Light Independent Reactions

Hi in this video, we're gonna be talking about light independent reactions. Also known as the Calvin cycle. So the Calvin cycle is best described as carbon fixation. So this is usually um or this is using A T. P. And N. A. D. P. H. Which was created in the light in light dependent reactions to fix carbon from C. 02. So it takes CO. Two and uses that carbon to create sugar. And the process that we're going to go over a lot um we're gonna talk occurs in what's known as C three plants, which is the majority of plants. And you may remember these from here by 0101 class. And so um how this happens is C. O. To the carbon from it is attached to this sugar called ribose close 15 phosphate. And it's a five carbon sugar. So when that one carbon here comes in and attaches to this five carbon, it actually creates the six or it creates the possibility of six carbons which is created into 23 carbon sugars. And that sugar is called phosphate, phosphate, glycerin. And that's gonna be step one Step two that is going to be reduced. Um and when that is reduced that releases oxygen as a waste product. So carbon fixation is the process of taking that carbon from C. 02 and using it and attaching it to sugars and in that process oxygen is released. So the really important part of carbon fixation is the enzyme that is responsible for it. And this enzyme is called disco. Um and I spelled it out for you but I'm not gonna try to pronounce it because what a waste of time and so rude Biscoe is the enzymes that catalyze is carbon fixation. So the removal of the carbon from carbon dioxide and adding it to a sugar. Now rube isco is one of those. It's such an interesting enzyme one because it works um really slowly like enzymes we think work really fast. But Disco is actually fairly slow. And so because it's such an important thing like this is the enzyme that allows plants to create sugar from light. Um they need a lot of it if it's gonna work slow they need a ton of it. And so it's actually thought to be the most abundant protein on earth because they need so much of it. And so um in the third step here the A. T. P. And N. A. D. P. H. Which I said was needed before this is from the light um dependent that's where it comes from. Are used to generate more sugar more of this five carbon sugar. And so in the end three carbon dioxides end up making one of these sugars and that consumes 9 80 P. And six N. A. D. P. H. S. Which is a lot of energy to create this one sugar. So here's an overview of the Calvin cycle I guess I can stand here, I don't need to write. And so you don't need to like these chemical structures, you don't need to know, like just sort of scribble them out because that's not what we're focusing on here. Instead. What we're focusing on is the fact that roux Biscoe is super important and that it uses a T p M and N A D P. H, which remember we got from the light dependent reactions um in order to produce sugars, which is the last step here. Um And so yeah, so this is the overview of the Calvin cycle. So with that let's now move on.

So now we're gonna talk about carbon fixation and other types of plants. And these are smaller classes of plants called C. Four and cam plants. So the carbon fixation that we talked about before occurs in what's known as C. Three plants which is most um most plants. But the problem with it is that it's really not efficient and hot environment. So things like deserts or really hot summers. Um And this is because there are these regions of plants called stromal which are essentially just pours in plant leaves and they close when it's hot to prevent the loss of water. But the problem with strom a closing means that C. 02 which is super important for carbon fixation which is I mean essentially it's required for carbon fixation can't get into the leaves if those are closed. So stromal when they're close prevents gas exchange. And so what happens is carbon fixation still going, I mean it's still pumping along but the C. 02 it needs is decreasing rapidly because it's not getting any more from the environment. But what is increasing is oxygen because remember it, carbon fixation is going to produce oxygen. So you get this super big build up of oxygen and plants which it doesn't need. And it's very much it needs more carbon dioxide but it's not getting it because it's hot. So the plants close their leaves. Now this is where we get back to rue Disco. So disco like I said it was this really kind of inefficient enzyme. We have a lot of it works slowly but it also works um to bind C. 02 or 02. And whether or not it works with C. 02 or 02, it will actually produce something different. So like I said before, if it is rue Biscoe working to fix carbon, it's going to produce this sugar which is what we know is photosynthesis, but if it works two on 02, what happens is it produces this um molecule. And instead of undergoing photosynthesis undergoes photo respiration. And this is just kind of this big waste of energy like it doesn't need to do this is not efficient. The plants just literally just like wasting all of its energy doing this when it wants to be doing this. So um So it so it doesn't want to do this. So if the Chama plan if they close their pores and there's this build up of 0.2, disco then is going to follow this pathway and do photo respiration instead of this one and you can just ignore this. I think this is a copy here. And so um what we see is that we don't want you doing this and this is what happens in hot environments because those plants close their poor so we can see here this is just kind of an example of photo respiration which Has to go through all these different processes travel through all these different organelles because rob isco is using 0.2, which is what's present and it's just this huge waste of energy for the plant to do this. So c. four plants which are things like corn and certain types of grasses and kind of grasslands. They handle this build up of oxygen in a specific way. And how they do this is they actually just separate carbon fixation. And so they have two different cell types that handle different things. So mesophyll cells handle the light dependent reactions and fixation of C. 02. And when it does this it forms this molecule called mallet. Now next to it it has bundle sheath cells. So what happens is that C. 02 which was originally formed in this mallet molecule actually can be released and then that C. 02 can be used in this Calvin cycle pathway. And so rude Biscoe here is actually only found in the bundle sheath cells. So it prevents this accumulation of 02 and prevents wasting energy. So back up and I can show you what this what this is like. So here we have the C. Four um photosynthesis pathway. So we have our two types of cells. We have the bundle sheath which is this weird color bundle sheath and we have the mesophyll and they're really close to each other. So what happens is C. 02 comes in, it goes through all of its different processes and what happens is it gets turned and fixed into this chemical called ballet. Then that gets transferred to the bundle sheath cells. And malaita is then um that carbon is released and then it undergoes the C. Three pathway. So that is um how c. four take or how c. four plants control the fact that um it's hot and so it needs to close its floors. And so but it has this build up so they actually just separate the cells. But there are other types of plant called cam plants. And these are mostly just cacti and they handle this oxygen build up very differently. And so what they do is they actually just control the amount of C. 02 differently at different points of the day. So at night um it's cool outside so the strom is open and then see CO. Two is fixed normally. So it's fixed using rib isco And that normal pathway that we talked about but in the daytime it's super hot. And so the Stroman is closed. So CO two then is fixed to this malaise that was we talked about before and stored in the cell. So they're just like we're not even going to deal with it. We're just going to store it here and then when the troma closes when this drama opens um What happens is that CO2 which is attached to this mallet, that carbon can be released and fixed normally by Romesco. So where the C. Four plants actually just separated the processes in different cells. The cam plants just say okay well we're not gonna do this during the day, we're gonna do this at night. So what you can see here is that this is at night, it's dark, that's not a pin, it's night and this is day. So what happens is at night, these pores are open, it can get through um and it can be processed by ra Biscoe. Then what happens during the day? It closes, it closes the sea that you can't get through. So what happens is um it will store it as mallet. You don't necessarily all these chemicals in these formulas are just ridiculous. You don't need to understand or follow this at all. But just know that it gets stored as ballet. And then whenever it starts undergoing it again that ballet is released and can be used by the cell normally and fixed by re Biscoe. So it's kind of a mouthful. But there are all these different ways that carbon is fixed, the sugars and plants. And so hopefully that was clear the difference between the C. Three, C four and cam plants so that let's move on