Blood makes up 7 per cent of the human body and the average person has five litres. Mammals' blood is always red due to the iron-based haemoglobin in red blood cells. The blood of most molluscs and a few arthropods has a blue tinge because it contains copper-based haemocyanin.
Log in or register for FREE to continue reading.
It only takes a moment and you'll get access to more news, plus courses, jobs and teaching resources tailored to you