Beyond the answers - interesting background to this quiz

A capital with a very long memory

Damascus is often described as one of the oldest continuously inhabited cities in the world, and it has served as a capital for far longer than modern Syria has existed. It was the seat of the Umayyad Caliphate in the seventh and eighth centuries, when it was one of the most important cities in the Islamic world. Aleppo, the country's other great historic city, is also ancient, which is why the two are so often confused in quizzes like this one.

The physician who corrected a 1,400-year-old mistake

William Harvey's 1628 work on the circulation of blood is one of the landmarks of medical science. The idea that blood circulates - pumped by the heart and returning to it - contradicted the teaching of Galen, which had dominated medicine since antiquity. Harvey reached his conclusion through dissection and experiment, and it took time for the medical establishment to accept it.

Why tungsten hides behind a W

The chemical symbol W for tungsten comes from wolfram, the name the element carries in German and several other languages. Tungsten sits in the same group of the periodic table as chromium and molybdenum, and it has the highest melting point of any metal. That property is why it was long used for light bulb filaments, and why it still appears in high-temperature and cutting tools.

Vitamin K and the bacteria inside us

Gut bacteria synthesise vitamin K, which the body needs for blood clotting. That is one reason newborns, whose intestinal flora is not yet established, are often given vitamin K shortly after birth. Vitamin K is also found in green leafy vegetables, so deficiency is rare in adults eating a varied diet.

The Amazon and the scale of a watershed

The Amazon has by far the largest drainage basin of any river, gathering water from parts of Brazil, Peru, Colombia, Bolivia, Ecuador, Venezuela and the Guianas. Its outflow is so vast that it measurably dilutes the Atlantic Ocean for hundreds of kilometres from the coast. The Congo, by contrast, drains a much smaller area, though it carries an enormous volume of water in its own right.