How does snow form?

How does snow form?

High up in the atmosphere, the air temperature is very cold. The water vapour may fall as rain if the water does not freeze. However, if the air temperature is so cold that the water droplets freeze, tiny ice crystals form in the clouds. These ice crystals collide with each other in the clouds or grow delicate shapes. The ice crystals combine to form snowflakes. There may be hundreds of tiny ice crystals in a single snow flake. These snow flakes fall from the clouds to form snow on the ground.

If the air temperature is not too cold and the air is very moist, the snow flakes may grow into very large flake up to 1 or 2 centimetres across.

Every snow flake is different. However, each snow flake has 6 sides.

What is sleet?

What is sleet?

When the air temperature is very cold, water vapour in clouds may fall as sleet, hail, or snow. Water droplets in the clouds get cold, but may not freeze completely. Sleet forms when partially frozen water droplets, or rainwater, in the clouds falls and freezes completely when it hits the surface of the Earth.

Like freezing rain, sleet may be dangerous because it coats roads and sidewalks with ice. Cars may not be able to stop on the slippery roads and many collisions between cars may occur. Slippery sidewalks are very difficult to walk along.

What is freezing rain?

What is freezing rain?

When the air temperature is very cold, water vapour in clouds may fall as sleet, hail, or snow. Water droplets in the clouds get cold, but may not freeze. Under certain circumstances, the temperature of the water droplet may drop below the freezing temperature of water, but the water remains in the liquid state. This water is super-cooled. When super-cooled water falls to the surface of the Earth, the water freezes instantly on any surface it hits. This is called freezing rain.

Freezing rain may cause lots of damage. Trees and power lines may break under the weight of the heavy ice. Cities may have to go without electricity when major power lines are broken.

How do clouds form?

How do clouds form?

As warmer air pass over the ocean or large open lakes, the air picks up water vapour. As the air warms, it rises because warm air is less dense than cold air. As the warm air rises, the air cools and the water vapour in the air condenses to form clouds of water droplets.

Clouds that form at the surface of the Earth are known as fog.

What is potential energy?

What is potential energy?

Potential energy is stored energy. An apple sitting on the edge of a table has stored potential energy. The potential energy changes to kinetic energy when the apple falls to the ground. A compressed spring has potential energy. That potential energy is converted to kinetic energy when the compressed spring is released.

What is energy?

What is energy?

Energy is the capacity to do work. Our energy comes from food, which contains stored chemical energy. Our bodies take the stored chemical energy and converts it to mechanical energy, heat energy or other forms of energy.

Light, sound, heat, and electricity are forms of energy

How does the sun produce photons?

How does the sun produce photons?

The surface of the Sun is very hot of course. It’s so hot that hydrogen becomes ionised into plasma so that you have photons and electrons as separate bodies, rather than bound together into atoms. And as those different charges interact, they exchange energy at the surface of the Sun and in the process of saving energy, they can lose energy and that is radiated as the photons that we see. Now that's not actually the powerhouse that drives luminosity of the Sun. That is the fusion of hydrogen atoms into helium which occurs at the core of the Sun. In fact, only in the central 20% or so of the Sun and so, you have another process which is convection which is carrying that heat which is generated at the centre of the sun out of the surface to keep the surface hot so that it continues to shine.

Are there no photons being produced deep inside the Sun? Presumably there are, but they just can't get out.

Photons are being produced all throughout the Sun, but the Sun is made of a cloudy material because these protons and electrons can interact with that light. And that means the photons produced deep down can only actually travel a few centimetres before they're reabsorbed.

And of course Bryan Fulton who was on this program, he’s professor of Astrophysics at the University of York. I think the point he made was that the photons that get made in the Sun are actually a million years old plus by the time they emerge because they have spent their entire life being bombarded around and absorbed and reabsorbed, ad infinitum almost before they finally escape. So if the Sun went out tomorrow, went out as in all reaction stopped, we’d still have a million years of the light locked inside.

The light is travelling at the speed of light, but it’s only hopping a few centimetres at a time and we don't know what direction it’s going to come back out again. It may end up going back towards the centre of the Sun again and it takes a million years. It’s quite a random walk for that energy to get to the surface.

Are air cavities in the body a problem when diving deep?

Are air cavities in the body a problem when diving deep?

