In the previous video, we were actually talking about the structure of the thylakoid and I told you that in the thylakoid itself, they have these things called ATP synthase, electron transport chains, photosystem 1 and photosystem 2. too together with that enzyme and most students have difficulties understanding these things called photo systems so this video is to just explain what these photo systems are all about about. So if I were to just take out one of the photo systems and draw it out on the right side, I don't care whether it's photo system one or photo system two. They have a lot of similarities.
If you notice in the photo systems, I'm drawing out these circles and these circles, they have different sort of colors, correct? And at the bottom there, there are two green circles, two large green circles joined together. Each of those circles are referred to as something called photosynthetic pigment. And in the first video about photosynthesis, I told you that the function of these pigments were to actually absorb light so that the light energy can be harnessed to synthesize ATP.
But as you can see over here, though, there are many different colored pigments. You can see, like, for example, like a, I guess that's maroon, maroon, orange, purple and green pigments. You don't have to memorize the colors, by the way. Don't worry about that. But the point I'm trying to make is that the pigments are actually going to absorb light.
to make here is there are many different types of pigments in the photosystem. The pigments at the top, the first six pigments at the top there, maroon, orange and purple, you don't have to know the number as well, they are referred to as accessory pigments and the two pigments at the bottom which are the two green ones joined together are called the reaction center. The reaction center is important too because you must know that the reaction center is made up of two chlorophyll A pigments. This is important, that's why I put a That's why I put a star over there.
You need to know that each photosystem, whether it's photosystem 1 or photosystem 2, it doesn't matter. The photosystems are made out of many accessory pigments and it also has two chlorophyll A molecules joined together to form something known as the reaction center. Why does the photosystem have different types of pigments?
The reason here is as follows. Each pigment can absorb a specific wavelength. length of light. As an example, you can see that there is a pigment which is the orange color pigment over there and also the purple pigment.
Now, the orange pigment, they can only absorb light at a 400 nanometer wavelength. Again, don't memorize this. And the purple pigment, for example, might only be able to absorb light with 700 nanometer wavelength.
Let's see this in action. For example, if I shine purple color light, light over here, which is 400 nanometer, I'm shining it to the purple pigment. Look at what happens to the light.
The purple light gets reflected. And this is not good because if the plant wants to carry out photosynthesis, it needs to absorb as much light as possible. So if it cannot absorb 400 nanometers, you know, that's light that is not being absorbed and that is light that is wasted. So that is why the orange pigments are present because when 400 nanometers nanometer wavelengths or purple light hits the orange pigment, what happens?
It doesn't get reflected. The orange pigment can then absorb the light. In another case, the purple pigment is not useless because the purple pigment can help to absorb different wavelengths of light. If the question asks you, why do photo systems have many different types of pigments?
The reason is because they allow the absorption of different wavelengths of light. to maximize the absorption of light, which is in a range of 400 nanometers to 700 nanometers. Now, once they absorb the light, what do they do to the energy that they have absorbed?
The energy is then transferred to the reaction center, which is made up of two chlorophyll A molecules. And when the reaction center receives enough energy, we will say that the reaction center becomes photoactivated, which means to say the reaction center has been activated. activated due to the presence of light.
And when there's enough energy in the reaction center, they will release out a high energy electron. So you might be thinking, okay, why does it have to release out an electron? Again, we will talk about that. As we go along, we are going to explain this bit by bit.
I just need you to understand what the photosystem is supposed to do. So in a nutshell, what the photosystems do is they will first... absorb different wavelengths of light, they will transfer the energy to the reaction center, which will cause something called the photoactivation of the reaction center, and an electron is released from the reaction center.
So again, why does it have to release the electron? We will talk about that when we are looking at the light-dependent reaction in detail. So again, just be aware of this.
Now, when you're comparing photons... photosystem 2. Remember, there are two types of photosystem, by the way, photosystem 2 and photosystem 1. The good news is both of them have the same, almost the same type of pigments. They function the same way, where they absorb the light, transfer the energy to the reaction center, and the reaction center releases out an electron.
The only thing I need you to be aware of is that photosystem 2, it has an enzyme over there, which I've represented in the blue pigment, and the enzyme in the photosystem 2 is called an oxygen evolving complex. What is the function of the oxygen evolving complex? I am gonna talk about this later. I know, I know, I know if you're listening to me in my videos you're gonna be like, he's always saying later, later, later, later, later. I swear I'm doing this for a reason because if I were to explain everything immediately, it's not going to make any sense at all.
So do not worry about this. So what I just need you to know is Photosystem 2 has an enzyme embedded within it called the oxygen evolving complex enzyme. That's it.
Now, this part over here is a very interesting part. I don't need you to memorize this part. This is not needed for the exam, but I need you to be aware of it because it makes photosynthesis so much easier to explain. You see, when the light energy is absorbed by the pigments and they transfer the energy to the reaction center, the reaction center has to release an electron, correct? We know that that that's how the photosystem works.
But when the reaction center releases out an electron, that electron that is lost must be replaced by another electron. You don't need to memorize that. I just need you to understand this. The reason is because, again, the reason is not important, but if the reaction center continues losing electrons, it will destabilize its structure, and it might might break down. So to prevent the reaction center from being broken down or oxidized beyond repair, whatever electron that is lost must be replaced, which means to say if it loses two electrons, two new electrons need to come in and replace it so that it stabilizes its structure.
You don't need to memorize this, but I just need you to be aware of this particular feature.