 So we're going to spend, from here on out, fleshing out this branch of our cladogram. We're just going to focus in on the eukaryotes. The first question that you should probably ask, we know that they all have nuclei. And we know that they have membrane-bound organelles. That says membrane-bound organelle. And we know that they have membrane-bound organelles because they have mitochondria, chloroplasts. They've got the whole endomembrane system. The nucleus is a membrane-bound organelle. The question that you should probably be wondering about is how did they get membrane-bound, they were prokaryotes. This ancestor right here, this guy is a prokaryote. This guy does not yet have membrane-bound organelles or nucleus. So what happened to do this? Well, back in the day, not that long ago, a woman named Lynn Margulis basically battled the scientific community because she argued that what happened was this process called endosymbiosis, where a big prokaryote, no nucleus, no membrane-bound organelles, actually ingested through the process of endocytosis, ingested a little prokaryote. And then instead of digesting it and turning it into prokaryote juice to eat, the big prokaryote was like, dude, this thing is awesome, I'm going to keep it. I'm going to keep it as a pet. And it's going to make energy for me. And whether it was producing ATP from glucose, that was mitochondria, or producing glucose from carbon dioxide and sunshine, that would be your chloroplast. Big cells, big prokaryotes, ended up with these membrane-bound organelles. Lynn had to fight the institution and provide an unbelievable amount of evidence, which there actually is, to support this hypothesis. And now it's pretty standard that people know that, yeah, that's what happened, but they were not happy about her idea when she first came up with it. So if that was the process to become a eukaryote, the next question is, okay, what distinguishes between these single-celled eukaryotes and the eukaryotic protists and the rest of the eukaryotic clan? So here's what I'm going to do, and this is only going to hurt your brain a little bit. I'm going to take this whole piece, just this. I'm going to leave the bacteria off of it. I probably could put them on it, and it would be just fine. But let's just think about starting our cladogram from here, okay? And I'm going to draw you a new one. And I'm going to show you the relationship between single-celled eukaryotes or protists and the rest of the eukaryotic clan. So we know that archaea, this is the group that branches off of a common ancestor the earliest. And we know that archaeans and eukaryotes, everybody beyond here is going to be a eukaryote. Eukaryote. Can you visualize this? Everybody beyond here has histone proteins, and that's what distinguishes. That's how we know that archaeans are more closely related to eukaryotes than they are to bacteria. So I'm going to show you, hopefully in your brain, you are aware that we've got plants, we've got fungi, and we've got animals. And those are three big groups of eukaryotes. And I want to show you how they're kind of related to each other. So at this stage, we get a nucleus, and we get the membrane-bound organelles. And now everything beyond here is a eukaryote. Here's a common ancestor of all eukaryotes. Probably was single-celled. Now look what happens. We get a branch, and this branch, I'm going to run out of room here. So this is my branch that includes plants. And you can imagine, dude, let's get some chloroplasts. Our membrane-bound organelles are going to include chloroplasts. And it also includes algae. Algae are among our protists. There are single-celled eukaryotic algae. So this includes protists. They both have chloroplasts. Plants are multicellular. And we'll talk a little bit more about multicellularity in the next section. Are you good? Do you have this a little bit of a visual? Who's left to branch off? We got a branch off both animals and fungi. That's what they have in common. They have a substance called chitin. This is basically related to glucose. It's basically a glucose molecule with few additional nitrogens. Everybody beyond this point have chitin. Now look, some of our chitin havers branch off and become slime molds. What? Seriously. And those are single-celled critters and some of them become fungi. Now look, slime molds are single-celled protists. All right. Are you seeing a pattern here? What do we have coming next? Well, we've got our animals next. We have two choc pounds of a feather. And true story, what do... Hmm. We're going to branch off animals. Do you remember what all animals had in common? Don't forget. It's the blastula, my friends. Blast-u-la. And they have a sister group. And I'm going to tell you more about these guys, but they're called choanoflagellates. They're choanoflagellates. We're going to learn about them in the animal lecture, but guess what choanoflagellates are? They're single-celled critters. They're protists. Animals are not single-celled. There are some single-celled fungi. Plants are not single-celled. And they actually, the characteristic that choanoflagellates share with animals are these special signaling molecules. They basically have the same molecular message that they send to their cells. They talk to each other using the same tools, which nobody else has those tools, which is kind of awesome. All right. So protists. You can't put them on the cladogram in one place. Not all protists share one ancestor just amongst themselves. The most recent common ancestor of the protist is this thing right here. And that most recent common ancestor is also the most recent common ancestor of plants, fungi, and animals. So really the term protist is not very descriptive. And all it means is that we're dealing with a single-celled eukaryote, but we really don't know much more beyond that. I think what I want to tell you next is I want to look at slime molds because they are an awesome example of colonial multicellularity. So slime molds actually found it beneficial. They're single-celled critters, but they found it beneficial to at certain points in their life cycle to grow, to join together and become multicellular for reproductive purposes really, which is kind of cool. Animals, fungi, and plants were like, dude, let's just stay multicellular because we can do bigger things as multicellular critters. Okay. Slime molds coming up.