Question 1

The gas transported mainly as oxyhaemoglobin in the blood is:

Accepted Answer

Oxygen. O₂ binds reversibly to the iron of haemoglobin, forming oxyhaemoglobin (about 97% of O₂ transport).

Question 2

The major form (about 70%) in which CO₂ is transported in the blood is:

Accepted Answer

As bicarbonate ions (HCO₃⁻). Around 70% of CO₂ travels as bicarbonate; ~20–25% as carbamino-haemoglobin and ~7% dissolved.

Question 3

Gas exchange across the alveoli and tissues occurs by:

Accepted Answer

Simple diffusion based on partial pressure gradients. O₂ and CO₂ diffuse along their partial pressure (pO₂/pCO₂) gradients — no energy is spent.

Question 4

The enzyme in red blood cells that catalyses the interconversion of CO₂ and water to carbonic acid/bicarbonate is:

Accepted Answer

Carbonic anhydrase. Carbonic anhydrase (in RBCs) speeds CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻, aiding CO₂ transport.

Question 5

The sigmoid oxygen-haemoglobin dissociation curve shifts to the RIGHT (favouring O₂ unloading) when there is:

Accepted Answer

High pCO₂, high H⁺ (low pH) and higher temperature. The Bohr effect: high CO₂, low pH, high temperature (as in active tissues) shift the curve right, releasing more O₂.

Question 6

In the alveoli, factors favourable for the formation of oxyhaemoglobin are:

Accepted Answer

High pO₂, low pCO₂, low H⁺ and lower temperature. At the alveoli (high pO₂, low pCO₂/H⁺), haemoglobin binds O₂; in tissues (opposite conditions) it releases O₂.

Question 7

The partial pressure of oxygen (pO₂) in the alveolar air is approximately:

Accepted Answer

104 mm Hg. Alveolar pO₂ is about 104 mm Hg, higher than the pO₂ of deoxygenated blood (40 mm Hg), so O₂ diffuses from alveoli into blood.

Question 8

The approximate percentage of carbon dioxide transported in a dissolved state through the plasma is about:

Accepted Answer

7%. Only about 7% of CO₂ is carried dissolved in plasma; roughly 70% travels as bicarbonate and 20-25% as carbamino-haemoglobin.

Question 9

In the blood, oxygen binds to haemoglobin at the:

Accepted Answer

iron-containing haem groups, each haemoglobin binding up to four O₂ molecules. Each haemoglobin has four haem groups, each with an iron atom that can bind one O₂, so one haemoglobin carries up to four oxygen molecules as oxyhaemoglobin.

Question 10

The diffusion membrane across which gases are exchanged in the alveoli consists of three layers: the thin squamous epithelium of the alveoli, the endothelium of the alveolar capillaries, and:

Accepted Answer

the basement substance lying between them. The respiratory (diffusion) membrane is made of the alveolar squamous epithelium, the capillary endothelium and the basement substance in between, keeping the barrier very thin.

Question 11

Regarding CO₂, the diffusion gradient runs from tissues/blood into the alveoli. Which pair correctly gives the pCO₂ (in mm Hg) in the alveoli and in deoxygenated blood entering the lungs?

Accepted Answer

alveoli 40 and blood 45. Deoxygenated blood has pCO₂ around 45 mm Hg and the alveoli around 40 mm Hg, so CO₂ diffuses from blood into the alveoli.

Question 12

Under normal physiological conditions, every 100 mL of oxygenated blood delivers roughly how much O₂ to the tissues, and how much CO₂ is carried to the alveoli by 100 mL of blood?

Accepted Answer

about 5 mL of O₂ and about 4 mL of CO₂. Every 100 mL of oxygenated blood delivers about 5 mL of O₂ to tissues, and about 4 mL of CO₂ is delivered by 100 mL of blood to the alveoli.

Question 13

About 20-25% of carbon dioxide is transported as carbamino-haemoglobin, which is formed when CO₂ binds to:

Accepted Answer

the amino (globin) portion of haemoglobin. CO₂ combines with the amino groups of the globin part of haemoglobin to form carbamino-haemoglobin; this is favoured in the tissues where pCO₂ is high.

Question 14

When bicarbonate (HCO₃⁻) ions diffuse out of the red blood cells into the plasma, chloride ions (Cl⁻) move into the cells to maintain ionic balance. This phenomenon is called the:

Accepted Answer

chloride shift (Hamburger phenomenon). The chloride shift, or Hamburger phenomenon, is the inward movement of Cl⁻ that balances the outward diffusion of HCO₃⁻ formed inside the erythrocyte.

Question 15

Assertion (A): In the tissues, oxyhaemoglobin readily dissociates to release O₂. Reason (R): Tissues have high pCO₂, high H⁺ concentration and higher temperature, which favour dissociation of oxyhaemoglobin.

Accepted Answer

Both A and R are true and R is the correct explanation of A. The high pCO₂, low pH and higher temperature in active tissues shift the dissociation curve to the right, promoting release of O₂ from oxyhaemoglobin (Bohr effect).

Question 16

Carbon dioxide is transported in the dissolved form to a much greater extent than oxygen mainly because:

Accepted Answer

CO₂ is about 20-25 times more soluble in water than O₂. The far higher solubility of CO₂ (roughly 20-25 times that of O₂) allows a larger fraction of CO₂ to be carried simply dissolved in the plasma.

Question 17

Exchange of gases

Accepted Answer

All. Gas exchange occurs at the alveoli-pulmonary capillary and at the blood-tissue interface, in both cases by simple diffusion.

Question 18

Which of the following factors affect the diffusion of gases?

Accepted Answer

All. Rate of diffusion depends on partial pressure gradient, solubility of the gases and thickness of the diffusion membrane.

Question 19

Which of the following statements about the partial pressure of CO2 is true?

Accepted Answer

It is higher in systemic veins than in systemic arteries. Systemic venous (deoxygenated) blood has pCO2 of 45 mmHg, higher than systemic arterial (oxygenated) blood at 40 mmHg.

Question 20

The partial pressure of CO2 in the venous blood is

Accepted Answer

Lesser than in the tissue spaces. pCO2 in deoxygenated/venous blood (45 mmHg) is lesser than in the tissues (45-46 mmHg), which allows CO2 to diffuse from tissues into blood.

Exchange & Transport of Gases — NEET Biology MCQs with Solutions

Questions with solutions