Curious Kids: why is blood red?

Why is blood red?

– Asher, 6 years 11 months, New South Wales

What an incredible query about something in our body, Asher.

Blood is inside our body, but we see it on the skin after we bleed, like after we get a cut or a nose bleed.

Blood is red due to something called haemoglobin. Haemoglobin is red and this makes our blood red.

But what’s haemoglobin for? Well, we’d like haemoglobin to hold oxygen in our blood.

This might sound a bit complicated, so let’s look more closely at why we’d like oxygen, and why we’d like haemoglobin to hold oxygen in our blood.

Everyone needs oxygen to remain alive

We need oxygen for our body to work.

Our body is made up of tens of millions and tens of millions of tiny cells. All the cells in our body need oxygen from the air we breathe and nutrients from the food we eat.

Cells use oxygen and nutrients to make energy so that they can do their job. For example, cells in our muscles need energy to maneuver us, and our brain cells need energy so we will learn.

Every time you are taking a breath in, you breathe oxygen into your lungs. Our heart pumps blood to the lungs to select up this oxygen.

The heart then pumps the blood with this oxygen to all our body’s cells.

After the blood drops off oxygen for the cells to make use of, it travels back to the guts and lungs to select up more oxygen again.

Our cells need oxygen on a regular basis because they’re all the time working.

So where does haemoglobin are available in?

Oxygen travels in blood to our cells in tubes called blood vessels. But oxygen doesn’t dissolve thoroughly in blood.

If we just had oxygen by itself in our blood, we could get air bubbles. These bubbles would persist with the perimeters of the blood vessels. This means the oxygen could get stuck and never travel to our cells.

Luckily, haemoglobin carries oxygen in our blood so it doesn’t form air bubbles and get stuck.

We can consider this like attempting to move a stone down a river. A stone can’t float down a river since it will sink to the underside. But if we put the stone in a container that floats, the container can float down the river and carry the stone with it.

Haemoglobin is sort of a red colored container for oxygen. It’s our oxygen carrier.

So, because we have now red haemoglobin in our blood to hold oxygen, our blood is red.

Blood could be vivid red or dark red

When haemoglobin carries more oxygen, it’s a brighter shade of red.

This means blood travelling from the guts and lungs to the cells with plenty of oxygen is vivid red.

After haemoglobin drops off its oxygen to the cells, it’s a dull, dark red. This means blood travelling back to the guts and lungs with less oxygen is darker red.

We can see a few of our veins (the blood vessels that carry blood back to the guts) just below our skin. For example, on the back of our hands.

The blood in these veins can appear a green-blue color. That’s because we’re this blood through our skin. This changes what color we see.

But we all know after we bleed, our blood isn’t blue or green – it’s definitely red.

Not all animals have red blood

An octopus can have blue blood and a few lizards even have green blood.

This blue and green blood can also be due to the color of their oxygen carrier. These animals don’t have red haemoglobin like we do. They have a blue or green oxygen carrier. This makes their blood blue or green.

If you would decide to have blood of any color, what color would you select?

Hello, curious kids! Do you could have a matter you’d like an authority to reply? Ask an adult to send your query to curiouskids@theconversation.edu.au