[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.09,0:00:05.80,Default,,0000,0000,0000,,Photosynthesis! It is not some kind of abstract\Nscientific thing. You would be dead without
Dialogue: 0,0:00:05.80,0:00:11.27,Default,,0000,0000,0000,,plants and their magical- nay, SCIENTIFIC\Nability to convert sunlight, carbon dioxide
Dialogue: 0,0:00:11.27,0:00:15.48,Default,,0000,0000,0000,,and water into glucose and pure, delicious\Noxygen.
Dialogue: 0,0:00:15.48,0:00:20.62,Default,,0000,0000,0000,,This happens exclusively through photosynthesis,\Na process that was developed 450 million years
Dialogue: 0,0:00:20.62,0:00:23.55,Default,,0000,0000,0000,,ago and actually rather sucks.
Dialogue: 0,0:00:23.55,0:00:28.95,Default,,0000,0000,0000,,It's complicated, inefficient and confusing.\NBut you are committed to having a better,
Dialogue: 0,0:00:28.95,0:00:33.05,Default,,0000,0000,0000,,deeper understanding of our world! Or, more\Nprobably, you'd like to do well on your
Dialogue: 0,0:00:33.05,0:00:39.40,Default,,0000,0000,0000,,test...so let's delve.
Dialogue: 0,0:00:39.40,0:00:46.40,Default,,0000,0000,0000,,There are two sorts of reactions in Photosynthesis...light\Ndependent reactions, and light independent
Dialogue: 0,0:00:48.91,0:00:52.43,Default,,0000,0000,0000,,reactions, and you've probably already figured\Nout the difference between those two, so that's
Dialogue: 0,0:00:52.43,0:00:57.85,Default,,0000,0000,0000,,nice. The light independent reactions are\Ncalled the "calvin cycle"
Dialogue: 0,0:00:57.85,0:00:59.28,Default,,0000,0000,0000,,no...no...no...no...YES! THAT Calvin Cycle.
Dialogue: 0,0:00:59.28,0:01:00.80,Default,,0000,0000,0000,,
Dialogue: 0,0:01:00.80,0:01:04.95,Default,,0000,0000,0000,,Photosynthesis is basically respiration in\Nreverse, and we've already covered respiration,
Dialogue: 0,0:01:04.95,0:01:09.36,Default,,0000,0000,0000,,so maybe you should just go watch that video\Nbackwards. Or you can keep watching this one.
Dialogue: 0,0:01:09.36,0:01:09.88,Default,,0000,0000,0000,,Either way.
Dialogue: 0,0:01:09.88,0:01:14.11,Default,,0000,0000,0000,,I've already talked about what photosynthesis\Nneeds in order to work: water, carbon dioxide
Dialogue: 0,0:01:14.11,0:01:14.83,Default,,0000,0000,0000,,and sunlight.
Dialogue: 0,0:01:14.83,0:01:16.52,Default,,0000,0000,0000,,So, how do they get those things?
Dialogue: 0,0:01:16.52,0:01:19.87,Default,,0000,0000,0000,,First, water. Let's assume that we're\Ntalking about a vascular plant here, that's
Dialogue: 0,0:01:19.87,0:01:23.79,Default,,0000,0000,0000,,the kind of plant that has pipe-like tissues\Nthat conduct water, minerals and other materials
Dialogue: 0,0:01:23.79,0:01:25.13,Default,,0000,0000,0000,,to different parts of the plant.
Dialogue: 0,0:01:25.13,0:01:27.28,Default,,0000,0000,0000,,These are like trees and grasses and flowering\Nplants.
Dialogue: 0,0:01:27.28,0:01:29.56,Default,,0000,0000,0000,,In this case the roots of the plants absorb\Nwater
Dialogue: 0,0:01:29.56,0:01:32.96,Default,,0000,0000,0000,,and bring it to the leaves through tissues\Ncalled xylem.
Dialogue: 0,0:01:32.96,0:01:38.64,Default,,0000,0000,0000,,Carbon dioxide gets in and oxygen gets out\Nthrough tiny pores in the leaves called stomata.
