Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Thank you for watching the video.

To unlock all 5,300 videos, start your free trial.

Diversity of Organisms

Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.


When most students are studying for the AP biology exam, they look at all the different kinds of creature there are to memorize. They think, this is impossible. The thing is, it is. It’s kind of like trying to memorize everything in your house. Nobody wants you to do that. But what could be important is, if you look at your house, where do things belong? Who do they belong to? If you just use some basic characteristics of the members of your family, like your father. He’s big and he like things dealing with business and the economy.

You, you’re a little bit smaller, got a good sense smile and you brother, he’s small but obsessed with cartoons. If you use those characteristic and you find something that you’ve never seen before, all you’ve got to do is think about it and then you can figure out who it belongs to. Say for example I find a fish, I assume this is not your dad’s. I’m going to go with your younger brother’s. It’s the same thing with all the different kinds of organisms. You focus in on a few key characteristics and once you know those, then you can zip in straight in on the ones that you want.

What I’m going to do is I’m going to go through and I’m going to describe how do scientists divide things up? I’m going to describe some of the different ways that they do it, then I’m going to zero in on the traditional five kingdom system. And I’m going to give you some of those major characteristics of each of those five. That way you can zero in, and not obsess over trying to memorize every single detail.

What we’re going to be doing now, is we’re going to be taking a look at how do the AP Biology people break down the various organisms that we see today. Originally, the idea was if I chase something, and I catch it before it manages to run away, and I eat it. Or as I’m chasing it, it turns around and starts to chase and me and tried to eat me, that was an animal. If on the other hand it never moves and I get to eat it that was a plant.

That’s a great system, except it’s got a lot of problems. If you take a look at things like fungi, you can chase them, and you catch them, no problem. However, they also try to eat you. And if you’ve ever had athlete’s foot, you’ve known that feeling.

What scientists came up with is something called the five kingdom system. Now with the five kingdom system, you wind up having Monera down here at the bottom, then the Protista. These are things like algae and amoeba. There is also the plants, the fungi; yeast and mushrooms, and then our favorite, the animals. Now, this system worked out pretty well, but it’s starting to show its age. Because as scientists started studying their biochemistry and their genetics, they started realizing things that had been lumped together, say in the Monera or in the Protista kingdom, they’re really not closely related.

It’s kind of like me and Brad Pitt. I know we look so similar, but we’re not cousins. And take a look at this Chihuahua, this German Shepherd and this wolf. Yes, you take a look, that doesn’t look like that. But these two are more closely related than those two, oddly enough.

So what scientists came up with is this new idea called the three domain system. I’ve been seeing those questions appear in essay questions recently so, be aware of it. Now the three domain system is this idea that there is this super groups. Eukarya consists of all these four other kingdoms. If we take a look it's Protista, Plants, Fungi and Animalia. They’re subsumed within that Eukarya.

But the Monera kingdom, the bacteria, they actually have two major divisions within them. And so they said these are the proper bacteria sometimes called Eubacteria and then the others are called Archaea. You need to be aware of this. But don’t completely dismiss the five kingdom system because, while it’s got it’s problems, and in fact some people are saying let's take those Protista and break them down to even more kingdoms. Until all the fighting has settled out amongst all the scientists, the AP Biology people aren’t going to change things.

Before I get started into the different kingdoms, I wanted to take a moment to just help you remember one of the key ways to help spot which organism you’re talking about. And that’s to zero in on these unique characteristics that you can find in each group. For example, if you ever hear the word chitin, you know that what they’re talking about is either a kind of fungus, or an arthropod.

So look at some other characteristics. If it says something about decomposing, that means it’s a fungus, it’s a kind of mushroom. And if they say it has jointed legs, that’s not a mushroom, that’s a bug, an arthropod. So bearing that in mind, let's start going into the kingdoms. And we’ll start off with the kingdom Monera, otherwise known as the bacteria.

Bear in mind as we’re doing this, you’ve got to remember there is that weird subdivision that’s going on called the domains. And it’s in the Monera that this whole thing started. What’s the big unifying characteristic of the Monera? They are the prokaryotes. That means, before the nucleus. And if we take a look, it means that they don’t have a nucleus, and in fact they don’t have any other membrane bound organelles like mitochondrion or chloroplast. Instead, their DNA is circular and they only have one molecule of DNA and it’s naked, naughty. That just doesn't mean that they're doing weird stuff with their DNA. That just means that it’s not wrapped around histone proteins.

