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Red blood cells





Red blood cells transport oxygen for aerobic respiration.

They must be able to absorb oxygen in the lungs, pass through narrow blood vessels, and release oxygen to respiring cells. [1]

Adaptations for efficient diffusion of oxygen

Red blood cells have very thin cell membranes – this lets oxygen diffuse through quickly.

The cells themselves are thin, so there is only a short distance for the oxygen to diffuse to reach the centre of the cell.

The biconcave shape provides a large surface area compared to the volume of the red blood cell, allowing diffusion to happen efficiently. [3]







- they contain haemoglobin (a red protein that combines with oxygen)

- they have no nucleus so they can contain more haemoglobin

- they are small and flexible so that they can fit through narrow blood vessels

- they have a biconcave shape (flattened disc shape) to maximise their surface area for oxygen absorption [2]

Adaptations for efficient carriage of oxygen

Red blood cells do not contain a nucleus so they can contain more haemoglobin.

Oxygen combines with haemoglobin to form oxyhaemoglobin:

Oxygen binds reversibly to haemoglobin [4]

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