NEET Biology Breathing and Exchange of Gases MCQs Set 19

Answer: (b) non-ciliated squamous

Explanation:
1. The alveolar wall is made of a very thin layer of flat (squamous) cells without cilia.
2. This thin wall allows quick diffusion of gases.

Teacher's Note:
1. Squamous epithelium is thin and suited to diffusion.
2. Cilia are found in the trachea and bronchi.

Answer: (b) frog

Explanation:
1. The frog has a moist skin rich in blood vessels and uses it as an accessory respiratory organ (cutaneous respiration).
2. Humans, rabbits and lizards depend on lungs.

Teacher's Note:
1. Frogs respire through lungs, skin and buccal cavity.
2. Skin respiration is important during hibernation.

Answer: (a) sigmoid

Explanation:
1. The oxygen dissociation curve plots percentage saturation of haemoglobin against pO2.
2. It is S-shaped (sigmoid) because the binding of one oxygen helps binding of the next.

Teacher's Note:
1. Sigmoid shape shows cooperative binding.
2. The curve shifts right with high CO2 and low pH.

Answer: (d) carbaminohaemoglobin and as carbonic acid

Explanation:
1. Most CO2 (about 70 percent) travels as bicarbonate formed from carbonic acid, and about 20-25 percent as carbaminohaemoglobin.
2. Only about 7 percent is dissolved in plasma.

Teacher's Note:
1. CO2 is carried in three ways.
2. Carbonic anhydrase speeds up the reaction in RBCs.

Answer: (b) Residual volume

Explanation:
1. Residual volume is the air that stays in the lungs even after a forced expiration (about 1100-1200 mL).
2. Tidal volume is about 500 mL and vital capacity is about 3500-4500 mL.

Teacher's Note:
1. Residual volume keeps the alveoli from collapsing.
2. It cannot be measured by a simple spirometer.

Answer: (b) alveolar epithelium and capillary endothelium

Explanation:
1. For gas exchange, the air in the alveolus is separated from the blood only by the thin alveolar epithelium and the capillary endothelium (with a basement membrane).
2. This diffusion membrane is less than a micrometre thick.

Teacher's Note:
1. Respiratory membrane has three thin layers.
2. Thinness speeds diffusion.

Answer: (a) simple diffusion

Explanation:
1. Gases move across the respiratory membrane by simple diffusion, from higher to lower partial pressure.
2. No energy is needed.

Teacher's Note:
1. Diffusion depends on pressure gradient and solubility.
2. CO2 diffuses faster than O2 because it is more soluble.

Answer: (d) Brain

Explanation:
1. The brain needs a constant supply of oxygen and is the most sensitive organ.
2. Brain cells begin to die within minutes of oxygen shortage.

Teacher's Note:
1. Brain uses about 20 percent of the body's oxygen.
2. It cannot store oxygen.

Answer: (a) chloride shift

Explanation:
1. When CO2 enters RBCs, bicarbonate is formed and moves out into plasma, while chloride ions move from plasma into RBCs.
2. This exchange keeps the electrical balance and is the chloride (Hamburger) shift.

Teacher's Note:
1. Chloride shift maintains ionic balance.
2. It was first described by Hamburger.

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

Explanation:
1. Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
2. So the foetus can take oxygen from the mother's blood at the placenta.

Teacher's Note:
1. HbF has two alpha and two gamma chains.
2. This is essential for the foetus.