Monday 16 December 1996
A First you need two sheep - sheep A and sheep B. To clone sheep A you take an ordinary body cell from it. Then take an egg cell from sheep B's ovaries, remove its nucleus, and put it into the cell from sheep A. Let this divide and grow for a while. When there's a small group of cells, put it back into sheep B's uterus: it will grow into a clone of sheep A.
Q Which animal is most threatened by extermination?
A This is a difficult question to answer. It's thought that there are about 10 million species alive today (although it could be as many as 100 million - we just haven't found them all yet). Recent estimates say that roughly 27,000 will become extinct every year - that's 74 a day, or three an hour. Most of these are unknown to us and invisible to the naked eye, but important even so. They are all equally threatened.
Q Why are there no insects in the ocean?
A Very few insects have colonised the marine environment - possibly because there are very few flowering plants (which many insects feed on) in the oceans. But this doesn't account for the absence of carnivorous insects in the oceans. These don't rely on flowering plants, so their absence is a mystery.
Q Why do snails and slugs produce a slimy mucus and how do they do it?
A Gastropod mucus has the unique property of being visco-elastic - part glue, part lubricant. The real question is, how does a one-footed animal walk on glue? By exerting different shear forces on the mucus with its foot the mollusc can change the properties of the stuff, allowing it to slide gracefully over a rough surface one moment and then stick firmly to a vertical smooth surface the next. The mucus comes from several very large glands in the foot which are filled with cells called goblet cells. The goblet cells manufacture things called glyco-proteins (sugar proteins) which are large spacious molecules that absorb lots of water. Mucus is actually about 95 per cent water - with a few calcium, magnesium and sodium ions. So the goblet cells produce these glyco-proteins which absorb water and swell. To watch a mollusc in action let it crawl over a sheet of glass and watch it from underneath. You'll see it sliding over the mucus in the centre of the foot while the edges of the foot ripple with muscles which propel it forward.
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