The root's main job is absorbing water and nutrients. The shoot's main job is to absorb CO2 and light, and to then carry out photosynthesis. The stem of the plant is the vertical growth structure. This is how the plant is going to reach its leaves up to get access to light. And when we talk about the stem of a plant, it's important to get some terminology straight. There are these points on the stem we call the nodes. This is basically the part of the stem where leaves and buds will grow out. And the space between these nodes is called an internode. So, basically, the stem of a plant is made up of a series of internodes and nodes.
Now, at these nodes, we have what is called a lateral, or sometimes an auxiliary bud, and you can see a picture of that here. We have these little buds represented in yellow, appearing at the nodes of the stem. Now, at the top of the plant, we'll have what's called the apical bud. You can see that up here. This image is labeled 'terminal', but this is also called the apical bud. Now, this apical bud is the primary growth point of the plant. This is where the plant is going to basically grow upward from. Those lateral buds are where leaves, branches, or flowers, you know, various lateral structures will develop. So apical bud is for vertical growth, lateral bud is for lateral growth.
Now, very quickly, branches are a special structure. That is a woody projection from the plant. Not all plants are woody plants, so not all plants are going to have those woody projections. Some stems are non-woody. So turning our attention to what grows on the stem, let's look at leaves. These are the organs of vascular plants that are the sites of photosynthesis and gas exchange, and they actually have 2 parts. The petiole, which is the stalk or this portion that connects the leaf to the stem. So this is the petiole, right here. And then the other portion is called the blade, like a blade of grass. That's really the portion we think of as the leaf, so to speak. Now, the interior tissue of the leaf is where the magic of photosynthesis, so to speak, happens. We call that area the mesophyll. So here, this is all mesophyll. And you can actually see, this layer on the outside, that's the cuticle, a structure we've talked about before that prevents water loss, from land plants.
And also, you might notice here in the bottom, the guard cells, these cells around the opening in the leaf known as the stoma, or stomata as the plural form you see here. So, those stomata are the pores in the leaf that control gas exchange, and help regulate water loss. So, they open and close based on the swelling or shriveling of the guard cells, which are these special cells that fluctuate their turgidity to open and close that pore, that stoma. And you can see that going on in these images here. And actually the way these plants swell or shrivel is by moving Potassium ions, and water follows those potassium ions. So either they're drawn into the vacuoles. Right? The central vacuoles, water follows, they get turgid. So here they're turgid, they swell up, and that pops open the pore, or, the potassium ions leave the vacuole, go to the extracellular environment, drawing water out of the vacuole, making those guard cells shrink and lose turgidity, and that causes the stoma to close. Alright. That's all I have for this page. Let's flip.