It is a very good film and it does seem very futuristic, but it is actually partly reality. These chemicals, these liquids do exist. They're called perfluorocarbons. They include fluorohexane for example, so a string of 6 to 8 carbon atoms with lots of flourines hanging off the side and they're very good at dissolving oxygen. So, one way of doing this would be to instil these fluids into the respiratory tract and you saturate them with the oxygen, and then you move the fluid in and out, in the same way that you would when you were breathing.

Why this is helpful is that when a person descends underwater, the pressure they feel from the surrounding water goes up and up, the deeper they go. So, you have to therefore put the gas into the lungs to keep the lungs inflated, under progressively higher and higher pressures. One consequence of this is that it drives other gases like nitrogen and things into the tissues at extremely high pressures which means that then when you decompress, those gases come out of solution in the tissues and form bubbles which can cause the bends, they can cause damage to the brain, and cause damage to bones and muscles and so on. So if you use a fluid in the lung, because fluids are incompressible then you wouldn’t have the same problem because the fluid would withstand the pressure being applied by the outside water much better.

The issue with these fluids though is that they're not very good at removing CO2. They're very good at putting oxygen in. They're not good at getting carbon dioxide out and to compensate for the fact that they don't move CO2 very well, you'd have to move a lot of the fluid a lot of the time, and that's one of the major hold ups with doing this. In terms of the liquid getting into other body cavities and body parts, this isn’t such a problem actually. The eustachian tubes that you mentioned, they run between the back of the throat and the ear, so they would just fill up with the fluid anyway. The other body cavities, well, they wouldn’t actually be exposed to the fluid directly because it will be in the respiratory tree. So, there wouldn’t be a problem there and if there were any leakages of the fluid into other places, you would just pass it, I would think. It certainly wouldn’t become part of the systemic circulation, so it should be okay.

If dark skin absorbs more heat, why aren't native African people white, and Inuit people black?

If dark skin absorbs more heat, why aren't native African people white, and Inuit people black?

Logically, it should be the case that if you have pale skin it’s going to reflect more light and more heat and would be suited to warmer, sunnier places. But what is actually happening is people with darker skin have more melanin, more pigment, in their skin and this prevents the short wavelengths of light, the UV, from penetrating deep into the skin. It also means the skin can produce vitamin D in suitable levels. So if you live in more northern climes where there is less sunlight, so for example in the UK, then it’s much better to have pale skin which allows more sunlight to get into your skin and more vitamin D to be produced. Vitamin D is great for strengthening bones. Iit prevents you from getting diseases like rickets which would be very selective against a population if you were living in northern Europe.

UV radiation damages folic acid which you need for the development of the nervous system. If you get folic acid depleted you get diseases like spinabifida, so in continents like Africa where there is a lot of UV in the sunlight, if you don’t protect yourself with lots of melanin you will depete your folic acid, leading to an excess of neural tube defects like spinabifida and this would manifest in a cost to reproductive fitness in the population. So as there is so much sunlight, Africans can afford to have dark skin and still make enough vitamin D and not lose their folate but once you get up to the parts of the latitudes we live in, where it’s miserable all the time, vitamin D becomes the real problem. You need to make enough vitamin D and so you have to have pale skin. There’s so little UV because we hardly ever see the Sun anyway that it doesn’t become a problem from the folic acid depletion, neural tube defect perspective.

Are any viruses good for us?

Are any viruses good for us?

This may be true, despite that fact that most people think of a virus as being something that makes them feel awful! A recent piece of research in Nature by Skip Virgin, suggested that being infected by one of the family of viruses known as Herpes viruses, such as herpes simplex, which causes cold sores, Epstein-Barr virus, which causes glandular fever. When they infected mice with the rodent equivalent of those infections, the mice developed a much better immune system than mice which had ever been infected. To prove this, they exposed the mice to the bacteria which causes plague and also listeria, and they found these mice to be 100% protected against these bacteria compared with animals which had never been infected with a Herpes virus. When they studies these mice they found molecules called interferon gamma at a much higher level, and this molecule is known to stimulate the immune system.
They think that because we've been living with herpes viruses for millions of years, the body has come to rely on infection to provide additional gene function which our body no longer has. This stimulated the immune system and we get some benefit. It's almost a symbiosis, we give the virus a home and it gives us a better immune system.

Why does lightning rumble?

Why does lightning rumble?

