What is the role of PEP carboxylase in C4 and CAM plants? a. It fixes CO2 into an organic acid. b. It produces ATP for the Calvin cycle. c. It replaces rubicso in the Calvin cycle. d. It releases CO2 from organic acids.

Video transcript

Hi everyone. Welcome back. Here's our next problem. It says blank enzyme is involved in carbon fixation to an organic acid in both c. four and cam plants. So let's recall from our content video um the process of carbon fixation, we know the majority of plants which are C. Three plants. Carbon fixation is that first step in the Calvin cycle. When a molecule of CO. Two is combined with the five carbon R. U. B. P. And enters the Calvin cycle catalyzed by the enzyme rube. IsCO. That first step there, The problem is that right Biscoe doesn't just react with co. two. It can also react with oxygen if it does that instead of the Calvin cycle, it goes through the process of photo respiration which is a wasteful process that produces less energy in the Calvin cycle. And which pathway rube ISCO will follow depends on the concentration of these gasses around it. So if there's more so to around it will go through the Calvin cycle. There's more oxygen. You'll have photo respiration taking place when sta mata are closed on a plant, you're gonna have a build up of oxygen concentration. Um No more gas exchange can occur. No new C. 02 can come in as the Calvin cycle proceeds, you're consuming CO. Two and producing O. To the 02 concentration will build up and you'll have photo respiration taking place. So see foreign cam plants we recall have an alternate method of carbon fixation to prevent photo respiration and that is because they actually both managed to separate the processes of carbon fixation from the Calvin cycle. So we have an alternate pathway of carbon fixation in the c. four and cam plants. And that occurs when we have a molecule of carbon dioxide that combines instead of with our UBP, it combines with a molecule called P. E. P. That goes on to form the molecule Uccello acetate. That's our organic acid. Sell acetate can then be transported to where the disco is And there it releases through a series of reactions. Its molecule of co two, that's C. 02 can then proceed to the Calvin cycle when it reacts with our UbP as catalyzed by rue Biscoe. But this process means that the ra Biscoe maintains a concentration of C. 02 around it. So which enzyme is it that catalyze? Is this step here? That's what we're looking for. And that is pep car box lace, which is choice A. Well, just briefly look at our other answer choices to understand why they are not correct. Choice B. Is ridiculous biz phosphate. Well, this is that not an enzyme at all. This is that molecule are UbP that we find right here. So that's not what we're looking for. That's the molecule that reacts with CO. Two in normal C. Three carbon fixation. So not our answer. Choice choice C. Says N. A. D. P. H. Productive this well this is an enzyme involved in the carbon cycle Calvin cycle but further on after carbon fixation that catalyze is the conversion of a molecule of N A. D. P. Plus to N A. D. P. H. So that's not our answer either. It's not the enzyme involved in carbon fixation. And finally I saw citrate leis, an enzyme not involved in the Calvin cycle at all, But an alternate A cycle called the glia CSA late cycle. And this is a pathway for the synthesis of carbohydrates allows them to use a C. Delco way to synthesize carbohydrates when simple sugars aren't available, but not part of our Calvin cycle, not what we're looking for. So, again, choice, a pep car box slice enzyme is involved in carbon fixation to an organic acid in both c. four and cam plants. See you in the next video.