&
In Numbers0.15mm
is the length of the smallest flying insect,
a fairyfly called the Kikiki huna. Like all
fairyflies, it lives much of its life inside other
insects’ eggs.Ozone depletion IS mainly caused by
chemical reactions between compounds
such as chlorofluorocarbons (CFCs) and
ultraviolet light. These occur in the
stratosphere, above 8km (5 miles)
altitude. By the time polluting man-made
CFCs get that high, they have evenly
dispersed around the globe, so whether
or not people live and work under the
ozone hole isn’t the determining factor in
its location.
The reason that the hole forms above
Antarctica is because the ozone-
destroying reactions happen much faster
on the surface of the tiny ice crystals found
in a type of cloud, called polar
stratospheric cloud, which forms in the
cold, dry conditions of the Antarctic. LVThese are names for cells in the visual
cortex of the brain, which processes raw
sensory data from the retina. Different types
of cells within the cortex handle different
aspects of the image, and the ‘simple’ and
‘complex’ cells react to edges and lines.
Simple cells respond to lines in an image
that are orientated at a specific angle.
Different cells have different preferred
angles, so when you look at a circle,
different brain cells recognise each part of
its circumference. The complex cells thenWhat’s the difference
between ‘simple’
and ‘complex’ cells?
Why is the hole
in the ozone layer
over Antarctica, if
it’s uninhabited?
take the input from lots of simple cells and
process it further, to allow the brain to
determine the direction and speed of a line
as it moves across the visual field.
Together, these cells of the visual cortex
assemble an outline view of the world, and
then other cells process the colour and
distance information in a scene. LVSimple and complex cells fulfil different information
processing roles within the brain’s visual cortexPHOTO: SCIENCE PHOTO LIBRARY X3, NOAA
NASA’s Aura satellite produced this map of the ozone
layer over Antarctica. Blue shows low ozone levels;
green, orange and yellow represent higher levelsCan DNA be synthesised?
Yes. Single YEAST genes were first
synthesized back in 1972. The process
involves assembling short sequences of
genetic code, called oligonucleotides,
one letter at a time. Chemical protector
molecules are temporarily attached
like scaffolding to make sure the
oligonucleotide only forms new bonds in
the right place. Oligonucleotides of up to
200 letters, or base pairs, can be made
this way, but these sequences can be
stitched together to make much longerstrands. In March this year, researchers
at New York University built an entire
yeast chromosome this way. This
contained 2,000 genes with more than
270,000 base pairs of DNA. As well as
allowing scientists to create customised
organisms, synthetic DNA can be used
to store computer data. DNA storage is
slow and expensive, but it’s very robust
and 5.5 million gigabytes can fit in a cubic
millimetre of DNA, which could make it a
good choice for archiving data. LVDNA could form
the basis of future
hard drives