If a lighting strike is very close to you it sounds like a very sharp crack and then a bit of a rumble afterwards, the further away you get the longer the rumble can sound. So a lightning bolt will make a sharp short noise, but first of all the noise is produced along a line up to a couple of kilometers long (if you live in Arizona), so because sound travels at 330m/s it could take up to 6 seconds for the sound from the top to reach you so the sound will be spread out over several seconds. The sound is then further spread out as you move further away from the lightning because the sound can get to you directly or by bouncing off things. This means that the sound will take lots of different times to get to you and therefore be spread out over several seconds as a rumble

How does food become radioactive?

How does food become radioactive?

there are various ways that food can become radioactive. It becomes radioactive when plants absorb it through their roots as they grow or animals ingest it and then you eat the animals. You also get fallout. So, in the initial blast where they vented the steam, there would’ve been some dissolved caesium and iodine, and probably some particles of fuel - very small amounts - in those vents, and those would have then come down around about the Fukushima prefecture. That's why the Japanese government has banned the sale of various different vegetables and milk within a certain radius of the plant.

Why does overeating chocolate make you feel sick?

Why does overeating chocolate make you feel sick?

This is probably down to the sugar and I've conducted lots of experiments in this area! You may notice that you feel sick after over indulging on any kind of very sweet food, whether it’s chocolate or cakes, or sweets... Not very good for you but tremendous fun! This gives your body a massive hit of sugar, all in one go. It raises the level of sugar in your bloodstream and causes something known as hyperglycemia. It’s this state of being hyperglycaemic that makes you feel sick. Now in most people, this just sends our pancreas into overdrive. We produce loads of insulin. The cells of our body take up this excess sugar, everything returns to normal, apart from maybe wanting to stay off the cake for a bit. But actually, in people who have diabetes, this doesn’t happen properly. Either they don't produce enough insulin or their cells don't respond to the insulin properly and take up the sugar. In fact, one of the symptoms of undiagnosed diabetes is feeling sick because you can't actually control this blood sugar and you do suffer from hyperglycemia. So yes, overeating chocolate will make you feel sick, but if you feel sick all the time after eating, you should probably go and get that checked out.

Is hot water heavier than cold water?

Is hot water heavier than cold water?

Hot water is actually a little bit heavier than cold water because as Einstein told us E=mc2. So if E, the energy in the water, goes up because it’s hotter then mass, m, must also go up to keep the equation balanced [c, the speed of light in a vaccuum, doesn't change]. So there will be a very subtle and very tiny increase in mass of the hot water, compared to the cold water.

The reason the ice floats is actually because it’s a lot less dense than the water. The ice is made of water but it’s pushing a bigger volume of water out of the way, than the ice itself weighs. For that reason, it’s actually feeling a big push up from the water underneath it which makes it float, so that's the reason.

Does Aspirin alter blood pressure?

Does Aspirin alter blood pressure?

A very small effect. If you take high doses of Aspirin, it can increase blood pressure slightly, but it’s not a problem in clinical practice.

Is the Sun Alive?

Is the Sun Alive?

No it isn’t. It is a big flaming ball of exploding helium or hydrogen, one of the two. Physics not my strong point but no, it is not alive. It is not cells in it.

We also put this to Dave Ansell, for whom physics is a strong point!

To think about this question we really need a definition of life, whilst it is obvious that a cat is alive at a first glance it is less obvious that lichen is alive, you would only notice if you look at it for a period of years.

There are various properties that we associate with living things.

Metabolism - converting energy from one form to another. Normally with living creatures this is light or chemical energy being converted into other forms, but there is no fundamental reason life shouldn't be powered by nuclear fusion like the sun.

Homeostasis - the regulation of an internal environment, eg your body maintains its temperature by sweating, but simple creatures will regulate the chemistry in their cell. If the sun gets too hot it will expand, slowing down the nuclear reactions that power it and cooling it down so it could be said to do this.

Response to stimuli - if you metaphorically poke almost all living things they will react in some way. Some creatures will react directly to being actually poked, but even single cell creatures will react to sunlight, or food. - I guess a star will alter if you apply a large enough stimulus, but not in a way very like a living creature.

Reproduction - this is a really important one, all living things can reproduce themselves and in the process they normally have to grow. - I can't think of any way in which the sun could reproduce. Conceivably large stars that go supernova trigger the formation of other stars, but this falls down on:

Inheritance - When a living thing reproduces, the children inherit features from their parents, such as the colour of eyes, shape of foot, the ability to make an enzyme which interferes with penicillin etc. And critically this inheritance isn't quite perfect - it is liable to mutation - so the creature can evolve.

