Red Blood Cells

The human body contains more red blood cells than any other cell. A single drop of blood contains millions of red blood cells that are constantly travelling through the body delivering oxygen and removing waste. Each cell has a lifespan of about 120 days so the body is constantly producing new ones to replace the ones that have died or been lost from the body.
Red blood cell are also known as erythrocytes. Each of the cells has a unique appearance, they are thinner in the centre and thicker on the edges. This makes the cell really flexible and allows it to twist and bend around blood vessels. Their small size and strange shape makes them ideally suited for gaseous exchange.
Erythrocytes are red in appearance because they carry a substance called hemoglobin. This combined with oxygen makes the cell become bright red in colour.
Red blood cells contain no nucleus, by having no nucleus the cells are more efficient transporters of oxygen.

If you were to look at a droplet of blood under a microscope you would be able to see smooth disc shaped red blood cells, white blood cells and platelets.