Another thing that they have is this peptidoglycan cell wall. Now that is different than the cellulose that you may be used to from plant cells or algae. Something else that they have, is they have a flagella like yours and mine. But instead, ours does this angulations, theirs does rotation.

Last in the Monera to bear in mind, is that Archaea bacteria. That’s the weird group that’s caused all the trouble that I was talking about before. Now the thing to think about with them, is that they’re weird. If you think about where are they found, volcanic hot springs, that’s weird. Very salty water, weird pit bugs, weird. And in fact, even in their cell walls, or cell membranes they have this weird molecule. Scientists prefer that you call it a branch fatty acid but it's just weird.

Let’s move on into the Protista. The Protista as a kingdom don’t have any one great unifying trait. So instead, they’ve broken down to these subgroups called the protozoa, the algae and the fungi like protists. Let’s take a look at them a little bit closer.

The first group is the protozoa, that name means early animal. And in fact they’re probably the organisms that we branched off of in our animal kingdom. Like us, they are heterotrophic. That means that they eat other things. They’re also mobile, that means that they move around in various different forms, and I’ll get into that in just a moment.

They’re also diploid, what does that mean? That means they have two copies of every gene. And they follow the gametic life cycle, and that means that they engage in sex like you and I do, not. Instead, what happens is that, one of their cells will bump into another one cell, and then fuse and then out pops a little baby amoeba, or other things like that. They’re also single celled. That’s the big difference between them and us.

Let’s take a closer look at some of these groups. In the protozoan, there are the amoeba. Their movement is what makes them unique. They use these things called pseudo pods, which literally means false foot. What they do is, they extend a portion of their body and then flow into it. Freaky.

Next up are the ciliates. The ciliates include this group here, the paramecium. And as you might be able to guess from their name, they use little tiny cilia to flow their way through the water.

The last group up is the flagellate. How do they move? You guessed it, with flagella. And they just use one or in this case four, five long flagella to swim their way through the water.

Next up are the algae. The big thing about the algae is that, they’re like plants but they’re in water. Now like plants of course, they are photosynthetic. Many of them using pigments like chlorophyll, like the plants do, or some of them use other different kinds of pigments, like xanthosine. They have cell walls often made of cellulose, but some of them use different materials. They follow many different life cycles. Some of them following life cycles kind of like the fungi, others following cycles kind of like the land plants. I’ll get into that more in depth later.

The other thing to remember about them is that, they include the green algae, which are the creatures that gave rise to the land plants. Now let’s take a look at some of the diversity within the algae.

They include things as small as these diatoms. These are unicellular creatures. Now diatoms is a good one to remember, because their unique characteristic to remember is that, their cell walls are made of glass. AP Biology people will try to trick you by saying silicon dioxide, but you know what that is. They’re wee, kelp is ginormous. They can grow upwards of a hundred or so feet long.

Last group that I’ll talk about real briefly in the algae are the green algae. Again, we mention them a lot because they’re the ancestors of the land plants. This right here is volvox, a commonly used example of colonial algae. You can see here’s the colony of algae, with little baby colonies inside. The last group in the Protists are the slime molds. This is a group that everybody is kind of more happy to not even pay attention to. Take a look at this.

This is literally called dog vomit, slime mold. It’s nasty. If you’re going through the forest and you pick up a log and you look and it looks like somebody just blew their nose on the ground, it’s not. Well maybe it could be, but generally it's not. If you watch it for a while, you’ll see it start to flow. And then if conditions get bad, it will just clamp together, shoot up little stocks and spray our spores. Others of them are just like little amoeba. And you and I look through a microscope we say it looks like a protozoan. It’s not. If you see them start to flow together, form a little slug thing kind of like the Power Rangers forming the megazord, it’ll move a long, shoot up a stock and out spray the spores. It’s just really bizarre.

Let’s move on to fungi, it’s a little bit nicer. The fungi include those mushrooms that you and I are all familiar with, but they also include thing like yeast, mould and mildews. We can see here these are the standard fruiting bodies of the fungi. This happens to be the shelf fungus. The big thing that you’ll see with them, is that they’re heterotrophic which means they eat other things. Usually they’re decomposers like, the fungus that will eat you when you die.

Their big thing is that chitin that I mentioned before. If you see chitin, again, it’s a fungus or an arthropod. They are haploid which means, every fungus only has one copy of every gene. They follow something called the zygotic life cycle. What does that mean? That means that the only time that they form diploid cells, is when they’re making zygotes. When they’re making little babies, which they will immediately undergo miosis and then form spores.

