That May Q&A!

Izzie Clarke received this chemical query from Europan Ocean on The Naked Scientists Forum, which also inspired fellow panellist Bill Colledge to chip in. It was over to chemist and writer, Kit Chapman, to sniff out an answer for them...

Kit - Well, you could set the material on fire, that will certainly get rid of everything. But assuming you want to keep your clothes, let's have a look at what body odour is. Your body will naturally release all kinds of secretions, sweat is a great example, and the natural bacteria that live on your skin, and everyone has it it's perfectly normal, they will start breaking those down and release molecules that stink. And they'll react with your nose sensors and that's how your find out that you're a bit wiffy.

So when things dry on your clothes, what can you do? One thing is to wash them. Water is fantastic for getting rid of those horrible smells and also you can use a detergent. Now, detergents are fantastically shaped molecules because they have what we call a hydrophobic tail.

Izzie - Now, that means that they are essentially afraid of water?

Kit - Exactly. The tail is afraid of water, but the head loves water. So it sticks the tail in those fats, it breaks things up and gets rid of them, and that's how we get rid of dirt, and that's why you use washing-up liquid to clean your plates, same kind of principle. So you can get rid of stenches that way.

The other thing you can do is try and neutralise them. One thing that works very well is actually using white vinegar in a bowl of water and that will absorb the smells from the room and neutralise them.

Izzie - And so why is it that combining that with water, that white vinegar, gets rid of it?

Kit - It's not necessarily combining it with the water, it's just making sure that the white vinegar is actually going around the room essentially. It's because of an acid-base reaction. It's very very basic chemistry.

Speaking of basic chemistry another thing, and other brands are available, but Febreze is a great example of how you can actually trap these smells. Febreze has a structure in it called a cyclodextrin and that's shaped like a donut. It has a big hole in the middle, it's a sort of a circular molecule. And what it'll do is it will get those molecules in there that are causing the horrible smells inside that circle and trap them. You can't smell it and the molecules are still there, but the BO's gone.

Izzie - Oh Bill, you've got a question.

Bill - Yeah. I know some people use sodium bicarbonate to put in the microwave to eliminate smells. How does that work?

工具——我们完全相同的路由s the vinegar. Sodium bicarbonate is a great version of a base and it will cause that same kind of reaction. So it depends really what the smells are as to how you get rid of them. But sodium bicarbonate - fantastic for cleaning products and these things are really really cheap. Everyone thinks that you need to go for really expensive cleaning product, but actually white vinegar, sodium bicarbonate, things that we've used for over a hundred years now are just terrific.

The Naked Scientists love chatting about mythconceptions; the common myths that can be de-bunked by science! Izzie Clarke is joined by physicist Ben McAllister, plant ecologist Howard Griffiths, chemist Kit Chapman and reproductive physiologist Bill Colledge who all brought in their own myths.

Ben - Right. Mine’s actually more of a science history myth than a science myth itself. I figured given that I’m here to represent the physical sciences I might confront a common myth about one of the most famous physicists of all time. You may have heard the idea that Albert Einstein supposedly failed some maths tests in school or maybe it was in university or something. And yeah, that’s not really true. He was something of an unconventional student, there is a bit of truth in that. He didn’t get along with his teachers, he didn’t like the way things were normally taught, he had a tendency to sort of not pay attention in school. But all signs point to him doing maths quite well at all times which probably makes a fair amount of sense if you think about the career he went on to have. But the origin of the myth is that when he did try and get into university he did fail his entrance exams, but it was not because he failed the maths section, it was because he failed the botany, zoology and language sections. So perhaps someone here on the panel could have helped him out there but yes, in the mean time, he was alone.

Izzie - Do we know where it came from or is it just one of those ones that just floating about?

Ben - Yeah, I think probably just spawned out of that, the fact that somebody read somewhere he failed is entrance exam into university and then wanted to create some kind of pseudo-inspirational myth surrounding it, which is a nice story. “Albert Einstein, one of the greatest physicists of all time, failed his maths, so if you're bad maths you might be good later,” I guess is the message. I don't know but yeah, something like that.

Izzie - If anything, he went on to be a very, very important person for the world of physics and maths. Howard, what are you putting down as a mythconception?

Howard - Okay. What really gets me wild is when I hear regularly on TV and radio programmes that the rainforests are the lungs of the Earth. Now don't get me wrong, I think trees are absolutely vital. I want to plant more trees. I want to stop people cutting down forests because forests are absorbing carbon, they're protecting us against climate change.

