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 in the image of the chloroplast organelle. On the inside of these chloroplast organelles are these green-looking pancake structures called thylakoids. If we zoom into just one of these structures, that is where we find the photosystem. Notice in this image, here, representing the membrane of the thylakoid. Inside the thylakoid, the inside of the green pancake itself, and just above the thylakoid membrane, we have the stroma, which is outside of the green pancake but still inside the chloroplast.
Embedded within the thylakoid membrane is where we find our photosystem, this complex of pigments, proteins, and other molecules. Photosystems are composed of several light-harvesting complexes that surround a reaction center. Notice our light-harvesting complexes color-coded here in this purplish color, which corresponds to the purplish colors seen below. We also have the reaction center up above in orange that matches the reaction center below. On our image below, notice in purple here and on the right, we have the light-harvesting complexes. They surround this central region, which contains the reaction center. The reaction center is highlighted in orange right in the middle, surrounded by light-harvesting complexes as described above.
Within the light-harvesting complex, you'll notice teal circles representing accessory pigments helpful in absorbing photons of light. Photons of light interact with the light-harvesting complex, enabled by these accessory pigments that absorb light. Looking at the reaction center again in the middle, notice it has two green molecules that are chlorophyll a molecules, the predominant pigment found inside chloroplasts. Also, in red, there is the primary electron acceptor, which will be covered more later in our course. This photosystem is crucial for absorbing light, which allows chloroplasts to absorb light due to its accessory pigments and chlorophyll a.
As we move forward in our course, we'll talk more about photosystems and their involvement in what's known as the light reaction. Most plants will have two photosystems involved in performing the light reactions of photosynthesis, which we'll discuss more later. But for now, this is our brief introduction to photosystems, how they are found inside the membranes of thylakoids, these green pancake structures within chloroplasts, and their importance in absorbing light and involvement with the light reactions. We'll be able to apply some of these concepts as we move forward in our course. So I'll see you all in our next video.