AP Biology Protists

Welcome to Educator.com.0000

In this section on diversity of life, we will be focusing on a group of organisms known as protist.0002

The term protist is an informal term that encompasses a wide array of eukaryotic organisms.0009

Most of these organisms are unicellular. Some form colonies, and others are actually multicellular.0018

These can be autotrophic, heterotrophic or a new term, mixotrophic, that we are coming across now.0026

And these are organisms that can function both as autotrophs and as heterotrophs.0032

As far as the classification of protist, in recent decades, it has been undergoing a lot of change. Originally, protist was a separate kingdom.0038

However, the more these organisms were studied especially with the adamant of molecular biology techniques,0049

scientists realized that some of these organisms were more closely related to organisms in other kingdoms such as plants than they were to each other.0056

What we ended up with is a kingdom that contains organisms that really should not have been together.0066

Right now, just for convenience, we use sometimes the term protist referring to these as a group, but it is not a formal classification.0074

Right now, what is happening is there have been some proposals to divide protist up according to their relationships.0082

And more closely related ones would be together in certain kingdoms.0090

There might end up being three or four kingdoms, but the protists are split up in two.0094

But for right now, as far as kingdoms in this course, I am just going to refer to the kingdoms Plant, Animal and Fungi,0098

as well as the three domains we discussed and protist as just a loose group.0106

Protists are all members of the domain Eukarya. They are eukaryotic cells, eukaryotic organisms.0111

And these were grouped the way they were because pretty much anything that was not an animal, a plant or a fungus was put in here.0127

It was eukaryotic cells or sometimes multicellular organisms that were not truly animals. They were not truly plants.0139

They were not truly fungi, and therefore, very diverse array.0146

As I mentioned, some of these organisms are autotrophs. Some are photoautotrophs.0152

They are actually able to use light as a source of energy and convert inorganic compounds to organic compounds.0156

And these protist are often described as plant-like.0165

To help you remember different features and qualities of these organisms,0171

I am going to talk about plant-like protist, animal-like protist and fungus-like protist, although again, these are not formal categories.0175

Plant-like protist that I am going to go over, you will sometimes hear called algae.0183

Many of them are algae, but again, this is just a loose informal term; but you may hear them just referred to generally as algae.0189

Another group of protist that I will be discussing are those with some qualities that are similar to animals,0199

so the animal-like protist that are sometimes called protozoans.0206

While the plant-like protist are photosynthetic organisms, the animal-like protozoans, or excuse me, the animal-like protists are heterotrophs.0215

These are heterotrophs, and they are usually motile.0227

There are other protists that have qualities most similar to fungus or fungi, and these are the fungus-like protist.0238

These are also heterotrophs for the most part, although, there are some autotrophs as well as some mixotrophs in here.0251

Some of the plant-like protists are mixotrophs, as well, meaning they can be either photosynthetic or heterotrophic.0266

And the reason the ones in this group are qualified as or called fungus-like is because they do often decompose organic material, so they are decomposers.0277

They reproduce via spores, and they have cell walls that are similar to those found in fungi.0289

They also have some structures that we are going to talk about, that contain the spores that are similar to the structures found in fungi.0307

Before we go on to delve into these different groups, I am going to introduce you to the concept of the serial endosymbiosis theory.0316

You will recall from our lecture on the origin of eukaryotic cells the endosymbiosis theory in general, and let's first review that.0324

When we talked about just endosymbiosis theory, we talked about it as organelles originating from a symbiotic relationship between prokaryotes.0334

In the endosymbiosis theory, a larger anaerobic bacteria engulfed smaller aerobic bacteria, so these were both prokaryotes.0346

So, way back, an ancestral larger anaerobic bacteria engulfed the smaller aerobic bacteria.0370

And it was a symbiotic relationship because the larger bacterium provided protection for the smaller bacterium.0376

The smaller bacterium utilized oxygen and formed energy from it.0385

And this was thought to have occurred around the time when oxygen levels greatly increased in the atmosphere,0389

and that oxygen actually was toxic to some anaerobic organisms.0394

Eventually, over time, through evolution, instead of this being a smaller independent organism, it evolved to become mitochondria or chloroplast.0399

Eventually, organelles evolved from this symbiosis between two independent organisms.0412

This endosymbiosis theory describes the formation, the eventual evolution - I am going to put evolution actually - of eukaryotic cells.0420

This event, this first endosymbiosis will be called primary endosymbiosis.0436

However, it is believed that some organisms, particularly some protist are the result of multiple episodes of endosymbiosis, so serial endosymbiosis.0441

Let's talk a little bit more about some photosynthetic plastids, protist, photosynthetic protist.0453

Plastids are organelles including chloroplast. Those are one type of plastids.0463

They are not exactly the same. This is one type, so one example is chloroplast.0472

What may have happened is that after plastids such as chloroplast originate, we get the primary endosymbiosis.0481

And eventually, we ended up with some types of algae, ancestral algae called red algae and green algae, and these are photosynthetic organisms.0494

The endosymbiosis that resulted in this some think that it may have been a heterotrophic that it was later on.0509

