I do not know how much information you need, so I will give as much as an High School student in UK would need to know.
-They contain haemoglobin (contains Iron, which gives it it's red colour) which binds to oxygen so that red blood cell can carry it around the body.
-They have no nucleus so there is more space for haemoglobin.
-Red Blood cells have biconcave shape to increase their surface area.
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