Can you run faster on the moon?

06 September 2009

This week we're taking on the questions you've waited all summer to find the answers to. We find out whether humans can run faster on the moon than here on Earth, if tea tastes better in china cups, and if talking to plants can help them grow. Plus we look into the world of statistics to learn how many ants it would take to carry a human and discover how many people in the world are having sex right at this moment! Plus, in Kitchen Science, we bring you a watery way to measure upthrust.

In this episode

19:04 - How Many Licks...?

How many licks does it take to eat a lollipop? How many ants would you need to carry a person? Aaron Santos' new book looks at the statistics of the everyday world, and how estimate...

How Many Licks...?
with Aaron Santos, University of Michigan

Chris -   Now, have you ever wondered how many babies are getting born everyday or how many solar panels it might take to power the UK?  Well, one man has not only answered these questions but he's also gone on to show us how we can work it out for ourselves.  He's written a book and it's called "How many Licks" and it's been published and it's come out this week in the US.  It comes out here in the UK very shortly and his name is Aaron Santos and he's a mathematician & physicist of the University of Michigan.  Hello, Aaron.

Aaron -   Hi.  How are you?

Chris -   Very well.  Thank you.  Good to have you with us on The Naked Scientists.  So first of all, before we come onto "How Many Licks" and perhaps why it's called that, tell us a bit about yourself and what do you do?

Aaron -   Well, I'm a postdoctoral researcher in the Chemical Engineering Department at the University of Michigan and my background is in physics which is basically where I learned to do all these sort of problems, these sort of calculation problems.

Chris -   What sort of physics are you doing?

Aaron -   I do mostly statistical physics.  So, a lot of the things with nano scale systems, a lot of different self-assembly systems and nano particles, and a little bit of biology, but much more just regular straightforward chemistry.

Chris -   And so, what led you to come out of the physics world and say, "Right.  Let's write a book in which we try and look at some of these complicated calculations about the world around us."

A girl with a lollipopAaron::  Well it was actually, it was in the middle of my graduate class when I was studying for them and there's a problem that was on the class that was basically, how do you - you have to calculate something that you have no idea how to calculate it first and it's a general problem first originally proposed by Enrico Fermi, and I think the problem he originally used was something like how many piano tuners are in Chicago and this was something that his students were expected to answer by just doing straightforward calculations.  So, it just seemed like it would be a good idea to just put a clutch of these problems into a book for math.

Chris -   And the name "How Many Licks," how did that come about?

Aaron -   Well, there was a commercial.  I'm not sure if in the U.K., you guys get Tootsie Roll pops, but it's basically a Tootsie Roll encompassed in a lolly pop and there was a pretty famous commercial back in the '80s about - there was this owl when the cape goes up and he asked the owl, how many licks does it take to get to the Tootsie Roll center of a tootsie pop and the owl basically just takes a bite out of it and says three.  So, this was kind of the real answer to that question because that's one of the things what we consider in the book.  How many licks would it really take if you were actually going to sit down there and do it?

Chris -   Well, one of the other things you've been considering is say, the question, you sometimes see TV adverts where they use scalability and lots of small increments of something, adding up something very big.  One of the examples you give in your book is how many ants would you need in order to carry humans.  So talk us through that one.

Aaron -   Yeah.  That's one of the simpler problems in the book.  So, it's commonly said that an ant can carry 50 times its own weight and if that's true, how many would you need to actually pick up a human being and just kind of use it to walk you around?  Well, ants come in a lot of different sizes.  If you look on, I think it's Wikipedia, I think there's a factor of 500 between the smallest ant and the largest ant weight.

Chris -   I wouldn't like to guess what the factor is for humans, probably depending on some countries is quite big.

Aaron -   Yeah.  One would imagine, those countries probably should remain nameless.

Chris -   I think our country is between the two of them, probably leading the way actually!  So go on.  How do we calculate this then?

Aaron -   So, if you look at the ants, the ones that are crawling around my apartment, they're about 20 milligrams in mass and if they can carry 50 times their own weight then that means that they can each carry a gram.  So, a normal human being is somewhere around 65 kilograms.  If I divide 65 kilograms by 1 gram, then you can calculate pretty simply that it's about 65,000 ants that you need to pick up one human being.

Chris -   Do you think it's reasonable?