And there was some heterotrophic eukaryotic cells engulfed cyanobacteria, which are photosynthetic bacteria,0516

so engulfed photosynthetic bacteria- cyanobacteria.0529

Eventually, this smaller bacteria, this bacteria that was engulfed by the larger eukaryotic cell,0542

became part of that cell eventually evolved to become a chloroplast.0550

And what we ended up with were different types of algae - red algae and green algae - that are photosynthetic.0558

Now, where this serial endosymbiosis comes into play is that a second or secondary endosymbiosis may have occurred later on.0566

And what happened there is there was another heterotrophic eukaryote engulfed red algae.0579

And somewhere else in evolution, a heterotrophic eukaryote engulfed green algae.0597

This symbiotic relationship allowed this heterotrophic eukaryote to perform photosynthesis because it is containing the red algae,0613

which is photosynthetic or the green algae, which is photosynthetic.0622

But these were photosynthetic in the first place because of this original endosymbiosis, so it is serial.0625

Eventually, this red algae seized through evolution over time.0632

Red algae was no longer separate free living organism, but it actually became a part of this eukaryote formed plastid.0639

So, It just became a part of this cell, and various photosynthetic protist descended from that - protist that still exist - and other lines from the green algae.0652

Now, evidence for this: when we look at primary endosymbiosis, when we look at plants, when we look at a chloroplast or when we look at mitochondria,0663

what we see is that mitochondria and chloroplast have two cell membranes. They have genetic material.0674

There is evidence for the fact that these were once free living organisms.0686

When we look here at plastids of these protists that we thought are the result of serial endosymbiosis, we notice something interesting.0690

We notice that they are plastids- have four cell membranes.0696

Because what happened is we had this first set of endosymbiosis resulted in plastids contained by red and green algae.0708

And since that organelle was an engulfed organism, that free living organism had a cell membrane.0717

It got engulfed by a heterotroph that was in a cell membrane.0725

Now, it is in here with its original cell membrane from this cyanobacteria plus the cell membrane from the ancestral organism. That is two cell membranes.0728

Now, when the red algae gets engulfed by this heterotrophic eukaryote,0737

that heterotrophic eukaryote has a cell membrane that is as it was engulfed wrapped around this red algae.0744

Now, that puts an extra layer as in here 1, 2, 3, 4 cell membranes.0752

Two cell membranes per incident of endosymbiosis, which is what we would expect, so that is the evidence for this.0759

There are groups of protist that are believed to have descended from secondary endosymbiosis.0767

One set of endosymbiosis after another serially may have been separated by a long period of time but one and then,0774

some long time later or another resulting in these protist that have plastids with four membranes.0783

In addition, these plastids with four membranes carry vestiges of a nucleus.0791

They do not have a true nucleus, but they have vestiges of their original nucleus; and these are called nucleomorphs.0797

So, this is further evidence supporting the serial endosymbiosis theory.0803

Just to give you some background on some of the plant-like or photosynthetic protist that were going to encounter,0808

protists have many different types of life cycle because they are a diverse group of species.0816

And this is the first time in the course we are encountering different life cycles because so far we have covered bacteria, which reproduce asexually.0822

Now, we are going to be talking about asexual reproduction as well as sexual reproduction and different life cycles.0831

So, I am going to start out with just an overview.0837

One type of sexual life cycle involves a diploid adult.0839

If we start out just looking at fertilization, the egg unites with the sperm in fertilization. Both of these gametes, egg and sperm, are haploid.0846

When they unite, they form a diploid zygote. The zygote becomes an embryo.0857

If we are talking about human beings, it becomes an embryo, undergoes mitosis, a child and then, an adult.0864

Here, we have an adult that is diploid. Within the adult, germ lying cells create gametes.0871

Those cells undergo meiosis.0880

So, germ cells undergo meiosis, halving of the chromosome number to form gametes, egg or sperm, and the cycle begins again.0883

Egg or sperm unites with the opposites. Fertilization occurs resulting in a diploid zygote, mitosis and then, an adult.0894

So, if you look at animals, if you look at humans, this is what we are going to be talking about.0903

There is that only the gametes which are unicellular haploid, so unicellular haploid gametes. The multicellular form of the organism is diploid.0909

A second type of life cycle exists in fungi and some protist, and this is a life cycle involving a haploid adult.0933

Starting here again with fertilization, the egg unites with the sperm, and both of these are haploid. They come together to form a diploid zygote.0943

However, instead of undergoing mitosis and forming an adult organism, the zygote undergoes meiosis.0955

This is a unicellular single-celled zygote, does not divide through mitosis, does not form an adult organism, just undergoes meiosis,0964

immediately having its chromosome number again to form spores, and these spores are haploid; so this bottom half is all haploid spores.0973

Now, these spores undergo mitosis to form an adult that is a multicellular or unicellular organism.0983

Mitosis can occur and form many unicellular organisms or it can occur and form one larger multicellular organism.0998

This adult organism, multicellular or unicellular- haploid.1006

Contrast that within the previous life cycle, the zygote underwent mitosis to form a diploid adult.1015

Now, we have a haploid adult. Then, egg or sperm gametes are formed.1024

Meiosis does not even need to occur because this individual is already haploid. Those unite in fertilization.1036

Some protists exhibit what is called alternation of generations.1043

An alternation of generations is fundamentally different than the two life cycles we just talked about.1048

In the two life cycles we talked about, there is a diploid phase. There is a haploid phase in all of them.1055

