Tuesday 12 August 1997
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Q What causes colour-blindness, and why is it mainly a male problem?
Colour-blindness occurs when cones - the light sensors in the retina that respond to colour - are damaged. There are three types of colour- sensitive cones, responding to either red, green or blue light. Activation of combinations of these three lets us perceive all the colours of the rainbow. Loss of just one type of cones disrupts your colour vision; loss of two turns the multicoloured world into black and white. A colour-blind person can see clearly, but cannot distinguish certain colours, most frequently red or green (sometimes both). Red/green colour-blindness is mainly a male problem: about 8 per cent of male western Europeans are colour-blind. Of these, about 75 per cent are green colour-blind, and about 25 per cent red colour-blind. The gene(s) responsible are on the X sex chromosome, so men can inherit it from their mothers, but a woman has to get the fault from both parents, which is much rarer.
Q Why does rubbing an injury make it hurt less?
If you get hurt, your first response is generally to rub the area vigorously until the pain ceases. The rubbing activates receptors in the skin which then act on endorphin-containing nerves. These release endorphins - the body's natural painkillers - and help to stop the pain. Eventually, if the rubbing doesn't work, you may have to resort to painkillers such as paracetamol and aspirin.
Q Why don't male mosquitoes bite?
The majority of mosquitoes don't bite. Of those species that do, only females require the additional blood as a protein source for the development of their eggs. Mosquitoes tend to get their energy from eating rotting fruit, not from drinking blood.
Q Is it a myth that there's a bird that eats bits out of alligators' teeth? If not, what's the bird?
Some birds have been said to pick food debris from the gums and teeth of crocodiles in Africa, usually those that are basking. However, this has never been officially observed. Some suggest that the Egyptian plover or the spur-winged plover may be responsible. Both species are known to associate with basking crocodiles, feeding close to them and on their ectoparasites (eg flies). Such behaviour is also seen by the common sandpiper, whilst in Africa during the northern winter. All three of these birds are waders.
Q How was the Giants' Causeway (on the coast of County Antrim, Northern Ireland) formed?
The 40,000 hexagonal basalt columns are about 55 million years old, and were formed by cooling lava. As basalt lava flows cool, they slowly solidify from the liquid. The top and the bottom of the lava flow are cooled respectively by the air and by the rock over which it has flowed, while the interior is insulated and remains hot. So the upper and lower surfaces harden first. As the lava on the surface cools, it hardens, at randomly scattered centres. Basalt shrinks as it solidifies, so the solid area spreads slowly out as ever-increasing circles. At an equal distance between any two, the solidifying basalt will be pulled in as it shrinks, forming a crack. The cracks will be roughly hexagonal over the whole surface, though they vary quite a bit. It's the same principle as hexagonal cracks forming in mud where a puddle has just dried up. As the interior of the lava cools, the cracks deepen.
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