Pigments of Photosynthesis: Videos & Practice Problems

Photosynthesis relies on pigments within chloroplasts, primarily chlorophyll a, which absorbs specific wavelengths of light to drive the process. Accessory pigments, like chlorophyll b and carotenoids, enhance light absorption by capturing different wavelengths. The absorption spectrum illustrates how these pigments absorb light, with green and yellow wavelengths being reflected, contributing to the plant's color. Photosystems, located in thylakoid membranes, consist of pigment-protein complexes that facilitate light reactions essential for photosynthesis, highlighting the importance of light energy in plant biology.

Pigments of Photosynthesis

In this video, we're going to begin our lesson on pigments of photosystems. But really, we're going to start off focusing on pigments, and we'll define what photosystems are a little bit later in our course in a different video. And so what you need to know now is that in order for plants to harness the light energy that's required to power photosynthesis, chloroplasts, the site of photosynthesis, need to have several different types of pigments. Ultimately, what we're saying here is that these pigments are really important for driving photosynthesis because they allow for the harnessing of the light energy. So, what exactly are these pigments? Well, pigments are defined as molecules that have this amazing ability to absorb wavelengths of visible light. And when these wavelengths of visible light are absorbed, they can be utilized to power photosynthesis.

Now, the main pigment that you all should be aware of is chlorophyll a, and chlorophyll is not to be confused with chloroplast. Remember, chloroplasts are organelles that serve as the site of photosynthesis. And chlorophyll, even though it sounds similar to chloroplast, is not the same thing as a chloroplast. Chlorophyll is once again a type of pigment, and in fact, chlorophyll a is the main photosynthetic pigment that is found within chloroplasts. Now, Chlorophyll a, even though it is the main photosynthetic pigment, is not the only photosynthetic pigment. Accessory pigments are pretty much all of the other photosynthetic pigments that are not chlorophyll a.

It's important to note that different pigments are going to absorb different wavelengths of light. And so, it's also important to note that some wavelengths of light are actually going to be absorbed and utilized to drive photosynthesis. But other wavelengths of light are not going to be absorbed. Instead, these other wavelengths of light will be reflected. The reflected light is really the light that we end up visualizing with our eyes. So, some wavelengths of light are absorbed, others are reflected. We visualize the reflected wavelengths of light, but the absorbed wavelengths of light are really the light that is being used to drive photosynthesis, not the reflected light.

Let's take a look at our image down below to get a better understanding of the different types of photosynthetic pigments. Across the top here, we have the name of the different photosynthetic pigments. Across the bottom here, what we are showing you is the light that is being reflected by these particular photosynthetic pigments. Here in this first column, what we are showing you is the main photosynthetic pigment, which is of course chlorophyll a. Chlorophyll a is going to mainly reflect green and blue. So you can see that green wavelengths of light are reflected almost the most. Here you can see the eye, this would be our eyes looking at the plant. The reason that we perceive plants to be green is that they reflect green wavelengths of light. But notice that the other wavelengths of light here like yellow and orange and so on, these are going to be absorbed by chlorophyll a. And that energy that is absorbed is going to be used to power photosynthesis.

Notice over here in this next column, what we have is a different type of chlorophyll, which is chlorophyll b. Chlorophyll b is not as predominant as chlorophyll a. It is found in smaller amounts. Chlorophyll b actually reflects mainly yellow and green wavelengths of light. So the yellow wavelength of light here is being detected by our eyes because that is the light that is being reflected. So, we can perceive chlorophyll b as being yellow in color, but once again it absorbs all of these other wavelengths of light and those can be utilized to drive photosynthesis.

Last but not least on the far right, what we have are the carotenoids. The carotenoids have this little carrot prefix in here which can remind you of the carrots themselves. These mainly reflect orange, red, and yellow wavelengths, and so you can see the orange wavelength of light being reflected here, and so we can see these as being orange because this is the light that's being reflected. But once again, the other wavelengths of light are being absorbed and utilized.

This here really concludes our brief introduction to the pigments of photosystems. As we move forward in our course, we'll continue to talk more about pigments and will also introduce photosystems as well. So, I'll see you all in our next video.