But there is not a multicellular diploid phase in the multicellular haploid phase.1060

The adult faces one or the other. Here, you have both.1066

Alternation of generations refers to life cycles in which there is a multicellular haploid phase and a multicellular diploid phase.1069

If you look at humans, yes, we have a haploid phase. Sperm or egg, those are haploid, but the only multicellular phase we have is diploid.1087

The difference here is that these organisms have a multicellular... up here, this sporophyte phase is a multicellular diploid phase.1099

So, humans have a multicellular diploid phase, but this organism also has a multicellular haploid phase.1112

Plants also undergo alternation of generations as we will see in lectures in the section of plants.1122

Looking here at haploid gametes, egg and sperm,1130

egg and sperm unite in the process of fertilization to form a diploid - 2n organism - to form a zygote, a cell that is diploid.1134

The zygote undergoes mitosis to form a sporophyte. The sporophyte is an adult multicellular diploid form of the organism.1144

Within the sporophyte, meiosis occurs to form haploid spores.1153

And again, we have mitosis to form a multicellular organism called a gametophyte, but the gametophyte is haploid.1161

Then, egg or sperm form within these gametophytes.1172

Meiosis does not have to occur because the gametophytes are already haploid.1179

Here, I see a multicellular diploid organism, a sporophyte form and a multicellular haploid organism, the gametophyte form.1184

And we are going to see this with some protist as well as plants.1193

We are going to start out talking about plant-like protist. These are photosynthetic protist.1198

And members of this group are frequently just called algae, but I am going to divide them up into various groups with the correct names.1205

These organisms are extremely important because they form the base of the food chain on aquatic environments.1216

These are mostly unicellular, but some, such as organisms that we commonly just call seaweed are multicellular, so they can be or some are multicellular.1226

Alright, we are going to cover first a group of organisms that is depicted here called the euglenids.1245

Like all the plant-like protist, these are capable of photosynthesis. However, they are actually mixotrophs.1254

With euglenids, if there is enough sunlight, they undergo photosynthesis.1262

However, if sunlight is low, it is night time or it is just really cloudy and there is not a lot of sunlight, these organisms can actually become heterotrophs.1267

They will absorb organic material from the water that they are living in, and they will be heterotrophic.1279

So, they are both photosynthetic and heterotrophic, so both autotrophs and heterotrophs.1287

Euglenids primarily live in fresh water, so these are mainly freshwater organisms.1297

And we are going to look at just some of the major morphological features of this organism.1306

They are motile. Here, you can see a flagella.1312

They often have two flagella, but here we have depicted, and near the flagella, this small pigmented area is what is called an eyespot.1314

And this allows these organisms to move towards light. This is called phototaxis- allows movement towards light1326

And since they are motile, they can swim over toward where the light is, and then, that allows them to get the light they need for photosynthesis.1336

Euglenids also have what is called a pellicle, and what a pellicle is, is these bands of protein- protein bands known as a pellicle.1346

Euglenids do not have a cell wall, and therefore, the pellicle provides some shape and support for these organisms. They reproduce asexually.1362

So, this is one group of protist, the euglenids- a plant-like protist.1378

The second group we are going to discuss are called the dinoflagellates.1382

Again, these are photosynthetic organisms because they fall under this heading of plant-like protist.1389

They live in both marine environments as well as in fresh water environments.1395

And the memorable characteristic about these organisms is that they have plates that contain cellulose.1403

And this provides them with strength and protection.1413

What they usually have is two plates, and there is a groove in between.1417

So, that would be the groove- plates containing cellulose, so hard plates containing cellulose, and within these grooves are flagella.1421

With the structure of this organism and the fact that they have two different flagella, they end up moving in a distinctive spinning motion.1445

They move the organism through the water with the spinning motion.1459

Some of these are phototrophs. Others are heterotrophs, or they may be mixotrophs.1467

These organisms are responsible for what is called red tides. You might have heard of red tides.1480

And dinoflagellates contain carotenoids, which are pigments that we have discussed earlier in the course that produce a reddish color.1488

They are responsible for the reddish color of these organisms, and when there is a bloom of these - most people call them algae blooms -1500

you can look out in the ocean actually see waves that really look reddish in color.1508

So, this is red tides. They produce red tides when there is a bloom of these organisms.1514

There are neurotoxins, so certain species of dinoflagellates produce neurotoxins.1521

And fish, shellfish, marine mammals that eat these organisms can, then, become ill and even die.1532

And humans who eat clams or other shellfish that have been exposed to high levels of these neurotoxins,1540

the humans that eat the shellfish can get sick, as well.1547

Dinoflagellates produce a neurotoxin, and an animal in the water eats this.1551

And then, a human eats that animal, and the human being can end up being sick.1557

And they reproduce either sexually or asexually, so these are dinoflagellates.1561

The next organism we are going to talk about under plant-like protist are a group called diatoms, so that is the third group we are going to talk about.1568

All three of these, so far, are unicellular photosynthetic organisms.1579

They are very, very abundant. There is over a hundred thousand species it is thought of these diatoms, and they are a very important part of plankton.1583

And as I mentioned, the photosynthetic plankton - excuse me - photosynthetic protist -1594

are extremely important because they form the base of the food chain in aquatic environments.1598

