To synthesize one glucose molecule, the Calvin cycle uses _________ molecules of CO₂, _________ molecules of ATP, and _________ molecules of NADPH.

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Welcome back. Let's look at our next problem. It says the mesophyll cells of C. Four plants utilize the following enzyme to fix C. 02. When we look over our answer choices. Let's notice briefly that choice D. Is none of the above. So there is a chance that none of these is the correct answer. So we want to think about carbon fixation in c. four plants. And what do we recall from our content? Videos about c. four plants. While C four plants are adapted to hot and dry conditions. That is by being able to still process photosynthesis efficiently even though they close their store mata, when the conditions are particularly hot or dry to prevent water loss through transpiration. So they have an alternate method of carbon fixation. Hello? Because when the tomatoes are closed no new C. 02 can enter the leaf. Well in C. Three plants when carbon is fixed, it is done by the enzyme rue Biscoe. Andrew Biscoe has an alternate pathway. It can also react with oxygen and perform photo respiration. As we recall that photo respiration is a much less efficient process. So it's to the benefit of the plant to maximize the use of the Calvin cycle and minimize photo respiration. But the way ruby sco determines which process is carrying out is the concentration of CO two vs. 02 around it. When the concentration of CO two goes up it will get kicked into photo respiration and when those tomatoes are closed, that's exactly what happens Calvin cycles taking along. It's using up C. 02. It's producing 02. That 02 concentration is going to grow rube, IsCO's going to switch to photo respiration. So C. Four plants have adapted to try and maintain a high CO. Two concentration around Disco. They still use Disco in the Calvin cycle. Is that first step but not for carbon fixation. And they've adopted by separating carbon fixation at the Calvin cycle in space. So carbon fixation happens in the mesophyll cells which are on the outer part of the leaf. And the Calvin cycle is restricted to bundle sheath cells in the interior of the leaf. And that means they're protected From 0. 2 in the interior at least in the atmosphere. And when carbons fixated fixated fixed in the mesophyll cells, it's by an alternate pathway. And the enzyme for that pathway is pep car box Alice. And that's our answer choice. C. The molecule it uses is pep P. E. P, which is a three carbon molecule, adds the C. 02 to generate the four carbon mallet. That's why they're called c. four plants since they generate a four carbon molecule and they fix carbon. Now that malic gets converted to excel acetate and goes on to the Calvin cycle. When it gets to the bundle sheath cells it releases its C. 02 and that C. 02 is fixed by rob isco and it goes down the Calvin cycle pathway. So this process of fixing the carbon in the mesophyll cells generate mallet which carries C. 02 into the bundle sheath cells means that the C. 02 concentration around rue Biscoe remains high and keeps photosynthesis being efficient even when it's hot or dry. And it has to close its tomato. So let's just look briefly at our other answer choices to understand why they're not correct. Of course we can eliminate choice D since we do have a correct answer. Choice A. Is our ubp car box lace. Well this is just our friend rob Isco. So again rib IsCO used to fix carbon and C. Three plants. Um And it's used as the first step in the Calvin cycle and C. Four plants but it doesn't fix carbon and C. Four plants. So that's not an answer. And in choice B. Is phosphor phosphor. Oh this is the enzyme at the last step of the Calvin cycle that regenerates R. U. B. P. That first molecule in the Calvin cycle. So that's not our answer here. So again, the mesophyll cells of C. Four plants utilize the following enzyme to fix C. 02. And that's choice C. Pep car box Alice. See you in the next video

To synthesize one glucose molecule, the Calvin cycle uses _____ molecules of CO₂, _ molecules of ATP, and _____ molecules of NADPH.

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Key Concepts

Calvin Cycle

Photosynthesis

Molecular Inputs of the Calvin Cycle