Question

……….is the respiratory pigment which carries oxygen in the blood.
a. Myoglobin
b. Bilirubin
c. Biliverdin
d. Hemoglobin

Answer 1

Hint: It is an iron-containing protein present in red blood cells. It is made up of four globular protein subunits and mainly found in humans and other vertebrates.

Complete answer
Hemoglobin is a respiratory pigment that has oxygen-carrying capacity in the blood, tissues, and other organs. It carries oxygen from the lungs to the body's tissues and takes carbon dioxide from the tissues back to the lungs. Hemoglobin has a quaternary structure consisting of many multi-subunit globular proteins. It has a heme group that consists of an iron ion held in a heterocyclic ring, called as a porphyrin

Functions of hemoglobin:
- Hemoglobin in blood transports oxygen from the lungs to the other parts of the body.
- It releases the oxygen to allow aerobic respiration to provide energy to power the functions of the organism in the process called metabolism.
- A healthy person has approximately 12 to 20 grams of hemoglobin in every 100 ml of blood.
- Hemoglobin molecules bind up to four oxygen molecules.
- It is also found in other cells like macrophages, alveolar cells, hepatocytes, etc. where it performs the non-oxygen-carrying function as an antioxidant and a regulator of iron metabolism.
- Deoxygenated hemoglobin is paramagnetic that is weakly attracted to magnetic fields.
- Carbon monoxide (CO) affects the binding of oxygen.

So, the correct answer is ‘Hemoglobin’.

Note: Leghemoglobin is a variant of the hemoglobin which is used to scavenge oxygen away from anaerobic systems. It is present in nitrogen-fixing nodules of leguminous plants.
Hemocyanin is the second most common oxygen-transporting protein found in the blood of many arthropods and mollusks.