Dialogue: 0,0:01:38.64,0:01:42.48,Default,,0000,0000,0000,,It's actually surprisingly important that\Nplants keep oxygen levels low inside of their
Dialogue: 0,0:01:42.48,0:01:44.92,Default,,0000,0000,0000,,leaves for reasons that we will get into later.
Dialogue: 0,0:01:44.92,0:01:51.14,Default,,0000,0000,0000,,And finally, individual photons from the Sun\Nare absorbed in the plant by a pigment called
Dialogue: 0,0:01:51.14,0:01:51.45,Default,,0000,0000,0000,,chlorophyll.
Dialogue: 0,0:01:51.45,0:01:55.60,Default,,0000,0000,0000,,Alright, you remember plant cells? If not,\Nyou can go watch the video where we spend
Dialogue: 0,0:01:55.60,0:01:57.23,Default,,0000,0000,0000,,the whole time talking about plant cells.
Dialogue: 0,0:01:57.23,0:02:00.67,Default,,0000,0000,0000,,One thing that plant cells\Nhave that animal cells don't... plastids.
Dialogue: 0,0:02:00.67,0:02:02.30,Default,,0000,0000,0000,,And what is the most important plastid?
Dialogue: 0,0:02:02.30,0:02:07.47,Default,,0000,0000,0000,,The chloroplast! Which is not, as it is sometimes\Nportrayed, just a big fat sac of chlorophyl.
Dialogue: 0,0:02:07.47,0:02:09.78,Default,,0000,0000,0000,,It's got complicated internal structure.
Dialogue: 0,0:02:09.78,0:02:14.17,Default,,0000,0000,0000,,Now, the chlorophyll is stashed in membranous\Nsacs called thylakoids. The thykaloids are
Dialogue: 0,0:02:14.17,0:02:18.69,Default,,0000,0000,0000,,stacked into grana. Inside of\Nthe thykaloid is the lumen, and outside the
Dialogue: 0,0:02:18.69,0:02:22.04,Default,,0000,0000,0000,,thykaloid (but still inside the\Nchloroplast) is the stroma.
Dialogue: 0,0:02:22.04,0:02:25.25,Default,,0000,0000,0000,,The thylakoid membranes are phospholipid bilayers, which, if you remember
Dialogue: 0,0:02:25.25,0:02:29.81,Default,,0000,0000,0000,,means they're really good at maintaining\Nconcentration gradients of ions,
Dialogue: 0,0:02:29.81,0:02:33.28,Default,,0000,0000,0000,,proteins and other things. This means keeping\Nthe concentration higher on one side
Dialogue: 0,0:02:33.28,0:02:37.88,Default,,0000,0000,0000,,than the other of the membrane. You're going\Nto need to know all of these things, I'm sorry.
Dialogue: 0,0:02:37.88,0:02:40.78,Default,,0000,0000,0000,,Now that we've taken that little tour of\Nthe Chloroplast, it's time to get down to
Dialogue: 0,0:02:40.78,0:02:42.27,Default,,0000,0000,0000,,the actual chemistry.
Dialogue: 0,0:02:42.27,0:02:46.70,Default,,0000,0000,0000,,First thing that happens: A photon created\Nby the fusion reactions of our sun is about
Dialogue: 0,0:02:46.70,0:02:50.04,Default,,0000,0000,0000,,to end its 93 million mile journey by slapping\Ninto a molecule of cholorophyll.
Dialogue: 0,0:02:50.04,0:02:54.73,Default,,0000,0000,0000,,This kicks off stage one, the light-dependent reactions proving
Dialogue: 0,0:02:54.73,0:02:58.42,Default,,0000,0000,0000,,that, yes, nearly all life on our planet is\Nfusion-powered.
Dialogue: 0,0:02:58.42,0:03:03.71,Default,,0000,0000,0000,,When Chlorophyll gets hit by that photon,\Nan electron absorbs that energy and gets excited.
