JOURNEY THROUGH YOUR BLOOD VESSELS

Every cell in the human body requires oxygen to produce energy, but most of our cells cannot access it directly. A single-celled life form interacts directly with its environment, exchanging nutrients and waste products as required. But our ancestors gave up that lifestyle hundreds of millions of years ago when they evolved to become multicellular.

As multicellular life grew more sophisticated, our ancestors’ cells became specialised and compartmentalised. Then, many millions of years later, their descendants