The last thing you recognize about them is that they form these things called hyphae. What’s a hyphae? That’s a long thread of cells that they form by mitosis. Now those of you who are up to date with your current West coast line, that makes it easy. Because just think, that fungi at the party, he was getting ‘hyphae’. We can make that even funnier if we say, "Hey why did the algae go home with the mushroom?" She took a ‘lichen’ to him because he’s a ‘fun gi’. That will help a lot of and be even funnier if you knew that a lichen is a symbiotic relationship between a green algae, or a cyanobacteria and a fungus. Actually it wouldn’t be any funnier.

Now as I previously mentioned, the animals evolved from the protozoa. And what happened is that, we went the step from being unicellular to being multicellular creatures. So what are the big unifying traits of the animals? Let’s take a look.

We don’t have cell walls or chloroplast, or things like that. Instead, unique organelles, our cells compared to the plants, are the centrioles. These are things that we have that we use during mitosis, during cell division. We are, as I previously mentioned, multicellular. Which means that, even the smallest animals that I can think of still have hundreds of cells. We do heterotrophic nutrition. We hunt down our prey, kill it.

Now we are often called irritable and that’s a big thing that makes us different from the fungi or the plants. That doesn’t just mean you’re cranky, that means we respond very quickly to stimuli. And we usually do that by using nervous systems and muscle systems. And that allows us to move generally.

Now our last big thing that we have is that we’re diploid. Again that means that we have two copies of every cell.

Now we are very sophisticated. Very complex compared to other organisms. And that means that in order to maintain that complexity, we are diploid almost all the time. The only time that you and I are diploid, is when we either form our sperm, that would be me, or eggs, that would not be me. Those things then fuse and form a zygote and that grows into a new baby animal.

Within the animal kingdom, there is huge diversity. And I hugely recommend that you spend some time with your text book reading through them because as our favorite kingdom, it winds up being something that the AP Biology people ask a lot of questions about. I don’t have time now to go through that, but what I’ll do is I’ll briefly mention some of the major groups and give you some clues as to how to organize it. Let’s start off with the simplest of the animals.

Those are things like the Porifera here; the sponges, which are filter feeders and then the cnidaria which are the things like jelly fish and sea anemones. The unique characteristic to listen for, is the fact that they have these stinging cells called cnidocytes, which have these little internal parpoons called nematocysts.

The next group up includes the things like the tapeworm here, or planeria, which are all members of the platyhelminthes. These are grouped together into this thing called acoelamates. The next groups up do have some kind of coelum. Whether it’s a pseudo coelum of the nematodes, or the true coelums of things like the molluscs, the arthropods and the annelids. If we take a look at them, the molluscs include things like snails but they can also include clams or octopi. They all share this thing called a mantle, which in the snails gets developed into the shell.

The arthropods are those bugs that I mentioned before. And remember, they’ve got chitin and jointed legs. So if you see chitin and jointed legs, you know you’re talking about an insect, a crustacean, or some kind of arachnid. The annelids are the segmented worms.

They are true coelemates, and they have a unique thing, at least for these guys.

They have what’s called a closed circulatory system. They’re landmark species, they’re often mentioned for closed circulatory systems or they’re going to be talked about as the chordates, or sometimes called the vertebrates. If we take a look at the other side of the animal kingdom, the things known as deuterostomes, all those guys previously were protostomes. That includes us, the incredibly handsome animals, chordates over here and then the echinoderms right here, the star fish and sea urchins.

That’s it for the animals, now it's time to move into the plants. The plants, those are the creatures that move up on land and they do photosynthesis, on land. They all do photosynthesis using the stuff called chlorophyll. They have those within chloroplast. The plants have cellulose cell walls. What does that mean? That means that they have these rigid box shapes around their cells and that gives them support and structure.

The big challenge to being of land is lack of water. So there are a lot of adaptations within the plant groups to help deal with this lack of water. One of which are roots. True roots are those specialized parts of the cells that absorb water from the soil, and bring it up to the plant. All the plants have them, except for the bryophytes. For those of you who don’t know, bryophytes are the mosses. Because they don’t have roots, they have a harder time dealing with getting water from the soil. In fact, all of the other plant groups besides the bryophytes, have vascular tissue.

