in this video, we're going to introduce photo respiration, which kind of sounds like photosynthesis, but not really, and they're actually really different from each other. And so what we need to recall from our previous lesson videos is that photo synthesis is going to use or consume carbon dioxide gas or CO two from the atmosphere in order to build sugars like glucose. But photo respiration is actually a process that causes plants to make carbon dioxide, gas or CO two rather than consume it like what photosynthesis normally does. And so, in a way, photo Respiration is kind of the opposite of photosynthesis, since again photosynthesis will use or consume carbon dioxide and decrease carbon dioxide levels, whereas photo respiration is going to make carbon dioxide rather than consume it, which is going to increase carbon dioxide levels. And so because photo respiration is kind of the opposite of photosynthesis in a way that is going to make photosynthesis really, really inefficient. Photo Respiration makes photosynthesis really, really inefficient because it kind of does the opposite of photosynthesis. It makes carbon dioxide instead of consuming it. Now, when you break down the roots in the word photo, respiration which will see is that it has the root photo, which we know is a route that means that it's going to occur with light. And we also know that photosynthesis has this route photos. So both photosynthesis and photo respiration occur with light, and so that means that they are going to kind of compete with each other in a way. But of course, photo respiration also has this respiration term in here, which is really referring to the ability for it to produce or release carbon dioxide gas just like well, you already indicated here. And so if you put it together, photo respiration means that it's going to occur with light and actually produce or release carbon dioxide gas. Now, in order to better understand photo respiration, we also need to recall from our previous lesson videos what the stone mata of a plant are. And so the stone Omada of a plant is not to be confused with the strom A of the chloroplast and so recall from our previous lesson videos that the stone Omada are these openings or pores or holes that were found in the leaves themselves that can open and close and control gas exchange between the leaf and the environment of the leaf. And so the Samata can either be in an open position or again, they could be in a closed position. And if the Samata are in the open position, then that means that gas exchange is able to occur. And that means that carbon dioxide is able to come into the leaf and oxygen is able to leave the leaf. And so if we take a look at our image down below, over here on the left hand side, notice what we're showing you is that in cooler temperatures, when the temperatures are relatively cool, then the stone Omada of the plant are going to be in an open position. And so if you take a look at this region of our image here, notice that we're zooming into Ah, leaf here and down below. This represents the missile field tissue of the leaf. And what you'll notice is that this structure right here represents the sto mata and notice that in cooler temperatures, the stone mata are gonna be in an open position, just like what we see right here. And so with this gap here, uh, between the tomato here, the open position of this tamada. When it's open, it allows for gas exchange so it allows for carbon dioxide gas to diffuse into the plant. And it allows for oxygen gas that's being produced to diffuse out of the plant. But it also allows for water molecules to diffuse out of the plant as well, through evaporation and so normally the stomach of a plant are going to be in the open position during photosynthesis so that the carbon dioxide gas is able to diffuse into the plant and the oxygen gas that's made in photosynthesis is able to diffuse out of the plant. However, in order to understand photo respiration, what we need to understand is what happens in a very specific scenario, and that very specific scenario is the scenario of a very hot environment such as a desert, for instance, and so in really, really hot environments, if the sta mata are in the open position like what they are over here, then the plant is going to allow for gas exchange so carbon dioxide will be able to come in and oxygen will be able to leave, but also in hot environments. Water is going to be mawr likely toe. Leave the plant via evaporation. And so, in really, really hot environments, plants are susceptible to dehydration by losing water molecules by evaporation. And so, in really, really hot environments, plants are actually able to prevent dehydration in hot environments by closing their stay mata. And so instead of leaving their Samata in an open position where they could lose water by evaporation and dehydrate and then wilt and unfortunately die the plants prevent dehydration and prevent themselves from dying by closing their stay. Mata. However, when the Samata are closed, they are going to prevent dehydration. But they also prevent gas exchange. And so when the Samata are closed, Uh, if you take a look at this image down below over here on the right hand side, where we have increasing temperature and hot temperatures, plants are going to close their Samata and so notice Here we have the Samata in the closed position. And yes, it is going to prevent dehydration because water will not be able to leave the plant. However, it also prevents gas exchange, and so carbon dioxide gas is no longer going to be able to diffuse into the plant like it was over here when the Samata are open and oxygen gas is not gonna be able to diffuse out of the plant like it was able to over here when the stomach was open. When the scimitar closed, oxygen gas cannot diffuse out. And so ultimately, when the star Mata are closed, preventing gas exchange, this is gonna lead to decreased carbon dioxide levels inside of belief. Because again, the carbon dioxide is not ableto enter