So here we have an example problem that asks, why was it advantageous for the host cell to keep the engulfed aerobic bacterium alive during primary endosymbiosis rather than dissolve it for food? And we've got these four potential answer options down below. Now, of course, recall from way back in our previous lesson videos that this engulfed aerobic bacterium, over a very long period of time, 1,000,000 if not 1,000,000,000 years, would have eventually evolved and developed into the mitochondria organelles that we can find in eukaryotic cells today. And we know that these mitochondria organelles are very specialized for producing energy in the form of ATP, and so we might expect that the advantage that the host cell received for keeping the engulfed aerobic bacterium alive was that the aerobic bacterium provided the host cell with ATP. And so notice that matches with answer option b, which is going to be the correct answer to this example problem.

So we can go ahead and indicate that. Now, option c is not going to be correct because it says it allowed the host cell to photosynthesize, but this aerobic bacteria nor mitochondria allow for the process of photosynthesis. So that's why option c is not correct. Option a says it helped protect the host cell from pathogens, which is not going to be the best option since option b is much more likely. And then option d says, it provided an opportunity to swap genetic information with the host cell.

And again, this is not going to be as likely as answer option b. And so, that concludes this example problem, and I'll see you all in our next video.