Chris - The thing we know mosquitoes are very good at transmitting is malaria. The way in which they transmit malaria is that people who have malaria are made more susceptible and they’re more attractive to mosquitoes in the first place. The mosquito flies in, bites the person who is infectious for malaria. The malaria parasite – plasmodium – then gets inside the body of the mosquito where it infects the gut cells of the mosquito and grows or replicates in there. This means that from a very small infected dose you get a very big dose inside the mosquito. The mosquito then goes and feeds on a second human who isn’t infected with malaria. In the course of feeding the mosquito injects some of its saliva into the person which acts as an anticoagulant and also as an immunosuppressant so the person’s immune system doesn’t attack the mosquito while it’s feeding. In the course of injecting that saliva it now injects some of those malarial parasites which are inside it, now at very high levels, into the person. That’s how the person catches malaria.

Kat - What about things like viruses and HIV?

Chris - With HIV the problem is that it’s not infectious but when it comes to a mosquito the problem for HIV is that it can’t infect the mosquito. A person who has HIV doesn’t actually have very much virus going around in the bloodstream until the latter stages of the disease when they’ve got AIDS or right at the very first part of the disease. The amount of virus taken into the mosquito is very low. When the virus gets into the mosquito it gets broken down or destroyed by the mosquito’s digestive juices. It’s not adapted to infecting or persisting inside the mosquito. When that mosquito bites another person the amount of virus that’s in there is vanishingly small, if not zero. Therefore the amount that gets put back into the next person that gets bitten is absolutely tiny. As a result the next person doesn’t get infected. That’s very useful and very fortunate because with 30 million people on Earth (or more) infected with HIV, if it could spread that way, it would be a major problem. Malaria affects about 3-5 hundred million people every year.

Kat - I’m assuming these are tablets which would make you wee more which would reduce your blood pressure. What do you think?

Chris - Yes. The simplest way to think about it is that when you take your diuretic, in other words something that makes your body lose water (that’s what water tablets are), then you’re reducing the volume of water in the body. Therefore you’re reducing the volume of water inside your blood vessels. Blood vessels are a fixed size and the more water which you put inside them, which is in your blood, then the more stretched they are and therefore the higher the pressure because liquids are incompressible. If you lose water from the body then this means that there’s less fluid in the vessels and, as a result, the pressure is a bit lower. That’s probably an oversimplification. There’s probably more to it than that. We know that some of these blood pressure tablets have other effects which affect metabolism and also affect the amount of sodium in the body. That’s principally how they work. Put simply, it’s because you’re reducing the volume of liquid inside a sealed container and if you take some liquid out then the amount of stretch, the pressure in the blood vessels must go down.

Kat - This is a great one because everyone wants to know, ‘can I drink red wine and will it prevent cancer?’ The answer is yes there are chemical differences between grape juice and wine, the main one being the presence of alcohol. There are physiological differences between drinking and the main thing is that alcohol is a very effective solvent A lot of the sort of biological chemicals that may be found in wine can be dissolved into fat using alcohol. That’s why it’s a great solvent. You’ll probably be able to get more chemicals into your body by drinking wine and this is actually why if you smoke and drink at the same time you’ll actually do yourself a lot more harm than if you just smoke or just drank alcohol. Alcohol does help all these nasty chemicals pass into your body much more easily. In terms of the absolute health benefits of what’s in red wine the main culprit is called reveratrol and tabloids get very excited about this and say, “Red wine you should all drink this!” Resveratrol is a really interesting molecule and organisations like Cancer Research UK are investigating it to see if it can prevent cancer. The amount that you get in the average bottle of red wine is actually relatively small. A scientist told me before that you would have to drink hundreds of bottles of red wine a day to actually get enough resveratrol to have an effect. I think the actual differences are quite minimal between grape juice and wine in terms of health benefits. We’re actually investigating resveratrol as a more – you purify the chemical and give it to people that way. In terms of alcohol health benefits the research has shown that there’s benefits for heart type things: cardiovascular disease. In a very small group of people  - and this is basically men over the age of 50 and women over menopause who drink one unit of alcohol per day [there may be health benefits]. But then alcohol does cause heart disease and strokes if you drink in reasonably large amounts. If you really want health benefits you’re best sticking to the grape juice.

