What is Blood composed of?

What is blood? Why is it red in color? What constitutes blood? What are enzymes? These are a few of the questions we would have asked at some point while growing up. Before understanding about the composition of blood, let us first try to understand basics about blood.

What is blood?

Blood is a liquid or fluid which circulates in our body and gives life to us. It is a connective tissue and provides our organs with oxygen which is essential for its functioning and takes away carbon dioxide which is given out by organs. Approximately 8% of the adult human body is constituted by blood. Female body contains around 4-5 litres of blood while a male body has around 5-6 litres mainly because they differ in the way we are built. Its average temperature is around 38 C with a pH level of 7.35-7.45 which is why it is slightly basic in nature. Blood is able to flow in our bodies because it is more viscous than water. This is vital in the functioning of blood, as it can affect the heart severely if the flow is too easy or with too much resistance.

Why is blood red in color?

Blood consists of a pigment called haemoglobin. This consists of subunits called hemes, hemes interacts with iron molecules which in turn interact with oxygen. This interaction which happens between iron molecules and oxygen causes blood to be red. Have a look at the sequence below to get a better understanding

Haemoglobin> Subunits-Hemes> Iron molecules – Oxygen (Interaction) 

After knowing about blood and why it is red in color, let us now understand about what is inside blood furthermore.

Composition of blood

Blood is composed of 4 basic components:

1. Red Blood Cells

Shortened as RBCs, constitutes for about 45% of the volume of blood. They are produced by bone marrow continuously every 120 days.

2. Platelets

These tiny disc-shaped blood cells are one of the most fascinating parts of our body. These cells keep a check on blood flow whenever we get hurt resulting in blood oozing out from a spot. These cells have the power to control and prevent blood flow. 

3. White Blood Cells

WBCs also known as leukocytes constitutes 1% of our blood, but that does not make them less important. They play a vital role in fighting against illness and is responsible for maintaining our immunity levels. They too are generated by bone marrow and flows in the bloodstream.


The largest component of blood, Plasma makes up for around 50% of blood. The liquid state of blood is because of this component. It is typically pale yellow in color when segregated from other components of blood. Contains hormones, salts and other enzymes apart from water, and transports this to different tissues of the body.

Role of enzymes in blood

Molecules of proteins in cells that act as catalysts are enzymes. Enzymes are present in every cell, every organ of our body through blood and are very important as they are responsible for bringing about chemical reactions. Following are the functions of an enzyme:

  • They act on molecules called substrates to give different molecules called products.
  • Increases the rate at which a reaction takes place
  • Aids in bringing about the digestion process by breaking up food we eat
  • Helps in clotting of blood
  • Keeping a check on enzyme levels can help diagnose various conditions

Whenever there is an abnormality of any sort in our body, enzymes are released in the blood. This is how we detect and diagnose various diseases in our body.

These were some amazing facts about blood, hope this information cleared all your doubts on blood which you had before you started reading this article. To know more about such interesting topics like the composition of blood, subscribe to BYJU’s YouTube channel. 0