... 120 days and are about 7mm in diameter. Red blood cells have a biconcave disc shape and have a large surface area to volume ratio. Oxygen can therefore diffuse very quickly into the cell and because the cell is so small, quickly bind to a haemoglobin molecule. They lack organelles means that there is more room for haemoglobin. Their size and flexible membrane also means that they can squeeze through capillaries and transport oxygen extremely close to cells. Another is type of cell is called white blood cells. These cells all have a nucleus and most are much larger than red blood cells and are spherical or irregular in shape. There are two basic types of white blood cells; the granulocytes with granular cytoplasm and lobed nuclei and agranulocytes which have smooth a cytoplasm and the nucleus is rounded or horseshoe in shape. There are three different types of granulocytes; neutrophils, eosinophils ...

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