Chris - There’s one other chemical in red wine which we should mention and that’s procyanadin. Roger Corder is a researcher at the London Hospital Medical College and St Bartholomew’s Medical College in London and he actually found out how this worked. You can find lots of procyanadin in tannat grapes which are in southwest France. So some of the grapes that grow at very high altitude. The reason you find that is because it’s an antioxidant molecule and it helps to protect the grapes from ultraviolet. If you put it into your body what Roger Corder found is that it helps to relax blood vessels. This is present in sufficiently high quantities in red wine that you would have at therapeutic levels, i.e. a glass at dinner. It will cause a reduction in things like blood pressure and heart disease and stroke risk. If you go and buy red wine look from tannat grapes because they’re the good ones.

Dave - This is a really neat trick which NASA and all the space agencies use called the gravitational slingshot. The way it works is that, because the planets are orbiting they’re moving. They’re not stationary so if you imagine firing yourself if you’re a space probe, going outwards towards a planet. Imagine going just behind the planet. The planet’s gravity is going to pull you towards it and because the planet is moving away from you all the time it’s going to pull you towards it more than it would do if it were stationary because you’ve got to catch up with it as keeps moving away from you. You don’t move towards it as quickly as you would have done so you gain energy. Once you have left the planet you actually gain a load of energy from the planet and you slow the planet down a bit.

Chris -  Do you have to get the angle of attack or approach to the planet so that as the planet moves away from you it doesn’t pull you off course again.

Dave - The whole point is that it’s using the planet to pull you off course in a way that helps you. You’ve got to have a very careful approach. If you want to speed up you’re behind the planet . If you want to slow down you go in front of it. Overall this will give you more energy or less energy and get you to where you want to be.

Kat - The only trees that lose their leaves are deciduous trees. They’re different from coniferous trees. The reason they do this mainly is because leaves fulfil an interesting function for trees. Not only do they help them produce energy from photosynthesis, that’s where the pigments live that help trees to make energy from sunlight from carbon dioxide and water but also they act as the tree’s disposal system. Throughout the year the tree will grow, produce energy, sugars and all sorts of things in its leaves and its waste products get put back into the leaves. Now very Autumn, basically because trees do need a lot of water, they start to have a less reliable supply of water, less light so the trees decide ok, now is the time to get rid of our leaves. They lose them and it’s basically tress are getting rid of their waste products. It’s also why they’re changing in colour as well because these waste products are different colours to the green chlorophyll pigment that helps them to make energy.  Basically, deciduous trees will lose their energy in this way but coniferous trees so pine trees: all these things with little needles, they don’t produce energy in quite the same way. They also don’t have this need for water. They have thin, very thin leaves that lose less water and they have a very waxy cuticle on them. Deciduous trees are basically throwing out the garbage when they get rid of their leaves.

Chris - i did also hear there’s quite a clever trick that researchers at Colgate University in the US discovered that acer trees also use this as the tree equivalent of chemical warfare. They pump into their leaves various toxins, which when the leaves fall to the ground, suppress the growth of other plants and things that would normally grow in the ground. This means that when their seeds try and germinate they have much less competition. The researchers who did this showed that they could kill lettuce plants with the leaf extract from these trees. You could say that when it comes to giving their offspring a fighting chance they’ve got an ace up their leaves.

Chris - If you see two railway track in the distance they seem to come to a point. The same thing happens with sunlight - these corpuscular rays or "God’s fingers", coming through the clouds they also seem to be coming from a focal point just beyond the clouds. Why is that?

