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Lecture Comments (3)

0 answers

Post by Hemant Srivastava on June 30, 2015

What category would plants such as Venus Fly Traps or Pitcher plants fall into? Are they considered autotrophs or heterotrophs, or is there some combination of both categories that these special plants fall into?

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Post by Kumar Sandrasegaran on May 30, 2011

May want to get spelling correct: eukaryotes, prokaryotes

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Post by Dr Carleen Eaton on February 3, 2011

The correct spelling for two words discussed during the slide titled "Coelomates" is as follows:



  • Phylogeny describes relationships among groups of organisms based on evolution.
  • A phylogenic tree visually represents a hypothesis about the evolutionary relationships among organisms.
  • A hierarchical system for the classification of organisms was developed by Carl Linnaeus. In its current form, the system includes the categories Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.
  • Domain Bacteria contains single-celled prokaryotes. Members of Domain Archaea are also prokaryotes, but have fundamental differences from members of Domain Bacteria. Archaea include extremophiles such as thermophiles and halophiles.
  • Plants, animals, protists and fungi are all eukaryotes and belong to Domain Eukarya.
  • Animals may be classified according to their body plans. Some animals have a body plan that lacks symmetry, while others exhibit radial symmetry or bilateral symmetry.
  • Diploblastic animals have two germ layers, an ectoderm and an endoderm. Triploblastic animals have an ectoderm, a mesoderm and an endoderm.


Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Systems of Classification 0:07
    • Taxonomy
    • Phylogeny
    • Phylogenetics Tree
    • Cladistics
  • Classification of Organisms 5:31
    • Example of Carl Linnaeus System
  • Domains 9:26
    • Kingdoms: Monera, Protista, Plantae, Fungi, Animalia
    • Monera
    • Phylogentics Tree: Eurkarya, Bacteria, Archaea
    • Domain Eukarya
  • Domain Bacteria 15:43
    • Domain Bacteria
    • Pathogens
    • Decomposers
  • Domain Archaea 19:43
    • Extremophiles Archaea: Thermophiles and Halophiles
    • Methanogens
  • Phototrophs, Autotrophs, Chemotrophs and Heterotrophs 24:40
    • Phototrophs and Chemotrophs
    • Autotrophs and Heterotrophs
    • Photoautotrophs
    • Photoheterotrophs
    • Chemoautotrophs
    • Chemoheterotrophs
  • Domain Eukarya 32:40
    • Domain Eukarya
    • Plant Kingdom
    • Protists
    • Fungi Kingdom
    • Animal Kingdom
  • Body Symmetry 39:25
    • Lack Symetry
    • Radial Symmetry: Sea Aneome
    • Bilateral Symmetry
    • Cephalization
  • Germ Layers 44:54
    • Diploblastic Animals
    • Triploblastic Animals
    • Ectoderm
    • Endoderm
    • Mesoderm
  • Coelomates 47:14
    • Coelom
    • Acoelomate
    • Pseudocoelomate
    • Coelomate
    • Protosomes
    • Deuterosomes
  • Example 1: Domains 53:01
  • Example 2: Match Terms with Descriptions 56:00
  • Example 3: Kingdom Monera and Domain Archaea 57:50
  • Example 4: System of Classification 59:37

Transcription: Classification

Welcome to

We are going to start our discussion on the diversity of life with the topic of classification.0002

I am going to start out with some definitions and discussing different systems of classifications.0009

And then, we will focus in on the Linnaean hierarchical classification that we will be using.0014

Taxonomy is the science of classifying and naming organisms. This is the science of classification and of naming organisms.0020

This is done according to the evolutionary relationships between organisms.0042

And now, with the advent of molecular biology, a lot of this is based on genetic studies of the relationships between organisms.0048

Formerly, morphology and other similarities between organisms helped us to classify them.0056

Phylogeny is a term that describes the relationships among groups of organisms based on their evolutionary history and their common ancestry.0065

This is relationships among organisms based on evolutionary history and common ancestry. The study of phylogeny is called phylogenetics.0079

What I have shown here is a phylogenetic tree, and what this type of tree does is it shows these or hypothesize relationships among organisms.0115

It is a way of helping us to visualize possible relationships among organisms and which organisms0128

have more recent common ancestors than others and, therefore, are more closely related than others.0133

Let's say we have a bunch of species, species A, B, C, D and E. And here, we have an ancestral organism way back.0142

What occurred here is a branch point where the two groups diverged, and this is a later ancestor of A and B.0158

This is a later ancestor or more recent ancestor of C, D and E. Then, these two branched out.0173

We have A and B. Over here, these two groups branched, and then, another branch point occurred.0182

So, D and E have a more recent common ancestor than C, D and E.0188

Therefore, D and E are more closely related than C and D, and D and E are more closely related than E and C.0194

