Chris Smith -   Ah, yes my kettle is no exception and the reason that kettles are noisy, they make that sort of thumping and bashing noise as they boil and then the noise intensifies as they warm up and then it goes silent as they boil.  It is because of the way that the heat is being transferred into the water. So you have an electric element inside the kettle, a high current is passing through that element which makes it get hot.  The heat from the element is therefore transferred by convection and conduction locally onto the water molecules around the element; they then get excited and get hot. So you have a bubble of hot water around the element which tries to expand and it also floats upwards away from the element because, of course, warm things rise but as it rises of course it loses its heat again to all of the surrounding water. So this bubble of water and water vapour collapses in on itself very quickly and that’s cavitation and you get a shocking, sort of knocking noise.  So those thumps that you hear and the sort of ‘shhh’ hissing that you hear, as the water vapour bubbles collapsing on themselves and emitting some sound waves, that’s what the sound is.

Dave -   Sounds of the bubbles, as the water is boiling, forming little bubbles of steam and as they rise up in the colder water they shrink and collapse and then smash into one another and make lots of noise.  So it gets a lot quieter once bubbles get all the way up to the surface and they stop cavitating.

Helen Scales -   It makes more noise I think when I have less water because I try and have as little as I need for a cup of tea, obviously covering the element but not lots more to save on energy and I think that’s noisier. 

Chris Smith -   It could be there’s a bigger rezonant cavity inside the kettle because the bubble makes a sort of note inside the cattle and if you got lots of free space then the air will help to move around and bounce and sound around inside the kettle like an echo chamber.  So that might be why you are hearing more sounds, probably what’s going on.

I have got a question for you Helen here. It is from Glenn Colson who says: ‘Do fish sleep?’

Helen Scales -   Well I think Diana talked about on Question of the Week a couple of weeks ago about whether fish have eyelids and they don’t.  So can they sleep? The answer is yes, they can but it also depends on how you define what sleep is because in humans the transition into sleep involves changes in the patterns of brainwaves in an area of our brain called the neocortex and fish don’t really have the same development in their neocortical region as mammals, really.

So it’s kind of difficult to say in the same way what sleep really means for fish but they do.  If you count up things like a reduced metabolic rate and slowing down activity then they do seem to sleep and Zebra fish, which are fresh water fish, have been studied in the laboratory. If you watch them, and I think this is rather sweet idea that. You can watch them during the day and they will actually sort of doze and their tails droop down and they stop moving around at certain times of the day and they do seem to sleep.

That’s one thing and in Antarctica, actually only last year they discovered the first hibernating fish and apart from mudfish that aestivate and keep themselves alive when things dry out.  In Antarctica they actually slow down and stop feeding and their heart rate slows down. They used heart rate monitors on these fish to see what was going on and we think that it was probably because it gets darker in the winter in Antarctica. In fact it gets completely dark because there’s no sun and they find it hard tracking down their prey because this prey is still out there but they are visual hunters and without the light around they find it very difficult to find their food so they sort of stop.

Chris Smith -   They just sleep.

Helen Scales -   And they’re a bit like bears. Some bears don’t sleep the entire winter. They will actually kind of wake up every few weeks, have a little wander around, find a bit food, go back and sleep again. That’s what these Antarctic cod seem to be doing as well.

Chris Smith -   It’s quite interesting because Glenn has written a few things he spotted and this question was provoked by things he actually saw himself.  He says: ‘A few years ago I was on a night dive in the sea of Cortez and we actually think we saw a fish sleeping in a number of different ways. There were fish in caves or nooks that were awake but only slightly responsive. There were also fish lying on the sea floor looking like they were dozing soundly and they weren’t at all perturbed by our diving light and there were others that had wrapped themselves in a cocoon of slime that seemed to act almost like a protective blanket.’

He says, ‘I suspect they have nightmares as well because as we watched a large moray eel swam slowly across the bottom of the seafloor stopping to sniff prospective meals as they were snoozing and then choosing his favourites but the moray left the blanketed fish alone.’ A wrass he believes (which he found interesting) because he said that the eels and they normally find it quite tasty.

