Respiration and Gas Transport

Hemoglobin (Hb or Hgb ) is an iron-containing protein present in erythrocytes or Red blood cells(RBC) of almost all vertebrates. Each hemoglobin is made up of 4 subunits, 2 alpha subunits and 2 beta subunits. Each subunit surrounds the central heme group that contains iron and binds to one oxygen molecule. Hence each hemoglobin molecule can bind to four oxygen molecules. It carries oxygen from lungs to tissues. It also helps in the transportation of carbon dioxide, hydrogen ions back to the lungs from the tissues. Hence haemoglobin in the RBCs helps in the transport of oxygen and carbon dioxide.

A single haemoglobin molecule contains four haem groups, each capable of binding one molecule of oxygen, allowing a total of four oxygen molecules to be carried per haemoglobin molecule.

Carbon monoxide binds to haemoglobin with much higher affinity than oxygen, forming carboxyhaemoglobin. This effectively reduces the amount of free haemoglobin available to transport oxygen.

It is a standard physiological constant that 1 gram of pure haemoglobin can bind approximately 1.34 mL of oxygen when fully saturated.

(b) To maintain electrostatic neutrality of plasma, many chloride ions diffuse from plasma into RBCs and bicarbonate ions pass out. The chloride content of RBCs increase when oxygenated blood become deoxygenated. This is termed as chloride shift or Hamburger phenomenon.

While plasma carries some dissolved oxygen, the vast majority of oxygen transport in the body is carried by the blood, specifically within the red blood cells via haemoglobin.

(d) One molecule of the haemoglobin has 4 haem groups and each of them is capable of taking up one molecule of $O _2$ .

Haemoglobin is the primary protein in red blood cells responsible for binding and transporting oxygen throughout the human body.

The sequence is: P (CO2 absorption), Q (formation of H+ and HCO3- in RBC via carbonic anhydrase), and S (H+ ions bind to HbO2, causing the release of O2 via the Bohr effect).

Hemoglobin is a protein found in red blood cells that carries oxygen throughout the body. It is a vital component of human blood.

Earthworms perform cutaneous respiration, meaning they exchange gases through their moist skin.

Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood. A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs per cubic mm of blood. RBCs are formed in the red bone marrow in the adults. RBCs are devoid of nucleus in most of the mammals and are biconcave in shape. They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells. These molecules play a significant role in transport of respiratory gases like oxygen and carbon dioxide.

Monocytes are a type of white blood cell that can differentiate into macrophages and are known to store and release serotonin, especially during inflammatory responses.

Brain cells are extremely sensitive to a lack of oxygen. Some brain cells start dying less than 5 minutes after their oxygen supply disappears. As a result, brain hypoxia can rapidly cause severe brain damage or death. 

Oxygen makes up approximately 21% of Earth's atmosphere by volume, making 20% the closest correct answer among the options. Nitrogen is the most abundant gas at about 78%.