In the ocean, plankton, it is the base of the food chain.1604

Organisms eat the plankton. Other organisms eat those and so on up, so part of the base of the food chain.1607

I am just going to write "base of the food chain". They are not alone, but they are part of this.1614

What is interesting about diatoms is that they have silica in their cell wall.1621

The cell wall, it contains two parts. It is comprised of two parts, and these contain silica.1627

It is sometimes described as being glass-like,.1635

And diatoms might be familiar to you because you might have heard the term diatomaceous earth or sometimes just DE, and this is the powdery substance.1638

What happens is when diatoms die, their shells become fossilized, sink down.1655

And eventually, through compression of water, they get compressed up into a substance that we can retrieve1663

from the bottom of a body of water and form into this powdery substance called diatomaceous earth.1670

And diatomaceous earth is very useful for things like filtration, so it can be used in pools as a filtering device, a filtering substance.1678

It is also used as an abrasive and also as a non-chemical insecticide because it does not kill insects through chemical means.1688

It actually kills them through physical means because diatoms often have these little tiny sharp-like spikes on them that can puncture the insects.1697

It has many uses, and that is where the term DE or diatomaceous earth comes from.1707

Alright, we have talked about some unicellular plant-like protist.1715

We are going to talk about one more unicellular one as well as some multicellular organisms.1720

Going on to talk about golden algae, like the protist that we just talked about, this one is also unicellular- golden algae.1728

And these are freshwater organisms.1741

Although, they can form colonies - some species form colonies - these also, like the dinoflagellates, contain carotenoids.1746

In this case though, the carotenoids give them, sort of, a yellow-brown color - a yellowish color - and hence, the name golden algae.1760

These are also a component of plankton, and they are like the other plant-like protist- photosynthetic.1771

But, they are capable of being heterotrophic, as well. They can feed on bacteria or other eukaryotes like diatoms.1781

And again, they are part of the base of the food chain because all these organisms we are talking about are producers in aquatic food chains.1787

These are actually mixotrophs because I mentioned, they can be phototrophic or heterotrophic, so that is golden algae.1798

The next...so, this is the fourth one we have talked about.1806

The fifth one plant-like protist that we are going to discuss is multicellular, and this is the brown algaes, so brown algaes.1809

And this term like golden algaes, it can encompass more than one species.1818

Brown algaes are multicellular, so this is the first one we are coming across as multicellular, again, photosynthetic.1822

These are commonly known as seaweed, so if you see seaweed, actually what it is, is a protist.1834

It is a type of what is commonly known as seaweed. A type of brown algae is kelp, so another example is kelp, which can be extremely large.1842

They can be 50 or more meters long.1855

Like the golden algae we have just talked about, they contain carotenoids.1860

So, you are getting the theme by now with these different colors red, brown, yellowish. The carotenoids are responsible for them- brown color.1864

These are not characterized as plants.1877

Here, is a sketch of a brown algae, and you might look at this and say "oh, these sound like plants, they are multicellular, they are photosynthetic".1880

Superficially, they may look like plants, but there are some important differences. For one thing, they do not have true roots, stems, or leaves.1888

What this structure down here is called is a holdfast, and this allows the brown algae to attach to a substrate, to a surface, but they are not true roots.1896

Then, we see a stem-like structure, but it has its own name. It is called a stipe, and then, photosynthesis occurs in what are called the blades.1907

If this organism is held to a substrate, but it needs to get near the sunlight to form photosynthesis,1921

there has to be a way to, sort of, make sure that it gets exposed to sunlight; and that is through what is called air bladder.1928

So, brown algaes contain air bladders, and these are structures that are actually air-filled sacs.1935

And they make these algae buoyant so that the blades are exposed to the sunlight.1946

Brown algae are used as a food source, so certain types of seaweed can be eaten.1966

They are also a source of iodine for some populations, and they are used as a thickener in food such as salad dressings.1971

The reproductive cycle of brown algae involves alternation of generations, which we just discussed earlier.1979

The gametes are mobile. They are motile.1993

They have flagella.1997

There is a stage in their life cycle that includes a multicellular diploid organism and a2002

stage that involves a multicellular haploid organism during this alternation of generations.2008

The next type of plant-type protist that I am going to just...2014

The red algae are also multicellular marine organisms commonly known as seaweed.2019

But there are some differences between these organisms and the brown algae.2024

Red algae, again, they are multicellular, often called seaweed.2034

They tend to be more delicate in appearance not quite as large as the brown algae,2044

so generally, smaller than brown algae with the more delicate appearance to their blades.2050

They contain a chlorophyll as a photosynthetic pigment. However, their reddish color is due to another photosynthetic pigment called phycoerythrin.2056

This is responsible for the red color, and these organisms are also capable of living in fairly deep water.2075

This is another organism that is used as a food source for human, another type of seaweed.2085

You may have had it. It is sometimes wrapped around sushi.2088

Also, there is a material within their cell walls that is used to make agar, and agar is the material that bacteria are cultured on, they are plated on.2092

So, the round clear plates contain agar, and a component of red algae, a substance that red algae makes, is used to actually manufacture agar.2107

They do reproduce sexually, so undergoes sexual reproduction.2117

However, unlike the brown algae, the gametes are not flagellated, and some undergo alteration of generations.2123

The next group that we are going to discuss, a plant-like protist, are the green algae.2137