Aaron -   I never get into whether things are reasonable or not in the book.  I mean, there's a lot of things to consider.  First of all, how are you going to fit that many ants underneath you?  You either need very large shoes or you need to be lying on your back and then there is some question, whether or not you could even fit that many ants.  So, I try to avoid any pretense of reality in any of these calculations.  It's not really what we're going for here.

Chris -   Now, I got sent an email the other day, Aaron, where someone - it said on there - it said that, "Don't scroll down until you've read the top line" and then it said, "Around the world, about 35 million people are having sex at this precise moment."  And it said "Now scroll down, now scroll down, it set apart from one old timer who's currently reading his emails."  So, how many people are currently engaging in sexual congress right now then and how would you calculate something like that?

Aaron -   I should say before I answer this one that I answered a similar question in a talk that I gave once.  And was heckled mercilessly by a woman in a crowd who was convinced that the percentage of time that I thought people were actually having sex was much too low.  So, you might get a few angry calls in from this but...

Chris -   We won't judge it by your own standards Aaron.  It's all right.

Aaron -   Okay.  So to do a problem like that, you'd want to say, "Alright, well how often does a normal person have sex and this clearly depends on what type of person you are."  If you're a priest, it's going to be much rarer than if you were in a committed relationship in your early 20s.  But the number I used to calculate this one, it was, I'd say once every three weeks seemed like a reasonable number.  You're certainly not going to be having sex once every day, at least not by my lifestyle.  And once a year seems much too long, so once a week seems like a good compromise.  And then you say well alright, how long does a typical sexual encounter last and then it depends on do you count foreplay, do you count what counts as a sexual encounter.  But I thought, 15 minutes seems like a reasonable amount of time for that.  So, that gives you...

Chris -   People here in the studio are nodding.  They think that's okay.

Aaron -   Okay good, good.  Although I have to say that the people that I have generally asked these questions to tend to be scientists, so I think my results might be a little skewed, but you guys fit that demographic.  So, maybe that's why you guys are nodding in agreement.  But that would be 15 minutes out of three weeks, so you could calculate that that's about 0.05% of the time and then if that percentage also applies to the number of people that are having sex, then it's just 0.05% of the population which would be about 3.3 million people.

Chris -   So also my estimate was far too high.  My email that I got then was ten-fold too high probably.

Aaron -   It could be or I could have messed up on one of the numbers that I gave you, but I would question the email more than the numbers because I at least know where those are coming from.

Chris -   But the point of all this is that it's basically showing people how you break down a big complicated problem which scientists frequently encounter into a series of small steps and make a few small assumptions in each step in order to arrive at a ball park sort of figure.

Aaron -   Exactly.  I mean, you want to start with the things that you know how to do first.  I mean, you don't want to just guess at the number of people having sex because you could be way off with that.  But if you start doing things that you are familiar with and then just multiplying them together then usually, you can come up with something that's pretty close.

26:55 - Weighing Buoyancy

Weighing Buoyancy

28:34 - Does Shaving make hair grow faster?

Does Shaving make hair grow faster?

Diana - Well, the short answer is no. We had a really good answer from the forum about this actually from databit who said that hair grows actually in a cone shape. So, when you let it grow naturally, the end looks thinner and therefore, the hair looks thinner. But when you actually shave it, you cut it right at the base where it's at it's very thickest and that makes it look much thicker. So, once you've start shaving your hair, the stubble will look much thicker and make it look like more like it's actually growing, but there isn't. It's the same.

Chris - And the other point I think also to make is that when you're cutting a hair that is growing already, it's got a head start because it's already an actively growing hair compared with a hair follicle that was not active because hair follicles go through various cycles of activity and inactivity. So therefore, you're cutting a growing hair already therefore, it's already growing. Therefore, it's going to grow back quicker.

Diana - That's right. You sort of bring all the hairs back down to the same level of growth and so, it appears as if they're all sort of growing at once.

29:40 - Can you run faster on the moon?

Can you run faster on the moon?

