Light Reactions of Photosynthesis - Video Tutorials & Practice Problems
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1
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Light Reactions of Photosynthesis
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4m
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in this video, we're going to begin our lesson on the light reactions of photosynthesis. And so the light reactions we already know from our previous lesson videos is the first stage of photosynthesis, and it specifically occurs in the Thilo coy aids of the chloroplast. And so recall that the fill a coid czar, those green pancake looking structures and the light reactions are going to occur in the Fila Coid membrane, as well as in the Fila Coid space or the space that's on the inside of the Fila Coy's. Now the light reactions is going to synthesize chemical energy in the form of a teepee and N a D. PH. And this 80 p and N a. D ph are going to be used to power the Calvin Cycle, which is the second stage of photosynthesis, while producing oxygen, gas or go to as a byproduct. Now, N. A. D. PH is really just another electron carrier that will carry or transport to energized electrons. And so N. A. D. PH is really just another electron taxicab, if you will, which will recall we covered electron carriers in our previous lesson videos. When we talked about the aerobic cellular respiration and so down below. Here in this image, which you'll notice is that we've got the image showing photosynthesis on once again in the background. What we have is the chloroplast and notice that we have. The regions that we want to focus on in this image colored on there also enlarged, and the regions that we don't really want to focus on right now are great out and they're smaller. So, like the Calvin Cycle, for instance, we're gonna talk about the Calvin Cycle mawr in another video later in our course. For now, we want to focus on the first part of this reaction, which is again. The light reactions and the light reactions occur specifically in the Theloke oId, or thes green pancake looking structures within the chloroplast. And so really, the light reactions is going to take solar energy or sunlight in the form of photons and use this solar energy of these photons along with water, uh, to generate chemical energy in the form of a T p and N a. D. PH, which is another electron carrier on electron taxicab, if you will, and it also creates oxygen gas as a by product, which we could see down below. And so, in terms of the reactant with light reaction to use, uh, solar energy or photons along with water and in terms of the products, uh, the light reactions creates oxygen, gas and chemical energy in the form of ATP and ADP H and this 80 p. And any DPH is going to be utilized in the Calvin cycle when we talk about the Calvin cycle later in our course. But for now, what you can see is that the any DPH are gonna be carrying two energized electrons, as you can see here in this image. And, of course, the Calvin Cycle is going to utilize this chemical energy and convert it back into the lower energy forms a, d, p and N a. D P plus, which are needed for the light reaction so that they can convert them into their higher energy forms. And so this year really concludes our brief introduction to the light reactions and how they occur in the Thilo Coy's within the chloroplast and in our next lesson, video will get to talk about the specific steps that occur in the light reaction. So I'll see you all in our next video
2
example
Light Reactions of Photosynthesis Example 1
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1m
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all right. So here we have an example problem that wants us to fill in the two blanks that we have here in each of these sentences, using one of the four potential answer options down below. And so notice that the first sentence says the light reactions are powered by blank energy. And then the second sentence says, in normal photosynthesis, the products of the light reactions are used to power blank. And so what you can see is when we look at these four answer options Options A and B both mentioned photo respiration, which we have not yet talked about in our course yet. But we will talk about this later in our course in a different video. But for now, because we have not yet introduced photo respiration, we should have been able to identify both Option A and Option B as being incorrect answer options here. Now moving on. We have here Option C and D, and really, the difference is that Option C says sunlight and option D says potential for this first blank. And, uh, it's true that in normal photo sent, this is the products of the light. Reactions are used to power the Calvin Cycle. So this part here is going to be the same for the second blank. And really again, What we're looking for is which one of these answer options is gonna be best for the first blank. And, of course, we know that photosynthesis is going to be driven by solar energy or sunlight energy from sunlight. And so the correct answer here is going to be answer options, See? And so we could go ahead and indicate that. See, here is the correct answer for this problem, and that concludes this example. So I'll see you all in our next video.
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Problem
Problem
Describe the primary function of the light reactions of photosynthesis.
a) Production of NADPH used in cellular respiration.
b) Use of ATP to make glucose.
c) Conversion of chemical energy to light energy.
d) Production of ATP and NADPH.
A
Production of NADPH used in cellular respiration.
B
Use of ATP to make glucose.
C
Conversion of chemical energy to light energy.
D
Production of ATP and NADPH.