Even if you could say that a star can reproduce by going supernova the created stars do not inherit features from the star which went bang, and although a star does appear to metabolise hydrogen to form helium I don't think that you could say that a star is alive.

Saying that, the surface star is a hugely complex thing with interactions between plasmas, nuclear fusion and magnetic fields It is conceivable that there is some form of life, entirely unlike creatures on earth, and we may not recognise it even if we were looking straight at it. But at the moment this is well into the realms of science fiction.

How does blood clot?

How does blood clot?

In blood, there are several elements. They include little bits of cells called platelets, which are programmed to recognise holes in blood vessels and bind on to them. There are also proteins which are dissolved in the blood which are able to work like tiny pairs of scissors and cut other proteins to produce a cascade of changes which culminate in formation of a fibrin network. This looks like a fishing net inside a blood vessel which traps blood cells in it, and acts as a plug to block a hole in a blood vessel, for example.

So if we look at how it works: If you have a blood vessel and injure it, what happens first is that the platelets, which are circulating in the blood, recognise the fact that when the blood vessel is punctured there are now foreign surfaces exposed to the blood. The platelets bind on and then release various factors that trigger the blood vessel to constrict, so it gets narrower and reduces blood loss from the area. It also starts to recruit these other proteins dissolved in the blood, the coagulation factors, activating them sequentially. They cut each other, activating other coagulation factors, and culminating in the production of this cleavage of a protein called fibrinogen, to make this fibrin network.

All of this happens in a very short space of time - literally seconds for platelets blocking up the hole, to minutes for the formation of one of these fibrin networks. Once the gap in the vessel has been plugged, then the cells locally which line the vessel over-grow the area which has been breached, and they establish a new smooth lining to the blood vessel. The clot is then slowly metabolised away by other cells called macrophages.

The thing that the platelets and some of these other factors are recognising is collagen, the main building block of connective tissue. The proteins, including one called Von Willebrand factor, in the bloodstream are able to recognise the presence of collagen which is not normally ever seen inside a blood vessel or in a healthy organ, because they’re normally kept separate from it. So whenever that interaction occurs, this tells the factors in the bloodstream that a vessel must have been breached, and therefore you activate the clotting system and it plugs up the hole wherever this occurs. Normally blood vessels keep themselves clear because the lining of the blood vessel, the endothelium, produces various factors which are anti-thrombotic, they antagonise or prevent blood from clotting. Obviously if you damage the blood vessel, you remove that anti-coagulative ability, so it shifts the blood into a pro-coagulation state, and then it starts to clot.

Can we extract energy from the Cold?

Can we extract energy from the Cold?

That is a very interesting question. You can't gain energy directly from cold, but what you can do is get a lot of energy by moving heat from somewhere which is warm to somewhere which is cold. And that’s essentially what a steam engine does or a car engine, any of the heat engines work exactly like that. However, the colder you get that cold into the system, the more efficient the process is. So if that cold end is absolute zero, then if you move a kilojoule of energy from something warm to there, then you've got a kilojoule of useful work out of that. If it’s hotter than that, then it gets a lot less. So, once you collect energy from cold directly, you can get a lot of energy by transferring heat to somewhere very cold

Why do roads look reflective?

Why do roads look reflective?

This is called a mirage. On a hot day the air above the road gets hotter than the air above that. When air gets hot it expands and becomes less dense. The less dense the air is the faster light goes through it. The light is going slower high up than it is really close to the road. The light then refracts as is comes down from the bright sky. It bends upwards and goes into your eye. What you’re seeing is an image of the sky in front of you.

Chris: When you have toast cooking in your toaster and you look at the air above it it’s all twisty and shimmery.

Dave: It’s the same phenomenon. You get hot air in swirly patterns above the toaster that bends the light which produces a distorted image behind.

How much water is in the world?

How much water is in the world?

Best estimate, is we think there are 1.37 billion cubic km of water on Earth!

Are air cavities in the body a problem when diving deep?

Are air cavities in the body a problem when diving deep?

It is a very good film and it does seem very futuristic, but it is actually partly reality. These chemicals, these liquids do exist. They're called perfluorocarbons. They include fluorohexane for example, so a string of 6 to 8 carbon atoms with lots of flourines hanging off the side and they're very good at dissolving oxygen. So, one way of doing this would be to instil these fluids into the respiratory tract and you saturate them with the oxygen, and then you move the fluid in and out, in the same way that you would when you were breathing.