And when we say green algae, this is a true green similar to the color of grass. I am going to say grass-colored.2143

These are mostly unicellular, so we are going back now to unicellular organisms, although, there are some that are multicellular.2153

And an ancestral form of green algae is very likely the ancestor to plants, so I am just going to put "ancestor to plants".2164

So, an ancestral form of the green algae is plants evolved from that as we are going to discuss in the section of plants.2176

And these are mostly freshwater organisms.2184

And as we talk about some of the features, they are more closely related to plants than the other members of protist.2188

They store excess sugar as starch. Their cell walls contain cellulose and pectin.2195

They have these photosynthetic pigments, chlorophyll A and B, and their gametes have flagella.2214

They can reproduce both asexually and sexually.2236

So, as I mentioned, these are mostly unicellular.2246

But an example of a multicellular organism is what is called sea lettuce, some multicellular form of green algae.2248

And the most important point here is that they are closely related to plants, and you can see some of the similarities now.2254

And when I do discuss plants, you will see how the two are related.2261

One type of green algae that I can use as an example as far as the reproduction is called Chlamydomonas.2266

This is a type of green algae, and like I mentioned, green algae can reproduce asexually or sexually.2280

And this protist, along with some other protists, actually go into the sexual reproduction mode when their survival is threatened,2285

sexual reproduction when their survival is threatened.2294

Why would that occur? How would sexual reproduction help these organisms to survive?2302

Well, here is what happens. There is actually two different mating types.2307

The gametes from these mating types can unite to form a diploid zygote, but the zygote is encased in what is called a zygospore.2313

The zygote is encased inside this form that is called a zygospore with a protective wall.2324

This allows the organism to survive during times when conditions are poor and survival is not likely.2331

Later on, when conditions get better, and there is a change in survival, meiosis will occur and form haploid offspring, so later on, meiosis.2339

They will end up with four haploid offspring, and these mature into haploid adults.2353

The haploid adults can also reproduce asexually. The haploid adults reproduce asexually, form other haploid adults.2366

Those reproduce asexually, but then, if conditions get bad, there is not enough nutrients or something,2374

then, the sexual reproduction cycle will get triggered so that the organism can end up surviving inside the zygospore when times are bad.2379

So, this concludes the section on plant-like protist.2392

What we are going to go on and talk about now, after talking about all these different2395

photosynthetic protist, are protist that can be loosely categorized as animal-like.2398

The animal-like protists are all unicellular, so they are unicellular heterotrophs; and they are usually motile.2405

Sometimes they are classified according to the method of motility.2413

For example, they may use flagella. They may use cilia or structures called pseudopods that we will talk about when we talk about the amoebas.2418

The first animal-like protist that I am going to discuss is a group of protist called sporozoans.2433

These are also known as the apicomplexans, and a representative example of this is Plasmodium.2442

Some species in the genus Plasmodium cause malaria, example species in the genus Plasmodium.2453

Now, why are these called apicomplexans?2463

The reason is that there is a complex or a group of organelles, complex of organelles at the apex of these cells that allows the cells to penetrate the host,2466

at the apex that allows organisms to penetrate the host cell membrane, the host cell.2488

Just for a second to get back to the idea of classification, as I mentioned, these are grouped - animal-like, plant-like, fungus-like -2502

according to certain characteristics that they have in common, but it does not mean that these are necessarily closely related.2510

In fact, the sporozoans are part of what is sometimes called a supergroup Alveolates.2515

Alveolates are a group of protist that have sac-like structures, so they have sac-like structures just beneath their cell membranes.2522

And there are other alveolates that are not animal-like.2537

For example, the dinoflagellates, which I had classed as plant-like because they are photosynthetic, actually are alveolates along with the apicomplexans.2544

This is just to show you that these groupings are based on characteristics.2555

But, there are many other ways to group them according to other characteristics, genetics and evolutionary relationships.2559

So, just keep that in mind as you are reviewing to just take each group for what it is,2566

learn about it, but not look at these as phylogenetic classifications or anything.2572

Getting back to the apicomplexans, these are primarily parasites.2580

And I mentioned that they use this complex of organelles to penetrate the host cell membrane.2584

These are mainly parasites, and in fact, certain species of Plasmodium does cause a very important disease worldwide known as malaria.2588

I will say "some Plasmodium cause malaria.2608

And we are going to talk a little bit about the life cycle of these Plasmodium species and how it ties into symptoms of the disease.2613

It is a complicated life cycle.2621

And it involves time period spent in the mosquito, time period spent in the human host and asexual as well as sexual reproduction.2623

What happens is first, an infected mosquito bites a human or an animal, and we are going to say “bites human".2632

And during that process, it injects the form of Plasmodium that we are going to call sporozoites.2644

These sporozoites travel to the liver, OK, sporozoites travel to the liver.2660

They spend two weeks or even more - it can be a month - in the liver, spend about two weeks in the liver.2674

And there, they undergo asexual reproduction, spend two week in the liver undergoing asexual reproduction, and then, they are released.2686

They are released as merozoites. These merozoites travel and enter the red blood cells.2700

So, the next stage here, merozoites, travel to the red blood cells.2707

They stay in the red blood cells for about 48 hours and, again, undergo asexual reproduction.2717