Dave - On the moon, the gravity is about a sixth of the earth so you can jump much, much higher. Whether this helps you with running, it depends on what kind of running you're doing, I think. If you're trying to sprint, if the sixth amount of gravity then you're going to have a sixth of the amount of friction between your feet and the floor because friction basically goes at how hard you're pushing against the floor, and this means - but your mass is still the same, so you still need the same force to accelerate. So, he'll be able to accelerate about a sixth of the rate as he could do normally. So, in a 100-meter sprint, he's almost certainly going to be a lot slower. But if you're running a very long way, you could probably get an advantage because you can take huge strides. So, you can sort of - you could take a huge stride and then not do anything for a three or four seconds while you fly through the air and then you can land and do a little bit of exercise and fly through the air for a bit. So, you get some time to recover in between so I think you could probably run long distances faster, but short distance is not maybe as quickly.Diana - So, it'd be like the laziest race ever then, wouldn't it basically?Dave - Oh, it depends how fast you're going but, yeah.

31:13 - What is Limonene?

What is Limonene?

Chris - Brilliant. Yeah, well limonene, it's the stuff that makes oranges and lemons smell orangey and lemony. So, if you take an orange and you scrape the peel a little bit and smell your fingers, it's that very intense orangey citrus smell, isn't there?Don - Yeah.Chris - And that is the limonene. The orange peel contains huge amounts of it. It's a very big organic molecule. It's lots of carbon and hydrogen atoms stuck together in giant ring structures. And in fact, we did an experiment on The Naked Scientists a little while back. Dave did it as a Kitchen Science where you actually blasted some of the limonene through a candle by squeezing the peel of the fruit and you spurted the limonene into the flame.Dave - That's right. You produce a sort of aerosol of limonene into the flame and limonene is really flammable and so, it catches fire.Chris - But the reason that fruit makes it is because it's also quite nasty for things other than humans who haven't got fingers to peel an orange. If you try to borough through the peel of an orange, you'd have to eat the peel and the peel doesn't taste too good. Limonene is mildly toxic and being organic and unpleasantly tasting as it is, it puts off insects and that's a way that the tree uses of keeping its fruit in good condition.Don - Okay. I find it also in my shower gel. Why is it in there?Chris - Sure. Well the answer is rather than trying to invent artificial flavours and colourings and things which would do the same job as a molecule which is already doing the job very well in nature, sometimes it's easier just to use the natural product and then you can also have a marketing benefit because you can say, "Hey! This is a natural product. It's got limonene in it." So, rather than having to use orange flavored stuff or a small molecule that smells the same, then you can just use the natural product and then you get two bangs for your buck. So, what it's doing in your shampoo is contributing a nice orangey aroma and which also, because it's fatty and oily, it will stick to your skin quite well. It won't get washed off by the water and it leaves you smelling vaguely with a faint aroma of oranges. Have you noticed that?Don - Yeah. I have.Chris - Then we've got the answer right. Thank you very much, Don.

33:18 - Why can light not escape a black hole?

Why can light not escape a black hole?

Chris - The point he's making is that a black hole is a collapsed star. So, all the mass of the star ends up in the black hole. So, if light can come out of the star in the first place, given that there's no more mass now in the black hole when it's collapsed, what's changed that now light can't get out?Dave - That's right. When you take a star and convert it into black hole, you actually normally lose an awful of mass. It involves all sorts of explosions and lots of energy given off so that black hole normally weighs an awful less than the original star did, but that mass is much, much closer together - it's much more dense. The force of gravity even the Newtonian force of gravity is essentially proportional to the inverse square. So, if you're twice as far away from it, the force gets four times weaker. So, if you take a star and squash all that mass very close together and then you stand on the surface of it, apart from being burned up and everything, you stand on the surface of it then you're going to be a lot closer, a lot more mass. So the gravity is going to be much, much stronger. And once you go into relativity and general relativity then that mass can bend space enough that light always gets bent around and it can never escape at all, ever.Chris - So, if the black hole blew up again and you took the same mass and put it back to something that was the original size of the star - so in other words, the density was low again then it would start to emit light again.Dave - Yeah then light could escape no problem.

34:55 - The Centre of the Cell

This week saw the launch of the Centre of the Cell, a new children orientated science center located in the heart of Tower Hamlets in London. We sent Meera along to find out more...

The Centre of the Cell
with Professor Fran Balkwill of Queen Mary’s University, London; Fiona Haddesly Smith & Esmee, Petchley Academy; Helen Skelton, Blue Peter.