This allows us to sort of organize and visualize these relationships and, therefore,0203

look at which groups are more closely and less closely related based on ancestry.0210

Cladistics is a method of classification that is based on organisms having a shared common ancestor, so classification based on common ancestry.0217

An ancestor and all of its descendants are called a clade.0239

For example, if I looked at this ancestor organism back here plus A, B, C, D and E, that would be a clade.0244

Or I could just say "OK, this branched out here, and we have this later ancestor plus C, D and E". This would be a clade.0253

This would be a separate clade as long as I include the ancestor and all of the descendants.0263

If I just said "OK, this ancestor and one descendant", that is not a clade.0268

I could look at this because there was a branch here, and then, there is a common ancestor here for D and E. This is a clade.0275

Now, what is a little bit difficult is that there is overlap between these systems, but they do not always perfectly align.0286

Taxonomists can give a name to an organism and classify it in a certain way.0299

And then, based on phylogenetic relationships, the classifications might be slightly different.0303

The two, they do not always match, but as we are doing more and more molecular studies and better understanding of relationships among organisms,0308

systems are being developed to hopefully help these to all align better; but for now, we are just going to work with the system that we have.0317

And we are going to talk more now about taxonomy, the names given to organisms and the hierarchal relationships between them.0325

The system that we are going to use is sometimes called The Linnaean system.0333

And this comes from the name Carl Linnaeus, whom we discussed in a previous lecture.0337

He lived in the 18th century, and he developed the two part binomial nomenclature system that we still use today.0343

We are going to go through this example with a cat but Homo sapiens for humans. The genus is the first part of the name.0354

The two part is binomial system, and then, sapiens gives the species. The genus is capitalized.0365

The species is not, and the whole thing should be put in italics.0373

Now, under The Linnaean system, there were kingdoms, phylum, class, order, family, genus and species.0378

Domains were added later, and I am going to talk about some history and explain why domains were added in the past couple of decades.0386

But just right now, focusing on this example and how this works and how it is hierarchical, if we just take the domestic cat as an example,0396

the domestic cat belongs to the domain Eukarya, and starting from the top going down, the top is the broadest category.0404

The organisms in that category are more loosely related than the organisms in the next category. There is fewer organisms in kingdom Animalia.0412

The cat is part of the domain Eukarya, but then, again, so are plants and fungi.0421

Then, we get down to the kingdom. There are fewer organisms there, and they are more closely related.0426

The common domestic cat is part of the kingdom Animalia, phylum Chordata, class Mammalia.0431

Fewer organisms, there are still because there are many animals that are members of this phylum chordates that are not mammals0442

But now, we are down just even fewer organisms, order Carnivora, family Felidae, genus Felis and then, finally, species Felis domesticus.0449

Just to talk more about how this works, if you look at family, lions, domestic cats and cougars or mountain lions all belong to this family.0464

But if I go down to the genus, lions are not part of the genus Felis, however, cat and cougars are.0486

Therefore, cougars and cats are more closely related than lions and cats.0497

This two are more closely related to each other than relationship between cats and lions or cougars and lions, and then, finally, we get down to cats.0503

The groups are nested within each other, and the groups became broader. They encompass more organisms who are less closely related.0519

Talking about how we ended up with domains because it is used to just be kingdom on down, how did we end up with domains and why?0529

So, let's go onto some history.0537

In the 4th century, Aristotle, philosopher, divided organisms in to two kingdoms- Plants and Animals.0540

However, much later, microscopic organisms were discovered and there needed to be a kingdom to include these.0549

More kingdoms were added, and by about the1960s, the system had expanded to include the following.0558

We are going to talk about domains as we trace this history of kingdoms.0568

Kingdoms, at one time, expanded to encompass Monera, Protista.0574

and those both included microscopic organisms, unicellular organisms, Plantae - plant kingdom -, Fungi, and Animalia.0581

Monera included prokaryotes, protist, mainly unicellular eukaryotes.0598

The problem was that Monera contained what was at one time called the Eubacteria or the true bacteria and Archaebacteria or the ancient bacteria.0606

These two were together in the kingdom Monera.0629

The problem was that scientists later realized that these two had differences that were as great as0631

some of the differences between bacteria and eukaryotes or archaebacteria and eukaryotes.0638

They were not necessarily more closely related to each other than they were to the eukaryotes.0645

They were group together but had major differences.0649

To solve this, what happened is Monera got broken up into two kingdoms.0654

We, then, end up with kingdom Protista, Plantae, Fungi, Animalia, Eubacteria and Archaebacteria. Now, we are up to 1, 2, 3, 4, 5, 6 kingdoms.0661

