So here we have a pretty tricky example problem that says, in an experiment, scientists found that over a certain period of time, the total respiration of an ecosystem exceeded the total amount of energy captured in photosynthesis. How is this possible? And we've got these 4 potential answer options down below. Now to solve this problem, I've gone ahead and drawn a little sketch here of a tree that represents the ecosystem, and I've drawn a yellow arrow here going into the tree representing the energy captured in photosynthesis, or in other words, it represents the gross primary productivity or the GPP. And then I've drawn this purple arrow over here going out of the ecosystem, which represents the total respiration of an ecosystem.

And notice that it's larger than the yellow arrow because, again, this exceeds the total amount of energy captured in photosynthesis. And this is unusual because usually, it's the other way around where GPP is going to be larger than respiration energy, but it is possible for this condition to exist under temporary circumstances. And when this does happen, when respiration is larger than GPP, what this means is that respiration is pulling energy from the existing biomass of the ecosystem. So some of the energy stored in biomass will be used as energy to power the metabolic needs of the ecosystem, used as energy to power cellular respiration. And so if biomass is being used as an energy pool for respiration under these conditions, what that means is that over time, the biomass is going to decrease.

And so notice that answer option b indicates that the ecosystem's total biomass is decreasing, and that's exactly what's going to be happening in this scenario. So option b is going to be the correct answer to this problem. Now a potentially tempting correct answer option would have been answer option c, which says that the ecosystem must be getting energy from another source. Now it could be possible that this ecosystem is getting energy from some other source, and that's how the respiration energy is able to exceed the energy captured by photosynthesis. However, most ecosystems are going to rely solely on the sun as an energy source and the process of photosynthesis, which captures the energy from the sun.

But, there are some other processes that can allow energy to enter the ecosystem. But this problem doesn't really tell us that or gives us any kind of indication that this is indeed the case, that the ecosystem is getting energy from another source. And then also this problem is specifically saying that the ecosystem must be getting energy from another source. Now it could be the case that it is, but it doesn't absolutely have to be, because it says must be really, that is what makes answer option c not the best answer option. Because again, it could be that the ecosystem is just pulling energy from its total biomass and decreasing its total biomass.

Now answer option a is not going to be correct because it says that the ecosystem total biomass is increasing and that's exactly opposite from the correct answer, answer option b. And then answer option d is also not going to be correct because it says animals must have been emigrating out of the ecosystem, but if animals are leaving the ecosystem, that means that the respiration is also going to decrease along with it since those animals respire. So, but here, that's not really what we're seeing. We're seeing kind of respiration being larger than photosynthesis, so we wouldn't expect something, you know, to decrease respiration to be the correct answer to that. So that's why option d is not correct.

So again, answer option b is the correct answer to this problem, and I'll see you on our next video.