Helen Scales -   Yes, they are parrot fish and they produce this kind of sleeping bags and we do think that stops them being able to smell, the predators can’t smell them but there are other fish that come awake at night. In fact if you go night diving you see a completely different eco system really because the ones that were sleep during the day tend to come out. They are often coloured red because they actually, that means they can’t be seen at night because the red colour is absorbed when light is absorbed in the water. So you see kind of a shift change in day and night fish when you go night diving. 

Dave -   Okay. A normal CD works by just having a sheet of aluminium with lots sort of pits in it.  You make the pits by having a glass.  You etch a glass thing which you push into the sheet of aluminium, that makes the bumps in the aluminium and then shine a laser on it. Then they get reflected differently from the pits and tops and bottom of the pits and you can read that information and then that information gets turned into sound and you can hear it.

The sheet of aluminium is a shiny thing.  It’s encased in polycarbonate and so it’s nice and protected.  A recordable CD works by having the same polycarbonate disc. They have a layer of dye over the top. This dye is sensitive to light and we have a shiny thing behind it.  There’s various different kinds of dye with different - some little better than others and survive a long time that’s why you have different colours of CDs and CD-Rs and so it changes colour.

Chris Smith -   Oh so when you zap it with a laser rather than burning hole in it what it actually does is changes the dye configuration so that what the reader is looking for is a dark spot rather than a hole.

Dave -   Yes, and the dye changes colour.

Chris Smith -   And then when you come along with another laser you can what, reset the dye to it’s original colour which overwrites the…

Dave -   I think they then hit it with a different pair of laser which heats it up to a different temperature which then re-sets it and then it cools down slowly and so it zeros everything and then you can come along with the second type analyser and we rewrite it.

Chris Smith -   My own take on this is no, because I have chronically cold feet.  But they say “cold feet and cold hands - warm heart” so I am all right.  But there’s no real evidence connecting going out in the cold with catching a cold.  It’s one of those urban legends that gets trotted out, “don’t go out with wet hair because you might catch a cold.”

The only real evidence in this favour was there was some studies done in Scandinavia in people who were dong very severe exercise and they found that in those individuals, exposed to very cold extremes as well, taking some vitamin C did help to ward off colds, but on the whole getting cold doesn’t increase your risk.  It’s actually physically being exposed to the pathogen that increases your risk.

The only sort of exception to that is if you get very very cold and you get so cold that you get damage to your mucus membranes, your linings of your nose in your mouth, then of course you might make yourself, if you get cracked skin or break down of the mucus membranes more vulnerable to say a bacterial infection coming in on top.  So you have to be careful for that but there’s not actually any evidence connecting getting cold or washing your hair and catching more pneumonias or colds or viruses.  So you are probably okay Emil.

Chris Smith -   So in other words you’ve got huge panoply of life on earth, all of it descended from some ancestor that must have got started something like 3.9 billion years ago, that’s when we think life started on earth, how do we have this massive and dramatic genetic diversity we have on earth today?

Well the answer is that we use as our genetic material DNA and some organisms use RNA, they are two related molecules and the basis of evolution and inheritance is that that genetic material has to be copied and passed on from one generation to the next in gametes, in other words, sperms and eggs.

Now in copying the DNA, a job which is done by enzymes — miniature machines in cells that read a DNA chain and then make an identical (hopefully) copy of it; then you end up with faithful transmission of the genetic message from one cell to another.

But occasionally mistakes occur and there are a variety of reasons why mistakes can occur. One of them is that those enzymes that do the copying make a mistake, it’s like me copying a book – I’ve got a book opened in front of me and I’m reading off the book and making a new copy in a second book, I might miss-copy and make some mistakes.

Secondly, there are things coming in from the environment that can damage DNA. There are drugs, there are chemicals in the environment; there’s also radiation in the environment that could be ultraviolet radiation, it could be chemicals you take into your body, you could be living in Aberdeen and breathing the radon gas that comes out of the granite there. Anything radioactive that gets into your body can also damage DNA.

If that happens to the cells that are making your gametes, your sperms or eggs, that can lead to mutations — changes in DNA. This can cause DNA to rearrange itself, bits of DNA can get copied or duplicated, and this means that there’s the opportunity for new genetic combinations to emerge; and once they emerge they can then get co-opted or changed or manipulated in order to do other jobs; and we know this happens because if you look in human DNA you can find the ghosts of genes long dead hidden in our genetic closet.