Examples of accessory pigments for photosynthesis are:

• A. Chlorophyll b and carotenoids.
• B. Chlorophyll a and chlorophyll b.
• C. Chlorophyll a and carotenoids.
• D. Carotenoids, chlorophyll b and chlorophyll a.

Answer: (A)

Absorption Spectrum of Photosynthesis

In this video, we're briefly going to talk about the absorption spectrum of photosynthesis. An absorption spectrum is really just a graph that shows the light absorption of pigment molecules. Notice that we're showing you a pigment light absorption spectrum. On the y-axis, the absorption of light is represented where low on the y-axis indicates a low amount of light being absorbed, and high on the y-axis represents a lot of light being absorbed. On the x-axis, we have the particular wavelength of light in nanometers, essentially showing you the visible wavelength of light. It's important to note that on this particular spectrum, we're showing you the curves for three different pigments: Chlorophyll a in green, Chlorophyll b in yellow, and the carotenoids in a dark orangish color. You can see the spectrums for each of these curves throughout this section.

These curves are showing the amount of light that's being absorbed at a particular wavelength. Wavelengths that fall into certain regions are mainly being absorbed. You can see these regions having the 'absorbed' label. Additionally, wavelengths in other regions are also mainly being absorbed, not by all the pigments, but by the collection of them together. However, in the middle region, most wavelengths, essentially greenish and yellowish, are not really being absorbed. We can assume that these wavelengths are being reflected. Since there are not a lot of peaks here, there is not a lot of absorption going on, so they are being reflected.

The biggest takeaway here is that different pigments are going to absorb and reflect different wavelengths of light, but collectively it is the amount of them and the particular wavelengths of light that are reflected that dictate the colors that we end up seeing in the plants. This concludes our brief introduction to an absorption spectrum, and we'll be able to get some practice as we move along in our course. I'll see you all in our next video.

Which of the following pigments does NOT absorb yellow/orange light (650-750nm)?

• A. Chlorophyll a.
• B. Carotenoids.
• C. Chlorophyll b.
• D. Both a and c.

Answer: (B)

Introduction to Photosystems

In this video, we're going to begin our introduction to photosystems. Photosystems are defined as complexes of pigments, proteins, and other molecules found in the thylakoid membrane. Recall from our previous lesson videos that these thylakoids are the green pancake-looking structures that are found inside of chloroplasts. To refresh your memory, down below on the left-hand side, we're showing you the image of the chloroplast organelle. Recall that on the inside of these chloroplast organelles are these green-looking pancake structures without, and these green-looking pancake structures are again called thylakoids. If we zoom into just one of these green-looking pancake structures here, that is where we will find the photosystem. Notice in this image here, this is representing the membrane of the thylakoid. We have the thylakoid membrane here. On one side of the thylakoid membrane, we have the thylakoid space, which is the inside of the thylakoid, the inside of the green pancake itself. Above the thylakoid membrane, we have the stroma, which is just outside of the green pancake but still inside of the chloroplast. Notice that embedded within the thylakoid membrane, this is where we find our photosystem, this complex of pigments, proteins, and other molecules found in the thylakoid membrane.

Photosystems are composed of several light-harvesting complexes that surround a reaction center. Notice that we have our light-harvesting complexes color-coded here in this purplish color, which color codes to the purplish colors that we see down below. We also have the reaction center up above that's in orange that color codes to the reaction center that we have down below. If we take it our look at our image down below, notice once again that here in purple over here and over here, we have this light-harvesting complex. So we can go ahead and label them as the light-harvesting complexes. Surrounding the light-harvesting complexes that you see here and over here on the right, notice that they are surrounding this center region here which has the reaction center. You can see the reaction center here in orange right in the middle, surrounded by light-harvesting complexes as we described up above.

Within the light-harvesting complex, you'll notice there are these teal circles, which represent accessory pigments, and these accessory pigments are going to be helpful in absorbing photons of light. You can see photons of light here interacting with the light-harvesting complex as its name implies, and it's able to interact with light because of these accessory pigments that absorb light. If we take a look at the reaction center once again here in the middle, notice that the reaction center has these two green molecules right here that are chlorophyll a molecules, the predominant pigment found inside of chloroplasts. Also, notice that in red, right here, there is the primary electron acceptor, which we'll get to talk more about later in our course. But for now, what we can see is that this photosystem here is going to be really important for absorbing light and allowing chloroplasts to absorb light. That's again because it contains accessory pigments and it contains the predominant pigment chlorophyll a.