Dialogue: 0,0:03:03.71,0:03:08.07,Default,,0000,0000,0000,,This is the technical term for electrons gaining\Nenergy and not having anywhere to put it and
Dialogue: 0,0:03:08.07,0:03:11.98,Default,,0000,0000,0000,,when it's done by a photon it's called\Nphotoexcitation, but let's just imagine,
Dialogue: 0,0:03:11.98,0:03:13.91,Default,,0000,0000,0000,,for the moment anyway, that every photon is\Nwhatever
Dialogue: 0,0:03:13.91,0:03:18.88,Default,,0000,0000,0000,,dreamy young man 12 year old girls are currently\Nobsessed with, and electrons are 12 year old girls.
Dialogue: 0,0:03:18.88,0:03:23.02,Default,,0000,0000,0000,,The trick now, and the entire trick\Nof photosynthesis, is to convert the energy
Dialogue: 0,0:03:23.02,0:03:23.91,Default,,0000,0000,0000,,of those 12 year old-
Dialogue: 0,0:03:23.91,0:03:27.62,Default,,0000,0000,0000,,I mean, electrons, into something that the\Nplant can use.
Dialogue: 0,0:03:27.62,0:03:31.46,Default,,0000,0000,0000,,We are literally going to be spending the\Nentire rest of the video talking about that.
Dialogue: 0,0:03:31.46,0:03:33.48,Default,,0000,0000,0000,,I hope that that's ok with you.
Dialogue: 0,0:03:33.48,0:03:39.03,Default,,0000,0000,0000,,This first Chlorophyll is not on its own here,\Nit's part of an insanely complicated complex
Dialogue: 0,0:03:39.03,0:03:45.24,Default,,0000,0000,0000,,of proteins, lipids, and other molecules called\NPhotosystem II that contains at least 99 different
Dialogue: 0,0:03:45.24,0:03:49.43,Default,,0000,0000,0000,,chemicals including over 30 individual chlorophyll\Nmolecules.
Dialogue: 0,0:03:49.43,0:03:54.36,Default,,0000,0000,0000,,This is the first of four protein complexes\Nthat plants need for the light dependent reactions.
Dialogue: 0,0:03:54.36,0:03:59.12,Default,,0000,0000,0000,,And if you think it's complicated that we\Ncall the first complex photosystem II instead
Dialogue: 0,0:03:59.12,0:04:04.63,Default,,0000,0000,0000,,of Photosystem I, then you're welcome to\Ncall it by its full name, plastoquinone oxidoreductase.
Dialogue: 0,0:04:04.63,0:04:07.81,Default,,0000,0000,0000,,Oh, no? You don't want to call it that?
Dialogue: 0,0:04:07.81,0:04:11.89,Default,,0000,0000,0000,,Right then, photosystem II, or, if you want\Nto be brief, PSII.
Dialogue: 0,0:04:11.89,0:04:15.76,Default,,0000,0000,0000,,PSII and indeed all of the protein complexes\Nin the light-dependent reactions, straddle
Dialogue: 0,0:04:15.76,0:04:19.23,Default,,0000,0000,0000,,the membrane of the thylakoids in the chloroplasts.
Dialogue: 0,0:04:19.23,0:04:23.57,Default,,0000,0000,0000,,That excited electron is now going to go on\Na journey designed to extract all of its new
Dialogue: 0,0:04:23.57,0:04:28.89,Default,,0000,0000,0000,,energy and convert that energy into useful\Nstuff. This is called the electron transport
Dialogue: 0,0:04:28.89,0:04:33.08,Default,,0000,0000,0000,,chain, in which energized electrons lose their\Nenergy in a series of reactions that capture
Dialogue: 0,0:04:33.08,0:04:36.44,Default,,0000,0000,0000,,the energy necessary to keep life living.
Dialogue: 0,0:04:36.44,0:04:41.94,Default,,0000,0000,0000,,PSII's Chlorophyll now has this electron\Nthat is so excited that, when a special protein
Dialogue: 0,0:04:41.94,0:04:44.30,Default,,0000,0000,0000,,designed specifically for stealing electrons\Nshows up,
Dialogue: 0,0:04:44.30,0:04:49.58,Default,,0000,0000,0000,,the electron actually leaps off of the chlorophyll\Nmolecule onto the protein, which we call a
Dialogue: 0,0:04:49.58,0:04:51.39,Default,,0000,0000,0000,,mobile electron carrier because it's...
