Monday 06 January 1997
Q What tells trees to shed their leaves for winter?
A In many trees leaf fall seems to be brought about by shorter days and falling temperatures toward the end of the growing season. Chlorophyll, the green pigment in plants, is lost; yellow and orange pigments called carotenoids become more conspicuous and, in some species, anthocyanin pigments accumulate. These changes cause the autumn colours of leaves.
There are some indications that day length triggers leaf loss in deciduous trees: some researchers think the lack of daylight breaks down a couple of plant hormones which are important in controlling leaf fall. Artificially increasing the level of two hormones, called gibberellins and auxins, in the autumn can halt leaf fall and preserve the leaves' greenness.
Q The sea is made of rain, the rain is made from the sea; so where did the first raindrop come from?
A When Earth first formed 4.6 billion years ago, much of its atmosphere was derived from volcanic out-gassings containing water vapour. This cooled and condensed to form drops of water - which would have collected in basins on the land, creating large lakes and oceans. So rain came before seas.
Q Why is the sea salty?
A The early oceans were probably not salty. Erosion of local rocks, by rivers which flowed into them, provided the salts. All fresh water in rivers contains traces of salts and minerals, but these get concentrated in the oceans because they are left behind when water evaporates (to form clouds). This water falls as rain which eventually washes more minerals into the sea. But if you measure the sea's salt content now, and work out how salty it should have been after billions of years of minerals being washed into it, it is much less salty than expected. Someone tried to calculate the age of the Earth from how salty the seas were and got a figure close to 5,000 years - so something else is happening.
Q How many teeth does a great white shark have?
A The front teeth of sharks are constantly replaced by rows of teeth growing behind them. The adult great white shark has an average of 30- 34 teeth in its front row. Each tooth has a new one ready to swing into place, so the actual number of teeth in the shark's mouth is 60-68, of which only half are in use.
You can visit the technoquest World Wide Web site at http://www.campus.bt.com/ CampusWorld/pub/ScienceNet. Questions for this column can be submitted by e-mail to firstname.lastname@example.org
- 1 I was a Woman Against Feminism too
- 2 Students offered grants if they tweet pro-Israeli propaganda
- 3 The Tory donor whose firm is one of Britain’s biggest tax avoiders - with HMRC's blessing
- 4 John Barrowman praised for Commonwealth Games opening ceremony gay kiss
- 5 Israel has discovered that it's no longer so easy to get away with murder in the age of social media
Peaches Geldof cause of death: Socialite had taken fatal dose of heroin after years of addiction, inquest concludes
Vladimir Putin employs a full-time food taster to ensure his meals aren't poisoned
Peaches Geldof: Her final day – and her fatal decision
Israel-Gaza conflict: Israel may have committed war crimes, says UN human rights chief
John Barrowman praised for Commonwealth Games opening ceremony gay kiss
Malaysia Airlines MH17 crash: Vladimir Putin is given 'one last chance' to end hostilities in Ukraine
The 'scroungers’ fight back: The welfare claimants battling to alter stereotypes
The truth about conspiracy theories is that some require considering
Malaysia Airlines MH17 crash: Ukrainian military jet was flying close to passenger plane before it was shot down, says Russian officer
Malaysia Airlines MH17 crash: Massive rise in sale of British arms to Russia
Malaysia Airlines MH17 crash: victims’ bodies bundled in black bags and loaded onto trains
£30000 - £38500 Per Annum + 25 days holiday, pension, subsidised restaurant: C...
£34000 - £37000 Per Annum + excellent benefits: Clearwater People Solutions Lt...
£40000 - £45000 per annum + Pension, Holiday, Flexi-time: Progressive Recruitm...
£280 - £320 per day: Progressive Recruitment: C#, WinForms, Desktop Developmen...