Hello, my name is Mr. Chipman. I teach biology, AP Biology at Murray, Kentucky, Murray High School in Murray, Kentucky. Here we're looking at AP environmental science unit one 1.8 primary productivity. It's a fun little topic. Let's talk about it. So, what is primary productivity? Um, this is the amount of biomass that is being created. Uh another thing way way to think about this is this is the amount of organic material that organisms are producing. How are they producing that? They're producing it with processes like photosynthesis, right? The amount of photosynthesis that's taking place in an area where solar energy is being converted to chemical energy, compounds like glucose, right? And so productivity has to do with producing glucose. All right? Very important concept. The more plants that are in the area, the more productivity that area has. The more sunshine plus water plus plants productivity, right? So, you need you don't just need sun. You need all of those things kind of coming together to produce sugar. Well, there's a couple other concepts that have to do with that. You have gross primary productivity and net primary productivity. It's kind of like a paycheck, right? when you get your check, you know, you get you get 10 bucks an hour, you work 40 hours, you get 400 bucks, but you don't get 400 bucks because there's some things that are taken out of your check like taxes and whatnot. And what you have left is the net, right? You have a net pay based on that that it's a percentage of your gross. So gross primary productivity is all of that produced. It's like uh like this picture says, it's the total energy that is captured via photosynthesis in an ecosystem. However, the plant is also using some of that to do respiration, right? To to do work. Cellular work is how this picture defines it. I think that's fine. But typically, you're going to think of that as cellular respiration, right? Glucose broken down to make ATP so the plants can do plant things. Whatever is left over is called the net primary productivity. This is how the energy is stored. It's going to be stored as biomass. It's going to create like trees and plants and all the stuff that you see. Plants are always storing this energy as starch, which is a molecule that we talk about in AP biology. It's a carbohydrate and it's that sugar is stored as starch in order to, you know, have long-term energy stores or for structural components or all these other different things that plants can use it for. And so what you have left is a net primary productivity. the the more net primary productivity, the typically you're going to have this in some sort of like rainforests, whereas less less primary productivity you're going to have in a place like a desert, right? Um the more net productivity in an area, the more energy that's going to be available to the things that are eating the plants and then the things that are eating those things and so forth. overall energy in trophic levels, which we're going to get to in the next uh section. And that means there's going to be more biodiversity because there's just more energy to have more things. Measuring productivity, how is it measured? Well, it's usually measured in kilo calories per square meter per year, which is an interesting thing to think about, right? You see it in maps usually. Uh places that have high productivity are like tropical rainforest, wetlands, estuaries as you can see here. Um highest productivity is in the southern United States and what would be considered wetlands and forested areas. And then as you move north of that, you still have a lot of productivity. And then out towards the mountains, there's a lot less. Just because there's no plants, there's no productivity, right? Right? And so you're going to have less and less uh biodiversity in those areas as well. Aquatic systems also produce quite a bit. Don't forget that in aquatic systems, even though there's not like plants, well, at least in ocean systems, there's not plants, there are organisms that are producing glucose. These are phytolankton. Phytolankton are little plant-like organisms that do photosynthesis in order to produce that. Now, the interesting thing about an aquatic system is aquatic systems actually produce a lot more than the terrestrial systems. It's just because they're so big. And so, a lot of the Earth's primary productivity is has to do with what's going on in the oceans. You can see here these areas um different areas have higher and or lower primary productivity. Um some of it has to do with the type of light. Red light is absorbed like in the first meter of water and red light is highly absorbed during photosynthesis. And so certain types of organisms are going to live in that first meter whereas blue light which is on the other end of the spectrum goes a lot deeper into the water and certain other kinds of organisms can use that light. And so depending on the type of organism, you're going to see that in different levels in the water column, but all of those are going to contribute to the net primary productivity. And the types of pigments that are going to be found are also going to differ in those different types of organisms. So let's look at some examples of this, how this is going to change based on what's going on around. Different ecosystems obviously are going to have different net primary productivity. Um, a forest is going to have more than the open ocean of course because you have all these big trees, but the ocean because it's so vast is going to produce more on a global level. Uh, we talked about the depth of water. Obviously, that's going to matter a whole lot. At the very deepest levels of the ocean, there's going to be very little productivity versus the top, there's going to be a whole lot. Or productivity in the deepest parts, there's none. as it pertains to light. And so there has to be a different way to produce glucose, which we can look at later. Uh, and seasons in places that have seasons, like where I'm from in Kentucky, we have seasons, or at least we're supposed to. Um, and you have trees that sort of look like this here in a few months, right? And what happens? Well, they're not producing anymore, right? And so productivity is going to change with seasonality depending on the types of organisms that live in an area which is usually going to be determined by things like latitude and elevation. So let's look at a practice question. Two students are comparing net primary productivity in rainforest in a desert. Student A claims desert's net is low because the GPP the gross is low. Student B claims that it's low because plant respiration is too high based on your knowledge of primary productivity. Which student is the most accurate? So student A is concluding that net is low because uh gross is low and student B says that net is low because respiration is high. We know that net is gross minus respiration. So if respiration is high the net is going to be be lower, right? So let's find that in the answers. Student B because plants in the desert have high metabolic rates. Not necessarily. And student B's uh no student A uh student A because deserts receive little rainfall limiting the gross or photosynthesis and gross primary productivity. I like that answer. Let's see what the next one is. Both students are correct. Uh that's not true because they're contradicting one another, right? They're not saying the same thing, so they both can't be true. Neither student is correct again. Uh this could be it. Uh but MP is related to gross. And so we're going to go with student A here. That is the correct answer. Student A because deserts receive very little rainfall. This is going to limit photosynthesis which necess needs water which is then going to limit gross primary productivity. Hopefully this was helpful. Let's go look at N 1.9 together.