You can find for example, lots of old genes that used to make our haemoglobin which are now no longer effective, and no longer functioning. They’re called pseudogenes. But this is where we have copied the genes somehow and then its becomes deactivated but it’s still in the genome.  Now some other process could come along and reactivate that gene and use it for something else so it’s a way of making genetic diversity.

Another way this happens, is something called transposons, you have bits of genetic material that can literally jump and they take themselves out of one bit of your genetic material and put themselves somewhere else carrying bits of DNA with them, and so this is another way of rearranging your genome and producing new forms of genetic sequences which can then become other important genes.

A final way is viruses, because viruses — certain kinds of viruses actually physically insert their genetic material into the DNA of their hosts.  HIV does that, other viruses could – retro viruses do that and a really elegant example of this is that there is a certain sea slug, it’s called a Sacoglossan sea slug which eats algae and when it eats that algae on the sea floor it actually gets the chlorophyll containing chloroplast — these are tiny bodies inside the algae that contain the green pigment that enables the algae to trap sunlight, and the slug gets hold of those chloroplasts and puts them into its own skin and keeps them alive so the slug can also use the energy of sunlight to get energy.

The interesting thing is that the slug has had to steal some genes from the algae in order to power those chloroplasts in its own cells, and the only way researchers think that could happen is if a virus added the genes to the slug in the first place.

So the answer is, it’s very complicated but it seems that with nature and evolution, almost anything is possible.

Helen Scales -   You’re talking about sperm and eggs, and barnacles if you’ve ever been down to this shoreline are rooted very solidly to the spot, so how do they move around and find a mate?  

Well lots of other marine creatures have a similar problem. Things like corals which are animals, they don’t move either but they solve that by sending their sperm and eggs up into the water and hopefully they’ll fertilize and they’ll meet each other and fertilization will take place and larvae will be created, but that’s not what barnacles do.

Barnacles look a bit like other types of mollusc on the seashore but they are in fact a type of crustacean, like crabs, and lobsters, and things like that, but very much smaller, but they do actually have sex directly and the only way they can do that is by having a very long appendage.

The male barnacles have very long penises, one of the longest in comparison to the size of the body, that there is in the animal world – animal kingdom, and –

Chris Smith - They didn’t include me in the analysis — I’d just like to say that.

Helen Scales -   No comment – and the barnacle males, will literally poke around next to them and see what they can find, so they don’t have much reach really in actual terms but they can reach out and fertilize female barnacles.

Chris Smith -      That’s amazing!  So if you look at the barnacle crop that you see on rocks, do you see sort of concentric rings of males, females –?

Helen Scales -   You must see some sort of patterning like that indeed, because you would have to be arranged in space, around on that rock to be able to reach other members of the opposite sex, and they obviously mate with lots of other different barnacles to produce lots of baby barnacles, and but that’s how they do it — and that seems rather wonderful. So take a closer look next time you’re down on the shore.

Chris Smith -   Thank you very much, Helen!

Dave -   Well, Hubble is an incredible telescope but looking up it’s resolution — I reckon it has a resolution of 0.05 arcseconds, that means it can distinguish two objects which are 0.000013 degrees apart, any closer together than that and they sort of merge into one object. Now –

Chris - In practical terms what does that mean?

Dave - That means if something – the distance of the moon away from us, Hubble is essentially near the earth its very level, but –

Chris -   So about a quarter of a million miles to the moon?

Dave -   About 384,000 kilometres—that means you can see something 9 to 10 metres across on the moon, so probably not.

Chris - That would be a very big footprint – Bigfoot literally. Okay, thank you Dave!

Chris Smith - Well, Fran, we know that the major culprit for making holes in the ozone layer are chemicals called CFCs — chloro-fluoro carbons. These are things that were used in aerosols, even in aspirin inhalers, but also in fridges as refrigerants, and they were used in huge amounts until the Montreal Treaty came in, in the late 80s to try and ban them. What provoked that was that a group of scientists including Brian Gardner (who appeared here on The Naked Scientists a few years back) had actually noticed this massive hole opening up over Antarctica in the mid-to-late 80s and this hole actually grew to be the size of Australia at its peak. It stopped growing; it’s actually beginning to shrink a little bit now and that’s because we have stopped using these chemicals. The reason that they concentrate down in the Antarctic is because the Antarctic is an isolated continent. It’s completely surrounded by ocean and this creates something called a circumpolar current, and this has a sort of whirlpool-like effect in terms of air; and it draws in and concentrates these molecules over the Antarctic over winter when it’s very dark. They then accumulate in high clouds over the Antarctic and when the sun comes out the following spring the sun breaks down the CFCs and they get turned into reactive chemicals that would then react with the ozone and deplete it. They are, by far, in a way the worst culprit. We don’t send enough rockets and spaceships up into space to make a huge difference, I wouldn’t have thought, in grand scheme of things. So I think although we have to be environmentally conscious, I think the benefit of sending rockets into space in terms of what they can do for satellites and furthering research is far greater than the small bit of damage they might make to the ozone layer. So I think on the whole, probably not, it’s probably more a manmade, anthropogenic problem. But great question, thank you for that.

