Beyond the answers - interesting background to this quiz

The organ you can never take off

Skin is the body's largest organ by both weight and surface area, and it does far more than hold everything together. It regulates temperature through sweating and blood flow, blocks many pathogens and ultraviolet radiation, and contains nerve endings that let you feel pressure, heat and pain. It also produces vitamin D when exposed to sunlight, which is why a little time outdoors matters for more than just mood.

Why gold hides behind two Latin letters

The symbol Au for gold comes from the Latin word aurum, and it is one of several element symbols that refuse to match their English names. Iron is Fe, from ferrum, and lead is Pb, from plumbum - the same root that gave English the word plumbing, since Roman pipes were made of lead. These odd-looking symbols are a small reminder that chemistry's vocabulary was built on Latin long before it was built on English.

A mountain range that runs along an entire continent

The Andes stretch roughly 7,000 kilometres down the western edge of South America, crossing seven countries from Venezuela to Chile. Their height and length create wildly different climates along the way: snow-capped peaks, high-altitude plateaus and dry desert slopes can all sit within a short distance of each other. The range is also geologically young and still growing, pushed upward by the collision of tectonic plates.

A moon that out-volcanoes every planet

Jupiter's moon Io is the most volcanically active body in the solar system, with hundreds of volcanoes and lava flows reshaping its surface constantly. The activity is driven by gravitational tug-of-war: Jupiter's immense pull, combined with the influence of nearby moons, squeezes and flexes Io's interior, generating intense heat. That is why Io looks blotchy and colourful rather than cratered like our own Moon.

A tower that was never meant to last

The Eiffel Tower was completed in 1889 as the entrance arch for the World's Fair, marking the centenary of the French Revolution. Many Parisians initially hated it, and the plan was for it to be dismantled after twenty years. It survived largely because its height made it useful for radio and telegraph antennas - a practical second life that turned a temporary exhibit into the city's most recognisable symbol.