So, reproduce in the red blood cell, and this takes about 48 hours.2725

Some merozoites are released. Some of these actually form gametophytes.2736

Merozoites are released from RBCs, and some are actually gametophytes capable of producing gametes.2744

Now, if a mosquito bites the host, they can take up the gametophytes.2762

If the gametophytes are not taken up by the mosquito, they die.2782

If they are taken up by the mosquito, then, gametogenesis occurs in the mosquito.2786

So, now, we have haploid gametes, and fertilization will also occur in the mosquito; so I am going to put "gametes form in the mosquito".2791

After those gametes form, then, they unite and become diploid organism again.2806

An oocyst is actually formed in the GI tract of the mosquitoes, so it is on the wall of the mosquitoes' GI tract.2815

After fertilization, the zygote forms what is called an oocyst on the wall.2824

Eventually, hundreds of sporozoites will be released, and they will travel up to the salivary glands of the mosquito to start the cycle all over again, OK?2833

So, just looking back at the beginning, when the mosquito bites the human, they inject the sporozoites.2845

Where the sporozoites came from is this mosquito bit into a human, injects it some gametophytes,2850

The gametophytes underwent gametogenesis, form gametes. The gametes united via fertilization to form a zygote.2855

The zygote formed an oocyte, and within that oocyte, hundreds of these sporozoites were formed, released.2865

They are motile. They go up to the salivary glands of the mosquito, and the whole cycle starts again.2872

Now, where did the symptoms of malaria come from, and what are the symptoms?2877

Well, symptoms of malaria include episodes of fever, chills and headaches.2880

So, an individual with malaria might feel OK, and then, a few days later, they get shaking chills, bad headache, fever.2885

And what has happened then, is the symptoms occur when the red blood cells open and lyse open.2892

And all of these hundreds or more of merozoites are released.2902

This disease, if untreated, can be fatal, and it is found primarily in tropical and subtropical regions of the world.2908

OK, so that was our first animal-like protist, the apicomplexans or sporozoans, and the example is Plasmodium.2916

An additional group of animal-like protist that we are going to discuss is the kinetoplastids.2931

The kinetoplastids contain what is called a kinetoplast, so what is a kinetoplast?2941

This is a region of the mitochondria that contains dark-staining DNA. So it is a region of mitochondria containing dark-staining DNA.2951

To give you an example, the organism that causes African sleeping sickness is a kinetoplastid. You might have heard the name.2971

Certain types of trypanosomes cause African sleeping sickness, and these organisms belong to the group kinetoplastids.2979

What happens is this is transmitted by the tsetse fly. The tsetse fly bites a human and a chancre forms.2997

The chancre forms at the site of the bite.3013

However, the trypanosomes spread through the blood stream, so spread of the infection through the bloodstream and through lymphatics.3015

And untreated infection can actually progress to the central nervous system, and it may be fatal; so that is a kinetoplastid.3032

The next group we are going to talk about are the ciliates, and right here is an example of a ciliate.3043

You can see that is covered in cilia, and I mentioned that there are multiple modes that protist use to move.3047

We have seen flagella already previously. Now, we are talking about cilia, and then, we are going to talk about pseudopods in a few minutes.3054

Ciliates are covered by cilia. That is where they get their name, but there are some other characteristics that you should be familiar with.3065

One of them is that they contain micronuclei and macronuclei, so here, you can see the macronuclei - macronucleus - and micronucleus.3073

They also have what is called an oral groove, and what they do is they use cilia to sweep water along in this oral groove and then, into their mouths.3093

Water that they are in contains food particles like bacteria.3109

And then, this food particle ends up entering a food vacuole where it can be broken down.3115

So, the particles are broken down, and then, waste is released through what is called an anal pore in the cell membrane.3127

Water enters these cells through osmosis, and these individuals usually live in hypotonic environment.3139

So, more water is going to want to enter the cell because it is a hypotonic environment.3146

And water is going to want to go to the more hypertonic environment inside the cell, so there are contractile vacuoles that pump out the excess water.3152

This is a lot of different organization within the cell involving nutrients, ingesting water and maintaining osmolarity, mobility, clearing out the waste.3166

So, this is an example of a ciliate.3180

Now, reproduction of these organisms can be asexual via binary fission, or they can undergo sexual reproduction in the form of conjugation.3185

We are going to go ahead and talk about conjugation and how it involves some micronucleus and the macronucleus.3196

So, we start out with two cells of compatible mating types, so two cells fused.3208

And they have to have compatible mating types, and here, we have a micronucleus and the other micronucleus.3215

They are partially fused, and then, meiosis occurs but no cytokinesis.3226

Meiosis results in four micronuclei per cell, but the cell membranes have not separated these into two separate cells. They are still together.3236

Then, what happens is three micronuclei per cell break down. They disintegrate, so that is what is happening here.3246

We still have the macronuclei, and three of the micronuclei have broken down. Then, what happens is the cells end up exchanging micronuclei.3258

We were left with one micronuclei per cell, and in order for them to exchange, they need to duplicate.3260

So, these undergo mitosis, mitosis of the remaining micronuclei.3287

So, then, we end up with this duplicate. That is what has happened at this next step- mitosis of the remaining micronuclei and then, the exchange.3298

This cell is going to keep one of its original.3311

And it is going send the other micronucleus into the other cell that it is mating with, and this cell is going to do the same.3314