But, when that phrase is used, it's often used to infer that the oxygen we breathe is being produced at this minute by the forests. And what you've got to remember are that forests are really giant compost heaps. There's as much rotting, degrading and material just being respiring and consuming oxygen as there are in the photosynthetic leaves above which are producing oxygen, so there's roughly a net balance.

Izzie - Okay. So do you know where the majority of our oxygen comes from?

Howard - Well, it did come from plants. It's come from plants both in the marine system and on land over the last 2.4 billion years and gradually, organic carbon made by plants has been buried either underground in the sediments, turned into rocks and so on, and that’s trapped carbon. Some of its turned into fossil fuels which, of course, we're now burning and releasing CO2 back to the atmosphere. But that's where the carbon went and that allowed the oxygen to gradually increase in the atmosphere.

Izzie——非常感谢霍华德。现在装备,是什么you putting down as something that gets on your nerves?

Kit - This myth that you can’t turn lead into gold. You absolutely can do that. You don't want to do that, but you can do it.

Izzie - How would you do that?

Kit - Well, in 1980 there was a very famous chemist called Glenn Seaborg and he was a nuclear chemist. And what he did was he got a particle accelerator and he fired carbon and neon atoms at a piece of lead and chipped off some protons, and protons decide what element you have and he bashed it way back down into gold.

Izzie - Right. Why aren't we all trying to make gold then?

Kit - This is the problem. To fire up a particle accelerator is a bit expensive. It cost him around $120,000 a day to do it.

Izzie - A day... wow.

Kit - So he worked out that to make one ounce of gold would cost one quadrillion dollars.

Izzie - Come on guys, we can put that down together, no?

Ben - It's definitely something we could scale as well. Maybe it cost that much today, but we’ll push that down in time if we all put enough effort into it.

Izzie - Bill, how about you?

Bill - Well this is a sort of myth that I’d like to debunk which is aimed at couples that are trying to conceive. And people are told that if you’re trying to conceive there’s a window of fertility which is the best time around the time of ovulation for the woman, and if you’re having sex around that time you should have intervals. You should have sex every other day. And it was thought that this is to allow the sperm to build back up to increase your chance of conception.

And actually, it’s completely not true. The best way to conceive during this window of fertility, the window of opportunity, is to have sex as often as you can, provided you’re up to it of course. And the reason that we now know it’s best to just have sex frequently comes from IVF clinics where men have gone in, they’ve given a sperm sample and then they’ve taken another sperm sample two hours later, and often the second sperm sample has more sperm than the first. So basically, you can have just have sex as often as you want during this fertile period and that will improve your chances of conception.

Izzie - Do we know why that happens that a few hours later there is a higher sperm count?

Bill - Well, we make a lot of sperm very, very rapidly. I think that we’re making 5,000 sperm every second - well we are, I’m afraid you’re not. But men are making 5,000 sperm or so every second so we’re making millions of sperm over a few hours. And I think what happens is that the first time you make sperm there maybe some there that has been sitting around for a while, whereas two hours later it’s sort of fresh stuff so they’re much more virile and much more potent.

Izzie - We talk about this ovulation period, the golden opportunity, six or so days a month, can a woman get pregnant outside of that period?

Bill - There is a reproductive window during which a female is likely to get pregnant and it lasts for about six days. The reason it is such a short window during the whole of the cycle is that an egg is only viable for about 12 to 24 hours once it's released. Sperm cells are a bit more robust, they can be viable in the reproductive tract for up to 5 days. So if you put these two together you've got a window of about six days when you're more likely to conceive, and outside this window you're ultimately much less likely to conceive and women often use this natural sort of rhythm method to monitor when they're going to ovulate and to make sure that they don't have sex close to that period.

Izzie - We're going to get to contraceptives later but is that a reliable method of contraception?

Bill - It's not the most reliable method of contraception. I think if you use that method you have to be prepared for failure some of the time. There are more reliable methods.

We received this question from SooYeah on The Naked Scientists Forum. Izzie Clarke asked Howard Griffiths from the University of Cambridge to dig out an answer as well as take on panellist Bill Colledge's own question.

霍华德——好吧,我认为你已经回答了你own question. But just to explain: beauty really is in the eye of the beholder. And if you're a naturalist and wandering through the countryside, many of the natural plants you see would be classed as weeds if you found them growing in a cultivated border. Equally so, you might see plants like invasive aliens, like Japanese knotweed, or a giant hogweed, or something like that, and you might think that's a weed of the countryside, we need to get rid of that one.

It really does depend where those particular plants are. I do remember as a child being told a joke, which I don't think is a very good joke, but it asked, how could you tell whether a plant is a weed or a border plant is: you pull them all up, and the ones that regrow are the weeds.

