Haemoglobin is an important pigment and protein component of which part of the blood?

Introduction / Context:
Blood is a complex connective tissue composed of cells suspended in plasma. Among these cells, red blood cells play a central role in transporting oxygen from the lungs to tissues and carrying carbon dioxide back to the lungs. Haemoglobin is the iron containing pigment and protein that makes this gas transport possible. Understanding where haemoglobin is located within the blood is essential in physiology and medicine, especially when interpreting conditions like anemia or polycythemia. This question asks you to identify which component of blood contains haemoglobin as an important part.

Given Data / Assumptions:
• The options are white blood cells, red blood cells, plasma, and all options combined. • The focus is on the main location of haemoglobin in the blood. • Standard composition of blood is assumed.

Concept / Approach:
Haemoglobin is a conjugated protein with iron and is found inside red blood cells (erythrocytes). It binds oxygen in the lungs and releases it in tissues, and also helps transport some carbon dioxide. White blood cells are involved in immune defense and do not primarily contain haemoglobin. Plasma is the liquid component of blood containing water, electrolytes, proteins like albumin and globulins, but not haemoglobin as a major constituent. Therefore, haemoglobin is an important component specifically of red blood cells.

Step-by-Step Solution:
Step 1: Recall that red blood cells are responsible for oxygen transport in the body. Step 2: Remember that haemoglobin is the pigment that binds oxygen and gives red blood cells their characteristic colour. Step 3: Recognize that white blood cells have nuclei and are involved in immune responses, not in oxygen transport. Step 4: Note that plasma is the fluid portion of blood and does not primarily contain haemoglobin. Step 5: Select red blood cells as the component of blood in which haemoglobin is an important constituent.

Verification / Alternative check:
Laboratory tests such as haemoglobin concentration and haematocrit are used to evaluate red blood cell status. When red blood cell count is low or haemoglobin content is reduced, conditions like anemia are diagnosed. These tests and clinical interpretations consistently link haemoglobin with red blood cells, not with white blood cells or plasma. This supports red blood cells as the correct answer.

Why Other Options Are Wrong:
Option A (White blood cells) is incorrect because these cells are primarily linked to immunity and do not contain large amounts of haemoglobin. Option C (Plasma) is incorrect because plasma contains proteins such as albumin, globulins, and fibrinogen, but haemoglobin is not a major plasma protein. Option D (All options are correct) is incorrect because haemoglobin is specifically concentrated in red blood cells and is not a common component of all blood parts.

Common Pitfalls:
Students sometimes choose all options if they think that a small amount of haemoglobin might be present outside red blood cells. However, in standard physiology, haemoglobin is almost entirely contained within red blood cells. Remember that anaemia, which involves low haemoglobin, is primarily a disorder of red blood cells, emphasizing their central role in oxygen transport.

Final Answer:
Haemoglobin is an important component of red blood cells.