Other problems emerged though.0674

For example, the protists - as we will see in the lecture on this topic - are just a very loose group of organisms.0676

And they contained organisms that actually are more closely related to plants than, say, to each other, so they were another like Monera.0684

They were another kingdom that just seemed to have a bunch of organisms put in it because they were0693

small or had morphological similarities but were not necessarily closely related in the evolutionary sense.0698

Because of this, a couple things happened.0705

One is domains were added. The other is that most scientists no longer recognized many of these kingdoms.0708

The three domains that we have now are Bacteria, Eukarya and Archaea, and what I am showing here, it is a phylogenetic tree.0719

It is sometimes called the tree of life, and bacteria contains what used to be called eubacteria.0730

And in a minute, we are going to go into each of the domains and the features of their members, but these contain the Bacteria.0738

Archaea contain what was called the archaebacteria, and they have some similarities to bacteria; but they have some important differences as well.0747

Bacteria are prokaryotes. Archaea are prokaryotes, but there are some very important differences between them; and then, Eukarya are eukaryotes.0755

Eukarya includes, so talking about the domain Eukarya, it does include some kingdoms that are still recognized- Kingdoms: Plants, Animals and Fungi.0770

Protists are part of this group, but they are for the most part, no longer recognized as a kingdom.0792

You may have seen some books with them described as part of a kingdom.0803

It is a convenient group, but although we sometimes just can say protist and talk about certain organisms under that, they are not a formal group.0807

And in fact, there has been proposals to split the protists into several different kingdoms so that we would have Eukarya, kingdom Plant, kingdom Animal, kingdom Fungi0815

and then, a few three, four or maybe even more protist kingdoms to separate out organisms that are not that closely related.0825

Because things are influx, what we are going to do is work with what is happening right now in science and that is to go by these three domains system,0833

recognize three kingdoms plus the group of protists that fall under Eukarya and then, Bacteria and Archaea separate.0842

And in fact, talking about how Bacteria and Archaea are used to be grouped together as Monera, you will see the way this tree is set up.0852

It shows a common ancestor, the origin of life down here with the common ancestor.0861

And then, we have a branch point here into the domain Bacteria and then,0867

the evolution and later branching in two directions that gave us domain Archaea and domain Eukarya.0879

and there is evidence that Archaea and Eukarya, those members, are more closely related to each other than they are to Bacteria.0886

And this is hypothesized right now but again, just more support for the idea that Archaea belong in their own group.0896

What you need to know is that when you are looking at this hierarchal classification system, domain is at the top.0902

It is the broadest group, and there are three domains, then, beneath that, Kingdoms, Plants, Animals, Fungi0909

and Protists just as a loose group that is still in the works as far as classification.0921

Next, what I am going to do is talk about the characteristics of member of these domains.0927

And then, in later lectures, we are going to go into detail about these separate groups0932

and even the kingdoms, separate set of lectures on plants, animals etc.0937

Starting out, though, with just understanding some of these domains, domain Bacteria, we discussed bacteria earlier on when we0942

talked about prokaryotic versus eukaryotic cells, but to review here, members of this domain are unicellular prokaryotes.0950

Prokaryote means that the cell lacks a true nucleus and other membrane-bound organelles.0959

Bacteria do have ribosomes, but these ribosomes are different than those found in eukaryotic cells.0966

The genome of bacteria is a circular genome. There are no histones associated with the DNA, and there are no introns in the bacterial genes.0986

Many bacteria are pathogens meaning they cause disease.1003

Some examples would be Clostridium botulinum, which causes botulism.1013

These organisms secrete a toxin when food is canned improperly, and then, if a person ingests that toxic, it can make them very ill.1033

Although in recent decades, there has been some medical uses found for very, very dilute amounts of botulinum toxin.1041

A second pathogenic bacteria is Mycobacterium tuberculosis, and the name pretty much tells you what it causes, which is TB or tuberculosis.1052

Many other bacteria, for example Salmonella, Shigella, some species of Streptococcus that cause strep throat,1060

many pathogenic bacteria, which you all probably already knew, but bacteria certainly are not always pathogenic.1082

And they do play an important role for other organisms. They may be decomposers.1088

In other words, they break down organic material and allow that material to be recycled or reused by other organisms.1095

A second very important function of bacteria is in nitrogen fixation.1111

We are going to talk about this in detail in the lecture on plants, but just briefly, atmospheric nitrogen cannot be used by most plants,1116

and so, what nitrogen fixation does is the bacteria that are nitrogen fixers have a symbiotic relationship with plants.1125

And they take atmospheric nitrogen and put it in a form plants can use.1136

One final word about bacteria structure, they have cell walls that contain peptidoglycan.1158

And we are going to talk in the lecture on bacteria about how bacteria can be classified based on the amount of peptidoglycan they have in their cell walls.1169