Why this is helpful is that when a person descends underwater, the pressure they feel from the surrounding water goes up and up, the deeper they go. So, you have to therefore put the gas into the lungs to keep the lungs inflated, under progressively higher and higher pressures. One consequence of this is that it drives other gases like nitrogen and things into the tissues at extremely high pressures which means that then when you decompress, those gases come out of solution in the tissues and form bubbles which can cause the bends, they can cause damage to the brain, and cause damage to bones and muscles and so on. So if you use a fluid in the lung, because fluids are incompressible then you wouldn’t have the same problem because the fluid would withstand the pressure being applied by the outside water much better.

The issue with these fluids though is that they're not very good at removing CO2. They're very good at putting oxygen in. They're not good at getting carbon dioxide out and to compensate for the fact that they don't move CO2 very well, you'd have to move a lot of the fluid a lot of the time, and that's one of the major hold ups with doing this. In terms of the liquid getting into other body cavities and body parts, this isn’t such a problem actually. The eustachian tubes that you mentioned, they run between the back of the throat and the ear, so they would just fill up with the fluid anyway. The other body cavities, well, they wouldn’t actually be exposed to the fluid directly because it will be in the respiratory tree. So, there wouldn’t be a problem there and if there were any leakages of the fluid into other places, you would just pass it, I would think. It certainly wouldn’t become part of the systemic circulation, so it should be okay.

I make it sound like it’s all easy and a problem that's been solved. It is being used in a limited way, but it’s certainly not mainstream yet by any stretch of the imagination.

Why does cooled water sometimes suddenly freeze?

Why does cooled water sometimes suddenly freeze?

It’s a beautiful effect it’s called super-saturation or super-cooling a liquid. What’s going on is that O°C is the temperature below which water is more stable as a solid than as a liquid. That doesn’t mean you can’t cool water below O°C. That’s because forming a very very small crystal takes quite a lot of energy and is quite unstable. So with water, it could be down to -3°C, you can supercool water to almost -20 °C, and if its below 0 every time a little tiny crystal starts to form it just gets knocked apart, so there are no small crystals there and nowhere the ice crystals can grow from, and the whole thing won't freeze. But if somewhere you get a crystal which is bigger than the certain critical size it’s much more stable for that crystal to grow and grow so you get a few small crystals spreading out and the whole things freezes very quickly, because its below zero. You also get that effect with sodium acetate. There are hand warmers based on this principle. You heat them it melts the liquid inside, you cool them down again, you flick a little clicky thing and that releases some crystals which causes the whole thing to crystalise. This releases lots of heat which warms your hand nicely.

We get bacteria in our gut. Where does it come from? Is it from our mums in the womb?

We get bacteria in our gut. Where does it come from? Is it from our mums in the womb? Does it come from the environment after we’re born or is it dropped off by the stork?

It will probably surprise you to learn that we’re actually passengers in our own body.

If you count the number of bacteria that live on us an in us there are roughly 50 times as many of them as there are cells in our entire bodies. There are roughly ten thousand trillion cells in humans so that’s a lot of bacteria.

Where do they come from? Well, the answer is when a baby first pops out, assuming it comes the normal way, its first taste of life is quite literally a mouthful of muck. It’s its mums muck. It’s bacteria and other debris that are all over the pelvic floor and perineum of the mother. When the baby comes out those bugs that are there on the mum go into the baby and they get washed down into the stomach and then into the intestine where they take root.

The reason babies can do that and in us most bacteria get killed is because babies don’t have much stomach acid at that stage so the bacteria can very easily get in and settle down into the gut. After a few years they develop and turn into a very unique spectrum which is almost as unique to you as your fingerprint is. If you come out via a different route, say you have a caesarean then the kinds of bacteria that a baby picks up will be different and that’s been demonstrated.

Because of the spectrum of bacteria being a bit different there can be consequences for your risk of future diseases including things like getting allergies and also having bouts of diarrhoea. Recent studies have shown that babies born by caesarean section are actually twice as likely in their first year of life to have doses of diarrhoea and to have allergic reactions to things. Coming out the right way and getting a mouthful of muck unless you absolutely have to come out the wrong way is probably the best way.

With home electrical wiring, why should the wires oxidise?

With home electrical wiring, why should the wires oxidise?