Meera -   This week saw the launch of the Centre of the Cell, a new children orientated science center located in the heart of Tower Hamlets and I'm inside the center itself now and it's very impressive, structurally, because it's basically a large orange pod that suspended from the ceiling over a working laboratory.  And with me now is the director of the project, Professor Fran Balkwill from Queen Mary University of London.  So Fran, tell me more about The Centre of the Cell.  What exactly is it and what does it hope to achieve?

Fran -   The Centre of the Cell is about inspiring the next generation of scientists and doctors and it's also a unique project, not only because of its location within the working research building, but because it's actually scientists who have led the project and its content has come from over 80 of our scientists.

Centre of the CellMeera -   And what is the content really?  So, what do scientists come up for it?

Fran -   The top-level message is that your body is made of millions of tiny cells.  When you're real, your cells have gone wrong and scientists in this building and all around the world are trying to find ways to make cells right again and make you better.

Meera -   And what would you say the aims of the centre are because it's located here in Tower Hamlets which is not necessarily most affluent of areas.  So, that's one of the primary goals of it, isn't it?

Fran -   Yeah.  It's about raising educational social aspirations.  It's about saying to the kids at Tower Hamlets, "You're worth it."  It's very much a local project.  We've involved 8,000 local children so far in evaluating every stage of the project but it's also got a global reach because we have our website which has had over 10 million hits from 140 different countries and many of the games in the pod are also available on the website.  But it is, in terms of the pod itself, it's about bringing in our local young people and inspiring them about science and having a dialogue with them.

Meera -   And what would a stereotypical visit then involve?

Fran -   It's free.  Booking is made online because it's a sort of planetarium type of experience.  As children come in, they look down over the research laboratories and they come into the pod.  Then there's an opening audiovisual sequence which is about cells and cell biology and then in the middle of the pod, the lighting changes and this amazing structure called the nucleus opens and inside, you find games about cells and cell biologies.

Meera -   Now, I'm just wondering around inside the Centre of the Cell and the pod has opened up to a variety of interactive games and I'm here with Esmee from the Petchley Academy.  Hello, Esmee..

Esmee -   Hello.

Meera -   Are you normally interested in science at school or has this helped you to learn?

Esmee -   I like science but I prefer more practical science and it helps me learn it.  So, I think this is helpful.  I mean, it's really interesting, the way it's actually in a laboratory and you can watch real scientists work.  It kind of puts into perspective.

Inside Centre of the CellMeera -  So we've heard the aims of the centre and the opinion of a student visiting it.  But is it really educating visitors?  Well, Fiona Haddesly-Smith is the Vice Principal of the Petchley Academy.  So Fiona, what do you think about the center?

Fiona -   I think the most significant thing will be that it is such an interactive set of games that are going on here.  And it is very, very interactive, and everything that the students have been learning in the classroom, they can actually take out of the classroom actually use it and see it working in practice.  Especially when the students are seeing the scientists working downstairs, so they do realize that scientists have real jobs and it's not just something that me as a teacher teaches in the classroom.

Meera -   And would you say then that the games and activities here really do then match what they're doing in their classrooms, so they match the curriculum?

Fiona -   They certainly do match the curriculum and I've been looking around and it is absolutely fascinating to see that a lot of the challenges that are presented at Key Stage 3 and actually Key Stage 4 are very precisely addressed here, especially modern science, modern treatments of medicine.  Looking at cancer, looking at the way in genes are inherited, looking at the way in which genetical traits are passed on from one generation to the next.  And it's really fantastic to see that you're talking now to a real life scientist who is saying the gene for deafness is passed on from one generation to the next.  And although I may be teaching that in the classroom, they can actually see it working in action here and that is absolutely brilliant.

Meera -   Today's launch was opened by Blue Peter presenter to Helen Skelton.  Hello, Helen.

Helen -   Hello.

Diana -   So Helen, what's your opinion on the Centre of the Cell here?

Helen -   Well, I was invited to come along and to be honest when I walked in, I just kind of stood there and I was going, "Wow!  This is cool."  I have to hold my hands and to be honest, if you said to me, "Helen, let's go and look at a science lab," I'd think, "Hmm.  I'd rather not.  That sounds a bit boring."  But this is isn't like that.  It's full of games, it's full of actual human organs that you can get your nose right up to and I think it just brings it to life and for me, science was always the boring subject at school, but this certainly isn't a boring experience.