As we move forward in our course, we'll get to talk more about photosystems and how they're involved in what's known as the light reaction, which again we'll talk about more in a later video later in our course. But what's important to note now is that most plants are actually going to have 2 photosystems. These 2 photosystems once again are going to be involved with performing the light reactions of photosynthesis, which again we'll get to talk about these light reactions of photosynthesis later in our course. But for now, this is our brief introduction to photosystems, how photosystems are found inside of the membranes of thylakoids, these green pancake structures within chloroplasts, and how photosystems are important for absorbing light and are involved with the light reactions. We'll be able to get some practice applying some of these concepts as we move forward in our course. So, I'll see you all in our next video.

Here’s what students ask on this topic:

What are the main pigments involved in photosynthesis?

The main pigments involved in photosynthesis are chlorophyll a, chlorophyll b, and carotenoids. Chlorophyll a is the primary photosynthetic pigment, absorbing mainly blue-violet and red light, and reflecting green light, which gives plants their green color. Chlorophyll b acts as an accessory pigment, absorbing light in the blue and red-orange spectrum, and reflecting yellow-green light. Carotenoids, which include carotenes and xanthophylls, absorb blue and blue-green light and reflect yellow, orange, and red wavelengths. These accessory pigments broaden the spectrum of light that can be used for photosynthesis, enhancing the plant's ability to capture light energy.

How do pigments absorb light in photosynthesis?

Pigments absorb light in photosynthesis by capturing photons of specific wavelengths. Each pigment has a unique absorption spectrum, which is the range of wavelengths it can absorb. When a pigment molecule absorbs a photon, its electrons are excited to a higher energy state. This energy is then transferred to the reaction center of the photosystem, where it is used to drive the light reactions of photosynthesis. Chlorophyll a, for example, absorbs light most efficiently in the blue-violet and red regions of the spectrum, while chlorophyll b and carotenoids absorb light in other regions, complementing chlorophyll a and maximizing the range of light energy captured.

What is the role of chlorophyll a in photosynthesis?

Chlorophyll a plays a central role in photosynthesis as the primary pigment responsible for capturing light energy. It is located in the reaction center of photosystems within the thylakoid membranes of chloroplasts. When chlorophyll a absorbs light, it excites electrons to a higher energy state. These high-energy electrons are then transferred to the primary electron acceptor, initiating the light-dependent reactions of photosynthesis. Chlorophyll a's ability to absorb light in the blue-violet and red regions of the spectrum makes it crucial for converting light energy into chemical energy, which is then used to produce ATP and NADPH, essential molecules for the Calvin cycle.

What is an absorption spectrum and how is it related to photosynthesis?

An absorption spectrum is a graph that shows the specific wavelengths of light absorbed by different pigments. In the context of photosynthesis, the absorption spectrum illustrates how pigments like chlorophyll a, chlorophyll b, and carotenoids absorb light at various wavelengths. The y-axis represents the amount of light absorbed, while the x-axis shows the wavelength in nanometers. This spectrum is crucial for understanding which wavelengths of light are most effective for driving photosynthesis. For example, chlorophyll a absorbs light most efficiently in the blue-violet and red regions, while chlorophyll b and carotenoids absorb light in other regions, collectively enhancing the plant's ability to capture light energy.

How do photosystems function in the light reactions of photosynthesis?

Photosystems are complexes of pigments, proteins, and other molecules located in the thylakoid membranes of chloroplasts. They play a crucial role in the light reactions of photosynthesis. Each photosystem consists of a reaction center surrounded by light-harvesting complexes. The light-harvesting complexes contain accessory pigments that capture photons and transfer the energy to the reaction center. In the reaction center, chlorophyll a molecules absorb this energy, exciting electrons to a higher energy state. These high-energy electrons are then transferred to the primary electron acceptor, initiating the electron transport chain. This process ultimately leads to the production of ATP and NADPH, which are essential for the Calvin cycle.