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Science Decoded: What Makes Blood Red?

Team StoryWeavers|June 09, 2022, 10:35 IST| 23

Hello, young learners, It’s me Kiki, and I am back with another episode of Knowledge Corner. I want to thank you for the enthusiasm that you showed for our post on Goosebumps. That made me think: how do we make this episode much more fun and enriching? 

Yesterday, I was playing with my friends Jax and Jane, when I had a fall and hurt my knee. It began to bleed. After bandaging my wound, I began wondering – Why is our blood red?

When I began exploring answers, I got really fascinated by the science behind how blood got its colour!  I can’t wait to share what I learnt with you. Before we get into it, let us first understand what blood is and what it does.

What is blood?

 Blood is a fluid that circulates inside the body in tubes called blood vessels. Around five litres of blood flow inside a human body. It’s red in colour and performs a very important function –  transporting oxygen and nutrients to our internal organs, such as the brain, skin, lungs, etc. The components in the blood help you fight diseases. It is one of the most important fluids present inside humans and other animals. 

And when you fall or get hurt, these blood vessels on the skin rupture and you begin to bleed. Blood oozes out of the place where you are hurt and once you finish the first aid, the wound closes up and you stop bleeding.

Your blood vessels rupture when you fall down

Why is blood red?

Human blood contains blood cells – red blood cells, white blood cells, platelets and a fluid called blood plasma. The name ‘red’ blood cells is an easy giveaway. Yes, the blood is red in colour because of these cells. However, why are these cells red? 

The red blood cells contain a component called haemoglobin (say hee-mo-glo-bin), which is rich in iron. And when the red blood cells transport oxygen inside them, the iron in the haemoglobin mixes with oxygen. It is a chemical reaction (You will learn more about chemical reactions in science later in school). When this chemical reaction happens, the colour of the blood becomes red!

That’s how blood gets its red colour!

Blood is red because of the red blood cells

Wait, but that’s not all! You must be wondering: what about the white blood cells and platelets? Don’t they lend any colour to blood?  Although white blood cells and platelets are present in the blood, the red blood cells are so much more in number. Imagine this: in one drop of blood, there are more than a million red blood cells, while there are only around a few thousand white blood cells and even fewer platelets. For every white blood cell, there are 1000 red blood cells. And that’s why it seems mostly red. 

Do animals have red blood too?

We have mentioned earlier that humans and animals have blood. This brings us to the next question: Do animals have red blood? Do their cells have haemoglobin too? A lot of animals have red blood, because of the presence of haemoglobin. However, some octopuses and spiders have blue blood. They have a component called hemocyanin, which is rich in copper. When the chemical reaction with oxygen happens, the blood becomes blue!

For some lizards, the blood is green because of a component called biliverdin. In short, most animals have red blood, with the exception of a few. Fascinating, isn’t it?! Here are some interesting facts about blood that you may not know about.

I hope you had a good time understanding how our body’s important fluid gets its colour. What more about the human body would you like to learn? Share your answers in the comments.

Liked this blog? Also read

Why do we eat food?

Why do we see stars at night?

About the Author

Aparna is a mom, singer and dreamer. At BYJU'S, she writes stories about learning for children. She believes in the power of music, especially ghazal, the magic of the universe and happy learners. When not writing or singing, you will find her intensely engaged in conversations about life and the power of words.

Leave a Comment




April 19, 2022

Interesting facts Kiki

Vishal Singla

March 27, 2022

It’s so fascinating to know the facts about our human body. Keep creating these stuff. My daughter really astonished as she is wondering that it is real thing?

Aashish Singh

March 23, 2022

Really amazing

shalvi sinha

March 21, 2022

Very nice
Very effective

shalvi sinha

March 21, 2022

Very nice
Very effictive

Aditya Panda

March 21, 2022

thanks kiki..have a great day


March 20, 2022

Very Interesting Facts explained in simple way

Arushi Dey

March 20, 2022

very nice. Thanks


March 19, 2022

Yes,I like to learn things like this

Yash Mondal.

March 19, 2022

I love byju’s.????????❤️❤️❤️❤️

Rahmath Aafiya

March 17, 2022

It is very nice and useful also.

Sunil Kumar Sahu

March 17, 2022

It’s really very much informative and interesting too. Thank you so much. Please keep going.


March 16, 2022

very useful information, thank you

Aksharaasree Raviram

March 16, 2022

Usefull information

Laya M

March 16, 2022

I love this concept of why blood is red in color.

I also like to know why do children get more coughs and colds?

Ila Sharma

March 16, 2022

Very nice thanks ma’am

Fatemah Zahra

March 16, 2022


Sree Harcitha

March 15, 2022

Very useful information.

Brijeet kundu

March 15, 2022

Very nice
Very effictive


March 15, 2022

How muscles are formed


March 15, 2022

Very nice


March 15, 2022

science class

Atul Amol garad

March 15, 2022



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