In this video, we're going to begin our lesson on the light reactions of photosynthesis. The light reactions, as we already know from our previous lesson videos, is the first stage of photosynthesis, and it specifically occurs in the thylakoids of the chloroplast. Recall that the thylakoids are those green pancake-looking structures, and the light reactions occur in the thylakoid membrane as well as in the thylakoid space, or the space that's on the inside of the thylakoids. The light reactions synthesize chemical energy in the form of ATP and NADPH. This ATP and NADPH are going to be used to power the Calvin Cycle, which is the second stage of photosynthesis while producing oxygen gas or O2 as a byproduct.
NADPH is really just another electron carrier that will carry or transport 2 energized electrons. NADPH functions as an electron taxicab. We covered electron carriers in our previous lesson videos when we talked about aerobic cellular respiration. In the image below, you'll notice that we've got an image showing photosynthesis. In the background, we have the chloroplast; notice that the regions we want to focus on in this image are colored and enlarged, and the regions that we don't want to focus on right now are grayed out and smaller. For instance, the Calvin cycle—we're going to talk about the Calvin cycle more in another video later in our course. For now, we want to focus on the first part of this reaction, the light reactions.
The light reactions take solar energy or sunlight in the form of photons and, using this solar energy along with water, generate chemical energy in the form of ATP and NADPH. It also creates oxygen gas as a byproduct, as we can see below. In terms of the reactants, the light reactions use solar energy or photons along with water, and in terms of the products, the light reactions create oxygen gas and chemical energy in the form of ATP and NADPH. This ATP and NADPH will be utilized in the Calvin cycle when we talk about the Calvin cycle later in our course. As you can see in this image, the NADPH are carrying 2 energized electrons.
In conclusion, this brief introduction to the light reactions and how they occur in the thylakoids within the chloroplast. In our next lesson video, we'll discuss the specific steps that occur in the light reaction. I'll see you all in our next video.