Dave - This is all to do with geometry. How big something looks on the back of your eye is to do with how big of an angle it takes up in front of you. If two things are a very small angle apart then they’re going to look very close together in the back of your eye. If there’s a big angle then it’s going to use more of your retina so they’ll look bigger. How do you make that angle? It’s all geometry done at school. If you imagine a big triangle with one side how far away something is and then a right angle between how far apart the two objects are. The farther away something is, the smaller angle they’re going to make between the two of them. The smaller they’re going to be on the back of your eyes. The reason why railway tracks look as if they’re getting closer together is that they’re a metre apart closer to you and a metre apart a mile away but the angle it makes closer to you is much larger than a metre will make a long way away from you.

Chris - Why do you think the visual system doesn’t compensate and tell us that things are just the same distance apart, even though they might be getting smaller?

Dave - I think your visual system does, to some extent, compensate because the moon looks different sizes depending on how high it is in the sky. If it’s right on the horizon or it’s near objects you think are much farther away you think it’s much bigger than when it’s up in the sky. You have no concept of how far away it is so you think it’s smaller which is how you get this optical illusion that the moon looks huge on the horizon but tiny up in the sky.

Chris - Great question. I think there are probably three, possibly four reasons for this. The principle reason is the temperature. When you take food and drink into your mouth what we call taste is large down to smell. You can prove this yourself. If you take something strongly flavoured into your mouth and then hold your nose you’ll notice that it appears to lose most of its taste. That’s because when you put warm things or things that are cold into your mouth the heat in your mouth volatilises, in other words, turns into vapour some of the volatile chemicals in the food. They then drift up the back of your nose into your nasopharynx where they dock with chemical receptors in what’s called your olfactory epithelium. That’s where you smell. This tells the brain that particular flavours are present. Most of the food we eat we actually experience the taste as a smell. When you put cold tea into your mouth the temperature means that many of the volatile chemicals that are in the tea don’t escape the tea in the same way or at the same rate that they would do with hot tea. The more energy that these chemicals are given the more of them will be driven off. This means that as a result less stimulation goes into the olfactory epithelium so the taste is less strong for some chemicals than others. The tea tastes different. The second point is that when tea’s cold the viscosity is very different. It’s a thicker fluid than when it’s hotter. This means that the stimulation into your mouth and tongue is a bit different. So it tastes and feels different in the mouth which also changes your perception of the flavour of the tea. Then there’s another possibility and that’s when tea has stood for a long time and gets cold it has separated out according to density of the different components of the tea. If you have got a hot cup of tea you have thermal activity in the fluid so hot things are rising to the top and cold fluid is going to the bottom. This keeps the contents mixed. When you have a tea cup standing there for a long time and the temperature’s fallen then it stops mixing like this and things get separated out. The fatty, less dense things go to the top and the more dense things go to the bottom. The mouthful of tea you get isn’t a mixture of tea like it would have been before when it was hot.

Dave - A Yagi aerial is the sort of thing you see, TV aerials, basically. The ones where you’ve got a long bit pointing towards the transmitter and lots of cross bars along it.

Kat - So a typical TV aerial.

Chris - Dave, why are they that shape?

Dave - What’s going on here is the idea of an aerial like this is to make the aerial very directional. It’ll only pick up signals from the direction of the transmitter and not pick up all the interference from all the other directions. Basically, radio waves are a form of electromagnetic wave. If they hit metal they’ll make and electric current flow backwards and forwards along it.  The bars on the aerial, when the radio waves hit it electricity sloshed backwards and forwards along it. That electricity sloshing backwards and forwards starts to transmit itself. It makes its own radio waves. You’ve got a whole series of these all absorbing radio waves and then re-emitting them again and again. The only direction whereby all the radio waves are re emitted by these little segments – the only direction where they all add up and increase the direction of the signal is in the direction along the bar, towards the tv transmitter. The signal gets bigger and bigger and you get a little detector at the back which detects that signal and sends it down to your tv. Quite often at the back they’ve got a little reflector so it reflects any signal that doesn’t get absorbed by the sensor at the back.

Chris - Why is it called a Yagi aerial?

Dave - I think it was invented by a Japanese guy called Yagi.

