Why is Blood Red?

We all know that the colour of human blood is red. But have you ever wondered what makes our blood look red. To know this we should be aware of the components of blood.


Main Components of Blood

The main components of blood are:

  • Plasma
  • Red Blood Cell (RBC)
  • White Blood Cell (WBC)
  • Platelets

1. Plasma

  • Plasma constitute about 55% of portion in blood. Basically it is a liquid part of blood in which blood cells float.
  • The main function of plasma is to carry essential body elements such as nutrients, hormones and proteins to different part of body.
  • It also helps cell (the smallest unit of human body) to discard their waste product in plasma.
  • Plasma also helps blood cells to reach different organ.

2. Red Blood Cell (RBC)

  • Red Blood Cells are the second largest component of human blood.
  • The red colour of blood comes due to the presence of  this cell.
  • Red blood cell consist of a component called haemoglobin.

  • Haemoglobin are iron rich protein compound of RBC. Hemoglobin carries an 3 essential compound called Heme that is red in colour and mainly responsible for red colour of blood.
  • The main function of RBC is to carry oxygen from lungs through the help of haemoglobin to other parts of human body and to carry back carbon dioxide to lungs to be removed from body by the help of respiratory system.
  • Red blood cells are also called as “Erythrocytes” (erythro- red in Greek, cyte- cell).

3.White Blood Cell (WBC)

  • WBC consist of about just 1% of blood components.
  • They are also called as “leukocytes”(leukos- white in Greek, cyte-cell).
  • Their main function is to fight against any infection or foreign body in simple words they protect human body against different kind of disease.
  • They are responsible for the immunity of body or can also be consider as immune cell. There are five different type of white blood cell named as monocytes, lymphocytes, neutrophils, basophils, eosinophils.


  • Platelets are also called as “thrombocytes” ( thrombos- thick drop/ clot in Greek, cyte-cell).
  • Platelets are the small, colourless fragments in our blood.
  • They are mainly responsible for the blood clotting to prevent excessive bleeding.

Why is Blood Red?

The blood without RBC will not be red. And the red colour is due to compound called heme present in Hemoglobin. It is iron rich compound and hence iron is indirectly responsible for red colour of blood.

Fun Facts

  • It takes around 20 seconds for blood to travel around the entire body.
  • Do you know, human blood also contains about 0.2 milligrams of gold!

Related Questions

  1. Why do Veins Look Blue?
  2. Does all animals have red coloured blood?
  3. How blood is produced in the body?
  4. What is the difference between arteries and veins?

True or False

  1. Human Blood is red in colour (True/False)
  2. Plasma is responsible for the red coloured blood (True/False)
  3. Red Blood Cell are also called as leukocytes (True/False)
  4. White blood cells helps in fighting against infection (True/False)
  5. Platelets are big, coloured fragment portion of our blood (True/False)

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