Respiration and Gas Transport

Oxygen is the gas which makes the most stable combination with RBC haemoglobin.

Cellular (internal) respiration refers to gas exchange between blood and tissue fluid, where oxygen diffuses from blood into tissues and carbon dioxide moves from tissues into blood. External respiration is lung alveoli-capillary exchange. Tissue respiration is cellular metabolic processes. Option C accurately describes blood-tissue fluid gas exchange.

At high altitudes, decreased atmospheric oxygen partial pressure triggers increased erythropoietin production, which stimulates red blood cell (RBC) production in bone marrow. This adaptive response, called polycythemia, improves oxygen-carrying capacity. The RBC count increases, not the size. Options C and D are incorrect as RBC count increases, not decreases. Size changes are not the primary adaptation.

Oxyhaemoglobin releases oxygen in tissues because tissue cells are constantly consuming oxygen for cellular respiration, creating a low partial pressure environment (low pO2) that favors dissociation. This oxygen delivery mechanism is essential for supplying oxygen to metabolically active tissues.

Carbon monoxide reduces the oxygen carrying capacity of the blood.

Iron in haemoglobin is in the ferrous state (Fe2+), which allows oxygen binding. The Fe3+ (ferric) state found in methemoglobin cannot bind oxygen. The ionic/unionic terminology is not standard; Fe2+ is the correct notation.

Lymphatic vessels collect interstitial fluid (fluid that leaks out of blood capillaries into tissue spaces) and return it to the bloodstream via the thoracic duct and right lymphatic duct. Lymph does not transport CO2 or O2 - those functions are performed by blood. Lymph nodes contain lymphocytes, not RBCs.

RBCs take glucose through facilitated diffusion and not by active transport.

RBCs take glucose through facilitated diffusion and not through active transport.

These compounds are synthesised in normoblastic stage of developing red blood cells. Two molecules of succinyl CoA and two molecules of glycine combine to form a pyrolle ring. Four pyrolles combine together to form protoporphyrin IX. Protoporphyrin IX combines with iron and polypeptide chain to form haemoglobin chain. Four such haemoglobin chains make up haemoglobin molecule.

Carbogen is a mixture of carbon dioxide and oxygen gas. 

Nitrogen fixation in legume root nodules is performed by bacteria like Rhizobium, which require oxygen-free conditions. The enzyme nitrogenase that fixes nitrogen is inhibited by oxygen. Respiration, combustion, and fossil fuel burning all require oxygen to proceed, while ozone formation involves oxygen reactions.

Heme oxygenase is the enzyme that catalyzes the first step in heme degradation, which is the oxidation of the methene bridge between the pyrrole rings. This cleavage produces biliverdin, free iron, and carbon monoxide (not carbon dioxide). The enzyme does require molecular oxygen for its activity, but option A describes the core catalytic function more specifically.

This is correct. RBCs carry oxygen oxyhaemoglobin and plasma carries carbon dioxide as bicarbonate ions.

Hemoglobin in red blood cells binds to oxygen in the lungs and transports it throughout the body to deliver oxygen to tissues. Nitrogen is mostly inert and is not transported by hemoglobin. Helium is a noble gas with no biological transport role. Hydrogen is not a physiological gas transported in blood.