Meera -   What do you think about the fact that it's hanging, kind of over the labs here at St Barts, do you think that helps the people to see what scientists do?

Helen -     Yeah, I definitely do because I think it's easy to go to a museum and you're sort of distant from things then.  But actually, what you're looking at is happening right beneath you.  And sadly, everybody can relate to cancer or HIV or whatever it is and the fact that there are people working right beneath their feet to combat those things is really quite remarkable.

41:26 - Can Refrigerators be made more efficient to actually generate electricity?

Can Refrigerators be made more efficient to actually generate electricity?

Peter - Hello. Well, my question is fairly complicated, so you have to bear with me a little bit. We start off with the refrigerator. Now, the refrigerator, actually, you get more benefits than the energy you put in. In the sense that you put a certain amount of electricity and to move heat from the hot to the cold or pump heat away from the cold areas. And you can pump significantly more heat in the energy you put in. So, you got sort of reverse efficiency where you can move several times and probably, I don't know three or four times. I don't know the exact figures. The energy reacted in.Dave - That depends on the temperature you've - the difference in temperature which the fridge is working across.Peter - Yeah, so you're actually moving physically more heat than the energy you're putting in. Now given that, can't we do the same thing in reverse and use the fact that we've created a heat differential to power a heat engine to generate the electricity back again. And now, one or two things will happen. Either will get more electricity out than we should in a sense that we've got an efficiency which is greater than the factor. For an example, let me say, if we pump in four times as much heat and to convert the heat back to electricity, we need only 25% efficiency or better to actually win in the game.Chris - So, this is worth making tons of free electricity just by running your fridge for cooling your beer down, Dave.Dave - Okay, so basically you're asking if a fridge can pump far more heat than the energy you put in, that's definitely true. In fact, if it's pumping for very small temperature difference it can pump 100 times more heat than the energy you put in. Can you make a heat - temperature difference with that and then use that temperature difference in order to generate electricity? We can use that temperature difference to generate electricity, we do use temperature differences to generate electricity all the time. Essentially by using a heat engine - something like a car engine is a heat engine. And basically they can produce high quality electrical energy by moving heat from a hot place to a cold place. But a fridge is essentially just a heat engine running backwards and again with a normal heat engine the amount of energy you can get out compared to amount of heat you can move is to do with the difference between the two temperatures. The bigger the difference in two temperatures, the more efficient it is. And so you'll never, ever going to get more energy out by going around to the circle like this.Chris - You'll just be violating the laws of physics basically, it's just not going to happen. Dave - Yeah, there's a really, really fundamental law of physics. Which essentially says you can't generate useful energy from nothing and this would violate it completely.Chris - It's an analogous question to, if I have a propeller on my car as I drove along, could I connect that to some kind of generator. And then power the car with the generator, it's kind of getting a free lunch isn't it? And it just doesn't happen, energetically speaking it's just not going to happen.Dave - Yeah, and I think actually with this one it would be far, far worse than, it would work far less well than that.

44:25 - Why does tea taste nicer out of china cups?

Why does tea taste nicer out of china cups?

Chris - I'd say, it's the placebo effect, wouldn't you? I think it's just because you automatically think it's nicer because it's in glass.Diana - Yeah, having lived, sort of six years on and off as a student, I think it starts to taste the same after a while anyway.Dave - A lot of what you experience from a meal food is to do with the surroundings which is why restaurants spends so much money on having pretty stuff in the room not just on the food.

45:02 - Can talking to plants make them grow faster?

Can talking to plants make them grow faster?

