BBC Focus - 09.2019

ELEANORTEW,YORK

HOWDO BABYBIRDSBREATHE

INSIDE THEIR EGGS?

It’s all down to some ni￿y engineering insidetheeggshell.

Early on in a chick’s development, it growsa hollow,

sac-like structure from its gut, known as an‘allantois’.

This pouch fuses with a second membrane(‘chorion’)

surrounding the chick and its yolk, which togetherform

the ‘chorioallantoic membrane’. With oneenda￿achedto

the chick, and one end close to the eggshell’sinner

surface, this membrane e￿ectively acts likelungtissue,

connecting the chick’s circulatory systemtotheoutside

world. Oxygen di￿uses through microscopicporesinthe

shell to the blood vessels in the chorioallantoic

membrane, and then on to the chick’s bloodstream.

Carbon dioxide, the gaseous waste productofrespiration,

passes in the opposite direction. CC

QESTION OF THE MONTH

EMAIL YOUR QUESTIONS TO [email protected]

WINNER

Eleanor wins an Airbus 24hr

watch, worth £115. The dial is

split into two parts: day (light,

upper part) and night (dark,

boom part) to logically

follow the natural course of

a day. According to Airbus,

ight crew find it useful to

help manage jetlag – perfect

for your holidays!

ightstore.co.uk

Many insects, particularly scarab and jewel beetles, have vivid, metallic

green, blue or gold colouration. This eect doesn’t come from pigments,

but is an example of ‘structural colouration’. Microscopic ridges and

transparent layers on the surface of a beetle’s carapace act as an array of

lenses that direct dierent wavelengths of light in such a way that some

colours cancel out and others are amplified – the rainbow eect on a DVD

is similarly caused by the microscopic pits on its surface. This metallic

sheen may have evolved because it oers bright colours that can serve as

a mating signal over long distances. Alternatively, some researchers have

suggested that it might mimic the appearance of raindrops on leaves,

helping to camouage the beetles. The ridges and layers may also take less

energy to grow than metabolically expensive pigment molecules –

particularly important for insects because they regularly shed and regrow

their outer skin. LV

WHY DO SOME INSECTS LOOK METALLIC?

So shiny, even

without an

application of

Pledge (other

polishes are

available)

Fizzy drinks do release carbon dioxide (CO 2 ), but this pales in
comparison with overall human CO 2 emissions. A can of pop contains
2-3g of CO 2 – a tiny proportion of the six tonnes of CO 2 per year (or 17kg
per day) that the average person in the UK is responsible for. What’s
more, the CO 2 pumped into carbonated drinks is usually a by-product
from power plants – meaning it would have been released into the
atmosphere anyway. AFC

JED FITZHARRIS and ADAM TEMPEST

DOES THE CARBON DIOXIDE RELEASED FROM

FIZZY DRINKS AFFECT THE ATMOSPHERE?

Chorion

Allantois

Shell

Yolk

(nutrients)

Embryo

Yolk s ac

Albumen

Amniotic cavity

with amniotic

uid

Amnion