What is it in our blood that makes it red, and why are other animals different?
Haemoglobin is the most efficient oxygen carrier and provides the red pigment in blood.
Not all animals have red blood.
The horseshoe crab has blue blood because its oxygen carrier, haemocyanin, contains copper.
Deep sea worms' oxygen-carrying molecule is hemerythrin, which has a pink pigment.
We all know human blood is red.
And we also know it does a brilliant job delivering oxygen throughout our bodies.
You may think all animals have red blood too. But some don't. What makes their blood colour different from ours?