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What flavour are you?

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Chapter 7 of Book 7: Quarks to Quasars begins with a quote from Lords and Ladies, a book by the most marvellous Terry Pratchett. This pleases me immensely - not just because I am a big Discworld fan, but for reasons that will hopefully become clear.

"It was here that the thaum, hitherto believed to be the smallest possible particle of magic, was successfully demonstrated to be made up of resons (Lit.: 'Thing-ies') or reality fragments. Currently research indicates that each reson is itself made up of a combination of at least five 'flavours', known as 'up', 'down', 'sideways', 'sex appeal' and 'peppermint'." Terry Pratchett

Firstly, this description of sub-magic particles is not so far from our description of subatomic particles. Including the flavours.

Secondly, "reality fragments" is not just a poetic way to describe the fundamental particles that make up the matter of the Universe, but is also pretty accurate. Reality fragments can be put together into larger and larger particles, as the stuff of the Universe is created in star factories.

In our world, until fairly recently (50 years ago or so), it was accepted that the Universe was built from protons, neutrons, electrons and electron neutrinos. Electrons and electron neutrinos, together with their antiparticles (everything has an equal and an opposite), are indeed fundamental particles. They cannot, as far as we know, be broken down further.

Electrons and electron neutrinos are in the lepton family, along with four other fundamental particles: the muon (about 200 times heavier than an electron) and its associated neutrino; and a tauon (about 3,500 times heavier than an electron) plus its neutrino.

So, there are six flavours of lepton. The electron, the muon and the tauon, which all have a negative charge, plus their neutrinos, which are neutral. And just to really confuse matters, there are also six antileptons, with a positive charge but the same mass.

The word "lepton" comes from the Greek leptos, meaning "thin" or "lightweight", which is reasonable really when you consider just how tiny these things are...

So are these the only fundamental particles? No. We now know that if two nucleons (a proton or a neutron) are banged together hard enough, smaller bits fall out.

Now, let's give the nucleons another name - just as a test of memory. Protons and neutrons are examples of hadrons. They are not the only hadrons - there are also baryons and mesons.

What makes up hadrons? Quarks!

(As an aside: if you google "quark" in images, you get the Star Trek character. This pleases me.)

This is where it becomes really fun, and has led me to believe that particle physicists are a bunch of hippies at heart. It wouldn't surprise me if they loaf around smoking pot and drinking absinthe while pondering the nature of the Universe (and there's nothing wrong with that). You see, quarks, too, have flavours. Sadly not "peppermint" or "sex appeal", but Terry wasn't far off.

The quark flavours are: up, down, charm, strange, top and bottom (or, on a particularly fuzzy day, top and bottom are known as "truth" and "beauty"). The up, charm and top quarks have a charge of +2/3e and the down, strange and bottom quarks have a charge of -1/3e. And don't forget that each quark has its corresponding antiquark...

A hadron can consist of three quarks (a baryon), three antiquarks (an antibaryon) or one quark and one antiquark (a meson); and it always has a whole number charge, so you can determine the recipe.

For example, a proton has a charge of +e and is composed only of up and down quarks. The only way to produce a net charge of +e with up and down quarks is with the recipe up, up, down (uud): 2/3e + 2/3e - 1/3e = +e.

Simples!

It is now accepted that these are all fundamental particles; that they cannot be broken down further. However, particle physics is moving at lightning speed, and boundaries are being pushed all the time, so who knows what else will turn up?

It is incredible that we have drilled down into the very fabric of the Universe, and pulled out particles that are so small they are incomprehensible. Much like trying to imagine the immense distances between the stars, numbers and sizes become almost meaningless at this point, and it's much more helpful to think in abstract terms.

Perhaps this is why physicists have come up with such whimsical names for the particles... at this stage, it may as well be pixie dust!

Permalink 2 comments (latest comment by Vicky Fraser, Sunday, 21 Aug 2011, 10:04)
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Blue hair, yellow sweater, big smile

Plants are busy little things, aren't they?

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Edited by Vicky Fraser, Thursday, 16 June 2011, 10:54

Today's topic is the light-dependent reactions of photosynthesis. Now, you may think that it's all fairly straightforward, thinking back to your GCSE biology classes (or O-Level for you oldies).

A bit of light for the leaves provides energy to turn water and carbon dioxide into sugar and oxygen. Simples, I hear you say. That is what I thought too. Just a short chapter, I imagined. How complicated can it be?

Well. Let me tell you that it's very bloody complicated. I've drawn two diagrams, and I'm still not entirely sure I've understood it. And I've only done the light-dependent reactions! The dark reactions are yet to come. I'm expecting them to involve Voldemort in some way.

Here is a short account of the principle reactions involved in this stage of photosynthesis, which I wrote as part of an activity to help us to understand the processes. I would include my diagram, but I'm not drawing it on a crappy laptop. It's not an Etch-a-sketch, you know. So I've pinched this one from my OU course book.

light-reactions2.png
The light-dependent reactions of photosynthesis

The thylakoids are part of the chloroplast in plants. I apologise for the word "thylakoid". All its consonants are in the wrong place, making it a bit of an assault course for the tongue. It reminds me of trying to learn German at school - I never was very good at German, partly because I had trouble getting my tongue around their words. I do, however, love the phrase: "Schnell, schnell, kartoppelkopf!"

They have an outer membrane, and a really convoluted internal membrane which is stacked into grana - and each little disc (or sac) in an individual granum is a thylakoid. The space inside the thylakoid membrane is called the thylakoid lumen, while the space outside the membrane is called the stroma. As illustrated above.

My summary is as follows. It's supposed to simplify the description of what's going on, and complement the diagram above. I'm not sure I've achieved that; any and all feedback is welcome!

When light strikes a chlorophyll molecule, a photochemical reaction takes place in which the hydrogen atoms of water molecules are split into their constituent protons (H+ ions) and electrons. (Oxygen is released as a by-product.) As shown above, the electrons move from the thylakoid lumen through the membrane to the stroma, by means of protein carriers within an electron transport chain (ETC). The protons are left behind, increasing the concentration of protons in the lumen. With me?

In the stroma, coenzyme NADP collects a couple of electrons and combines them with a couple of protons, reducing to NADP.2H (see above). This lowers the concentration of protons in the stroma. This will be important later.

One of the electron carrier proteins in the ETC is a little shuttle that collects protons from the stroma, bimbles across the membrane, and deposits them in the lumen, further increasing the concentration of protons in the lumen.

As a result of these processes, a transmembrane (yes, it's a word!) protein gradient is formed across the thylakoid membrane - this works much like a hydroelectric plant (think of the reservoir at the top, and all that potential energy waiting to be turned into electricity). Now there's an imbalance of proton concentration, enabling the protons to flow down the concentration gradient back into the stroma through channel proteins called ATP synthase (shown on the right of the diagram above).

The flow of electrons through these proteins enables the manufacture of ATP from ADP (adenosine diphosphate) and Pi and their transfer provides the energy required.

The products of these light reactions, ATP and NADP.2H, are used in the dark reactions of photosynthesis by the Dark Lord to reduce carbon dioxide to glucose.

I do apologise for the extreme biology - but this is the third time I've written the process in my own words, and I do believe it's finally beginning to sink in. In a manner that ensures I understand and remember it.

Stay tuned for the Dark Reactions - I suspect they may be sexier.

Permalink 2 comments (latest comment by Vicky Fraser, Friday, 17 June 2011, 19:11)
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