Monday 09 December 1996
Q Why are our elbows better than our hands when testing the temperature of babies' bath water?
A Although there are more nerve endings in the hands and feet, the skin in these regions is usually quite thick and shields our skin temperature receptors from any temperature we are trying to measure. Using a region of our body which has thinner skin is more effective. It also leaves your hands free to hold the baby.
Q How and why do frogs sing? Is it because they're territorial?
A Frogs have a larynx and vocal chords like other vertebrates, so sound production is essentially the same as in humans, birds and mammals. However, different species show a range of singing ability, from virtually silent to very loud calls. They probably sing for several reasons - advertising for a mate, intimidating predators or even to get other males to release them from a mating embrace. Generally, males call and females stay silent - or quietly call back to let the male know they're there. Some frogs are territorial only in the breeding session, while others may guard an area all year round.
Q How does a Venus fly trap digest a fly?
A When a fly enters the Venus fly trap, it knocks a trigger hair that sets the trap. It's not until the fly moves again and triggers another hair that the trap is sprung and the plant closes its "jaws". Once the jaws are closed, the plant lets out digestive juices which dissolve the fly. The juices and dissolved fly are absorbed by the plant. This is similar to how food is digested in our stomachs.
Q How does water move around in a tree?
A Water molecules are very good at sticking together - where one goes, the rest will follow. This is called surface tension. When you pull on one molecule, the rest tend to move, too. Water is sucked out of the tree by evaporation from its leaves; this pulls water up from the roots.
Q Why do male spiders let themselves be eaten by females after mating?
A Only a few species of spider go through this bizarre ritual. The males often try to escape, but as females are many times larger, this is not easy. The males' drive to pass on their genes to the next generation is greater than their desire to live long but ultimately mortal lives. Sacrificing themselves to the female also provides her with extra nutrition, improving her chances of fathering his offspring.
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