Apicomplexans are a type of alveolata that are all parasitic, and mostly they're parasitic to animals. Their cells lack cilia and flagella, and contain these modified plastids, which are called apicoplastids. Most likely, these arose from red algae, which remember, are acquired, so they would have been acquired, that is, by secondary endosymbiosis. Now these cells, names, basically, or the name apical complex comes from the fact that these cells have what are called apical, complex structures. So, here we actually, in this image, we actually have 2 cells. Hopefully, you can see them. I'll try to outline them right here. And hopefully, you can notice that these cells have these tips. Those are the apical complex structures. And essentially, these apical complex structures are there to help these cells penetrate into their host cell, which, kind of reaffirms the fact that they're all parasites. Right? Their defining feature is something that enables their parasitism. Now, another cool thing about these organisms is they have kind of interesting life cycles. They reproduce, both sexually and asexually, and they actually sometimes move between species to do so.

So, an apicomplexin that is near and dear to my heart is this organism called Toxoplasma. It's actually a group of organisms. It's a genus. So, Toxoplasma, are these cool apicomplexans and they reproduce sexually in cats. So, they have sexual reproduction in cats, and then they actually will be excreted, so the cat poops them out, they live in the intestines of the cat. They reproduce sexually there and then the cat poops them out and they'll get picked up by other animals and they'll reproduce asexually in these other warm-blooded animals. And, important to note, people are able to be infected by these organisms. And what's so cool about Toxoplasmosis is they actually go into animal's brains, and they change their brain wiring basically. Specifically, they make rodents, like we see here, they make rodents stop being afraid of the smell of cats. So that, the organisms, like these rodents, get infected with the Toxoplasma, stop being afraid of cats, which are their predators, right? And then they'll be eaten by the cats again, and that is how the Toxoplasmosis will get back into the cat's intestines where they can reproduce sexually again. So, kind of this really wild life cycle. Right? And it all revolves around this very strange kind of crazy feature of these organisms, where they can rewire a rodent's brain to make them stop being afraid of cats.

Totally wild. Also, this is kind of a side note, but this is sort of, people have theorized that this is sort of where the idea of the "cat lady" comes from, right? She has all these, you know, a person who has a lot of cats and is like kind of weirdly obsessed with cats, so it’s because the Toxoplasmas have gotten into their brain. They've been converted. You know, I'm just kidding. But just a fun little, weird idea that relates back to this class of organisms. Now I also want to talk about the parasite that causes malaria, Plasmodium. And these organisms, also apicomplexans, also have an interesting life cycle where they reproduce, asexually and form their gametocytes in humans. And then in mosquitoes, they form zygotes and produce what are called sporozoites, which, you know, if you think back to, alteration of generations, these are kind of like spores. So the similar idea. They're asexual, they're units of the organism that will reproduce asexually, and, eventually form gametocytes.

So let's take a look at this life cycle. So, you don't really need to worry too much about the terminology here or all steps. I just want you to have, like, a general sense of how this works. So the gametocytes, will get together inside the mosquito. They'll form, what is essentially sort of like the zygote. Again, the terminology is different here. Oocyst is ultimately what they're forming, which is basically just full of those sporozoites, and those sporozoites will, when a mosquito bites a human, the sporozoites will be passed into the human's bloodstream. They'll make their way to the liver, where they'll infect liver cells, and they're going to ultimately form these structures, again, don't worry about the terminology too much, they're going to form these structures in liver cells that will then infect blood cells, and those infected blood cells are where the gametocytes will be produced. Right? And then, of course, a mosquito drinks your blood. Right? The mosquito will slurp up your blood, and those gametocytes will get back into the mosquito, where they can form the gametes, and the osis, and eventually more sporozoites to infect more humans. So pretty crazy life cycle here. Right? Not only are we switching between organisms, but within humans, first something has to happen in liver cells, and then something has to happen in blood cells. There's like, complex stages to this life cycle and totally wild that this organism, right, this Plasmodium, depends on moving between, mosquitoes and, it's not just humans, animals in general, but still, moving between mosquitoes and animals like humans, or cows, or whatever.

Totally wild, wild life cycle that, you know, requires the movement between species. So it's kind of a weird and cool thing about some of these apical complex and species. Alright. Let's turn the page.