Photosynthesis: The Calvin Cycle

The Calvin cycle is the second set of reactions in photosynthesis and occurs after the light-dependent reactions. Sometimes the Calvin cycle is called the Light-INDEPENDENT reactions or even the dark reactions because light is not directly needed to make the Calvin cycle happen. Nevertheless, two key products from the light reactions are needed to make the Calvin cycle work: ATP and NADPH.
You may recall that both ATP and NADPH were made during the light reactions at the thylakoids. The Calvin cycle takes place in the fluid surrounding the thylakoids, known as the STROMA.
ATP provides the energy, and NADPH provides the electrons and hydrogens that are needed to reduce carbon dioxide to build sugars in the Calvin cycle.
Here’s how it works:
Phase 1: Carbon Fixation
An enzyme called Rubisco takes CO2 from the air and adds it to a 5-carbon compound called RuBP. This is called carbon fixation. This makes a 6 carbon compound that immediately splits in half to make two molecules of 3-phosphoglycerate. Notice that we did carbon fixation for 3 molecules of CO2. You will see why soon!
 
Phase 2: Reduction
In the reduction phase, ATP from the light reactions provides energy to make an intermediate compound. This reactive intermediate can then be reduced, or gain electrons and hydrogen. The electrons and hydrogen come from NADPH and are used to reduce the intermediate compound to make Glyceraldehyde-3-phosphate, more commonly called G3P (or sometimes triose phosphate). G3P is the key product of the Calvin Cycle that can be used to make sugar! Notice that for every 3 molecules of CO2 brought into the Calvin cycle, there is a net gain of 1 G3P. 3 carbons in, 3 carbons out… makes sense, right?
Phase 3: Regeneration
Notice in our model that only one G3P is removed from the cycle, but 5 more remain. These 5 G3P molecules get converted back to our starting compound, RuBP. Remember, the Calvin cycle is a cycle so we need to make our starting compound again to keep the cycle going. Now, I’m going to give you a moment to think… If we have 5 G3P molecules and each one has 3 carbons, how many carbon atoms do we have? Now that you have the answer, how many 5-carbon RuBP molecules can we make using those carbon atoms? I’m guessing that you’ve figured it out… we can make 3 RuBP molecules. To do this, energy is required. Can you guess where that energy comes from? If you said ATP, you are right. Let’s watch.
Now that we’ve completed the Calvin cycle for 3 carbon atoms, let’s go through the process again so that we can make glucose! Remember, our overall photosynthesis equation has 6 carbon dioxides being used to make 1 glucose molecule with 6 carbons. With this in mind, how many G3Ps are needed to make one glucose? If you said 2, you are correct!
Now you have seen how the Calvin cycle is used to make glucose and how the light-dependent reactions provide the NADPH and ATP that were needed to make the Calvin cycle work!
The glucose and other organic compounds made as a result of these processes in photosynthesis are what allow plants and algae to grow and support practically all life on earth, including you!
To become an expert on the Calvin Cycle by doing it yourself, play Photosynthesis Interactive at BioMan Biology!
Music by Bensound.com/royalty-free-music

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

Thanks, I'm glad you have been enjoying the videos! I'm planning to release one on the nitrogen cycle soon (with a game that goes with it). Please be sure to subscribe if you want to be notified when it comes out. Thanks for the well wishes too! All the best to you!

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[@BioManBiology]

I'm happy to hear that! Thanks for your comment!

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

I actually teach IB Biology, so I'm happy to hear that! Thanks for your comment!

[@jishnushah2001]

This is such a great video. IN my textbook it didn't show 5 G3P were recycled to form more rubps for the production of glucose. GREAT VIDEO

[@BioManBiology]

Thanks for your comment! I'm glad you found it helpful and that it clarified how RuBP gets regenerated!

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[@BioManBiology]

You're welcome and good luck on your test! Thanks for your comment!

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[@BioManBiology]

I'm glad it is helpful to you! Thanks for your comment!

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[@BioManBiology]

Thanks, I'm glad you enjoyed the video! I will be making more soon (I just had a busy season, so I couldn't make many this past year). I'm planning to ramp up soon, so please feel free to subscribe if you'd like to be notified when new content comes out! Thanks!

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[@BioManBiology]

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[@BioManBiology]

You're welcome, I'm glad that they are helpful to you!

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

Thanks, I'm glad it was helpful! Also I do have videos on cellular respiration here: kzbin.info/aero/PL3X4Gc6kV7xsm6VEUVNQYxuw3-XW24QLk&si=db0vfPSAyUzAhNq1 I hope they help you too!

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[@BioManBiology]

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[@Nigga-xd]

Where is the H from NADPH utilized Does it leave in the form of H+

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[@BioManBiology]

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[@BioManBiology]

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[@BioManBiology]

You're welcome! Those are good ideas and I hope to get to them one of these days!

[@squidsqueeze_5098]

Hello, your explanations make me understand the concept more and more. But I have a question, why do we need to make 3 turns of carbon fixation? I’m a little bit confused at that point. If so, do we need 6 Calvin cycles to produce 1 glucose molecule or 2 times for one?

[@BioManBiology]

Thanks, I'm happy to hear that! In answer to your question, you need 3 carbon dioxides to be fixed in order to get 1 G3P. Notice that 3 carbon atoms come in (3 CO2 molecules) and 3 carbon atoms come out (G3P has 3 carbons). I think following the number of carbons is the easiest way to conceptually understand the Calvin Cycle. In order to make glucose (C6H12O6) which has 6 carbons, you need 6 CO2 molecules. 6 carbons in...6 carbons out. Does that help?