Normally, the current passing through the wires in your house does not generate enough heat in order to make them react with oxygen. Most wiring is copper, and you need to get copper to quite a high temperature to make it react with oxygen and produce copper oxide. This shouldn’t happen unless the wiring actually catches fire.

However if the wires get wet dissolved oxygen can react with the copper much more easily, so they will oxidise even at normal temperatures

Could we make a vaccine for coughs and colds?

Could we make a vaccine for coughs and colds?

Not easily because (a) there are hundreds of different types of cold virus and (b) they’re continuously on the move. They’re a moving target because they use a genetic form of information called RNA which makes mistakes when it copies itself and that means that they’re continuously changing their shape. It’s like having a facelift at the level of a virus on a daily basis so you don’t recognise them from the perspective of your immune system very easily. They can easily re-infect you and a really good example of this is norovirus which is causing diarrhoea and has had 3 million people locked to a loo seat for longer than they’d like in the UK this year.

Norovirus is an example of this. It very quickly adapts and changes its appearance so, even though you’ve had it once, six months later you can catch it again because it looks entirely different by then.

How many 'flu inoculations can you make from a single egg?

How many 'flu inoculations can you make from a single egg? Secondly, how do people ensure that the eggs that are used don’t contain the bird flu virus?

The answer is that you put the vaccine virus into the egg, which has a chick inside. The chick turns into chicken soup with some 'flu added. You get the 'flu out, purify it and you end up with about three doses per egg.

So, if you do some maths, if you want to immunise the entire population of the U.K. with, let’s say (for "eggs-ample"), 60 million to make the numbers easy, you would need - just for the U.K. - 20 million laboratory grade chicken’s eggs. So a lot is the answer.

In terms of egg-safety, the eggs used are laboratory grade eggs. They are high-grade, disease-free, guaranteed to be safe chickens' eggs. And also, the testing that goes on is incredibly rigorous. The eggs are tested, the vaccine progeny is testesd and what comes out is tested to make sure that there’s nothing in there that shoudn't be.

Do children typically grow out of food allergies?

Do children typically grow out of food allergies?

That depends on the food allergy. So if you had egg or milk allergy as a young child, there's a very good chance of growing out, but if you had a peanut allergy, only a tiny minority of the very mild ones might grow out. So it’s very dependent on which food we’re talking about.
We don’t know for sure why this is, but we’ve done some research on egg allergy, looking at those who resolve and those who persist, and we can see changes in the immune system. The development of these T regulatory cells and various chemicals they produce occurs in the children who grow out of egg allergy. So it may be that it’s somehow easier with certain foods, like egg and milk, to develop the right sort of immunity to grow out. And perhaps that’s due to small amounts of these things being in foods.

How true is it that some genes that protected people from the Black Death

How true is it that some genes that protected people from the Black Death are the same genes that are now protecting people from HIV today?

There was a hypothesis a little while ago that a mutation in one of the receptor proteins; a so-called Delta 32 for CCR5, might have had some protective effects against the plague. I'm not sure that that’s ever really been verified, but it’s certainly true that the Delta 32 allele, if one has two copies of that gene, there’s no functional receptor for the virus, so individuals with that genetic composition are in general resistant to infection.

How is bone marrow turned to blood and how is the marrow replaced once it’s used up?

How is bone marrow turned to blood and how is the marrow replaced once it’s used up?

Bone marrow is found in the bone marrow cavity of bones, so if you cut across a bone and have a look, you'll see there’s a sort of hole in the middle with lots of plates of bone which jut out into that hole, and those plates in healthy bone are covered in stem cells. These stem cells are dividing very, very fast to produce new blood cells. In fact, the body destroys something like 1011 cells every single day and makes another 1011 cells every single day, and that's just red blood cells. In fact, we worked out over the course of lifetime, that you make a quarter of a million kilograms –a quarter of a ton of new red blood cells over the course of a whole lifetime, so it’s a very fast process. And these cells are just dividing all the time and pumping out daughter cells which then slowly, over a course of maturations, turn themselves into the new blood cells. This includes platelets as well. You have big cells called megakaryocytes and those megakaryocytes bleb off little bits of their cytoplasm, the stuff inside the cell, which become these little bits that floats around inside the blood, and they’re what causes you to be able to clot if you have a hole in the blood vessel, the platelet would stick on, and it causes the blood to clot. And then you have white blood cells as well, lymphocytes. They're also made by stem cells in the bone marrow which then go out from the bone marrow, go around the body, and turn into mature immune cells.