99 Red Balloons
Dr Kelly Burrowes, Billy Bowman and Dane Gerneke
The human lung contains around 480 million alveoli. If these were laid flat, they would cover an area equivalent to around 20 king-sized beds. Alveoli are tiny balloon-like structures which bring air to and from the gas exchange surface.
This image was made using a scanning electron microscope using a small section of tissue from a rat lung.