top of page

Photosynthesis: Calvin Cycle

The Calvin Cycle is the last cycle of photosynthesis where the energy made in the chloroplasts (ATP and NADPH) is used to build and break apart and rebuild complex carbon molecules. The breaking apart and rebuilding, in a new configuration, results in the production of glucose in a plant cell. This glucose can be used within the plant to make cellulose fibers, starch, and many other necessities for growth and life. Watch the video for a complete explanation of the steps of the Calvin Cycle.

Click the video above or the link to watch "Calvin Cycle" on YouTube:

The complete reaction for photosynthesis is:

3 CO2 + 6 NADPH + 5 H2O + 9 ATP --> C6H12O6*

*This is a simplified representation of the products of photosynthesis. There are other products and glucose can be transformed into other important biomolecules as needed by the plant.

To download a free pdf of the Photosynthesis: Calvin Cycle Worksheet, click the link.

Photosynthesis: Calvin Cycle worksheet -

Related Biology lessons from Beals Science:

Below is the complete transcript for the Photosynthesis: Calvin Cycle Video

We’re going to dive into the Calvin Cycle.

So we’re looking at photosynthesis and all the parts and pieces that allow a plant to take in sunlight and breathe in CO2 and water and make glucose, or sugar, of that.

So if you haven’t seen the previous videos: Photosynthesis overview and ADP / ATP you may want to check those out. But the Calvin Cycle gets a little more involved.

Mainly because I am going to take it one step further in the chemistry with this whole thing.

Now, the Photosynthesis Overview, umm, I’ve got this on other videos, you may want to check that out. Again, we’re just going to focus in on that area of the Calvin Cycle and what happens to finally produce this glucose at the end of the process.

The Calvin Cycle is not an organelle inside of there so I am just representing it as a cycle because you are going to see that it cycles.

So here’s how we’re going to look at this to begin with:

Inside the chloroplast you have this five carbon chain, now it’s not just carbon, there’s a whole bunch of other stuff with it, alright, but we are just representing it with those carbon nuclei to keep things as simple as possible.

So, you’ve got this five carbon chain, and it’s a molecule and its got a really big name, you can look it up, if you want it but I am not going to share all that technical stuff here, it’s just a little bit overwhelming when you are learning the process.

This is where a cell needs to breathe in CO2. When it breathes in that CO2, it undergoes another chemical reactions it breaks that carbon off and that oxygen goes away and gets used in other stuff. We’re not going to follow that oxygen right now, we’re going to follow that carbon.

As part of the Calvin Cycle, when that gets broken off of there it gets attached to those five other carbons.

Now we’ve got a six carbon chain, that’s important. We’re going to see a six carbon chain later on but this is a different one, this is not really one that our body can use to make sugar, a few things have to happen first.

So, we go back to the photo part of photosynthesis where we made ATP. That ATP, as part of the calvin cycle, it releases that energy. So that phosphate group breaks off of there. When that phosphate group breaks off it pours out its energy and that energy slams into our six carbon chain but its not quite enough. There’s a slight configuration change, it’s not enough to get the full reaction to happen that we need to have happen, which is why the plant also needs NADPH. OK. Again, trying to stay away from getting too technical but this NADPH has got those two electrons. When those electrons break off it releases energy into this cycle and we’re left with NADP+.

Now remember the NADP+ is like the wagon we’re carrying along but it doesn’t have anything in the wagon, it’s just something that can store that energy.

You might have to go back all the way to the photosynthesis overview video if you don’t understand what that is all about.

So now this six carbon chain has been hammered - bam, bam, bam. Hit by two different sources of energy. When that happens it breaks it apart; it breaks it into two, three carbon chains. There is other stuff attached to all of this carbon, I’m just not showing that.

Three of those leave the cycle, there just going to wait. Now this is happening very fast but those are just going to wait. The other three stay in the cycle, they’re going to be recycled and they are going to be used again to make the next step.

So this three carbon chain that is still in the calvin cycle, it’s going to get hit with the energy from ATP one more time. ATP comes in - BAM! - it releases that phosphate. That energy slams into this three carbon chain. And then there’s another two other carbons, another two carbon chain floating around. You just have to trust me in the fact that these are in there, they have complex names but those in there. That energy, so, to attach those onto the other three carbons requires energy - ATP provides that energy. And all the sudden BAM, once that energy is released it allows those to attach on there.

Now we have a five carbon chain again. Well, that’s what we started with. So, all we’ve done here is taken that three carbon change that has changed into a five carbon chain and that’s what we started with when [breathes in] that plant breathed in the CO2, so this happens again.

More CO2 comes in, it gets broken apart. The carbon gets broken off, it gets hooked onto that five carbon chain making a six carbon chain. And then ATP comes in and slams into that and releases it’s energy. NADPH comes in, the electrons break off, it releases it’s energy and this thing breaks apart again.

And all the sudden, down here at the end of the calvin cycle, we’ve gone through the Calvin Cycle one time, two times. We’ve got two three-carbon chains. So, two three-carbon chains get attached together and they make another six carbon chain.

What is that six carbon molecule? Well, that’s what we’ve been working with the whole time, or trying to get to the whole time. This is the product of all of the steps of photosynthesis - we’ve just made sugar: C6H12O6

That C6 means six carbons. And remember there’s some Hydrogens hanging off there, there’s some oxygens hanging off of there, um that’s how we get that whole configuration.

But this is the sugar that plants make. I’ve got the complete reaction down there at the bottom. It requires 3 CO2 molecules, requires 6 NADPH’s that break off those electrons, we need 5 waters although for some reason that H got really small, that should be 5 H2O, with a big H, little 2, O.

We need 9 ATP, that’s our source of energy and when all that comes together - BOOM - we end up with sugar. We end up with some other stuff as well with is why I have the little star by the sugar, but what we’re really trying to focus on here are the steps of photosynthesis, going from sunlight, water and CO2 and finally ending up with sugar at the end.

Now, if you go back to the overview of photosynthesis, you know that a plan actually takes that sugar and converts it into a number of other things. Um, here’s the overview, we got to that last step down there at the bottom, making Glucose and again there are videos explaining the other steps of you need them.

I’ve also got a handout for this one, a worksheet that I use in my class to explain what happens at each of the steps; a good overview and a good sort of assessment to see how well you understand what’s happening in all of these things. And, I do have that attached down at the bottom, you can go to the link. Also there will be a link here at the end that pops up.

Um, again we created our sugar at the end through all these processes. And you’re going to see, if you missed all those other videos they’re going to show up all around here, somewhere on this page and then we’ll move into the next step which is Cellular Respiration.

Cellular Respiration is what happens when you, or an animal, goes and eats that plant and gets the glucose out of there. The glucose goes into your body and it makes energy.

So, that’s the next step. Good luck. Keep on Learning.

Keep on Learning! ~Craig


Recent Posts

See All
bottom of page