Haemoglobin are present in blood that makes it look like red in colour.

Blood is red coloured due to the presence of Haemoglobin.

Explanation:
Blood is a vital fluid in our body that carries oxygen and nutrients to different parts of the body and removes waste products. It consists of various components, including red blood cells (RBCs), white blood cells (WBCs), platelets, and plasma. The red color of blood is primarily due to the presence of a pigment called hemoglobin.

Hemoglobin:
Hemoglobin is a protein found in red blood cells that is responsible for the transport of oxygen from the lungs to different tissues and organs in the body. It also helps in carrying carbon dioxide, a waste product, from the tissues back to the lungs for exhalation. Hemoglobin contains iron atoms that bind to oxygen and give blood its red color.

Structure of Hemoglobin:
Hemoglobin is composed of four protein subunits, each containing a heme group. The heme group is a complex structure consisting of an iron ion (Fe2+) surrounded by a porphyrin ring. It is this iron ion that binds to oxygen molecules and gives blood its red color.

Interaction with Oxygen:
When oxygen is inhaled, it diffuses into the bloodstream through the lungs. It then binds to the iron ion in the heme group of hemoglobin, forming oxyhemoglobin. This oxygenated form of hemoglobin is bright red in color. As the oxygen-rich blood circulates through the body, oxygen is released from the hemoglobin and diffuses into the tissues. This results in the deoxygenated form of hemoglobin called deoxyhemoglobin, which is a darker red color.

Other Factors Influencing Blood Color:
Apart from hemoglobin, other factors can also affect the color of blood. For example, the presence of other pigments or chemicals can alter blood color. For instance, when blood lacks oxygen and has a high concentration of carbon dioxide, it appears dark red or even purple. Additionally, certain diseases or conditions can cause abnormal coloration of blood.

Conclusion:
In summary, the red color of blood is due to the presence of hemoglobin, a pigment found in red blood cells. Hemoglobin binds to oxygen and gives blood its characteristic red color when oxygenated. Understanding the role of hemoglobin in blood color is crucial in comprehending the vital functions it performs in our body.