What is that? That’s the transport tubes that allow a tree, like a sequoia tree, to get water from the soil, all the way up, hundreds and hundreds of feet to the top of the tree. The bryophytes since they lack that, they’re completely restricted to being about this tall, because that’s about as far as they can get water through simple osmosis or diffusion. What are some of the other big things?

We see here that the gymnosperms. What are those? Those are things like pine trees. What they do is they take advantage of the fact that there’s wind on land. What they do is, they spread pollen from their cones and that’s how they get the pollen from one tree to the next.

Later on when that pollen fertilizes the cone, it then turns into a seed, or releases seeds. And those seeds are then dispersed again by wind. The angiosperms on the other hand, they use animals to spread their pollen. And that’s the whole birds and the bees thing that your parents really did a bad job of explaining.

Now they also use it to disperse their seeds. How do they do that? Have you ever looked at fruit? Fruits are bright. What are they trying to get you to do? The fruit is saying come here. The plant gives you the fruit, you eat it and then 24 hours later, after you’ve wandered away, you deposit that seed in a big steaming pile of fertilizer and that helps that angiosperm out.

Now the big thing that the plants all do is the sporic life cycle. This is sometimes called alternation of generation. And you should probably spend some time with your textbook reinforcing this, but I’ll go through the basics right now. With the sporic life cycle, you have two different forms of the creature. Two different generations; one is diploid; that is called the sporophyte. The other one is haploid, that’s called the gametophyte.

Let’s start off with that gametophyte. The gametophyte is a plant that is like I said, haploid. It produces gametes, that’s why it’s called a gametophyte. Those are either sperm or egg. They’ll swim or fly or be carried by an insect to one of the eggs. And then that will fertilize and form a zygote. That eventually is dropped and forms the sporophyte. The sporophyte is the diploid organism. That will eventually undergo meosis and produce spores, spore’s a single cell that is haploid and when it lands it grows into a complete gametophyte, completing the cycle.

Obviously, the sporophyte with its diploid or two copies of every gene, it winds up having a lot more information in it. And that allows those plants that have the sporophyte generation as the dominant generation, to have a lot more sophistication. If you take a look at a rose bush, that has a dominant sporophyte. In fact, the gametophyte is contained within the flowers. If you look at a pine tree, it’s also a pretty elaborate.

And that also possesses this dominant sporophyte with the gametophyte being contained within the male and female cones. The only ones that really have a dominant gametophyte are the mosses.

Let’s take a quick look to just make sure that you know what these different plant groups are. If we take a look here, here I see the bryophyte. This is the moss. These little tiny things here that are sticking out here, those are called the sporophyte living off the big leafy mat that is the parental gametophyte. Over here, that’s a fern or pteridophyta, as they’re more properly called. What you’re seeing here is the sporophyte. Its gametophyte generation is independent, but it’s it tiny little heart shaped profilis and that looks like somebody just tore off a leaf and crumpled it on the ground. It is very, very small.

Now let’s take a quick look at the gymnosperms. If you take a look at the gymnosperms, they include the pine trees like this. And anything that has a cone, that’s a gymnosperm. Their name literally means naked seed. While these are the angiosperms, flowering plants. And that’s it. That’s the five kingdoms.

I’ve covered a lot of information and I strongly recommend again going back to your textbook and read through the chapter summaries. Yes, the chapters are important, but the summaries will make it faster. Just bear in mind that there are those five kingdoms, subdivided into the super domain groups, called the Archaea and the bacteria for the kingdom Monera. And then all the others are lumped together in the Eukarya.

Remember the five kingdoms in this order; the Monera or the bacteria, the Protista, are subdivided into the protozoan, the algae and the fungus, like slime molds. Then there is the fungi with the chitin and the decomposing. The plants which are the green things living on land. And then there is us, the animals. Heterotrophic, multi cellular, mobile creatures. That’s it.

If you take a good look at this stuff, you’ll do really well in the AP test.

That’s it, that’s the five kingdoms. You now have enough information to do just fine on the AP Bio exam in case they ask any questions about them. Prokaryote, it’s a member of the Monera. Does it have flagella and is eukaryotic and single celled, heterotrophe? That’s a flagellate Protista from the protozoan group. Does it have chitin? Does it have legs? If so, it’s and arthropod animal. If it’s a decomposer that means it’s a fungus.

What I do recommend though is that to really firm up this information, go back through your textbook. And with that idea in mind that, you’re always looking for those one or two unique traits that make that one group stand out from the others. Do that and you’ll do just fine.

© 2023 Brightstorm, Inc. All Rights Reserved. Terms · Privacy