So, that is domain Bacteria.1182

Domain Archaea: members of this domain are also all prokaryotes.1184

So far, there have not been any archaea found that are pathogens, so I am going to go ahead and write that they are not pathogens.1190

These include these extremophiles. Extremophiles, just like the name suggests, live in extreme environments.1199

By extreme environments, it could be a very hot environment.1206

Thermophile means heat loving. These organisms tolerate extremely hot temperatures.1209

They can live in temperatures from, let's say, 120°F up to 180 or even higher.1216

They are found in areas such as the hot springs in Yellowstone park or near hydrothermal vents deep in the ocean.1222

These live in very hot environments that other organisms could not tolerate.1231

Halophiles, this means salt loving. The halophiles live in environments with very high salinity.1234

They can live in water that has even up to ten times the salt concentration of sea water.1246

An example would be organisms that are found in the Great Salt Lake in Utah, so these are couple kind of extremophiles.1251

There are other archaea that are not extremophiles. An example would be the methanogens.1258

These organisms produce methane from hydrogen, so they take carbon dioxide plus hydrogen and form methane.1267

Oxygen is actually usually toxic to these organisms.1282

They are found in areas in wetlands such as marshes. They are also found in the GI tracts of cattles and humans.1286

Now, I mentioned that these are prokaryotes, but they do have differences from bacteria.1301

Let's talk about what these differences are and what some of the similarities are.1304

They are prokaryotes, therefore, no true nucleus and no membrane-bound organelles,1312

no Golgi apparatus and endoplasmic reticulum and all those things, no membrane-bound organelles.1320

They do have a circular genome, so circular genome, circular piece of DNA. However, they may have histones.1332

Some types of archaea do have histones, so in this way, they are more similar to eukaryotic cells.1344

These cells have similarities to bacterial cells and to eukaryotic cells. They may have histones associated with their DNA.1352

Another difference is they may have introns. Some genes in certain archaea have introns.1362

Again, that is more similar to eukaryotic cells- two members of Eukarya.1371

In addition, they have no peptidoglycan in the cell walls. There are differences in cell membrane structure.1380

The cell membrane structures contain branched hydrocarbons, whereas, in bacteria, cell membranes only contain unbranched hydrocarbons.1395

So, I am just going to put "different membrane structure than bacteria".1403

Bacteria have growth that is inhibited by certain antibiotics.1419

And then, when we look at different antibiotics such as streptomycin and chloramphenicol, we will see that they do stop the growth of bacteria.1423

However, the growth of members of archaea is not stopped by chloramphenicol and1429

streptomycin just as eukaryotic cell growth is not stopped by these antibiotics.1434

So, that is another difference between bacteria and archaea.1439

OK, to sum up, members of domain Archaea are prokaryotes. They do not have a true nucleus or membrane-bound organelles.1444

They have a circular genome. However, unlike members of domain Bacteria, they may have histones associated with their DNA.1450

Some of their genes contain intron. They do not have peptidoglycan in their cell walls, and they have a different cell membrane structure than bacteria.1458

And the members of Archaea include extremophiles that can grow in very extreme conditions like hot temperatures or salty environments.1468

Before we go on and talk about domain Eukarya, organisms can be classified based on the1478

source of energy that they use, as well as their method of obtaining organic compounds.1483

So, we are going to go ahead and take a minute to discuss what phototrophs, autotrophs chemotrophs and heterotrophs are,1488

and how those different modes can be combined, and how they differ, so let's start out just by talking about phototrophs and chemotrophs.1494

These two have to do with the source of energy.1516

When we talk about phototrophs versus chemotrophs, we are classifying according to the source of energy used.1524

Phototrophs use light as an energy source. An example would be plants that perform photosynthesis using light as an energy source.1529

There are protists such as algae that are phototrophs. Some bacteria, the cyanobacteria are phototrophs.1549

Now, we are going to look at chemotrophs, so this is classification based on source of energy.1557

Second grouping is chemotrophs. Chemotrophs use chemical source of energy.1566

What I mean by this is the energy stored in chemical bonds. Animals are an example, humans.1574

What we do during cellular respiration is release energy that is stored in chemical bonds and then, use that to make ATP to fuel the cellular functions.1585

So, rather than light, the source is energy stored in the chemical bonds of organic compounds.1595

Alright, so that is classification based on the source of energy.1601

The second type of classification is the method of obtaining organic compounds.1605

Can an organism make organic compounds, or does it have to obtain them from elsewhere?1610

So, these are the two possibilities.1616

Autotrophs are often called the producers because they can make organic compounds from inorganic compounds. Again, an example is plants.1617

What plants are able to do is to take carbon dioxide and water and use it to make glucose.1648