the plant. Instead, the carbon dioxide is going to be blocked from entering the plant. So that means that inside of the plant, carbon dioxide levels are gonna decrease. And also because oxygen is not able to leave the plant when the stay moderate closed oxygen is going to remain and build up inside of the plant. And so when oxygen builds up inside of the plant, this is going to lead toa. Increase oxygen levels inside of the plant when the Samata are closed. And if the oxygen gas concentration remember the bracket here represent the concentration of if the concentration of oxygen gas is too high when it's increased. What this means is that the oxygen gas is going to compete with the carbon dioxide gas for binding to the enzyme. Rube isco, which recall from our previous lessons of the Calvin cycle, is the enzyme that performs carbon fixation of the carbon Calvin cycle. And so if oxygen is too high, then oxygen is going to compete for binding to rub isco and rub. ISCO is going to actually add oxygen to the first molecule of the Calvin cycle. Are you BP? Instead of adding carbon dioxide to argue BP like what normally happens during photosynthesis and so during photo respiration photo respiration is more likely to occur in hot environments when the storm mata are closed and these conditions exist. Decreased carbon dioxide and increased oxygen and during photo respiration when oxygen levels are so high, Rube ISCO adds oxygen toe are UBP instead of adding carbon dioxide. And ultimately, uh, this is going toe waste the A, T P and the D. PH. That was made by the light reactions. And so the during photo respiration 80 p and any DPH are wasted, and it also ends up making carbon dioxide instead of making glucose. And so if we take a look at our image here in the middle. Notice what we're showing you is a zoom in of one of the chloroplast of the mess a fill cells. And so this is a zooming of the chloroplast and over here on the left, notice what we're showing you is actually the normal conditions when the Samata are open and this over here represents normal photosynthesis, which includes the normal Calvin cycle. But over here, on the right hand side, what we're showing you is the process of photo respiration and how photo respiration occurs in hotter environments when the Samata are closed. So if we were to go over this, notice that if by covering the left hand side and cooler temperatures, uh, the leaves and the plant are gonna have open the mata and when the Samata are open in these cooler temperatures, it allows for gas exchange. It allows for carbon dioxide to diffuse in and oxygen to diffuse out. And so oxygen carbon dioxide levels inside of leaf are gonna build up. And so there's gonna be high carbon dioxide levels. High Co two levels and the High Co two levels allows carbon dioxide or CO two to interact with Rue Biscoe and be bound to our UBP, Um, as it normally proceeds in the Calvin cycle. And so, under these conditions and cooler temperatures when the Scimitar opened, the normal Calvin cycle occurs, and glucose is going to be produced as normal. And so you could see the glucose over here being produced is normal. But over here, on the right hand side, what we're showing you is what happens in hot temperatures. The Samata are going to close, and so in hot temperatures, as this says, the leaves and the plants are going to close their Samata. There's gonna be close to Mata and close. The motto is gonna prevent gas exchange? Yes, it's going to prevent dehydration, but it also prevents gas exchange, and so carbon dioxide is no longer gonna be able to enter the plant. So carbon dioxide levels are gonna get really low inside of the plant, and oxygen levels are no longer oxygen is no longer able to leave the plant, and so oxygen is going to start to build up inside of the plant under these conditions, and so there's gonna be a quite a high levels of oxygen here under under photo respiration conditions. And so when oxygen levels are really, really high, oxygen will compete with carbon dioxide for binding to Rue Biscoe and binding toe. Are you BP? And so, ultimately, when oxygen binds to rub isco and eyes bound to argue BP instead of carbon dioxide, this leads to photo respiration and ultimately photo respiration. When oxygen interacts with rube isco, it's going to waste the A, P and a. D. PH that would have normally been used during the Calvin cycle. Instead, this 80 p and any DPH is gonna be used for photo, respiration and photo Respiration ends up producing carbon dioxide, whereas recalled the Calvin cycle over here is going to consume carbon dioxide. And so ultimately, what we can see here is that photo respiration is going toe waste a teepee in any DPH, and it's going to make photosynthesis really, really inefficient. And so photo respiration is something that the plant would want to try to avoid. And so notice down here. What we have is a little boxing match occurring here between these, uh, this person with the blue gloves and this person with the red gloves, and this is really just supposed to represent how carbon dioxide over here and the Calvin cycle is going to compete with oxygen and photo respiration. Uh, and so the whole idea here is gonna all depend on whether the still mata are in a open position or if the stem mata are in a closed position. And so again, photo respiration occurs when the Samata are in the closed position, as we've indicated here. And photosynthesis as we've discussed it previously in our previous lesson, videos occurs when the stigmata are open. On this one occurs when its the matter closed. And so this here concludes our introduction to photo respiration and we'll be able to get some practice applying the concept that we've learned here as we move forward in our course. So I'll see you all in our next video.
Plants are more likely to use Photorespiration instead of the Calvin Cycle when:
Stomata remain open and CO2 concentrations within the plant are high
Stomata remain closed and O2 concentrations within the plant are high