Izzie - Very true. Of course, they're really hard to get rid of. You can spend so much time pulling them out and thinking great, got that one done, and then give it a couple of days it's back again, so how can you actually get rid of them?

Howard - Well, I'm not a great believer in using chemicals and sprays although, of course, you can use those very selectively and very carefully if you paint them onto individual plants, and some of them will be taken down into the plant and kill the actual deep roots, that are the ones from which the plant will regrow. I'm a great believer in weeding, and hoeing, and using rather traditional methods of weed control.

Izzie - And speaking of annoying things in the garden…

As a bit of a follow-up - it seems to be on everyone’s mind at the moment - Emma has also got in touch to say

Q - How on earth do mealybugs/other bugs grow on plants? Where do they come from?

Are these those small green bugs that we see on plants, that we actually don’t want there?

Howard - Mealybugs are a kind of a scale insect. They're rather similar to aphids, they are a slightly different class of organisms, but they have similar penetrating mouthparts. We talked earlier about the water conducting system of plants, this is
the sugar conducting system of plants. So they dip into the phloem and they feed on that. And that's why they often exude droplets of honeydew, aphid honeydew, which you may hear of.

So where do they come from? Well, they overwinter in cracks and crevices, or in the soil, or they may be laid down as packets of little eggs from which the new instars will germinate once the cold weather has gone away.

Izzie - Are they a problem for plants?

Howard - They're a real problem for plants. Not only because they're feeding on some of the sugars that the plants are trying to supply to some of its growing areas, but they also transmit lots of diseases: lots of viruses are transmitted through these sap-sucking insects. And there's some very interesting science being done by my colleagues which shows how even the viruses change the behaviour of the insects in order to make them move on and move to another plant and so on.

Izzie - My goodness! Is there anything you can do to get rid of them?

Howard - Well, again, I'm all in favour of using warm soapy water to wash them off, or gently going along and squiging the blackfly on my broad beans with my fingers. I'm afraid it's a bit messy. But you can use safe sprays that are available from garden centres and so on.

Izzie - Bill, what would you like to ask?

Bill - When I was doing biology at school, my biology teacher told me a story and I just like to know if this is true. Scientists wanted to know what the composition of the sap was from the phloem and you mentioned the aphids tapping into it. And he said that what the scientists did was they took aphids and they chopped off effectively their head and left the bit that was in the sap, and they collected the droplets of sap coming out and they analysed it and that's how they did it. Is that correct?

Howard - There's some fascinating videos available on YouTube which can show scientists excising aphid stylets and collecting the sap as it drips out. The very clever trick that aphids have learnt to do is to is to plumb into the phloem without it blocking. If you artificially try to put a needle into the phloem, it will automatically coagulate and block and prevent the sap from flowing, but the aphids have learnt how to circumvent that problem.

Izzie Clarke asked Chemistry World's Kit Chapman to tackle this explosive question from James on Facebook.

Kit - Well, the energy isn't actually coming from anywhere. We don't make energy. If you know how to make energy, contact me, we'll win the Nobel prize, it'll be fantastic. Energy is just transferred. What's happening here is we're transferring it from the chemicals themselves out into the atmosphere. When you have a chemical reaction this is what we call an exothermic reaction, so something that gives off heat, and what you're doing is breaking up the bonds. So, if you think about it, you've got your molecule, that's atoms attached to each other with bonds, those bonds have to be broken and reformed to make whatever you're making. And so when you break those bonds you're releasing the energy there. When you're reforming the bonds, that takes up less energy usually and so that means that there is energy left over, and that's given away as heat.

Sam wants to know about the pros and cons of nuclear power. Izzie Clarke asked physicist Ben McAllister, from the University of Western Australia, to start by explaining what nuclear power is...

Ben - Okay. There are two primary types of nuclear power. I'll very quickly run through both of them. We already heard from Kit before that we can’t just create energy out of anywhere, we have to get it from somewhere else. In the context of nuclear power we are making use of a very famous relationship that was first, I guess you'd say discovered, by a person I mentioned before - Albert Einstein with this very famous equation e = mc squared, which tells you that the energy that a given thing has is essentially equal to its mass times a constant, the speed of light squared, which is really just a way of saying that mass, how heavy something is if you like, is just another form of energy. So, if you can change a thing’s mass then you can harness some energy by breaking off a little bit of mass and converting it into energy, and the amount of energy you can get out is really really really big.