And then, oxygen is released as a by-product, which we talked about in the lecture on photosynthesis.1654

Plants do not need to ingest organic compounds.1659

They can just survive of water, mineral, carbon dioxide and some sunlight and make their own organic compounds.1663

Whereas, if we look at heterotrophs, heterotrophs are also known as consumers.1670

Heterotrophs cannot produce organic compounds. Therefore, they need to ingest other organisms.1682

Animals, for example, eat plants, other animals and fungi.1700

As we talk about different groups of organisms, in subsequent lectures, we are going to talk about their modes of nutrition.1708

And when you combine phototrophs, chemotrophs, sources of energy and sources of organic compounds,1714

you come up with four possibilities for the type of organism that you have.1725

The first type is photoautotroph. This is combining phototrophs that use light for energy and can produce organic compounds.1731

Plants are an example of this. Organisms that perform photosynthesis use light as energy, and they synthesize organic compounds.1757

That is photoautotrophs.1767

The second would be photoheterotrophs. Photoheterotrophs also use light for energy.1769

However, they cannot produce organic compounds.1779

They must consume other organisms as a source of organic compounds, so cannot produce organic compounds. Some bacteria fall into this category.1782

Those are the two groups that use light as an energy source, and then, we have two different means of obtaining organic compounds.1800

Now, looking at organisms that use chemical sources of energy, you could have an organism that is a chemoautotroph.1807

They obtain energy from a chemical source.1817

And chemoautotrophs that exist do fall in within - some of them - the domain of Archaea and also some Bacteria.1820

What some organisms can do is oxidize inorganic compounds for energy for example hydrogen sulfide, ammonia, iron compounds.1831

So, by oxidizing inorganic compounds, these organisms can get an energy source.1855

However, they are able to - because they are autotrophs - make organic compounds from inorganic compounds.1860

So, just to keep these straight, the difference between a photoautotroph and a chemoautotroph is that the photoautotroph uses light for energy.1882

The chemoautotroph oxidizes inorganic compounds for energy, so it uses a chemical source of energy.1889

However, both of them are able to produce organic compounds.1894

Finally, chemoheterotrophs, such as animals, they derive energy from organic compounds.1898

And they cannot make organic compounds from inorganic compounds.1908

So, they need to use chemical source of energy and cannot produce organic compounds.1914

Photoautotrophs: light for energy, make organic compounds. Photoheterotrophs: light for energy, cannot produce organic compounds.1927

Chemoautotrophs oxidize inorganic compounds to produce energy- can form organic compounds.1936

And finally, chemoheterotrophs get their energy from chemical bonds and need to ingest other organisms as a source of organic compounds.1944

Now, going on to talk about the domain Eukarya, this domain contains eukaryotic organisms.1958

We talked about eukaryotic cell structure in one of the earlier lectures in the course.1967

And you will recall that eukaryotes have a true nucleus, and they also have membrane-bound organelles, so true nucleus, membrane-bound organelles.1971

Some members of Eukarya have cell walls, but they do not contain peptidoglycan. No peptidoglycan in the cell walls.1990

They do have introns and histones, so introns in the genes.2007

Recall that introns are sequences that are sometimes thought of as interrupting sequences between genes that are noncoding sequences.2017

Histones are proteins associated with DNA, and the DNA is not circular like with bacteria. It is organized in a different way.2030

The growth of these organisms is not inhibited by antibiotics.2052

So, those are some characteristics of the domain Eukarya, and this domain contains three kingdoms plus the group of protist.2057

First kingdom is the Plant kingdom. These are all autotrophs.2065

They can produce organic compounds from inorganic compounds, and they are multicellular.2078

We have several lectures on this, and plants range from the more primitive plants such as moss,2089

which do not have true roots and leaves, to ferns, which are vascular plants but lack seeds.2095

Then, we are going to go on to talk about seeded plants such as conifers and then, finally, flowering plants such as angiosperms.2103

The cell walls of plants contain cellulose, so various categories: mosses, seed plants like ferns, conifers2110

Actually, correction, vascular plants such as ferns, conifers, more advanced, these are seed plants and angiosperms, which are flowering plants.2133

And we are going to go through these different categories in detail.2145

Next, we have protists, which are not a kingdom but a group of organisms. Many of which are unicellular, but some of which are multi cellular.2149

This group includes both heterotrophs and autotrophs, mostly unicellular.2163

Some members form colonies, others, such as what is commonly known as seaweeds, which are actually types of usually brown algae or red algae.2176

Those seaweeds are multicellular like kelp. Also, it is multicellular.2196

Again, the classification systems that have been proposed involve splitting these up into different kingdoms.2207

