trophic levels described the position and organism occupies on the food chain, and it's going to be determined by its feeding habits. Primary producers will be the foundation of these food chains, and that's because they're able to generate biomass from inorganic matter so that they can support all other trophic levels. So primary producers are gonna be autotrophs or self feeders. Thes air generally gonna be photosynthetic organisms, but they can also be chemo autotrophs like the archaea and bacteria that formed the foundations of the ecosystems around deep sea hydrothermal vents. Now primary consumers feed on primary producers, and these air usually gonna be things like herbivores that feed on plants. Now these and other consumers are considered hetero tropes because they're organisms that cannot fix carbon from inorganic sources like what happens in the Calvin cycle of photosynthesis. Now they indeed need to use carbon for growth, so they have to consume organic matter in many cases, consume other organisms. Now, secondary consumers are generally carnivores that feed on primary consumers, and tertiary consumers are carnivores that feed on other carnivores. So, as you can see, we are working our way up the food chain, and here in our little food chain model, we have our first level. This is our primary primary producer, our primary consumer here. A the second level, our secondary consumer here in this third level and our tertiary consumer here at this fourth level. So what is missing from this food chain? That is very important. That you can see over here are the D composers. So the autotrophs, the producers, they're going to get energy from the sun. And they're going to use that to create biomass that will feed herbivores. And those herbivores will feed carnivores. But the D composers are going to return all of that organic matter back into the nutrient pool. So they served on incredibly important role because they're going thio return matter back to be used by other living organisms. So they're kind of like the recyclers. Almost now. We call the d composers Detroit of wars because they eat detritus. They wore eat to trade us, and basically, they're just hetero tropes that consume detritus. And this detritus is just non living organic material. So dead organisms and organic wastes like feces, for example, Now the food chain like what we just saw, right here is linear network of those trophic levels, and we will often look at a grazing food chain, which is what we saw with this food chain right here, which is going to have primary consumers feeding on plants. But we can also make a decompose er food chain where the primary consumers are going to be actually feeding on Dead Plant Matter, and we call those primary D composers. Now food chains will be linked together both grazing and decomposing food chains into a food web, which is a much better representation off the interactions between the different trophic levels in an ecosystem. And here I have a picture of some nice primary D composers. These fungi that air going to eat dead plant matter. With that, let's turn the page.