Flaming nuts! And why beans means genes!

The older you get, the more satisfyingly broad the horizons of science become - including everything from magnetism to sexual reproduction

1 How much energy is there in a peanut?

You need: saucer, candle, notepad, pencil, metal tongs, wire cooking rack, bowl of water, uncooked peanuts, piece of wood the same weight as a peanut, ceramic tile wrapped in foil, thermometer, matches, drink can, goggles and heat-resistant gloves.

This experiment requires adult help. Half fill the can with water and place it on the rack. Using the tongs, hold a peanut in the candle flame. When it catches fire, place it on ceramic tile and beneath the can on the rack. Heat from the peanut will warm the water. Note down how long it takes for the temperature to reach its highest point. Repeat the process with wood. Which heats the water more? Therefore, which has more energy?

Our food is broken down to release chemical energy, in the same way that energy is released when burning the peanut. We measure energy in joules. The average 12-year-old uses 3-4kj (3,000-4,000 joules)/minute. Running raises this to 30-40kj/minute.

2 Making a compass

You need: needle, magnet, polystyrene tile, plastic pot, cocktail stick, plastic putty, craft knife and tape.

Cut a circle (small enough to fit in the plastic pot) from the polystyrene tile. Put a cocktail stick in a block of putty on the inside bottom of the pot. Hold the needle by its eye and rub a magnet from eye to tip 100 times. Test if the needle is magnetised using a paper clip. Tape the needle to the middle of the circle. Balance the polystyrene on the cocktail stick. Fill the pot with enough water so that the polystyrene tile floats. The needle should spin to point north.

In the 16th century, William Gilbert discovered that the Earth is a giant magnet. Compasses are small magnets, pointing north. Using the compass, find out which direction your house faces.

3 Looking at genes

You need: notepad, pen, kidney beans and black beans, and two large containers.

Put black beans in both containers. Each bean represents the genes of one parent. Two sets of genes are needed to make a child. Take a bean from each container. Since both parents have black genes, their children will have black-black genes.

Next put red beans in one container, leaving black ones in the other. Again pick out pairs. One parent has black-black genes, the other has red-red genes – each parent passes one set of genes to their child, who will have black-red genes.

Now put equal numbers of red and black beans into each container. Take one bean from each container and pair them. There will be three types of gene pair: black-black and red-red in equal numbers, but twice as many black-red pairs.

Humans have 30,000 genes, containing the instructions to build our bodies. Each gene is formed from a molecule called DNA. Some characteristics are purely genetic, such as eye and hair colour and whether you can roll your tongue into a U shape.

4 DNA samples

You need: bottle of methylated spirits, bowl of ice, cooking salt, washing-up liquid, measuring jug, one ripe kiwi fruit, sharp knife, chopping board, small bowl, saucepan of hot water, coffee filter and funnel, a tall thin glass and a piece of wire.

Cool the meths in a bowl of ice (not in the fridge). Measure half a teaspoon of salt and two teaspoons of washing-up liquid into a jug. Add 100ml of water and stir to dissolve the salt. Peel and finely chop the kiwi. Add to the mixture. Sit the bowl in tap-hot water (no hotter than 60C) and leave for 15 minutes. Pour mixture into the coffee filter and collect drips in the glass.

This green goo is broken down cells, including DNA. Dribble meths down the side of the glass, forming a purple 3-5cm layer above the goo. A white film will form between the green and the purple. Hook it out with the wire. This is DNA – the instructions for life itself.

The washing-up liquid strips cell membrane from the kiwi cells. The temperature difference between the kiwi and meths makes the DNA rise.

For further information, see www.science/scienceshack.experiments/ madna.shtml