Why do you think the blood in the system is labelled with two different colours?

The blood in the system is typically labelled with two different colours, red and blue, to indicate the level of oxygen in the blood.

1. Red represents oxygenated blood: This is blood that has passed through the lungs and picked up oxygen. It is bright red in colour and is carried from the heart to the rest of the body through the arteries.

2. Blue represents deoxygenated blood: This is blood that has delivered its oxygen to the body's tissues and has become dark red or bluish in colour. It is carried from the body back to the heart through the veins.

This colour coding helps in understanding the functioning of the circulatory system and the process of oxygenation and deoxygenation of blood.