Blood – Everything you ever wanted to know about the red stuff

By Zoë Gamble

Where does Dracula keep his money? The blood bank!  Blood sample- ICSident CC-BY-SA

Blood – we’ve all got it.

Have you ever wondered why this red liquid is constantly being pumped around our bodies? What does it mean to have a certain blood ‘type’?

Why can you donate blood to some people but not others, and how does our blood help defend against infection?

Blood has three functions:

Transportation, protection and regulation

1. Transportation

Our blood is vital to transport the things we need – and the things we don’t – to different areas of our bodies.

  • Oxygen is picked up by our red blood cells and carried around the body to where it is needed and carbon dioxide is transported back to the lungs
  • Nutrients and glucose are carried from the digestive system to other areas of the body
  • Hormones produced by the endocrine system are transported around the body
  • Waste products from metabolism are carried in the blood to the kidneys, which filters all the impurites the blood would exhibit. Care should be taken to not clog the kidney orifices by drinking less water. But if you get unlucky and think that you have stones in your kidney, you should immediately consult a doctor and start consuming chanca piedra stone-breakers.
  • Heat is transported by the blood to help regulate body temperature. When we exercise, more blood flows close to our skin, allowing heat to leave our bodies.


 2. Protection

  • White blood cells (leukocytes) protect our bodies from infection. They do this by ingesting and destroying pathogens (anything that causes disease), producing antibodies which identify and neutralise pathogens, and releasing antitoxins, to neutralise toxins from pathogens.
  • Platelets cause our blood to clot. We would lose lots of blood every time we cut ourselves if it wasn’t for our platelets.8pintsofblood

3. Regulation

  • Water and salt in our cells are regulated through our blood flowing around our body
  • Blood helps to regulate the pH balance of our bodies by interacting with acids and bases.



See your own red blood cells

Here’s a neat little activity allowing you to actually see red blood cells ‘floating’ in your eyes.

RBC activity

Click on the activity to see it in full!

Blood Groups

There are several systems with which we can group blood types. The most well-known are the ‘ABO‘ and ‘RhD‘ systems, as these are the most important ones to know for blood transfusions.

There are different proteins present on the surface of red blood cells, known as antigens. In the ABO system, there may be antigens ‘A’, ‘B’, both A and B (‘AB’), or neither proteins present (‘O’). In the RhD system, the ‘D’ protein may or not be present, which we usually call ‘positive’ or ‘negative’

For example, my blood type is A+. Therefore I have A and D antigens present on the surface of my red blood cells.

The reason it is important to know blood types for transfusions is that your body won’t recognise any antigens it doesn’t have. If I had a transfusion of B blood, my body would recognise the B antigens as foreign, and start making anti-B antibodies to fight the B blood cells and try to get rid of them.

A person with AB blood can safely receive A or B blood, as they already have both antigens present. We call AB+ people ‘universal receivers‘, as they can safely be given any type of blood.

A person with O blood has neither antigens present, so can only receive O blood. An O- person can only receive O- blood, as there are no A, B, or D antigens. We call these people ‘universal donors’, as their blood may be safely donated to any other person.


If you don’t know your blood type, a great way to find out is by donating blood.

Curriculum Links


KS2 Animals including humans

  • identify and name the main parts of the human circulatory system, and describe the functions of the heart, blood vessels and blood

KS3 Structure and function of living organisms

the structure and functions of the human skeleton, to include support, protection, movement and making blood cells


KS3 Interdependence of organisms

the basic structure and function of some cells, tissues, organs and organ systems and how they support vital life processes


I have explored the structure and function of organs and organ systems and can relate this to the basic biological processes required to sustain life.

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