In this module, you will learn:

  • state that the main function of blood
  • identify the components of blood and their function

Resources to help you:

  • Textbook: page 42, 43 and 44
  • Notebook: page 11

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Learn about the components of the blood


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What is the function of blood?


Our body contains about 5 litres of blood. It has a very important function.

The function of the blood is to transport (carry) useful substances such as food (nutrients) and oxygen and removes waste products such as carbon dioxide.

Remember that in respiration, our body uses oxygen and food to give us energy, and produce carbon dioxide, which is a waste product.

A nurse drawing blood from patient

Credit: @photovs via Twenty20

Components of Blood

There are four main components of blood:

  1. Red blood cell
  2. White blood cell (Leukocytes)
  3. Plasma
  4. Platelets

Scanning electron micrograph of blood cells. From left to right: human red blood cell, platelet, white blood cell.

Credit: @NCI-Frederick via Wikipedia CC0

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See how oxygen is transported around the body


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Blood Cells photographed using a microscope

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Group of red blood cells

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Red Blood Cells


Red blood cells are important for their function in transporting oxygen throughout the body. They contain haemoglobin that gives it its red colour.

To help to red blood cell to allow it to transport more oxygen, it has a biconcave shape to increase its surface area.

Note: Biconcave means the red blood cell has a concave shape on both sides.

White Blood Cells


White blood cells are larger than red blood cells. There are also less white blood cells. The function of the white blood cell is to protect the body against infections and diseases.

There are different types of white blood cells. Some release chemicals to destroy bacteria or virus, while some engulfs them.

Immune Cells Eating Bacteria (Phagocytosis)


Blood separated into its components through centrifuging

Credit: @Flydragonfly via Depositphotos



Plasma is made up of mostly water. It is a light yellow liquid.

Many substances are dissolved in it, such as nutrients and carbon dioxide.

Red blood cells, white blood cells and platelets are suspended in plasma.



Platelets is much smaller than the red blood cell or the white blood cell. Less than 1% of the blood is made up of platelets.

The platelets' function is to stop bleeding by allowing the blood to clot. . When there is a cut on your skin, these platelets will group together and form a barrier to prevent the loss of blood.

Platelets in a Giemsa-stained blood film

Credit: Graham Beards via Wikipedia CC BY-SA4

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Learn how blood clots


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