Dialogue: 0,0:04:51.39,0:04:53.38,Default,,0000,0000,0000,,...a mobile electron carrier.
Dialogue: 0,0:04:53.38,0:04:57.80,Default,,0000,0000,0000,,The Chlorophyll then freaks out like a mother\Nwho has just had her 12 year old daughter
Dialogue: 0,0:04:57.80,0:05:02.27,Default,,0000,0000,0000,,abducted by a teen idol and is like "WHAT\NDO I DO TO FIX THIS PROBLEM!"
Dialogue: 0,0:05:02.27,0:05:08.11,Default,,0000,0000,0000,,and then it, in cooperation with the rest\Nof PSII does something so amazing and important
Dialogue: 0,0:05:08.11,0:05:11.52,Default,,0000,0000,0000,,that I can barely believe that it keeps happening\Nevery day.
Dialogue: 0,0:05:11.52,0:05:16.55,Default,,0000,0000,0000,,It splits that ultra-stable molecule, H2O,\Nstealing one of its electrons, to replenish
Dialogue: 0,0:05:16.55,0:05:17.91,Default,,0000,0000,0000,,the one it lost.
Dialogue: 0,0:05:17.91,0:05:20.10,Default,,0000,0000,0000,,The byproducts of this water splitting?
Dialogue: 0,0:05:20.10,0:05:25.93,Default,,0000,0000,0000,,Hydrogen ions, which are just single protons,\Nand oxygen. Sweet, sweet oxygen.
Dialogue: 0,0:05:25.93,0:05:29.58,Default,,0000,0000,0000,,This reaction, my friends, is the reason that\Nwe can breathe.
Dialogue: 0,0:05:29.58,0:05:33.61,Default,,0000,0000,0000,,Brief interjection: Next time someone says\Nthat they don't like it when there are chemicals
Dialogue: 0,0:05:33.61,0:05:37.30,Default,,0000,0000,0000,,in their food, please remind them that all\Nlife is
Dialogue: 0,0:05:37.30,0:05:41.21,Default,,0000,0000,0000,,made of chemicals and would they please stop\Npretending that the word chemical is somehow
Dialogue: 0,0:05:41.21,0:05:42.65,Default,,0000,0000,0000,,a synonym for carcinogen!
Dialogue: 0,0:05:42.65,0:05:48.74,Default,,0000,0000,0000,,Because, I mean, think about how chlorophyll\Nfeels when you say that! It spends all of
Dialogue: 0,0:05:48.74,0:05:52.08,Default,,0000,0000,0000,,it's time and energy creating the air we\Nbreathe and then we're like
Dialogue: 0,0:05:52.08,0:05:54.49,Default,,0000,0000,0000,,"EW! CHEMICALS ARE SO GROSS!"
Dialogue: 0,0:05:54.49,0:06:00.76,Default,,0000,0000,0000,,Now, remember, all energized electrons from\NPSII have been picked up by electron carriers
Dialogue: 0,0:06:00.76,0:06:03.92,Default,,0000,0000,0000,,and are now being transported onto our second\Nprotein complex
Dialogue: 0,0:06:03.92,0:06:05.20,Default,,0000,0000,0000,,the Cytochrome Complex!
Dialogue: 0,0:06:05.20,0:06:08.86,Default,,0000,0000,0000,,This little guy does two things...one, it\Nserves as an intermediary between
Dialogue: 0,0:06:08.86,0:06:13.70,Default,,0000,0000,0000,,PSII and PS I and, two, uses a bit of the\Nenergy from the electron to
Dialogue: 0,0:06:13.70,0:06:16.42,Default,,0000,0000,0000,,pump another proton into the thylakoid.
Dialogue: 0,0:06:16.42,0:06:20.58,Default,,0000,0000,0000,,So the thylakoid's starting to fill up with\Nprotons. We've created some by splitting water,
Dialogue: 0,0:06:20.58,0:06:24.54,Default,,0000,0000,0000,,and we moved one in using the Cytochrome complex.\NBut why are we doing this?
