A camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as "humps" on its back.
The two surviving species of camel are the dromedary, or one-humped camel (C.
Bactrian camels weigh 300 to 1,000 kg (660 to 2,200 lb) and dromedaries 300 to 600 kg (660 to 1,320 lb).
The male dromedary camel has in its throat an organ called a dulla, a large, inflatable sac he extrudes from his mouth when in rut to assert dominance and attract females.
It resembles a long, swollen, pink tongue hanging out of the side of its mouth.
Camels do not directly store water in their humps as was once commonly believed.
The humps are actually reservoirs of fatty tissue: concentrating body fat in their humps minimizes the insulating effect fat would have if distributed over the rest of their bodies, helping camels survive in hot climates.
When this tissue is metabolized, it yields more than one gram of water for every gram of fat processed.
This fat metabolization, while releasing energy, causes water to evaporate from the lungs during respiration (as oxygen is required for the metabolic process): overall, there is a net decrease in water.
Camels are able to withstand changes in body temperature and water consumption that would kill most other animals.
As the Pope ends his visit to Britain, historian Dr Thomas Dixon delves into the BBC's archive to explore the troubled relationship between religion and science.
From the creationists of America to the physicists of the Large Hadron Collider, he traces the expansion of scientific knowledge and asks whether there is still room for God in the modern world.
The relationship between science and religion has been long and troubled: from the condemnation of Galileo by the Catholic Church in 17th century Italy, through the clashes between creationism and evolution in 20th century America, right up to recent claims that the universe does not need God.