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Video transcript

let's talk about one of the most important biological processes frankly if this process didn't occur we probably wouldn't have life on earth and I wouldn't be making this video for you because there would be no place for me to actually get food and the process is called photosynthesis photo synthesis and you're probably reasonably familiar with the idea if the whole idea is is is plants and actually bacteria and algae and other things but we normally associate it with plants let me make it in very simple term so we normally associate it with plants and it's the process that plants use and we might have learned this when we were very young it's a process that plants use to take carbon dioxide plus some water plus some water plus some I'll do it in yellow plus some sunlight plus some sunlight and turn it into and turn it into some sugars or some maybe carbohydrates carbohydrates or sugars plus oxygen and obviously this has to vary for profound pieces to it for us as a living species one we need carbohydrates or we need sugars and in order to fuel our bodies you saw that in the cellular respiration videos we generate all of our ATP by performing cellular respiration on glucose which is essentially a byproduct or a broken-down carbohydrate it's the simplest one for us to process in our in cellular respiration and then the second hugely important part is getting the oxygen once again we need to breathe oxygen in order for us to break down glucose in order to a respire in order to perform cellular respiration so these two things are key key for life key for life especially for life that breeds oxygen key for life so this process other than the fact that it's interesting that you know we're able to that that there are organisms around us mostly plants that are able to harness actual sunlight you know you have this fusion reactions in the Sun 93 million miles away and it's releasing these photons and some small subset of those photons reach the surface of earth you know they make it their way through clouds and whatever else and then these plants and bacteria and algae are able to harness that somehow and turn them into sugars that we can then eat or maybe the cow eats them and we the cow if we're not vegetarians and we can then use that for energy not that the cow is all carbohydrates but this is essentially what is used as the fuel or the energy for all of the other important compounds that we this is where we get all of our fuel so this is fuel for animals fuel for animals or you know if you eat a potato directly you are directly getting your carbohydrates anyway this is a very simple notion of photosynthesis but it's not incorrect I mean if you have to know one thing about photosynthesis this would be it well let's delve a little bit deeper and try to get into the guts of it and see if we can understand a little bit better how this actually happens I find it amazing is somehow photons of sunlight are used to create these sugar molecules or these carbohydrates so let's delve a little bit deeper so in general we can write the general the general equation for photosynthesis well I've almost written it here but I'll write it a little bit more scientifically specific you start off with some carbon dioxide you add to that some water and you add to that instead of something I'm gonna say photons because these are what really do excite the electrons in the chlorophyll that go down and you'll see that this process probably in this video and we'll go in more detail in the next few videos but that excited electron goes to a high energy state and as it goes to a lower energy state we're able to harness that energy to produce ATP's and you'll see NADPH is and then those are used to you produce carbohydrates but we'll see that in a little bit but the overview of photosynthesis you start off with these constituents and then you end up with you end up with a carbohydrate and the carbohydrate could be glucose doesn't have to be glucose so the general way we can write a carbohydrate is C h2o and we'll put an N over here that we could have n multiples of these normally you'll n will be at least three in the case of glucose n is six you have six carbons 12 hydrogen's and 6 oxygen so this is a general term for carbohydrate but you can have many multiples of that you could have these long chain carbohydrates so you end up with a carbohydrate and then you end up with some oxygen and you end up with some oxygen so this right here isn't so different than what I wrote up here in my first overview of how we always imagined photosynthesis in our heads in order to make this equation balanced and so you have n carbons here so I need n carbons there let's see I have two n hydrogen's here right Hydra two hydrogen's and I have n there so I need two n hydrogen's here so I'll put an N Out there and let's see how many carbons I have how many oxygens I have two n oxygens plus another ends of three and oxygens let's see I have one n let's see put an N here and then I have two n and I think this equation balances out so this is this is a 30,000 foot view of what's going on in photosynthesis but when you dig a little deeper you'll see that this doesn't happen directly that these goes this happens through a bunch of steps that eventually gets us to the carbohydrate so in general we can break down photosynthesis I'll rewrite the word we can break down photosynthesis photosynthesis and we'll delve deeper into future videos but I want to get you the overview first into two stages two stages we can call one the light reactions light reactions or sometimes they're called the light dependent reactions and that actually would probably be a better way to write it let me write it like that light dependent means that they need light to occur light dependent reactions and then you have something called the dark reactions and that's actually a bad name because it also occurs in the light dark reactions I wrote in a slightly darker color and the reason why I said it's a bad name is because it still occurs in the light occurs in