How to work with the Circulatory System: Part 2

Did you know that the blood of different animals can be different colours. Pigments and proteins found in the blood cause the different colours, which help the animals survive in different conditions.

Animals like the large Antarctic octopus, living in very cold water, have light blue blood. They have lots of haemocyanin, a copper based protein which is blue. The haemocyanin helps the blood to take in oxygen at low temperatures. Not only do octopuses have blue blood, but they also have three hearts. One of these circulates oxygenated blood around the body. While the other two pump it to the gills to absorb oxygen from water. As haemocyanin is not as efficient as haemoglobin at carrying oxygen, the octopus has evolved three hearts to compensate for this.

Spider blood is also pale blue. Spiders use blood pressure to shed their old skin as they grow. Unlike us, they have an open circulatory system, meaning their blood ( or haemolymph) is not contained in vessels. Instead it directly bathes their organs and tissues. This assists them in movement. Their haemolymph generates hydraulic pressure, which alongside muscle contractions. forces their legs outwards. When they walk or jump, this pressure increases, allowing them to extend their legs quickly.

Some animals, like the peanut worm have purple blood! The protein hemerythrin, which transports the oxygen, is colourless until it combines with oxygen and  then it turns purple. The protein also helps worms regenerate parts of their bodies if they get cut off.

Also there are animals with green blood – these are usually lizards and worm like animals. A pigment called biliverdin makes the blood green. It can also turn your skin green if you are wounded!