Chris - The answer is probably not. But I did a bit of poking around, in fact we have covered a story on the Naked Scientists a couple of years ago by Scientists (the reference is Meh Jong Jong) who is a crop researcher over in South Korea. And published this in the journal of Molecular Breeding. So it's a peer reviewed journal but I'm not sure how robust the science is. But what they did was to, for some reason - and they don't say why in their paper, they were playing classical music to different plants. And they tried 14 different types of classical music to see what effect this would have on the plant growth. And the plants, not surprisingly, did not respond at all. So then they thought well perhaps it's a mixture of tones and perhaps plants are sensitive to a range or specific set of tones. So then they started playing sounds at specific discrete frequencies at plants and monitoring gene expressions. So they would grind up the plant and see which genes have been turned off or turned on in response to the presentation of a tone over a period of time. When they played certain plants a tone at 50 Hz, a series of genes went down, turned off. When they played the same species of plants some sounds of 150 Hz, 125 Hz or 250 Hz, the same genes increase their activity. And when they use the molecular machinery, the bits of genetic sequence that turned those genes on and off and link them to another gene, that made the cells change colour, that's called a "reporter gene" they could, by playing certain sounds to the plants, get these plants to change colour. Suggesting that plants are are sound sensitive, so maybe in the case of cereals we know they have ears, so maybe they are sensitive to sounds and therefore maybe, there is some validity in saying you should talk at them. I think it's more likely though, that the CO2 that you are emitting in your breath when you talk to your plants is going to have a bigger effect than the range of frequencies. But maybe Bloke's voices being more low frequency dominate it would have a better effect than women's voices, I don't know.Diana - So, Prince Charles was right then?Chris - Maybe Prince Charles is right, maybe.Dave - Are plants vibration sensitive? Because when wind blows past them they'll vibrate, and if it's windy then they're going to want to have all sorts of different settings, than if it's not.. Chris - Yeah, plants definitely response to being moved around. Because they realize that this is bending them and they therefore need to strengthen and so they deposit more growth related products and then they turn on growth related genes in the other side of the stem to the one in which they are bending. So they strength from the side that they are bending away from. So in other words, it makes it stiffer on that side. And that's why trees can look a little bit bent but still stand up despite say an on shore breeze or something. So that's why.

47:44 - Why aren't planets compressed by gravity like stars are?

Why aren't planets compressed by gravity like stars are?

Dave - Well, yeah. Star, it's not actually the fusion which is holding the stars up directly. It's actually their temperature. If you had a gas, the hotter it is the more pressure it will exert, the harder it would push out. So stars are basically supported, they're basically made out of very, very hot gas - plasma that are supported by their temperature. So if a star gets hotter it will expand, star cools down it will shrink. A planet doesn't have to be supported like that, planets are made out of solid, lumps of things they're basically supported by the repulsion between atoms and molecules, in the same way as the table is supported or you're supported. So they are not big enough for the need the temperature to support them and basically just molecules and atoms are strong enough.Chris - Because planets like Jupiter are just around the threshold of what we call brown dwarfs, aren't they, they're failed stars are not quite big enough to squeeze themselves enough to trigger a fusion to actually get going.Dave - Yes, small stars it can also be supported just by this molecular strength basically.

52:00 - Why is laundry lint always blue?

Why is laundry lint always blue?

Diana - That's a good question actually. And now, Dr. Karl Kruszelnicki has worked a bit on on this and he actually did win an IgNobel Prize for his lint research. But he says that for both belly button fluff and laundry lint, is actually an average of all the colours of your clothes. So all the stuff that comes off even your white laundry, will end up being sort of slightly grayish, bluish, horrible colour. And if you think about even if you do have a lot of black clothing, and I'm sure most people will have at least one item of black clothing, will tend to sort of fade to grey and those are the bits that are more likely to disintegrate and fall off and become lint.Dave - It's not always blue. I once washed a bathroom mat from the floor, which was already fluffy and bright red. And that shed completely, it jammed up the whole washing machine and the lint that came out of that was definitely red. Chris - And the other slights a bit of additional information or perhaps you might or might not wants to know about Dr. Karl's study, he actually invited to send in their belly button fluff, to see that colour that was. I think it came out pretty much the same, didn't it?Diana - Yeah, the IgNoble people told him to never, ever do research on this again.

53:22 - How should or why should a polyester sheet make a fluorescent light bulb glow?

How should or why should a polyester sheet make a fluorescent light bulb glow?

Dave - No, this is perfectly normal. In fact we did a Kitchen Science on this a couple of years back. Basically polyester is a polymer which is quite good at charging up. So if you rub that against your hair or against other sheets it would tend to, as it touches the sheets it would slowly get electrons transfer to it (or away from it, I'm not sure which way with polyester) and so it gained a charge. This means if you move it near a fluorescent tube, a fluorescent tube is basically hollow tube with some very low pressure mercury gas in it. Some of that mercury gas will be ionized, it would've lost electron, you move a charged thing near that some of those ions will move towards or away from the charged thing, will accelerate along, will hit other mercury atoms and knock electrons off those and then you'll get a cascade effect. And get a little bit of electric current flowing through the tube one way, when you take it away then it will flow back again, and that will transfer energy to the mercury atoms some of that they will release as ultraviolet light. This will hit the sort of white coating inside of the tube and that will emit visible light, which you can see as this flash of light. Chris - So there's nothing radioactive about your bed, it's okay then, you're okay.

