In this video, we're going to talk a little bit about leaf and chloroplast anatomy, and we're going to start off by defining the mesophyll. And so the mesophyll is referring to the interior leaf tissue consisting of, of course, lots of mesophyll cells. And so these mesophyll cells are characterized by having a lot of chloroplast organelles and recall that the chloroplasts serve as the site of photosynthesis. And so because these mesophyll cells have a lot of chloroplasts and these mesophyll cells make up the mesophyll tissue, this means that the mesophyll tissue of a leaf is responsible for performing photosynthesis for the plant. And so within the word mesophyll, you can see these roots. Meso is a root that means middle, and -phil is a root that means leaf. And so if you put them together, mesophyll, it's really just referring to the middle leaf or the interior leaf tissue. And, if we take a look at our image down below over here on the left hand side, notice that we're showing you a leaf that you might be able to walk outside and see in a tree or find on the ground somewhere. And so if you zoom into this leaf, you'll notice that it's going to have tissue, that has mesophyll, tissue consisting of mesophyll cells. And so notice that these mesophyll cells are found right here in this interior middle region here of the leaf. And so each of these mesophyll cells, which you can see side by side by side here, each of them contains lots of chloroplasts. And the chloroplasts are these tiny little green circles that you see within each of these mesophyll cells. And you can see that if we were to zoom into one of these chloroplasts, the chloroplasts would look like this.
And so, what's important to note is that the leaf also had these very important structures that are referred to as stomata. And the stomata are not to be confused with the stroma, which is a region within the chloroplast itself. The stomata are different from the stroma, and so you don't want to confuse those two terms. So what in the world are these stomata that we're referring to? Well, the stomata are tiny little holes or pores that are in the leaf itself, and these tiny little holes or pores in the leaf can actually open and they can close, and what they do is they control gas exchange between the leaf and the environment. And so these stomata are responsible for allowing the gas exchange of carbon dioxide gas, oxygen gas, and even water as water vapor, which are all components of photosynthesis. And so really the stomata being in an open position will allow for the gas exchange and allow for photosynthesis to proceed as normal. And so, later in our course, when we talk about different types of photosynthesis, comparing C3, C4, and CAM photosynthesis, we'll be able to talk a lot more about these stomata. But for now, you should just know that the stomata are tiny holes in the leaf that allow for gas exchange with the atmosphere.
Now in addition to this, we need to recall the anatomy of the chloroplast itself, which recall are the organelles that act as the site of photosynthesis. This is where photosynthesis is going to take place within each cell, is within the chloroplasts. And the chloroplasts themselves have very important anatomy which we can also review here in this image down below on the right. So, first off, notice that the stomata, you can actually visualize here as these little openings that you can see here within the leaf itself. And so this is referring to the stomata. And so you can see that the stomata is really just this opening here. And through this opening, this can allow for gas exchange. It can allow for carbon dioxide to diffuse in, and it can also allow for oxygen gas that's produced to diffuse out, and it can even allow for water to diffuse out or in as water vapor. And so this opening here, the stomata is going to be very, very important for, again, allowing for gas exchange. And when it is open, it will allow for gas exchange, but when it's closed, it will not allow for gas exchange. And we'll talk about what happens when it's closed again later in our course in a different video when we're talking about different types of photosynthesis. But for now, again, within each of these mesophyll cells, there are a bunch of chloroplasts, and if we zoom into one of the chloroplasts, you will see that it looks like this. And chloroplasts also have very important anatomy to refresh our memories on. So recall that chloroplasts have two membranes. They have an outer membrane that surrounds the entire organelle, but then they also have an inner membrane, and the inner membrane is embedded within here. And then within the inner membrane, what you'll notice is that there are these stacks of green looking pancakes here, and these green looking pancakes are not actually pancakes, they're actually called thylakoids. Okay? So inside of the chloroplast are these structures that look like green pancakes, but they're actually called thylakoids. And each individual green pancake is called a thylakoid. However, the stacks of green pancakes have a different term. So if you're referring to an entire stack of thylakoids, then that stack is referred to as a granum or grana for plural. And so just outside of the thylakoids, but still within the chloroplast, this region within the chloroplast, but just outside of the thylakoids, is referred to as the stroma. And the stroma, once again, sounds kind of similar to the stomata, but they're referring to very different things. The stomata, once again, are referring to the openings or the holes or pores that are in the leaf that allow for gas exchange. The stroma is within a tiny little chloroplast that we're zooming in here, and it's just this fluid filled space here within the chloroplast. So it's important to keep in mind. Now once again, the chloroplasts are the site of photosynthesis, and ultimately what we're going to see is that photosynthesis is going to be powered. The power for photosynthesis is going to come by absorbing what are known as electromagnetic waves of light. And so we'll be able to talk more about these electromagnetic waves of light as we move forward in our course. But for now, you should note that electromagnetic waves of light are going to provide the power to drive photosynthesis. And chloroplasts are able to obtain that power by absorbing these electromagnetic waves of light. And so this here concludes our brief introduction to leaf and chloroplast anatomy, just, defining the mesophyll, the stomata, and reviewing chloroplast anatomy. And as we move forward in our course, we'll continue to talk more and more about photosynthesis. So I'll see you all in our next video.