This one is going to go this way. That one is going to go the other way.3323

Now, we are going to end up with two cells, each with a micronucleus that it originally had and another micronucleus that came from the other cell.3331

Here, cytokinesis will finally occur, and then, we get cytokinesis; so the two cells separate, and I am just showing this one going out here.3343

It is going to go through the rest of the steps that this one is going through, but for clarity I am just going to leave one up here.3356

These two micronuclei fuse, and that is why these are shown, kind of, one on top of the other.3363

They are going to fuse, and then, mitosis occurs three times.3368

After they fused, there is just going to be a single micronuclei. Mitosis times 3 is going to give us 2, 4, 6, 8 micronuclei.3373

Four of these remain micronuclei. The others end up fusing into a macronucleus, and the cell's original macronucleus disintegrates.3383

Cytokinesis will, then, occur twice, so this one is going to disintegrate.3401

And were going to end up with 1, 2, 3, 4 offspring each with a micronucleus and a macronucleus3407

and some new genetic material that they did not start out with due to conjugation.3416

So, this is a type of sexual reproduction that can occur in these protist.3420

Continuing on with some other animal-like protist,3428

the ones that I am going to discuss now or some of the ones that I am going to discuss now have modified mitochondria.3432

Originally, there were certain protists that were believed to lack mitochondria completely, but further studies showed that they did have mitochondria,3437

that they had been modified and were quite different from what we expect when we looked at mitochondria.3446

The first group are the parabasalids. These organisms have modified mitochondria and produce energy anaerobically.3452

These are also called hydrogenosomes, and some of these species are free living. They live in an aquatic environment.3480

There are other parabasalids that are parasites. They are flagellated.3492

As far as the parasitic ones, these are more well-known, and termites are a huge problem because they eat wood.3499

So, the question is how do they digest wood? Well, actually it is due to protist from this group that live symbiotically within the termite guts.3510

Those protist secrete enzymes that allow the termites to digest cellulose.3519

Another well-known example of parabasalids that are parasitic is Trichomonas vaginalis.3525

It causes the infection Trichomonas, which is a sexually transmitted disease, and these, again, organisms have modified mitochondria.3536

A second group of organisms with modified mitochondria are the diplomonads or sometimes just called monads.3548

They have modified mitochondria, multiple flagella. They also have two nuclei.3559

A well-known example is Giardia. The disease Giardia - giardiasis - is caused by Giardia.3576

Giardiasis is the disease, and this is an intestinal parasite found in humans.3586

It is caused by drinking water that has been contaminated with either sewage, so human waste or where animals such as sheep and cattle eliminate.3592

It causes GI symptoms like abdominal pain, nausea, vomiting, diarrhea, so both of these can be parasites and can cause infection in humans.3601

The next group of organisms we are talking about on this slide are the rhizopods, so we will talk about them up here.3613

This is a very diverse group of organisms. Some of these are free-living.3624

Some live in aquatic environments. Others live in moist soil.3628

Others are parasites.3632

Now, we are getting to the method of motility known as pseudopods, and here, you might recognize this classic protist is a type of amoeba.3634

And I am going to focus on one type of amoeba called Entamoeba because it causes the human disease amoebic dysentery.3644

So, Entamoeba is just going to be my example because it is very important because it does cause disease.3654

And we also already looked at flagellated protist. We looked at ciliated protist, and now, we are going to look at a protist with pseudopods.3671

This extension, the cytoplasmic extension, is known as a pseudopod.3680

And it allows for motility because within there, what is going on inside the cytoplasm is assembly and disassembly of microfilaments,3687

OK, so move via assembly and disassembly of microfilaments within the cytoplasm, and these can also be used to help the organism ingest food.3697

We used to just group all the amoebas together and just say "OK, these are amoebas".3713

But, it turns out that some of the amoebas are more closely related than others.3719

Others belong really to a different class. They are parasitic amoebas as well as rhizopods and just many different types.3723

So, just remember the important characteristic I would say to focus on is pseudopods.3739

OK, the next group that we are going to talk about are the forams.3746

These are found in both salt water and fresh water environments.3750

They are unicellular organisms, and they have a hard that is called...they are not actually called shells.3754

They are called tests. That is the actual name, but they are like shells in that they are hard and protective; and they contain calcium carbonate.3761

They also use pseudopods, but since they have a shell around them, these tests or shells contain pores.3773

And what happens is they can reach out their pseudopods, stick them out through these pores so that they can move and so that they can feed.3781

What is interesting about these organisms is that they have formed some very large sediments that have ended up forming into rock formations.3791

So, that is one thing that is notable about them. They reproduce asexually.3802

The final group we are going to talk about of animal-like protist on this page is going to be the radiolarians.3808

These are found in marine environments, and they have internal skeletons made of silica, so silica, I will say skeletons.3823

This is a very old group of organisms, and they go back to the Cambrian period.3833

And what is important about them because they have a very long history and are very abundant is that when their remains are found in rocks,3838

they can be used to help date the deposits there and give us information about the age of other3847

organisms that we are looking at in the areas that are being studied where these fossilized remains are.3858

OK, that covered the animal-like protist. The final group of protist that we are going to study are the fungus-like protist.3865