4
concept
Steps of the Light Reactions
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15m
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okay, In this video, we're going to talk about the steps of the light reactions and recall from our previous lesson videos that the light reactions is the first stage of photosynthesis and also recall from our previous lesson videos that the light reactions occur in the file a coid within chloroplasts and recall that the Thilo coins are really just those green pancake looking structures that air within chloroplasts and also recall from our previous lesson videos that if within the Thilo coid membranes, uh, they contain photo systems and recall from our previous lesson videos that photo systems are really just light harvesting complexes that are made up of pigments, proteins and other molecules as well. And so because they are light harvesting complexes, they're gonna be needed for the light reactions. And so if we take a look at our image down below notice that were zoomed into one of the Thilo coins within a chloroplasts because here we're showing you the Thilo coid membrane. So all the way across, this represents the pill, a coid membrane or the membrane of one of those green pancake looking structures within the chloroplast and then down below here. What we have is the Thilo Coid space, which represents the inside of the Thilo Coid or the inside of one of those green pancake looking structures. And then up above. What we have is the Strom A off the chloroplast, which is the space just outside of the fill accords, the fluid filled space that fills up the innermost regions of the chloroplast. And so this is important to note as we make our way through the steps of the light reactions. Now, notice that here in our lesson, we've consolidated the steps of late reaction down to five steps that are labeled a, B, C, D and E, and notice that each of these five steps labeled with these letters corresponds with each of the letters that we have down below for the steps of the light reaction. So that's also important to keep in mind. Now. Also recall from our previous lesson videos that most plants contain two photo systems and those photo systems are conveniently named photo system one and photo system to, And it turns out that these photo systems were named just based on the order of their discovery, and so photo system one was discovered first, so they called it Photo system one and then photo system to was was discovered later on, so they called it photo system to. But it turns out that later they found out that photo system to actually comes before photo system one in the steps of the light reaction. And so it turns out that this entire process starts with photo system to and then photo system One comes later on. And so the very first step of the light reaction step A I's gonna start with photo system to and recall photo systems are light harvesting complexes so they can absorb photons of light. And that's exactly what photo system to does. Photo system to is going to absorb photons of light. And those photons of light contain energy. And so the photo system to its going to absorb the photons of light and transfer that energy to electrons in order to energize those electrons and these electrons that are being energized, they're actually coming from a water molecule. And so these electrons are being donated by a water molecule. And really, this is the entire reason why one of the biggest reasons why water is needed for the process of photosynthesis. And so it turns out that these water molecules are actually going to be split and oxidized in order to provide electrons to this process. And when the water molecules are split and oxidized in order to provide electrons, they're going to react to form oxygen, gas or 02 And really, this is the oxygen gas that's associate ID with photosynthesis producing oxygen. And so let's take a look down below it. Our image and step A to get a better understanding of step A And so once again in the steps of light reaction were zoomed into one of the Thilo coid membrane so noticed that within the Thilo coid membrane, we have these photo systems. We have one photo system here in the second photo system over here. But it turns out that photo system to is actually the photo system that comes first in this process. And so this is gonna be photo system to right here and photo system one. What we'll see is it comes later in the process and step seat when we get there. But taking a look here we can see photo system to is right here and in the first step of light reaction step, a photo system to is going to absorb photons of light. And so you can see that these accessory pigments and the primary pigments are able to absorb photons of light and transfer the energy of those photons of light to electrons, which are being represented here as these circles with these little negative symbols on the inside. And so these electrons are being provided by water molecules, and when water molecules get split in half, they are able to generate oxygen. And this oxygen gas here is really the oxygen that's associated with photosynthesis and photosynthesis producing oxygen. It all comes from the splitting of this water molecule, and also splitting the water molecule also provides the electrons that are going to be used in this process. And so once again, photo system to is going to absorb photons of light and transfer those photons of light, the energy of those photons of light, two electrons and so in step, be the second step of the light reactions. What's going to happen is these energized electrons are going to move from photo system to two photo system one and they're going to do this via an electron transport chain which is really just going to allow for electrons to move from component to component and a Siris of redox reactions. And as these electrons move from photo system to over two photo system one, these electrons are gonna be used to generate a hydrogen ion Grady int or an H plus Grady int or Proton Grady int. And so we'll be able to see that down below in our image of step be And so you can see here in step be these electrons that are here. They're going to make their way over to photos system one over here. And they do that the way that these electrons go from photo system to over the photo system. One, it is via this electron transport chain