Many things to do with Chemistry are to do with electrons!  There are various ways in which glue can work - The simplest is that if you have two slightly rough surfaces, with tiny pits in them, putting a liquid which can set between them creates lots of little 'plugs' in the pits.  Once it's set you can't pull these out of the pits, so you can't pull the surfaces apart.

If you have two perfectly flat surfaces, the will tend to stick together by a force called the Van der Walls force – the molecules of the surface tend to attract.  Normal surfaces, though, will have dust or imperfections, and so cannot get close enough together to allow these forces to act.  If you put something squidgy or fluid between surfaces, glue for example, it fills the lumps and bumps and allows the Van der Walls forces to act.  This is the same way the geckos can stick to most surfaces, they have lots of tiny hairs on their toes which increase the surface area and allow Van der Walls forces to act, sticking them to walls, windows, ceilings etc.

Other glues chemically bond to surfaces, actually making molecular connections to both surfaces.

We’ve never heard before that the actual amount of stings each jellyfish has would actually vary, but we certainly know there is annual variation in the amount of people who get stung.  This is due to the annual variation in the number of jellyfish in the sea; they change over seasons and are often linked to blooms of plankton, their main food source.  Recently there was a boom in the number of jellyfish around the UK, and this caused a big problem for fish farms around the coast.

Another interesting fact - Portuguese man-of-war are actually not jellyfish, they are a form of colonial hydroid, lots of little tiny animals stuck together!

Good question.  There’s probably almost zero chance of that. The virus that causes cold sores, the Herpes Simplex Virus (HSV), most of us acquire this when we’re very young because of our parents kissing us and children dribbling over each other in nurseries – it spreads in saliva.  When you first get it, it produces a sore throat, ulcers in the mouth, swollen glands in the neck and a high temperature.  It then invades the sensory nerves that supply your mouth and tongue, as well as other parts of the body it can infect.  It goes inside these nerve cells and switches off.  It exists there as a piece of DNA, loitering alongside the cell’s own DNA, and periodically comes back to life.  We don’t know exactly what triggers it to come back to life, but we know that things like damage to the skin, for example sunburn, menstruation, depression and immune depression, can bring it out again.  The virus turns back on its DNA, makes new virus particles which come down the nerve and pop out of the skin, causing the infectious lesion, the cold sore.  When you kiss someone who’s got one, that’s how you pick it up.  

Thankfully, it doesn’t really get into the blood stream, so you should be safe from HSV from blood products.  Other members of the herpes family do spread through blood, but not HSV.

This is all to do with how water interacts with light.  When water is a vapour in the atmosphere, the molecules are not glued together in the same way they are in a liquid.  Water molecules tend to stick together with hydrogen bonds, but in a vapour they can spread out.  In this state they are very good at soaking up infra-red light, but not visible light.

When water forms a liquid – lots of molecules stuck together – it stiffens the bond between the hydrogen and the oxygen, and instead of absorbing infra-red, it now absorbs light at the red end of the spectrum.  White light is a mixture of lots of different wavelengths, and if you take out some of the red light, it looks a little bluer.  The more water you have, the more red is absorbed and the bluer things look.

We put this question to Jim Grey from the UK's Health Protection Authority.  You can read and listen to the whole interview here.

Jim:  Well, women probably have more infections because they have more contact with children.  They change the nappies whereas the fathers rarely change the nappies.  Its contact with the virus, really, that’s causing the disease.  Why children have milder disease than adults is because these viruses are circulating all the time in children.  They’re having multiple infections and therefore have some level of immunity to the virus, whereas the adults haven’t seen this virus since they were a child, and therefore they have very low, or no, immunity to the virus.

There are two concepts involved here, which are very often confused.  One of them is weight, which is how heavy things feel, and the other is mass.  Mass can be considered as being how hard it is to accelerate or stop things.  It just happens that the bigger the mass, the heavier the weight, i.e. the amount they are attracted to the Earth; this is because weight is a product of the mass and the strength of gravity.

In orbit, you take away the weight but the mass is still there.  This means that if you try to start it moving, or stop it moving, it’s very difficult.  So if you were to throw a hammer at someone on the shuttle, although it’s weightless it will still have mass and inertia, and so it will still hurt when it hits!

We put this question to Mark Peplow, editor of Chemistry World Magazine.

I have to say I’m fairly sceptical. What they’re saying is that somehow, negative ions, anions, are being generated by the shirt and this is having an effect on blood flow in the bodies of the players that wear the shirts. When you actually read down the story, their reporting a supposed improvement in mean performance of 2.7% and that’s probably quite hard to judge anyway. But that level of improvement, 2.7%, one can imagine a performance boost coming from the positive moral of wearing a high-tech shirt, so I have to say I’m a little sceptical about this.

Plutonium is not found in the ground.  All the Plutonium we use is artificially made in a nuclear reactor.  Uranium is found in the ground.  Today it would be very difficult to accidentally create a nuclear explosion, or a nuclear reactor, because there’s very little of the active form, Uranium-235, left.  It’s slowly decaying away, and the longer we leave it the less there is.

A couple of billion years ago, there was a case where some bacteria concentrated Uranium underground in Africa, and we have since discovered that it did form a nuclear reactor.  The reaction caused the area to get so hot that it killed off the bacteria, and so stopped them from concentrating more Uranium.

A lot of the heat locked away in the core of the Earth is thought to be the result of radioactive decay of things like Thorium and radioactive Potassium, but this doesn’t have the chain reaction that a nuclear reactor does have.

You probably can date shellfish in this way, and that would suggest that this shell was 52 years old.  Like many things in nature, shellfish have annual seasons of rapid growth, and during this far more shell is laid down.  This way, you can probably count shell layers just as you would count tree rings.

A little while ago, Helen said on the show that she had trouble getting up in the morning, and that in particular she hates alarms which wake her suddenly.  This spawned a huge email response with possible solutions for her, including:

Jen Brokeman in Columbia recommends a system that uses natural sounds which gradually get louder to wake you gently.

Also Kara Sentance, Catherine Meissner in Washington and Martyn Holden in Scandinavia, all suggested an alarm clock which has a progressive light, which switches on 30 minutes before you want to wake up, and gradually increases in brightness – like having a sunrise on your bedside table!

Thanks everyone!