FREE NEET Biology Practice MCQ Test: Breathing And Exchange Of Gases Exercise 3 Questions Answers With Detailed Explanations [PDF]

Answer: (a)

Answer: (d)

Respiratory centers that regulate respiration are located in medulla oblongata. Respiratory centre regulates normal breathing and also automatically adjusts the breathing rate to varying requirements of body during stress conditions.

Answer: (a)

Earthworm respire through their moist cuticle while aquatic arthropods respire through trachea. Fishes respire through gills, and birds/reptiles respire through lungs.

Answer: (c)

Inspiration in the mammalian lung occurs by means of negative pressure produced by contraction of the diaphragm. Thus, the pressure in the lungs falls below atmospheric pressure.

Answer: (d)

All the given statements are correct.

Answer: (a)

Answer: (d)

Answer: (a)

Oxygen-haemoglobin dissociation curve demonstrates a progressive increase in the percentage of haemoglobin bound to oxygen as blood $pO_{2}$ increases which is called percent saturation of haemoglobin. The total quantity of oxygen bound to haemoglobin in normal systemic arterial blood, which is 97 percent saturated, is about 19.4 milliliters per 100 milliliters of blood. While passing through the tissue capillaries, this amount is reduced, on average, to 14.4 milliliters (p$O_{2}$ of 40 mm Hg, 75 percent saturated 14.4 millititers (p$O_{2}$ of 40 mm Hg, 75 percent saturated haemoglobin). Thus, under normal condition,s about 5 milliliters of oxygen are transported from the lungs to the tissues by each 100 milliliters of blood.

Answer: (b)

Answer: (c)

Answer: (b)

Answer: (a)

Answer: (d)

Answer: (b)

Blood is the medium of transport for O₂ and CO₂ . About 97 percent of O₂ is transported by RBCs in the blood. The remaining 3 percent of O₂ is carried in a dissolved state through the plasma. Nearly 20-25 percent of CO₂ is transported by RBCs whereas 70 percent of it is carried as bicarbonate. About 7 percent of CO₂ is carried in a dissolved state through plasma.

Answer: (c)

About 70% of CO₂ released diffuses into the plasma and then into the RBCs. Here, it combines with water to form carbonic acid. Carbonic acid dissociates into bicarbonate and hydrogen ions. Hydrogen ions are picked up by proteins and a small amount of bicarbonate ions is transported in the RBCs, whereas most of them diffuse into the plasma to be carried by it. About 7% of CO₂ is transported as dissolved in plasma and 23% of CO₂ combines with Hb to form carbaminohaemoglobin.

$CO_2  + H_2 O  ⇌↖{carbonic}↙{anhydrase} H_2 CO_3(carbonic acid)$

$H_2 CO_3 ⇌ H^{+} +  HCO_3^{-}(bicarbonate ion)$

Answer: (a)

The correct labelling are: 1 - Lung, 2 - Diaphragm, 3 - Pleural membrane, 4 - Alveoli. Diaphragm is a dome-shaped muscular partition separating the thorax from the abdomen in mammals. It plays a major role in breathing, as its contraction increases the volume of the thorax and so inflates the lungs.

Answer: (b)

Answer: (b)

When the chest expands, stretch receptors in the lungs reflexly excite the expiratory center in the medulla which tends to produce expiration. Partial exhalation lessens the intensity of this reflex, allowing breath to be held for a longer time. Exhalation does not change the blood $CO_2$ concentration unless fresh air (low in $CO_2$) is brought into the lungs, allowing more $CO_2$ to diffuse out of the blood.

Answer: (c)

About 70% of carbon dioxide is transported as sodium bicarbonate.

Answer: (b)