Dialogue: 0,0:06:24.54,0:06:27.78,Default,,0000,0000,0000,,Well...basically, what we're doing, is charging\Nthe Thylakoid like a battery.
Dialogue: 0,0:06:27.78,0:06:31.36,Default,,0000,0000,0000,,By pumping the thylakoid full of protons,\Nwe're creating a concentration gradient.
Dialogue: 0,0:06:31.36,0:06:34.28,Default,,0000,0000,0000,,The protons then naturally want to get the\Nheck away from each other, and so they push
Dialogue: 0,0:06:34.28,0:06:39.32,Default,,0000,0000,0000,,their way through an enzyme straddling the\Nthylakoid membrane called ATP Synthase, and
Dialogue: 0,0:06:39.32,0:06:46.17,Default,,0000,0000,0000,,that enzyme uses that energy to pack an inorganic\Nphosphate onto ADP, making ATP: the big daddy
Dialogue: 0,0:06:46.17,0:06:47.00,Default,,0000,0000,0000,,of cellular energy.
Dialogue: 0,0:06:47.00,0:06:51.39,Default,,0000,0000,0000,,All this moving along the electron transport\Nchain requires energy, and as you might expect
Dialogue: 0,0:06:51.39,0:06:55.61,Default,,0000,0000,0000,,electrons are entering lower and lower energy\Nstates as we move along. This makes sense
Dialogue: 0,0:06:55.61,0:06:57.44,Default,,0000,0000,0000,,when you think about it. It's been a long\Nwhile since
Dialogue: 0,0:06:57.44,0:07:02.03,Default,,0000,0000,0000,,those photons zapped us, and we've been\Npumping hydrogen ions to create ATP and splitting
Dialogue: 0,0:07:02.03,0:07:06.33,Default,,0000,0000,0000,,water and jumping onto different molecules\Nand I'm tired just talking about it.
Dialogue: 0,0:07:06.33,0:07:11.51,Default,,0000,0000,0000,,Luckily, as 450 million years of evolution\Nwould have it, our electron is now about to
Dialogue: 0,0:07:11.51,0:07:14.26,Default,,0000,0000,0000,,be re-energized upon delivery to Photosystem I!
Dialogue: 0,0:07:14.26,0:07:18.88,Default,,0000,0000,0000,,So, PS I is a similar mix of proteins and\Nchlorophyll molecules that we saw in PSII,
Dialogue: 0,0:07:18.88,0:07:20.70,Default,,0000,0000,0000,,but with some different products.
Dialogue: 0,0:07:20.70,0:07:25.03,Default,,0000,0000,0000,,After a couple of photons re-excite a couple\Nof electrons, the electrons pop off, and hitch
Dialogue: 0,0:07:25.03,0:07:27.29,Default,,0000,0000,0000,,a ride onto another electron carrier.
Dialogue: 0,0:07:27.29,0:07:33.20,Default,,0000,0000,0000,,This time, all of that energy will be used\Nto help make NADPH, which, like ATP, exists
Dialogue: 0,0:07:33.20,0:07:37.06,Default,,0000,0000,0000,,solely to carry energy around.\NHere, yet another enzyme
Dialogue: 0,0:07:37.06,0:07:41.46,Default,,0000,0000,0000,,helps combine two electrons and one hydrogen\Nion with a little something called NADP+.
Dialogue: 0,0:07:41.46,0:07:44.82,Default,,0000,0000,0000,,As you may recall from our recent talk about\Nrespiration, there are these sort of
Dialogue: 0,0:07:44.82,0:07:49.50,Default,,0000,0000,0000,,distant cousins of B vitamins that are crucial\Nto energy conversion. And in photosynthesis,
Dialogue: 0,0:07:49.50,0:07:52.48,Default,,0000,0000,0000,,it's NADP+, and when it\Ntakes on those 2 electrons
Dialogue: 0,0:07:52.48,0:07:55.14,Default,,0000,0000,0000,,and one hydrogen ion, it becomes NADPH.