And we are just going to discuss each group later on and the different characteristics that they have rather2213

than trying to divide them up into kingdoms, since that system is still in the works, and it is just a proposal at this point.2219

Next we have Fungi. This is also a kingdom.2228

The organisms in this kingdom are all heterotrophs. They are mostly multicellular- maybe unicellular, though.2234

The cell walls of fungi contain chitin, and these organisms obtain nutrition through absorption.2247

What fungi do is they actually secrete digestive enzymes outside of their body.2269

The nutrients are, then, broken down outside the organism, and then, the fungi absorb these already digested nutrients.2275

So, this is an external method of digestion.2282

An example of a fungus is yeast. Candida is a type of yeast.2285

Humans carry Candida. but when it overgrows, when it gets out of balance with the other organisms in the body, it can cause symptoms.2292

One disease or disorder that can develop is called thrush, and sometimes, when thrush occurs, you can even see whitish plaques growth on the tongue.2300

And that is a Candida infection, which is actually a fungus infection.2312

Finally, we get to the Animal kingdom. These organisms are heterotrophs, and they are multicellular.2317

It encompasses a huge range of organisms from insects to jellyfish ranging up to elephants.2330

And what we are going to do later on is study invertebrates versus vertebrates, the major animal phyla.2335

And then, we are going to go into some detail in animal physiology and anatomy.2342

Right now, what I would like to focus on concerning animals is some of the ways in which we divide them up, not necessarily according to genus or species.2349

But according to characteristics of their body plans, as well as characteristics of their embryological development,2358

one way in which we can group animals is according to body symmetry.2368

Some animals are asymmetrical. Others have what is called radial symmetry, and still, others have bilateral symmetry.2374

Very simple animals lack symmetry, so they are asymmetrical.2382

An animal that lacks symmetry would be very primitive like a sponge, and these organisms are going to be non-motile or what is called sessile.2390

Because if an organism is not symmetrical, it makes it harder to move, so most of these are going to be non-motile.2406

Now, when we go up a step, we get to organisms that are radially symmetrical. More advanced organisms have bilateral symmetry.2414

An example of an animal that has radial symmetry is the sea anemone or jellyfish. Here, we see the example of the sea anemone.2425

And what radial symmetry means is that if you put a plain through a central axis anywhere, the two sides are going to be mirror images.2435

So, if I go through this central axis, and I cut anywhere here; and then, I just look at the two halves, or I could cut here and see two halves,2446

or I could cut here and say "OK, here is one half, here is the other half", it is going to be symmetrical.2455

You can think of it as radiating outward. Sometimes it is compared to the spokes on a bicycle wheel.2462

This is a circular body plan, and these organisms can be motile. However, their movement is not as directional.2469

They tend to, just like a jelly fish, kind of, float along or be carried along compared to more advanced organisms that can move in a very deliberate manner.2482

We have radial symmetry with animals such as jelly fish and sea anemone.2491

Now, we go up to the more complex animals.2496

Whereas, with radial symmetry, the animal might have a top and a bottom, there is no left or right side. There is a top and bottom, though, often.2498

Contrast that with an organism that is bilaterally symmetrical like humans. They have a top, a bottom and a left and right side.2517

So, if I divide this organism along the center using a long longitudinal axis here, I am going to see that it is a mirror image.2528

The legs, the two halves of the body, the antenna, it is a mirror image of each other.2537

This allows an organism to move very deliberately.2542

It could walk, or it could swim somewhere; and this is a type of body plan that you are going to in a more advanced organism.2545

Just to go on to some terms that are useful when we are talking about the anatomy of an organism, anterior is the front or the head end of an organism.2554

It is in the front. Posterior is in the back.2571

Dorsal is going to be the top, so this is dorsal; and then, if you went underneath in the belly, that is going to be ventral or the bottom.2579

This organism is crawling along, and if you look down at the top, you are looking at the dorsal side.2593

If you flipped it over and looked at the underside, that is the ventral side.2600

The end where the head is anterior. The back end is posterior and the idea of anterior.2603

And the idea of anterior and posterior ends brings us to the topic of cephalization.2609

This is the development of the concentration of sensory organs in the central nervous system at the head end of the organism,2618

so concentration of sensory organs in CNS at what is called the head end or the anterior end.2628

What happened was animals that are bilaterally symmetrical over the period of evolution came to have sensory organs.2644

Their sense organs were concentrated in one area so eyes, ears, nose, and in addition, the CNS was also concentrated in that area.2652

The CNS became very well developed, formed a brain, and that brain is able to interpret the information that is coming in from the sense organs.2662

And this allows organisms to have a very complex set of behaviors and movements that are not possible with more primitive organisms.2672