Kat - The animal is not very pleasant: they chew it off. Nice sharp teeth, chew it off. This is because many animals, in fact the mother, after birth will eat the placenta. The [umbilicus] is not actually attached to the mother, it’s attached to the placenta. The placenta’s full of lots of goodies. If you’re an animal you probably don’t want it to go to waste.

Chris - It’s the one piece of meat a vegetarian can eat without harming anybody.

Chris - Well it’s things which tickle your skin but how does that itch reach consciousness? It looks like there are itch-specific classes of nerve fibres. They’re very tiny, thin calibre nerve fibres. They’re about 1-6 microns (that’s millionths of a metre across) so some of the tiniest nerve fibres in the body. If you stimulate those nerve fibres then people do detect a sensation of itch. They seem to be there specifically to convey the sensation that something is tickling you and they go up to the spinal cord and they squirt out a chemical transmitter called gastrin-receptor releasing peptide which is the transmitter which tells the spinal cord there’s an itch in a certain part of the body. The purpose of itching is in fact to protect you because things that are usually chemical irritants, physical irritants or parasites. Things like mosquitoes that might transmit an infection to you so it’s important you know where on the body there’s a problem. It draws attention to it so you can scratch and get rid of it. How does scratching work? In the same way that you punch the wall, go ouch and then rub the affected body part better this helps to gate the pain and stops things hurting so much. When you scratch an itch what you’re doing is inflicting a little bit of pain. What scientists have found is that when you trigger a bit of pain in the area where you have an itch that gates or switches off the itch sensation.

Chris - That’s a very good question. It’s all to do with where the moon comes from. If you look at the composition of the moon and we know what the moon’s made of because one of the people we just heard mentioned, Neil Armstrong, was there and scientists have brought back bits of the moon’s surface We know the composition of the moon and the answer is that it’s largely made of the same stuff as the Earth’s crust. Where did it come from? Scientists have pieced back together a theoretical model of how the moon could have been made. The moon’s relatively big relative to the Earth. It’s much bigger than most moons are. What scientists think is that around about the time when the Earth was first forming about 4.5 billion years ago when the solar system  was very young two planets: the Earth and a second planet which is notionally called Thea ended up on a planetary collision course. They had the planetary equivalent of an RTA. The two ran into each other and the massive catastrophic collision that ensued meant that a lot of debris from the crust of those planets got ejected like a cocoon around the earth and this other planet and the cores of those two planets merged together. What you ended up with is one bigger planet with a very dense iron core and this cocoon of very crusty material round the outside which then slowly settled just like the planets formed in the first place to form a moon which was all that debris aggregating in orbit around what was then the Earth. The core of the Earth has got a lot of iron in it. It’s a mobile iron core and we think that’s the ingredient you need to create a magnetic field. The moon being a bit smaller, colder, smaller and made principally of crust material doesn’t have that iron core that’s liquid, spinning around making that magnetic dynamo effect and therefore doesn’t have that magnetic field. If we didn’t have that magnetic field on earth we would largely resemble Mars: a dried out prune of a planet because our magnetic field helps to deflect off the solar wind.

Dave - Also the moon being so much smaller than the Earth lost its heat a lot quicker. It’s entirely solid all the way through so you don’t get this molten conducting metallic core which you need to create a strong magnetic field like the Earth has.

Kat - In the UK human tissue is regulated by the human tissue authority so there are quite a lot of rules about how you’d have to dispose of it. With some things that are taken off people you may be offered them to take them home, if you’d like to. Most things you probably don’t want your diseased leg back. It depends what was wrong with the part of you that has been taken off. For example, it may be sent down to the pathology lab so it can be cut up. You can look at it, you can see what was wrong with it. In some cases with the consent of the person whose tissue it was it may be for research. This happens for things like cancers. We try and bank them so we can study them in the future. There’s been quite a lot of things in the news, not so much recently, about people’s organs being stored without consent. If you don’t consent to research and they don’t want it, you don’t want it it’ll probably just be destroyed. Usually by incineration. Here in the UK a lot of this disposal is contracted out to companies that take all the nasty body bits and tissue away and burn it somewhere.