Dialogue: 0,0:07:55.14,0:07:59.88,Default,,0000,0000,0000,,So, what we're left with now, after the\Nlight dependent reactions is chemical energy
Dialogue: 0,0:07:59.88,0:08:04.64,Default,,0000,0000,0000,,in the form of ATPs and NADPHs. And also of\Ncourse, we should not forget the most useful
Dialogue: 0,0:08:04.64,0:08:08.01,Default,,0000,0000,0000,,useless byproduct in the history of\Nuseless byproducts...oxygen.
Dialogue: 0,0:08:08.01,0:08:12.42,Default,,0000,0000,0000,,If anyone needs a potty break, now would be\Na good time...or if you want to go re-watch
Dialogue: 0,0:08:12.42,0:08:15.01,Default,,0000,0000,0000,,that rather long and complicated\Nbit about light
Dialogue: 0,0:08:15.01,0:08:19.81,Default,,0000,0000,0000,,dependent reactions, go ahead and do that...it's\Nnot simple, and it's not going to get any
Dialogue: 0,0:08:19.81,0:08:20.85,Default,,0000,0000,0000,,simpler from here.
Dialogue: 0,0:08:20.85,0:08:24.12,Default,,0000,0000,0000,,Because now we're moving along\Nto the Calvin Cycle!
Dialogue: 0,0:08:24.12,0:08:28.54,Default,,0000,0000,0000,,The Calvin Cycle is sometimes called the dark\Nreactions, which is kind of a misnomer, because
Dialogue: 0,0:08:28.54,0:08:33.04,Default,,0000,0000,0000,,they generally don't occur in the dark. They\Noccur in the day along with the rest of the
Dialogue: 0,0:08:33.04,0:08:37.82,Default,,0000,0000,0000,,reactions, but they don't require energy\Nfrom photons. So it's more proper to say
Dialogue: 0,0:08:37.82,0:08:43.93,Default,,0000,0000,0000,,light-independent. Or, if you're feeling\Nnon-descriptive...just say Stage 2.
Dialogue: 0,0:08:43.93,0:08:47.92,Default,,0000,0000,0000,,Stage 2 is all about using the energy from\Nthose ATPs and NADPHs that we created in
Dialogue: 0,0:08:47.92,0:08:50.48,Default,,0000,0000,0000,,Stage 1 to produce something\Nactually useful for the plant.
Dialogue: 0,0:08:50.48,0:08:55.46,Default,,0000,0000,0000,,The Calvin Cycle begins in the stroma, the\Nempty space in the chloroplast, if you remember
Dialogue: 0,0:08:55.46,0:09:00.72,Default,,0000,0000,0000,,correctly. And this phase is called carbon\Nfixation because...yeah, we're about to
Dialogue: 0,0:09:00.72,0:09:06.10,Default,,0000,0000,0000,,fix a CO2 molecule onto our starting point,\NRibulose Bisphosphate or RuBP, which is always
Dialogue: 0,0:09:06.10,0:09:09.95,Default,,0000,0000,0000,,around in the chloroplast because, not only\Nis it the starting point of the Calvin Cycle,
Dialogue: 0,0:09:09.95,0:09:13.18,Default,,0000,0000,0000,,it's also the end-point...\Nwhich is why it's a cycle.
Dialogue: 0,0:09:13.18,0:09:19.31,Default,,0000,0000,0000,,CO2 is fixed to RuBP with the help of an enzyme\Ncalled ribulose 1,5 bisphosphate carboxylase
Dialogue: 0,0:09:19.31,0:09:26.31,Default,,0000,0000,0000,,oxidase, which we generally\Nshorten to RuBisCo.
Dialogue: 0,0:09:28.40,0:09:30.90,Default,,0000,0000,0000,,I'm in the chair again! Excellent!
Dialogue: 0,0:09:30.90,0:09:34.40,Default,,0000,0000,0000,,This time for a Biolo-graphy of RuBisCo.
Dialogue: 0,0:09:34.40,0:09:39.38,Default,,0000,0000,0000,,Once upon a time, a one-celled organism was\Nlike "Man, I need more carbon so I can make
Dialogue: 0,0:09:39.38,0:09:42.70,Default,,0000,0000,0000,,more little me's so I can take over the\Nwhole world."
