Three more teams challenge for the title and the Royal Institution trophy. Presented by Paddy Feeny Heat 3
NOTTINGHAM: turning organic household waste into a usable fertiliser.
HEXHAM: investigating worm populations in land restored after open-cast mining.
PERTH: using a weedkiller not to stop plant growth but to increase it. Judging their work:
PROF GEOFFREY EGLINGTON organic geochemist
PROF BRYAN CLARKE , biologist
PROF TONY BRADSHAW , botanist
Studio director JOHN GORMAN Producer PETER BRUCE