BBC Focus 02.2020

Q&A

GETTY IMAGES X2 ILLUSTRATIONS: DAN BRIGHT

Around 700 million years ago,

plants began to appear on land.

One of the key adaptations

needed for this transition was

some way to protect against the

Sun’s ultraviolet (UV) rays; plants

in the sea had hitherto been

shielded by the seawater.

Scientists have known since 2011

that plant cells have a protein

called UVR8 that can detect

shorter wavelength UVB rays,

which is the type of UV radiation

most responsible for sunburn.

This protein signals the cells to

begin producing compounds that

block further UV damage and

repair DNA damage. In 2014,

researchers at Purdue University

in the US identified one of these

protective compounds as

‘sinapoyl malate’ and found that

this molecule harnesses quantum

mechanical eects in order to

absorb UVB rays. The ability to

produce this natural sunscreen

seems to be common to all land

plants and algae, which suggests

it is an ancient adaptation.

Plants aren’t invulnerable to

the Sun, however. Prolonged

exposure to the UVB in strong

sunlight causes cell damage to

the leaves and bark of many

plants. This is worse when plants

are dehydrated, because this

limits their ability to move

sunscreen chemicals to the

worst-aected sites. Ironically,

there is a widely-held belief

among gardeners that watering

plants in the midday sunshine

can cause sunburn, because

droplets of water supposedly act

as tiny lenses to focus the

sunlight onto the leaf surface.

However, this myth was

debunked in 2011 by researchers

at Eötvös University in Budapest,

Hungary. They used computer

modelling and direct experiment

to show that the refractive index

of water isn’t strong enough to

focus sunlight from a water

droplet onto the surface of a

leaf. LV

ERIC WILLIAMS, LANCASHIRE

WHY DOES

BLOWING HARD ON

OUR HANDS COOL

THEM, BUT JUST

BRE ATHING ON

THEMWARMTHEM?

This is essentially due to a

dierence in the speed of

the airow in each case.

When we breathe out

slowly on our hands, the

warmth and moisture from

our mouths has time to

transfer to our hands,

warming them up. But

pursing our lips speeds up

the airow, and as this

passes over our hands, it

blasts away any air that’s

been warmed by contact

with our hands, cooling

them. In addition, the

fast-moving column of air

draws in, or ‘entrains’, the

air around it. This tends to

be cooler than our breath,

so it boosts the cooling

eect. RM

CHRIS MCMULLON, BARNHAM, WEST SUSSEX

ARE THERE ANY ANIMALS

THAT CAN SEE WI-FI OR

BLUETOOTH SIGNALS?

Wi-Fi and Bluetooth are radio signals with a wavelength of 6cm to
12.5cm. This is about 100,000 times longer than the wavelengths of
visible light that humans can see. Many animals, including vampire bats
and certain fish and snake species, are able to sense infrared radiation,
but this only goes up to wavelengths of 1mm. Longer wavelengths carry
much less energy and can’t be detected without some kind of resonator
to amplify the signal. In 2009, the French virologist Luc Montagnier
claimed that bacterial DNA can emit radio waves, but his results were met
with widespread criticism from the scientific community, and have not
been replicated. So to date, we don’t know of any organisms that can
detect or communicate with radio frequency signals. LV