Dialogue: 0,0:09:42.70,0:09:47.40,Default,,0000,0000,0000,,Luckily for that little organism, there was\Na lot of CO2 in the atmosphere, and so it
Dialogue: 0,0:09:47.40,0:09:53.63,Default,,0000,0000,0000,,evolved an enzyme that could suck up that CO2 and convert inorganic carbon into organic carbon.
Dialogue: 0,0:09:53.63,0:09:53.88,Default,,0000,0000,0000,,
Dialogue: 0,0:09:53.82,0:09:57.88,Default,,0000,0000,0000,,This enzyme was called RuBisCo, and it wasn't\Nparticularly good at its job, but it was a
Dialogue: 0,0:09:57.88,0:10:01.90,Default,,0000,0000,0000,,heck of a lot better than just hoping to run\Ninto some chemically formed organic carbon,
Dialogue: 0,0:10:01.90,0:10:05.81,Default,,0000,0000,0000,,so the organism just made a ton of it to make\Nup for how bad it was.
Dialogue: 0,0:10:05.81,0:10:10.43,Default,,0000,0000,0000,,Not only did the little plant stick with it,\Nit took over the entire planet, rapidly becoming
Dialogue: 0,0:10:10.43,0:10:12.05,Default,,0000,0000,0000,,the dominant form of life.
Dialogue: 0,0:10:12.05,0:10:16.21,Default,,0000,0000,0000,,Slowly, through other reactions, known as\Nthe light dependent reactions, plants increased
Dialogue: 0,0:10:16.21,0:10:21.26,Default,,0000,0000,0000,,the amount of oxygen in the atmosphere. RuBisCo, having been designed in a world with
Dialogue: 0,0:10:21.26,0:10:24.87,Default,,0000,0000,0000,,tiny amounts of oxygen in the\Natmosphere, started getting confused.
Dialogue: 0,0:10:24.87,0:10:29.80,Default,,0000,0000,0000,,As often as half the time RuBisCo started\Nslicing Ribulose Bisphosphate with Oxygen
Dialogue: 0,0:10:29.80,0:10:34.45,Default,,0000,0000,0000,,instead of CO2, creating a toxic byproduct\Nthat plants then had to deal with in creative
Dialogue: 0,0:10:34.45,0:10:35.67,Default,,0000,0000,0000,,and specialized ways.
Dialogue: 0,0:10:35.67,0:10:40.00,Default,,0000,0000,0000,,This byproduct, called phosphogycolate, is\Nbelieved to tinker with some enzyme functions,
Dialogue: 0,0:10:40.00,0:10:44.45,Default,,0000,0000,0000,,including some involved in the Calvin cycle,\Nso plants have to make other enzymes that
Dialogue: 0,0:10:44.45,0:10:49.28,Default,,0000,0000,0000,,break it down into an amino acid (glycine),\Nand some compounds that are actually useful
Dialogue: 0,0:10:49.28,0:10:50.24,Default,,0000,0000,0000,,to the Calvin cycle.
Dialogue: 0,0:10:50.24,0:10:54.67,Default,,0000,0000,0000,,But plants had already sort of gone all-in\Non the RuBisCo strategy and, to this day,
Dialogue: 0,0:10:54.67,0:10:59.15,Default,,0000,0000,0000,,they have to produce huge amounts of it (scientists estimate that at any given time there
Dialogue: 0,0:10:59.15,0:11:05.97,Default,,0000,0000,0000,,are about 40 billion tons of RuBisCo on the planet) and plants just deal with that toxic byproduct.
Dialogue: 0,0:11:05.97,0:11:10.09,Default,,0000,0000,0000,,Another example, my friends, of unintelligent\Ndesign.
Dialogue: 0,0:11:10.09,0:11:11.10,Default,,0000,0000,0000,,Back to the cycle!
Dialogue: 0,0:11:11.10,0:11:15.11,Default,,0000,0000,0000,,So Ribulose Bisphosphate gets a CO2 slammed\Nonto it and then immediately the whole thing
Dialogue: 0,0:11:15.11,0:11:19.67,Default,,0000,0000,0000,,gets crazy unstable. The only way to regain\Nstability is for this new six-carbon chain
Dialogue: 0,0:11:19.67,0:11:26.02,Default,,0000,0000,0000,,to break apart creating two molecules of\N3-Phosphoglycerate, and these are\Nthe first stable products of the calvin cycle.
