Beyond the answers - interesting background to this quiz

A capital with a thousand years of history

Cairo sits on the Nile and has served as a centre of government for more than a thousand years, founded in the tenth century. Alexandria, once the intellectual capital of the ancient world, lies far to the north on the Mediterranean coast. The two cities reflect very different chapters of Egyptian history, which is one reason a question about the capital can trip people up.

The curious case of lithium

Lithium is the lightest metal and the least dense solid element, light enough to float on water. It is soft enough to be cut with a knife and reactive enough that it must be stored in oil. The same element powers the rechargeable batteries in phones and laptops, which is why demand for it has grown so sharply in recent decades.

Vitamin B6 and the body's protein factory

Vitamin B6 is a family of related compounds that help the body break down proteins and use the amino acids they contain. It also plays a role in producing neurotransmitters and in keeping red blood cells healthy. Good sources include poultry, fish, potatoes, chickpeas and bananas, so a balanced diet usually supplies plenty of it.

Mushrooms: the visible tip of a hidden network

A mushroom is not a plant but the fruiting body of a fungus, and most of the organism lives underground as a network of fine threads called mycelium. Bacteria and amoebae are single-celled, which makes the mushroom the odd one out in any multicellular comparison. Fungi were once classified as plants, but they are now recognised as a kingdom of their own.

Paper, one of China's most enduring inventions

Papermaking is traditionally associated with China, where early forms of paper were produced from plant fibres around two thousand years ago. The technique gradually travelled west along trade routes, reaching the Islamic world and then Europe. Before paper, scribes wrote on materials such as papyrus, bamboo and parchment, all of which were heavier or more expensive.