that we see here. And so in this electron transport chain, the electrons get passed from component to component to component, and those that energy in those energized electrons is gonna be used to pump hydrogen ions into the Thilo Coid space. And so you can see that the Thilo Coid space here is building up. Ah, hydrogen ion concentration Grady int just as we indicated up above. And so ultimately, this hydrogen ion concentration ingredient is gonna be used in a process called Chemie osmosis later on to generate some 80 p. But we're going to continue to follow these electrons here before we jump over to how these hydrogen ions are gonna be used. And so in the next step step See, of course, the electrons have now made their way over to Photo System one and photo system One is also a light harvesting complex, just like photo system to is. And so photo system one is also going to absorb photons of light. And it's going thio take those electrons and energize them even mawr using the photons of light on the energy that it absorbs from those photons of light. And so, photo system one is going to, uh, photo system One electrons are gonna get energized, even mawr, And when they're energized even more, they're going to continue their way through the electron transport chain. And so down below, if we take a look at steps see here, notice again. What we have is photo system one right here, and it is also a light harvesting complex similar to photo system to. And so it's also going to absorb photons of light. And those photons of light are going to contain energy that could be transferred to the electrons reenergizing the electron so that they can make their way through another, uh, continue their way through the electron transport chain. Yeah, and so this leads us into the fourth step of the light reactions here, which is Step D and in this step D. What's going to happen is something called N A. D. P plus is going to serve as the final electron. Except ER and N A. D P plus is really just the oxidized form of N a. D. PH. So it is basically an electron carrier, an electron taxi cab that has to empty seats. And so the N A. D P plus has two empty seats in this electron taxicab, and it's going to service the final electron except er so those electrons, which they started on water. Uh, those water gets split to provide the electrons. The electrons get energized, make their way through an electron transport chain. They get re energized and continued through the electron transport chain and Ultimately, those electrons are going to end up on N a. D P plus and generate an a d. PH. And that's what we're saying here in Step D is that any D P plus serves as the final Elektronik center and is going to be reduced. It is going to be reduced toe form N a. D pH and any DPH is the full electron carrier that's carrying two electrons. And so if we take a look at our step d down below, what we can see is that we're seeing n a d p plus uh, reduction. So N a D P plus is going to be gaining electrons being reduced to n a. D. PH. And that's exactly what we see right here is any DPH is being formed through the reduction of n a. D P plus. And so any D P plus acts as the electron carrier uh, the empty electron taxicab, if you will, and two electrons are going to be transferred to any D P plus to generate any DPH, and ultimately these two electrons are going to originate from the water molecule that was split over here. And so ultimately, the water molecule is providing the electrons that air used in this process and end up on N a. D pH. And so this takes us to the fifth and final step of the light reaction Step E. And in this step, the hydrogen ion, or H plus concentration Grady int that was generated earlier is actually going to be utilized to generate some A T. P. And this 80 p that's gonna be generated is generated via the process of Chemie Oz Moses or the as Moses of ions across a semi permeable membrane. And so here in step e, uh, notice that we have an 80 Pecent, these protein that's embedded right here and this 80 Pecent This is going to allow hydrogen ions to defuse down their concentration. Grady int. And as these hydrogen ions diffuse down their concentration radiant, it's going to energized the fossil relation of a D. P to generate a teepee. And so, ultimately, what we have is some 80 p being generated here in the final step of Kenya's Moses. And so what you can see here is that ultimately, what the light reactions is producing or actually, let's start with the reactions with the with light reaction starts off with the ingredients of the light. Reaction are photons of light and water molecules, and ultimately the water molecules are being split to provide electrons. Uh, the photons of light are going to be utilized to energize those electrons, which allow the electrons to move through the electron transport chain from photo system to to photo System one. And those electrons end up on N a. D. PH. And so, in terms of the products of the light reactions, it ends up forming oxygen, oxygen gas from the splitting of water molecules to provide electrons. It also ends up providing N a. D. PH, and it also ends up providing a teepee and ultimately, the oxygen gas that's produced it can either be utilized by the plant for aerobic cellular respiration, or this oxygen can actually diffuse out of the plant through the stoma of the plant, the openings and leaves and be released into the atmosphere. This oxygen could be released by the plan into the atmosphere, but the n a. D. PH in the A t p that air generated are actually going to be utilized in the second stage of photosynthesis which is the Calvin Cycle. And that's really one of the biggest takeaways here of this lesson is that the light reactions is going to generate N A. D pH and ATP Chemical Energy and the N A. T pH in the 80 p are going to go to the second stage of photosynthesis, which is the Calvin Cycle. And so the Calvin Cycle is going to rely on products produced by the light reactions. And so this year concludes our lesson on the steps of the light reactions of photosynthesis, and we'll be able to get some practice applying the concepts that we've learned here as we move forward in our course, So I'll see you all in our next video.
5
Problem
Problem
Where do the electrons that are excited in photosystem II come from?
a) CO2.
b) O2.
c) Glucose.
d) Photosystem I.
e) Water.
A
CO2..
