent saturation of $\mathrm{Hb}$ against time is sigmoid, at $38^{\circ} \mathrm{C}$ and $\mathrm{pH} 7.4$. Dissociation of oxyhaemoglobin can be promoted by rise in the body temperature and low $\mathrm{pH}$ (high $\mathrm{CO}_2$ ).

Question

 Carbon dioxide is transported from tissues to respiratory surface by only [CBSE AIPMT 1993]

(a) plasma and erythrocytes

(b) plasma

(c) erythrocytes

(d) erythrocytes and leucocytes

Answer/Explanation

Ans. (a)

Carbon dioxide is transported from tissues to respiratory surface by only plasma and erythrocytes. Carbon dioxide $\left(\mathrm{CO}_2\right)$ transportation by blood is much easier than oxygen due to the high solubility of $\mathrm{CO}_2$ in water. During transport of $\mathrm{CO}_2, 7 \%$ of $\mathrm{CO}_2$ is dissolved in plasma, $23 \%$ as carbaminohaemoglobin and 70\% transported as bicarbonates $\left(\mathrm{HCO}_3^{-}\right)$.

Question

Carbonic anhydrase occurs in [CBSE AIPMT 1991]

(a) lymphocytes

(b) blood plasma

(c) $\mathrm{RBC}$

(d) leucacytes

Answer/Explanation

Ans. (c)

The erythrocyte(RBC)contains sufficient amount of carbonic anhydrase enzyme which catalyses the reaction between $\mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}$ and
helps in transportation of $\mathrm{CO}_2$ from tissues to the lungs.

Scroll to Top