What on Earth? Your questions answered

The tiniest mammals; How do cells grow? A burning issue


Why are there no mammals smaller than a shrew?

Why are there no mammals smaller than a shrew?

The answer to this question comes down to heat loss. Shrews are mammals, so in common with other mammals, they maintain a constant body temperature that's nearly always above that of their surroundings. As a result, they lose heat from their bodies to their surroundings. The source of the heat is the energy that the mammal gets from food. The more heat is lost, the more food is needed to replace this energy loss.

Heat loss is a bigger problem for smaller animals because they have a high surface-area-to-volume ratio: they have a lot of surface area to lose heat through. And, as the smallest mammals, shrews suffer from heat-loss like no others. As a result, they need to eat a prodigious amount of food to stay alive.

This principle explains why mammals that live in cold climates tend to be large (for example, polar bears). These have quite a large volume for a relatively small amount of surface area, so they do not lose heat so readily.

Any mammal smaller than a shrew would not be viable on a heat-loss basis. If you think about animals smaller than shrews, they are always cold-blooded, for example insects.

In an embryo, how do the cells begin to specialise? How do they decide, for example, to become brain cells?

This answer applies to mammals only. Other animals can have very different developmental strategies.

In the initial stages, the fertilised egg divides to form a ball of cells. Cell position in the ball gives the cue for the first differentiation step. Cells on the outer surface of the ball become one kind of tissue (which will contribute to the placenta only) and cells on the inside become another cell type, which will give rise to the baby that is born. It is believed that the number of cell contacts is the key feature: outside equals a few cell contacts, inside equals many.

Once you have two cell types, there is further scope for interaction. Some of the "outside" cells are in contact with "inside" cells, and some are not. This leads to another two different types of cell arising. And so it goes on in a cascade of increasing complexity. During that cascade, genes come into the picture. While every cell has the same set of genes, its position (outside/inside) determines which genes are read and used to make the proteins that the genes encode. Depending on which genes the cell uses, even more varying sets of genes are activated, and so on, leading to this astonishing number of different tissues such as brain cells, bones and others. Just from one fertilised egg.

What happens to the candle wax when a candle burns? Where does it go?

Candle wax is the fuel which is burnt to keep the candle going. When you light a candle, the flame melts the wax at the top of the candle into liquid form. This liquid travels up the wick via capillary action and is transformed into a gas by the heat of the flame. This gas combines with oxygen in the air, giving out the heat and light that you see as a flame. Candle wax is a mixture of chemicals, which contain carbon, nitrogen, oxygen and hydrogen. When combined with the oxygen in the air, new chemicals are created. These are gases – carbon dioxide, nitrogen, and water vapour – which float into the atmosphere, so you can't see where the wax has gone.

Further information: www.sciencenet.org.uk. Ask your own questions on Science Line, freephone 0808 800 4000 or e-mail scienceline@independent.co.uk

Start your day with The Independent, sign up for daily news emails
ebooks
ebooksAn introduction to the ground rules of British democracy
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Home Care / Support Workers

£7 - £10 per hour: Recruitment Genius: This care provider is looking for Home ...

Recruitment Genius: Web Team Leader

£30000 - £35000 per annum: Recruitment Genius: One of the UK's leading web des...

Recruitment Genius: Client Manager

£27000 - £35000 per annum: Recruitment Genius: A growing, successful, friendly...

Recruitment Genius: Property Negotiator - OTE £20,000+

£16000 - £25000 per annum: Recruitment Genius: This family owned, independent ...

Day In a Page

Greece says 'No': A night of huge celebrations in Athens as voters decisively back Tsipras and his anti-austerity stance in historic referendum

Greece referendum

Greeks say 'No' to austerity and plunge Europe into crisis
Ten years after the 7/7 terror attacks, is Britain an altered state?

7/7 bombings anniversary

Ten years after the terror attacks, is Britain an altered state?
Beautiful evening dresses are some of the loveliest Donatella has created

Versace haute couture review

Beautiful evening dresses are some of the loveliest Donatella has ever created
No hope and no jobs, so Gaza's young risk their lives, climb the fence and run for it

No hope and no jobs in Gaza

So the young risk their lives and run for it
Fashion apps: Retailers roll together shopping and social networking for mobile customers

Fashion apps

Retailers roll together shopping and social networking for mobile customers
The Greek referendum exposes a gaping hole at the heart of the European Union – its distinct lack of any genuine popular legitimacy

Gaping hole at the heart of the European Union

Treatment of Greece has shown up a lack of genuine legitimacy
Number of young homeless in Britain 'more than three times the official figures'

'Everything changed when I went to the hostel'

Number of young homeless people in Britain is 'more than three times the official figures'
Compton Cricket Club

Compton Cricket Club

Portraits of LA cricketers from notorious suburb to be displayed in London
London now the global money-laundering centre for the drug trade, says crime expert

Wlecome to London, drug money-laundering centre for the world

'Mexico is its heart and London is its head'
The Buddhist temple minutes from Centre Court that helps a winner keep on winning

The Buddhist temple minutes from Centre Court

It helps a winner keep on winning
Is this the future of flying: battery-powered planes made of plastic, and without flight decks?

Is this the future of flying?

Battery-powered planes made of plastic, and without flight decks
Isis are barbarians – but the Caliphate is a dream at the heart of all Muslim traditions

Isis are barbarians

but the Caliphate is an ancient Muslim ideal
The Brink's-Mat curse strikes again: three tons of stolen gold that brought only grief

Curse of Brink's Mat strikes again

Death of John 'Goldfinger' Palmer the latest killing related to 1983 heist
Greece debt crisis: 'The ministers talk to us about miracles' – why Greeks are cynical ahead of the bailout referendum

'The ministers talk to us about miracles'

Why Greeks are cynical ahead of the bailout referendum
Call of the wild: How science is learning to decode the way animals communicate

Call of the wild

How science is learning to decode the way animals communicate