In the context of nuclear power what we're doing is essentially taking - well I mentioned it as well before with uranium and elements that can break down and become other elements - you're taking something, for example, big like uranium, and it has a certain mass. So a uranium atom has a certain mass, it breaks down into two smaller atoms, but when you look at the mass of those two atoms combined, it doesn't quite add up to as much as the uranium atom that you started with.

Izzie - So you've lost a bit?

本,你没有失去它,它只是转换ed into energy and it’s radiated away. And that's sort of the fundamental principle of what's called nuclear fission power and that's what goes on in all nuclear power plants that actually generate energy in the world today. You could also, theoretically, make use of another nuclear process that works in a similar way, which is called nuclear fusion and that's what the Sun does when it wants to make energy. So what you would do with nuclear fusion is you take a light thing like hydrogen - the lightest element - and you’d smash a bunch of hydrogens together until you got a helium, which is the next lightest element. But, again, the mass of that helium atom is going to be slightly less than the mass of all the hydrogen that you put in so you get a bit of energy released.

And the pros and cons of these things? Well, if you're talking about nuclear fission which is the one that we know how to do, again there are no fusion plants on earth yet, although we're getting there, the Sun is an example of one. You take a nuclear fission reactor and you break down stuff like uranium. The great thing is you don't produce a lot of carbon dioxide, you don't produce a lot of other harmful greenhouse gases and it is pretty good for the environment in that way.

The cons are you can produce a lot of radioactive waste. Personally, I actually think the amount of radioactive waste that you produce is pretty acceptable from modern plants compared to the kind of toxic stuff you put out from every other kind of energy production that we use. You've got to put something out. And the other con is that there is the possibility for, essentially, huge disasters. Like you may have heard of the Chernobyl reactor meltdown, there was Fukushima in Japan a few years ago, where the reactors essentially 'run away'. They generate so much energy and they create what’s called this chain reaction that runs away and you can’t control it,and they just keep putting out so much energy and they melt down.

Izzie - Looking at nuclear fusion though, are we close to getting anywhere near getting to dod that process?

Ben - Nuclear fusion is difficult because you essentially need to create conditions similar to the Sun which means you need very very high temperatures. You need to have things very very close to each other, very condensed, very high pressures. We have been able to make nuclear fusion reactions happen on earth, it’s just that we haven’t been able to do it in such a way that we’re getting out more energy than we’re putting in, and we’re able to keep them sustained for a really long time, which is what we would want to do if we were going to build a reactor, essentially build a small sun. If we could do it would be great because nuclear fusion will get around basically the two biggest problems associated with nuclear fission, whilst also still producing no CO2.

第一个是,没有有毒废物或a very very small amount of waste produced. The main byproduct from a nuclear fusion reactor is helium, which is really inert, it’s not going to do anything to the environment and in fact, we actually need it to do other science. It’s a thing that we need and that we’re actually running out of. So if we could make a bunch of it as a byproduct of creating energy, that would be kind of cool. The other thing is it’s very very hard for a fusion reactor to melt down so we can reduce the danger there as well.

Charles sent this question into The Naked Scientists on Facebook. Izzie Clarke was joined by reproductive physiologist Bill Colledge, from the University of Cambridge, who took us through the history of puberty.

Bill - Yes, they are. If you look historically at the age at which, particularly girls, first start going through puberty - and usually this is measured by their first period - in 1850, let's go back to 1850, it was about 17 years old. By 2010 it’s 12 years old. So there's definitely been a decrease in the age at which children go through puberty.

Izzie - And do we know why that is?

Bill - Well, partly this is caused by better nutrition, so people are better fed now. Certainly from 1850 onwards we've got better nutrition. And what is happening is people are growing more rapidly, they're gaining a critical body mass, and you have to achieve a critical body mass to go through puberty. But importantly, is not just about how much you weigh, it's about how much fat you carry in your body. And it's thought you have to have about 17% of your total body mass as fat to go through puberty, and you've got to have about 22% of your total body mass as fat to maintain fertility, and if you fall below those you either won't go through puberty or you will become sub-fertile. Top athletes that have less than 5% body fat, the females often don't cycle, they don't menstruate, they're infertile, because they have less body fat.

So what we think is happening with the Western diet of course, children are perhaps becoming obese, they're carrying a lot of body fat at a much earlier age, and this means they're actually going through puberty at an earlier age.

Izzie - Does that impact your life later on?

Bill - It can do, yes. It can increase the risk of developing certain types of cancer - ovarian cancers - because as soon as you go through puberty you start making all the various female hormones, and you are having a longer exposure to those over your lifetime. So it does increase the risk of some types of cancer.