Again, these are concepts that we will talk about when we discuss embryology and development, but just to give you an idea, now,2682

of some ways in which organisms can be categorized and terms we are going to use when we talk about the diversity of life,2687

organisms can also be divided according to the germ layers that they have.2696

So, germ layers or tissue layers are found in embryos, and as the embryo develops, various tissues and organs form from these layers.2700

Specific tissues or organs form from certain layers.2713

Diploblastic animals have two germ layers - di meaning two - and those two layers are an ectoderm and an endoderm.2719

Triploblastic animals have three layers - tri meaning three - so they have an ectoderm and an endoderm as well as a mesoderm.2726

And briefly, if we look at ectoderm, what types of tissues and organs does it become?2736

Well, the ectoderm forms the outer layer. It becomes the outer layer of an organism.2744

It develops into the epidermis. This accompanies things such as hair, nails, also in the outer layer of the organism, the covering of the organism.2750

The CNS is derived from the ectoderm.2763

The endoderm: the linings of the gastrointestinal tract, the GI tract, the lining of the respiratory tract,2768

the linings of the tubes in our bodies, those come from endoderm, also glands.2785

For example the pancreas are derived from endodermal tissue.2796

Finally, the third layer, the mesoderm: the mesoderm develops into the circulatory system and the musculoskeletal system, so muscles and bones.2801

Some triploblastic animals developed a fluid-filled body cavity called the coelom, and these organisms are known as coelomates.2825

Starting actually with organisms that do not have a coelom, these are called acoelomates.2837

Now, why is this coelom important anyways, and what would be the disadvantage of being acoelomate?2842

Well, like I said, a coelom is a body cavity. It is actually a fluid-filled body cavity, and what it does is it provides a separate space for the internal organs.2847

This way, the internal organs are contained in an area where they are protected because the body cavity is often fluid-filled.2863

And there are tissues that the organs are attached to, they are suspended from.2871

This provides for cushioning, and it also allows the internal organs to form and move and grow separately from the outer wall of the body.2877

The kidney can grow without having to grow right along with the outer wall of the body.2885

It forms a separate protected cavity that cushions internal organs and allows for their2891

separate growth and allows them to be less affected by the movement of the outer body.2897

Looking at acoelomates, what we have is ectodermal tissue, which forms the covering, and then, we is some mesoderm.2903

And then, just stuck right through the mesoderm, no body cavity, there is the GI tract derived from endoderm.2918

Flatworms, you see how this is shaped, sort of, flattened out? So, in acoelomate an example would be a flatworm.2931

Pseudocoelomates have a body cavity, but it is called a pseudocoelom because it is not just derived from the mesoderm.2939

So, it is not what is called a true coelom. It is a pseudocoelom.2948

It is derived from both mesodermal and endodermal tissue.2952

Again, we have the ectoderm. We have this outer covering and the mesoderm, but here, you can see the pseudocoelom.2955

This is a body cavity, and then, within that derived from the endoderm, is the GI tract.2964

Finally, we get to the coelomates, so these are organisms with a true coelom.2971

And we have the ectodermal tissue, which is going to form the outer covering and then, the mesodermal tissue.2977

Well, here, we have the coelom. We have the cavity, and we also have mesodermal tissue.2990

And what this tissue does - it is the yellowish brown hair - the mesoderm provides tissue lining the body cavity that the organs can be suspended from.2996

Annelids are coelomates as are mammals and other more advanced animals.3014

So, this coelom allows for the separation of internal organs from the outer wall of the body.3020

We can divide coelomates further into two categories called protostomes and deuterostomes.3032

Protostomes exhibit a development of cleavage pattern that is a spiral pattern.3047

So, I am just going to say spiral cleavage, and this is what is called a determinate cleavage pattern.3053

Meaning that, in the embryo, even at a very early stage, let's say the 4-cell stage, those cells are already destined to go down a certain pathway.3061

If you took an embryo at the 4-cell stage, separated out one cell, it would not develop into a full organism.3070

It would just develop into the part of the organism that it is destined to become.3076

By contrast, deuterostomes exhibit a cleavage pattern that is known as radial cleavage, and radial cleave is indeterminant.3082

So, if you took a cell from a very early embryo, and you separated it out, then, it would be possible for that cell to develop into an entire organism.3094

And this how identical twins result is the zygote divides into two, and two embryos form because those cell types have not yet been determined.3104

In addition with protostomes and deuterostomes, there is an opening that forms called a blastopore.3108

So, I am just going to write that word here, and one difference, just to be aware of, is the outcome of what that blastopore forms.3127

In protostomes, the mouth develops from the blastopore, and the anus develops from a second opening.3137

In deuterostomes, that first opening actually becomes the anus. This blastopore becomes the anus, and the second becomes a mouth.3147

So, there are differences in the way the organism develops. There are differences between protostomes and deuterostomes.3152