light but the reason why they probably called it the dark reaction is that you don't need light or that part of photosynthesis isn't dependent on photons to occur so a better a better term for it would have been light light in dependent light independent reaction so just to be clear the light reactions actually need sunlight they actually need photons for them to proceed the dark reactions do not need photons for them to happen although they do occur when the Sun is out they don't need those photons but they need the byproducts from the light reaction to occur so that's why it's called a light independent reaction they occur while the Sun is out but they don't need the Sun this needs the Sun so let me make it very clear let me so this requires sunlight this requires photons this requires photons and and let me let me just make a very brief overview of this this will maybe let us start building a scaffold from which we can dig deeper so the light reactions need photons and then it needs water so water goes into the light reactions and out of the other side of the light reactions we end up with some molecular oxygen so that's what happens in the light reactions and I'm going to go much deeper on what actually occurs and what the light reactions produce it produces ATP which we know is the the cellular or the molecular or the biological currency of energy it produces ATP and it produces na dhih pH now when we studied cellular respiration we saw the molecule NADH NADPH is very similar you just have this P there you should have this phosphate group there but they really perform similar mechanisms that when you have that this agent right here this molecule right here is able to give away now let's think about what this means it's able to give away this hydrogen and the electron associated with the hydrogen so if some if you give away an electron to someone else or someone else gains an electron that something else is being reduced right let me write that down a good reminder oil rig right oxidation is losing an electron reduction is gaining an electron your charge is reduced when you gain an electron right it has a negative charge so this is a reducing agent it it gets oxidized by losing the hydrogen and the electron with it I have a whole discussion on the biological versus chemistry view of oxidation but it's the same idea when I lose a hydrogen I also lose the ability to hog that hydrogen's electron so this right here when it reacts with other things it's a reducing agent it gives away it gives away this hydrogen and the electron associated with it and so the other thing gets reduced so this thing is a reducing agent reducing agent and what's useful about it is when this hydrogen and especially the electron associated with that hydrogen goes from the NADPH to say another molecule and goes to a lower energy state that energy is also B it can be used in the dark reactions and we saw in cellular respiration the very similar molecule NADH that that through the Krebs cycle or actually more important that through the electron transport chain was able to help produce ATP why is that as that as it gave away its electrons and they went to lower energy states but I don't want to confuse you too much so the light reactions you take in photons you take in water it spits out oxygen and it spits out ATP and nadph that can then be used in the dark reactions and the dark reactions for most plants we talked about it's called the Calvin cycle Calvin cycle and I'll go into a lot more detail of what actually occurs in the calvin cycle but it takes in the ATP the NADPH and it produces it produces it doesn't put direct ly produce glucose it produces a well you probably saw this if you could call it P gal you could call it G 3 P these are all stands for let me write these down this is this is phosphoglyceraldehyde let me write that down phospho phospho glitter glyceraldehyde my handwriting broke down or you could call it glyceraldehyde 3-phosphate let me write that down glyceraldehyde 3-phosphate same same exact molecule you can almost imagine it is this is a very gross oversimplification as three carbons with a phosphate group attached to it with the phosphate group attached to it but this can then be used to produce other carbohydrates including glucose if you have two of these you can use those two to produce glucose so let's just take a quick overview again because this is super important I'm going to make videos on the light reactions and the dark reactions those will be the next two videos I make so photosynthesis you start with photons now all of these occur when the Sun is out but only the light reactions actually need the photons the light reactions take photons we're going to go into more detail what actually occurs and it takes in water oxygen gets spit out ATP and nadph gets spit out which are then used by the dark reaction or the calvin cycle or the light independent reaction because these still occur in the light they just don't need photons so they're the light independent reaction and it uses that in conjunction we'll talk about other molecules that are used in conjunction and I've used I forgot a very important a very important constituent of the dark reaction in it needs carbon dioxide that's where you get your carbons to keep producing these phosphoglyceraldehyde Zoar glyceraldehyde 3-phosphate so that's super important it takes in the carbon dioxide the the the the products from the light reactions and then uses that in in the calvin cycle to produce this very simple building block of other carbohydrates and if you remember from glycolysis you might remember that this pee gal molecule or this g3p same thing this was actually the first product when we split glucose in two when we performed a glycolysis so now we're going the other way we're building glucose so that we can split it later for energy so this is an overview of photosynthesis in the next couple of videos I'm actually going to delve a little bit deeper and tell you about the light reactions and the dark reactions and how they actually occur
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