Dialogue: 0,0:11:26.02,0:11:26.82,Default,,0000,0000,0000,,
Dialogue: 0,0:11:26.82,0:11:29.78,Default,,0000,0000,0000,,For reasons that will become clear in a moment,\Nwe're actually going to do this to three
Dialogue: 0,0:11:29.78,0:11:31.44,Default,,0000,0000,0000,,molecules of RuBP.
Dialogue: 0,0:11:31.44,0:11:33.17,Default,,0000,0000,0000,,Now we enter the second phase,
Dialogue: 0,0:11:33.17,0:11:33.61,Default,,0000,0000,0000,,Reduction.
Dialogue: 0,0:11:33.61,0:11:38.71,Default,,0000,0000,0000,,Here, we need some energy. So some ATP slams\Na phosphate group onto the 3-Phosphoglycerate,
Dialogue: 0,0:11:38.71,0:11:45.05,Default,,0000,0000,0000,,and then NADPH pops some electrons on and,\Nvoila, we have two molecules of Glyceraldehyde
Dialogue: 0,0:11:45.05,0:11:50.20,Default,,0000,0000,0000,,3-Phosphate, or G3P, this is a high-energy,\N3-carbon compound that plants can convert
Dialogue: 0,0:11:50.20,0:11:53.70,Default,,0000,0000,0000,,into pretty much any carbohydrate. Like glucose
Dialogue: 0,0:11:53.70,0:11:58.19,Default,,0000,0000,0000,,for short term energy storage, cellulose for\Nstructure, starch for long-term storage.
Dialogue: 0,0:11:58.19,0:12:02.96,Default,,0000,0000,0000,,And because of this, G3P is considered the\Nultimate product of photosynthesis.
Dialogue: 0,0:12:02.96,0:12:08.81,Default,,0000,0000,0000,,However, unfortunately, this is not the end.\NWe need 5 G3Ps to regenerate the 3 RuBPs that
Dialogue: 0,0:12:08.81,0:12:15.69,Default,,0000,0000,0000,,we started with. We also need 9 molecules\Nof ATP and 6 molecules of NADPH, so with all
Dialogue: 0,0:12:15.69,0:12:17.71,Default,,0000,0000,0000,,of these chemical reactions, all of this chemical\Nenergy,
Dialogue: 0,0:12:17.71,0:12:24.11,Default,,0000,0000,0000,,we can convert 3 RuBPs into 6 G3Ps but only\None of those G3Ps gets to leave the cycle,
Dialogue: 0,0:12:24.11,0:12:29.55,Default,,0000,0000,0000,,the other G3Ps, of course, being needed to\Nregenerate the original 3 Ribulose Bisphosphates.
Dialogue: 0,0:12:29.55,0:12:32.86,Default,,0000,0000,0000,,That regeneration is the last phase of the\NCalvin Cycle.
Dialogue: 0,0:12:32.86,0:12:38.04,Default,,0000,0000,0000,,And that is how plants turn sunlight, water,\Nand carbon dioxide into every living thing
Dialogue: 0,0:12:38.04,0:12:44.48,Default,,0000,0000,0000,,you've ever talked to, played with, climbed\Non, loved, hated, or eaten. Not bad, plants.
Dialogue: 0,0:12:44.48,0:12:49.39,Default,,0000,0000,0000,,I hope you understand. If you don't, not only\Ndo we have some selected references below
Dialogue: 0,0:12:49.39,0:12:54.11,Default,,0000,0000,0000,,that you can check out, but of course, you\Ncan go re-watch anything that you didn't get
Dialogue: 0,0:12:54.11,0:12:57.51,Default,,0000,0000,0000,,and hopefully, upon review, it will make a\Nlittle bit more sense.
Dialogue: 0,0:12:57.51,0:12:59.97,Default,,0000,0000,0000,,Thank you for watching. If you have questions,\Nplease leave them down in the comments below.