OK, what we talked about today is taxonomy classifying organisms according to domains and phylums and classes and all.3159

We also talked about different ways of thinking about and dividing organisms3169

according to methods of nutrition, obtaining energy, body plans, embryology.3172

So, now, we are going to go ahead and review some of these concepts starting with example one.3179

List two similarities between domain Archaea and domain Bacteria.3184

And then, list two similarities between members of domain Archaea and members of domain Eukarya.3192

Starting out with two things that are similar about Archaea and Bacteria, well, one major one is that they are both prokaryotes.3197

Prokaryotes lack a true nucleus.3211

You could put these as separate, or you could just, sort of, put them on both being prokaryotes- no true nucleus and no membrane-bound organelles.3215

Second similarity, we are talking about similarities, that they both have circular chromosomes. That gives us two.3236

Now, we are looking at two similarities between the domain Archaea and members of the domain Eukarya.3247

Well, they both lack peptidoglycan in their cell walls.3254

Bacteria have peptidoglycan, but both these domains do not. They both lack peptidoglycan in cell walls for members that have cell walls.3261

Second similarity is they may have introns. Members of Eukarya have introns, and some genes in some members of Archaea also have introns.3275

The same goes for them both having histones. Some members of Archaea have histones and members of Eukarya have histones.3293

Another similarity, actually, between these two that I did not go over but I am going to mention now is that members of domain Archaea3306

and domain Eukarya have several kinds of RNA polymerase, whereas, members of domain Bacteria only have one kind of RNA polymerase.3315

Finally, the growth of Archaea and Eukarya members is not inhibited by the antibiotics we discussed:3331

strep for streptomycin and chloramphenicol, which are both antibiotics.3347

So, two similarities between these two groups, and I listed five similarities for the other two groups; but you would just have to list two.3352

OK, example two, some matching: match the following terms with their descriptions- cephalization, protostomes, coelomates and mesoderm.3361

Cephalization: the layer of germ tissue that develops into the circulatory system, muscles, and bone in triploblast.3373

Concentration of sensory organs in the CNS at one end of the organism.3382

C: organisms that have a body cavity derived from the mesoderm.3387

D: organisms with a spiral cleavage pattern resulting into determinate cleavage.3391

Well, when we talk about cephalization, we are talking about development of a head end of the anterior end3397

of an organism that has sensory organs, and the central nervous system function is all concentrated in there.3407

So, that is B, so I am going to put B right up here next to cephalization.3414

Protostomes: we talked about protostomes versus deuterostomes and how they have different cleavage patterns.3420

And protostomes have a spiral cleavage pattern and determinate cleavage.3427

Whereas, deuterostomes have a radial cleavage pattern and indeterminate cleavage, so protostomes- D. That is done.3433

Coelomates: recall that a coelom is a fluid-filled body cavity, and organisms that have a body cavity derived from the mesoderm are called coelomates.3444

Finally, mesoderm is one of the germ layers, and it is the layer that does develop into the circulatory system, muscles and bones.3457

Example three: kingdom Monera included Bacteria and members of what is now domain Archaea. Why was Monera eliminated?3470

Well, with the advent of molecular genetics, we could compare organisms on a completely different level than3479

we were able to before when we just had to look at morphology and nutritional modes and biochemistry metabolism.3484

Now, we can actually look at the genomes, and additional structures, as well, were looked at more carefully.3490

And what was found is that members of Archaea and Bacteria were as different from each other as they were from some of the eukaryotes.3499

They were scattered in a kingdom although, they were not as closely related as we thought.3510

They were split because Bacteria and Archaea have fundamental differences.3515

And Archaea are, in some ways, as different from Bacteria as they are from eukaryotes.3532

And therefore, this kingdom was originally split into two: Eubacteria and Archaebacteria.3565

And then, eventually, those kingdoms were eliminated and turned into domains.3570

Example four: A new organism is discovered. Its cells contain a nucleus and membrane-bound organelles.3577

It has cell walls that are made of chitin. It cannot perform photosynthesis and ingest nutrients through absorption.3584

What kingdom will this organism mostly likely be classified in?3594

Let's look at the characteristics of this organism. Its cells contain a nucleus and membrane-bound organelles, so I know that this is a eukaryote.3598

Therefore, it is going to be in the domain Eukarya. It is asking me the kingdom.3608

It has cells walls that are made of chitin. It cannot perform photosynthesis.3616

Plants have cell walls containing cellulose, and they can perform photosynthesis; so it is not a plant, and it ingests nutrients through absorption.3621

Given the chitin in the cell wall and this nutritional method of ingesting nutrients through absorption, this is most likely a member of the kingdom Fungi.3632

That concludes this session of on the classification of organisms.3645