B
O2..
C
Glucose/
D
Photosystem I.
E
Water.
6
Problem
Problem
During the light reactions, photosystem I functions to_________, and photosystem II functions to __________.
a) Reduce CO2; oxidize NADPH.
b) Synthesize ATP; Produce O2.
c) Produce O2; oxidize NADPH.
d) Reduce NADP+; oxidize H2O.
A
Reduce CO2; oxidize NADPH
B
Synthesize ATP; Produce O2.
C
Produce O2; oxidize NADPH.
D
Reduce NADP+; oxidize H2O.
7
concept
How to Memorize the Light Reactions of Photosynthesis
Video duration:
5m
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in this video, we're going to talk about how to memorize the steps of the light reactions of photosynthesis. And so here, a clutch prep. We've come up with a really unique and interesting story designed specifically to help you guys remember the most important components and the most important events of the light reactions in the correct order. And so really, you'll only be able to find the story here at Clutch Prep. So you guys were pretty lucky. Alrighty. So let's get started here with this image. And so when you're thinking about the light reactions, you want to think about Luke and Ryan. So Luke and Ryan, when you're thinking about the light reactions and so notice that we have a picture of Luke and Ryan down below right here. And so when you're thinking about the light reactions, you think about these two kids, Luke and Ryan, who just want to play their PlayStation two. That's all they wanna play is their PlayStation two. And their PlayStation two is, of course, abbreviated as P s to. And if you don't know what a Playstation two is, it's a video gaming console. You can play video games on it. And so PlayStation two, this PS two here, is supposed to represent photo system to. And so by remembering this PlayStation two, you'll be able to remember that photo system to is actually coming first in this process of the late reactions. But then, after Luke and Ryan wanted to play their PlayStation two, uh, they realized that they could not find their Elektronik controllers to play their PlayStation two. And so the E. T. C here in the Elektronik is going to represent the electron transport chain. And so this represents the E. T. C. And so after the photo system to there is the electron transport chain. And so because Luke and Ryan tried to play their PlayStation two, but they couldn't find their electronic controllers to play their PlayStation two. They then decided to try to play their older PlayStation one or PS one for short. And, of course, the PS one is older. It was discovered first before PlayStation two, but of course, the kids want to play their PlayStation two first before they play their older PlayStation one. And so here PlayStation one, the PS one here, is representing photo system, one, which again was discovered first before photo system, too. And that's why they called it Photo System one. But then later they realized that photo system to comes first in the process of the light reactions before Photo System one. So then Luke and Ryan they went to play their PlayStation two. They couldn't find the Elektronik controllers to play their PlayStation two, so they decided to try to play their PlayStation one. But then they forgot that their mom had reduced their number of games that they had for their PlayStation one. And so what that means. What this is supposed to represent. The reduction of the number of games is supposed to represent the reduction of N a. D p plus into N a. D. PH. And so the ends here in the number can remind you of the n n n a, d, p h and n a d P plus. And so it's n a D P plus that's going to get reduced. Here. It's going to gain electrons and become an a D. PH. And so because Luke and Ryan they went to play their place, they should, too. But they couldn't find their electronic controllers they tried to play their PlayStation one but forgot that their mom had reduced the number of their game so they couldn't even play their PlayStation one. They then decided to just study chemistry. Instead, they decided to just study chemistry and the chemin chemistry. The key Me I'm sorry in chemistry is supposed to represent the key, me and Chemie as Moses. So the key me and chemistry is supposed to represent the Kimmy and Kimmy osmosis. And so you can see here that Luke and Ryan are now studying their chemistry here. And so you can see by just remembering this crazy, unique and interesting story here. You can remember the most important components and the most important events off the light reactions in the correct order. And so this year concludes our lesson on how to memorize the light reactions of photosynthesis. And we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video
8
Problem
Problem
What is the correct order of steps of the light reactions of Photosynthesis?
a) photosystem I, ETC, photosystem II, NADP+ reduction, chemiosmosis.
b) photosystem I, photosystem II, ETC, NADP+ reduction, chemiosmosis.
c) photosystem II, ETC, photosystem I, NADP+ reduction, chemiosmosis.
d) photosystem II, photosystem I, ETC, NADP+ reduction, chemiosmosis.
A
photosystem I, ETC, photosystem II, NADP+ reduction, chemiosmosis.
B
photosystem I, photosystem II, ETC, NADP+ reduction, chemiosmosis.
C
photosystem II, ETC, photosystem I, NADP+ reduction, chemiosmosis.
D
photosystem II, photosystem I, ETC, NADP+ reduction, chemiosmosis.