Helen Scales -   That’s a great question but fundamentally photosynthesis actually began in the oceans — in underwater, because that’s where plants and algae first evolved. They then moved onto land.  So light definitely gets into the upper layers of the ocean and that’s where the process of photosynthesis traps that light and converts it into energy — into carbohydrates really, that the rest of the food chain relies on. So it’s really the idea is that you have to maintain plant life, algae has to maintain itself in the upper layers of the ocean because once you get further down into the depths of the ocean, first of all red light gets absorbed which is why the oceans look blue and green-y colours. Light does get down there but it has to maintain itself up in the high levels. So if you look, for example, at coral reefs and they have plants living inside their tissues or algae and those types of coral have to maintain themselves by growing on big reefs, depositing calcium carbonate in great big layers that build up and build up and as sea levels rise, they have to keep up their pace to keep themselves in that lovely, sunny, gorgeous bit of tropical oceans where we all love to go snorkelling and diving. But as you go deeper down, they tend to peter out, and there are some types of corals actually that don’t have photosynthetic algae in their tissues; they actually rely on catching their food like other animals. They catch it from the water, and those are the ones that live deeper down. So you do see this zonation. You see similar things on the beach with different types of seaweed using different types of pigments to harness light both in the open areas where there’s lots of light and then lower down where light start to get absorbed.   

Dave - Is that why seaweed is a sort of reddish colour, because it doesn’t absorb red if it’s deep under water, blue-light can get all the way down so it absorbs blue but not red?

Helen Scales -   Some of the seaweeds are red seaweeds, that’s right and that’s a kind of branch of the algae. They have different types of pigment that do—yes, they use up the green and the blue lights and red is reflected back and that’s why they look red.

Chris Smith -   So the bottom line is that basically, there’s very little difference between the photosynthesis that’s occurring in the oceans and the photosynthesis on land because it’s all the same process. It’s just been tweaked a little bit to make use of the light that’s available and there is slightly more light of different wavelengths available out of the water than in it but the bottom line is it’s pretty much all the same.

Helen Scales -   It is and it is very important in the oceans. So much photosynthesis goes on and carbon dioxide gets fixed in that process in the oceans and we know that’s really important too.

Chris Smith -   Of course, because the oceans are the biggest carbon dioxide sink of the whole planet, aren’t they?

Dave - It’s all about boiling points really. If you look — the bigger the molecule, the higher temperature it will boil at.  So butane will boil at sort of -0.1 degrees centigrade, so you don’t need very much pressure to keep that as a liquid at sort of room temperature, so you can have really quite weak-like tanks.  Propane boils at about -42 degrees centigrade, which means you have to have 10 or 12 atmospheres of pressure to keep that a liquid at 40 degrees centigrade. But that’s not difficult to make with a small, light steel tank; and it’s quite practical to carry around, that would be sensible. Natural gas is methane which boils at -161 degrees centigrade roughly. To keep that a liquid at all that temperatures you have to have tanks that are strong enough to survive 200 to 220 atmospheres of pressure and from the experiment that we are doing earlier that’s going to involve about 2,000 tonnes of pressure on every square metre of that tank so it’s going to have to be made up incredibly strong steel, it’s going to be very heavy.  It just makes it expensive and impractical to carry around — and very dangerous to carry around in vehicles.

Chris Smith -   So that’s why we have it coming down the pipeline but we don’t store it locally.  We use propane, much easier to compress and get lots of it into a small space in a tank. 

Dave - That’s right. In a pipeline it never has to be at a very high pressure. You never have to liquefy it.