54:52 - Why can we not gain immunity to the common cold?

Why can we not gain immunity to the common cold?

Chris - I wish I knew the answer to that. It's actually just simple numbers. There are two reasons for this. One is to be immune to something, your immune system has to see it in the first place. So you have to be infected with the thing, so you then learn to neutralize it in the future. Now, that would be simple if there was one virus, but in fact there are hundreds.If you look at the rhinovirus family, which is the cause of the common cold, around most of the year, there is about a hundred of those. If you look at the enterovirus family, there's about a hundred of those. There is 50 or 40 adenoviruses, many of which cause upper respiratory and eye infections. Then there are the corona viruses, the parainfluenza viruses, the influenza viruses and to add insult to injury, these viruses also mutate. So not only are there hundreds of them around for you to get your immune system's head around but also they are moving target. They are changing their molecular appearance, so even if you have learned to recognize it, there's no guarantee that you'll recognize it again the next time. And given that there are all these hundreds of viruses and the average person gets about two or three colds per year, that's three life times worth of cold infections before you've actually got any chance of being immune to all of them, by which time they probably have changed.So, I don't think there's really any prospect of ever being able to cure the common cold with the exception that what scientist including Steven Legit who is a researcher of University of Maryland had done, is they've sequenced genetically all of the rhinoviruses so far. And they know how they divide up to a little subfamilies and it might be that if you a made a vaccine based around some members of some of those subfamilies, then every time you immunize someone who gets one of the subfamilies you are protected against all the other members of that family. So you could make a vaccine but it would have probably be based around lots and lots a different members and probably be unfeasible. Who knows, let's hope though that we come up with some kind of common cold cure soon because since you have children you're into a whole different ball game.

56:48 - Do plants have immunity?

Animals have wonderful and complex immune systems, with antibodies, compliment, t-cells... But what about plants?

Do plants have immunity?

John Carr from the Department of Plant and Sciences at the University of Cambridge:John - Most microbes like bacteria, fungi, and viruses can't infect the plant. But some through evolution, have gained the ability to break down the initial barriers to infection such as cell walls and so on and these can cause disease. Now in response the plants have evolved the ability to respond to and recognize particular types of pathogens. So, that's why some plants have resistance genes and these is a sort of genetic mechanism of allowing them to pass on the ability to fight off particular diseases. Now when this occurs, you might find that the cells which are initially infected with a virus or a bacteria or fungus actually commit suicide. And this is one way of creating a kind of a scorch earth against the pathogen but also it's a way of creating signals, lots more interesting chemicals that float out through the plant tissue. Sometimes plants will produce salicylic acid, it is the parent compound of aspirin and it is a very, very powerful inducer of resistance. So if plants are producing salicylic acid, they are better able to fight off perhaps the first pathogen to attack them unremarkably they're able to fight off possibly lots of other types of pathogen as well. So salicylic acid itself aspirin like compound can give rise to something they call methyl salicylate and this can float off to other plants and influence other plants so they become more resistant.Jonathan Jones, Sainsbury Laboratory, Norwich:Jonathan - Hi, I am Jonathan Jones. I worked at Sainsbury Laboratory in Norwich. Humans have two kinds of immune system, they've got the innate immune system, which recognize molecules that pathogens can help making like flagellum of bacteria for example. And they've got the adaptive immune system which involves antibodies and that's what is triggered when you immunize against viruses for example. Plants and many others sort of less sophisticated organisms have only an innate immune system. They can recognize molecules and pathogens and activate defense. The defense components involve making a sort of bleach - an active oxygen cocktail that inhibits microbes and can culminate in cell death. They also in plants make a lot of anti-microbial proteins that inhibit growth of microbes but also many pathogens squirt proteins into plants cells, to shut down that immune system. And then there's another immune system involving proteins inside the plant cell that recognizes when these molecules show up inside the plant cell and activate defense.

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