A mature human red blood cell
- A. has no nucleus and is biconcave in shape
- B. has a large nucleus and many mitochondria
- C. is amoeboid and can leave the capillaries
- D. lives for about ten days
Explanation
Losing the nucleus makes room for more haemoglobin, and the biconcave disc shape gives a large surface area for gas exchange and enough flexibility to squeeze through capillaries. Having no mitochondria means the cell cannot use the oxygen it carries. Its life span is about 120 days, after which it is broken down in the liver and spleen; white cells, not red, can squeeze out of capillaries.
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