[@squidsqueeze_5098]

@@BioManBiology Sure! It helps a lot and makes sense. Thank you so much.

[@GarlicBreadEnjoyer]

@@BioManBiology So it only takes 2 turns then? Sorry, I'm still confuzzled about the number of turns required for the cycle to make one G3P :(

[@hiva7873]

Hey man, what do you use to make your visuals for the lesson? Is it PowerPoint?

[@BioManBiology]

Hi, No, I don't use PowerPoint. I use other graphics and animation programs like Serif Drawplus and Adobe Premiere Pro to put the video together.

[@Rio-ik7nx]

Thanks

[@BioManBiology]

You're welcome!

[@btkvideoeditor5255]

In regeneration step 5 G3P has already 5 phosphate which mean that only 1 phosphate is required to make Rubp but how how 3 Atp come ?

[@BioManBiology]

5 G3P molecules would have a total of 5 phosphates and 3 RuBP molecules would have a total of 6 phosphates. The extra phosphates from the extra ATP don't become part of RuBP. Rather, these ATP provide the necessary energy to rearrange bonds to form RuBP (a 5 carbon molecule) from G3P (a 3 carbon molecule). I hope that helps!

[@itburnswhenip671]

HL bio ptsd rn. I remember pulling an all nighter before the final just studying this and the Krebs cycle. Good times

[@BioManBiology]

😊 yeah, it's not the easiest thing to remember...

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tq

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Bioman the 🐐

[@BioManBiology]

😄 Thanks!

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[@BioManBiology]

😊 Thanks!

[@rajkumarthoungambaningthou1169]

Honestly saying i learn photosynthesis from this video but sometimes it is hard to catch some word since english is my second language. I just wondering if you can add proper subtitles anyway thanku so much☺️❤️

[@BioManBiology]

I'm glad it was helpful to you. I put the transcript for the entire video in the description and I think you can see subtitles by clicking the CC (closed captioning) button. I hope that helps!

[@arshiyabhat]

do you have a video on c4 cycle?

[@BioManBiology]

Not currently, but perhaps someday!

[@user-vi2mj5uy7r]

0:40 Very important screenshor for me

[@avigoyal9422]

The video was great but I have one question, in the reduction phase, what is the point of ATP adding a phosphorus to phosphoglycerate to create biphosphoglycerate only for it to be reduced by the NADPH and removing the added phosphorus?

[@BioManBiology]

Thanks, I'm glad you enjoyed the video! That is a good question. The addition of this phosphate essentially destabilizes it, making the next reaction possible. You can think of it as adding potential energy to the molecule. This energized molecule can now drive the subsequent reaction. Does that help?

[@avigoyal9422]

Thanks a lot and I understand, keep up the good work

[@marchedobejas6428]

what happens to the left out g3ps?

[@BioManBiology]

The G3P that doesn't continue in the cycle is the final product that is used to build glucose and other organic molecules. 👍

[@kniga7763]

bro your music is too quite, i can still hear your voice

[@user-xx9bd4gn1r]

where do the oxygen molecules from CO2 go after carbon fixation?

[@BioManBiology]

The oxygen atoms found on the CO2 molecule become part of the organic molecule you end up producing (G3P or glucose etc.) Some of the oxygen also ends up in water molecules, but these are often not shown in the overall photosynthesis equation because it is a net equation. I hope that helps!

[@user-xx9bd4gn1r]

​@@BioManBiology Thank you so much for the clarification! Hope you have a wonderful day :))

[@ubaid780editsyt]

I couldn't understand 2nd phase the reduction one , it's a little bit difficult

[@BioManBiology]

In the reduction phase, NADPH gives electrons and hydrogens that are needed to produce the final product, G3P ( which can then be used to make glucose). This also needs energy (ATP) to occur, which is why ATP is also shown. Does that help?

[@Jubby4Iife]

@@BioManBiologythank you, I’m studying for my test, and that help a lot

[@user-vi2mj5uy7r]

3:18 This is where I stop I did not get it 😂

[@G82_M4]

Please turn the music up even higher 😑

[@G82_M4]

but still a great vid

[@BioManBiology]

Thanks, I'll keep your feedback in mind for future videos.

[@celinaandrade9918]

Ungrateful much m this video is great !!!!

[@BioManBiology]

@@celinaandrade9918 Thanks, I'm glad you enjoyed the video!

[@smcm.c1689]

@@BioManBiologyit is a great set of videos ! I can’t find a decent one in my mother’s language so thank you 😊 I would just agree with the volume but please keep it going ❤️

[@willlagergaming8089]

3:43 "become an expert on the calvin cycle by doing it yourself "

[@BioManBiology]

Yeah, the interactive really helps you practice what you learned and makes it stick! Here it is: biomanbio.com/HTML5GamesandLabs/PhotoRespgames/photointeractivehtml5page.html

[@user-vi2mj5uy7r]

1:18

[@focus_on_deen4050]

thanks for the explanation, but please remove the music in the background. Its annoying, and its hard to pay attention to the video

[@BioManBiology]

Thanks for your feedback!

[@nvm9182]

The music is too loud

[@BioManBiology]

Thanks for the feedback. I'll keep that in mind for future videos

[@shukriamohamed-nq3rg]

I wish you could be lecture

[@BioManBiology]

Thanks!

[@KenMyles-xt2yw]

Why the music ? Do you realize that the music competes with your teaching ? You are giving the wrong message. That incorrect message is that to learn we need music. If that were true there would be no learning. I give you a thumbs down. The music is the reason. It is absolutely a distraction. The commentor who wrote to turn the music up is likely being sarcastic or likely not actually interested in listening to you.