Q Why does bread rise?

A.Yeast makes bread rise. When cereal grain is ground to make flour, starch inside the grain is exposed. Adding water activates enzymes - amylases - which turn some of the starch into glucose. Yeast added to the dough uses the glucose to produce carbon dioxide and alcohol. If yeast has no oxygen, it will produce more alcohol than you want, which is why bread is kneaded to trap air inside it, and why dough often smells like barley hops. The carbon dioxide produced by the yeast is trapped in bubbles which make the bread light. The alcohol evaporates during baking - fortunately!

Q Can gold be turned into lead or vice versa?

A Elements such as gold and lead are characterised by the number of protons and neutrons in their nucleus - their atomic mass. By adding protons to the atom, chemists can theoretically turn lighter gold atoms with 79 protons into heavier lead atoms with 82 protons. Converting gold into lead takes a lot of energy and so costs more than the value of the lead created. The reverse process of converting heavier lead atoms into lighter gold atoms is also possible. Tampering with elements at an atomic level is more likely to produce radioactively unstable atoms of a new element rather than sparkling gold.

Q. Why doesn't glue dry out in a glue pot?

A Glue is made up of the glue that sticks and a solvent that keeps it liquid. When you put glue on paper, the solvent evaporates until the glue becomes sticky. There's a limit to the amount of solvent that can evaporate to fill the space in the bottle above the glue. Once the space is full of gas, no more solvent evaporates and the glue stays runny.

Q How does a water softener work?

A Water softeners work using a principle called ion exchange. Magnesium and calcium ions in the water are replaced with sodium ions from sodium chloride in the water softener. The magnesium and calcium ions prefer to be joined to the chloride ions in the water softener and the sodium ions prefer to end up in the water. Removing magnesium and chloride stops limescale forming on taps and inside kettles.

Q If an insect has a head, thorax and abdomen, what are the body parts of a spider called?

A In insects, the head, the thorax and the abdomen are separate. In spiders, the head and thorax are continuous, forming something called the prosoma. Eight legs are attached to the prosoma and their abdomen is joined to it at the lower end.

Q Why does chopping onions make you cry?

A The answer to this was only discovered fairly recently. Research done by Spaere and Vitonen in 1963 showed that when you chop an onion, you break open some of the onion's cells. This releases enzymes which take part in complex biochemical reactions. One of these produces a substance called propenyl sulphuric acid. This is a very volatile irritant. It "fumes" up from the onion and irritates your eyes.

Questions and answers are provided by Science Line. You can use its Dial-A-Scientist service on 0345 600444.

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