These are also heterotrophs. They do have cell walls, and they are often decomposers.3871

Like fungi, they reproduce via spores. You can see the similarities.3880

They are heterotrophs, decomposers. They have cell walls, and they reproduce through spores.3884

And in fact, at one time, some of the protist that I am going to talk about were classified as fungi.3890

However, they were removed from that class and classed as a separate group of organisms.3896

Protists include the slime modes and the water molds as well as couple other groups that we are going to talk about.3902

But, we are going to start out with the slime molds.3916

There are two types of slime molds, and the first is plasmodial slime molds; and the second is cellular slime molds.3919

The plasmodial slime molds are organisms that live in decaying logs or in plant or in moist soil, and they are very colorful.3935

So, you may have seen these. They can be just bright colors such as orange or yellow.3944

They are very colorful, found in decaying logs, plants, wet soil.3952

Their name plasmodial slime molds comes from the fact that they form a structure called a plasmodium.3962

Plasmodiums represent the feeding stage for these organisms, and they are actually multinucleated.3969

They are just a single structure with a lot of cytoplasm and then, many nuclei.3984

Cytoplasmic streaming occurs within this gigantic cell to allow nutrients to get dispersed through all that cytoplasm.3993

They do have pseudopods, which they use to grab food particles, and then, they ingest those through phagocytosis. As I said, this is the feeding stage.4006

Their life cycle involves the formation of stocks, and these stocks contain sporangia.4019

So, they form stocks with sporangia, and within the sporangia, haploid spores are formed.4027

When conditions are good in the environment, good for survival, these spores will germinate and release gametes.4047

There are actually two types of gametes. Some have flagella.4061

Others are what is known as amoeboid, so they have pseudopods; and the two types join together via fertilization.4066

A zygote forms and then, undergoes mitosis without cytokinesis, so we get fertilization; and then, the zygote forms.4077

And when mitosis occurs, but no cytokinesis, what you end up with is the plasmodium again.4091

Because now, since cytokinesis has not occurred, the cell membrane has not been divided up.4104

The cytoplasm has not been divided up, but the nucleus has been multiplied during mitosis.4108

So, you just get this big structure that consists of a lot of cytoplasm plus nuclei.4113

Again, that would be the feeding stage, and it would start all over where this organism is going to - with pseudopods - feed and then,4119

eventually, form stocks with sporangia on it, release spores that are haploid, form spores that are haploid, release gametes.4128

Fertilization will take place. The zygote is produced, mitosis with no cytokinesis to produce the plasmodium again.4139

You can see the similarities of fungi, these fruiting bodies that are the stocks with the sporangium on it, the fact that they release spores.4148

But, in terms of evolutionary history and common ancestry, these belong in a separate group.4157

The cellular slime molds have a feeding stage that does not consist of one gigantic cell like this, so this is an important way in which are they different.4162

The feeding stage consists of individual cells. However, these cells sometimes aggregate.4173

So, what can happen during the feeding stage is the cells release cyclic AMP, and this is a signal that causes these cells to come together to mast together.4191

The feeding stage is haploid. These cells are haploid.4204

The cellular slime molds produce both asexually and sexually.4214

During sexual reproduction, two individual haploid cells unite to form a diploid zygote.4219

The zygote goes through meiosis and then, some rounds of mitosis to form haploid amoebas, so that is sexual reproduction.4226

However, when there is bad conditions, then, these aggregate forms that I just talked about; and a stock forms.4234

On top of that is a body that contains haploid spores, and these spores are more resistant to bad conditions.4242

And when conditions are better, they will germinate.4251

So, we have talked both in this slide and previously about how the reproductive method can differ depending on conditions.4253

When there are bad conditions, the organism will switch to whichever method is going to give it the most protection.4260

We talked about a zygospore that forms. Now, we are talking about another spore that is more protected.4266

And then, these will not germinate until conditions get better.4272

The final type of fungus-like protist that we are going to talk about are the oomycetes. The oomycetes consist of several groups.4276

I already mentioned one of them above when I said the water molds.4286

There is also what is called white rust and downy mildews. These were also once considered fungi and have been reclassified as a separate group.4289

They are decomposers or parasites.4309

Some are decomposers. Some are parasites.4314

For example, you might see a water mold on a dead plant.4318

In terms of history, it was a water mold that was responsible for the Irish potato famine.4322

That potato famine destroyed crops in Ireland, and at that time, the Irish were very dependent on that crop for their nutrition.4328

This resulted in the death of about a million people as well as about another million or more4335

people emigrating and leaving Ireland because of the conditions there at the time.4343

So, you can see the human impact that these organisms can have,4350

causing disease directly in humans that we have talked about before like with malaria or causing disease in food sources.4355

The life cycle of these can include both sexual and asexual reproduction.4364

However, their cell walls actually contain cellulose like plants rather than chitin like fungi, so cell walls contain cellulose in these organisms.4369

OK, we have covered quite a few different organisms today.4378

So, try to focus on the important points about each one, and we are going to go ahead and do some review now.4381

Example one: how does alternation of generations differ from the other two types of sexual life cycles?4387

So, we talked about three types of sexual life cycles.4395

One in which the diploid stage...it is a diploid adult. The diploid stage is dominant.4397

And another when there is a haploid adult, the haploid stage is dominant and then, alternation of generations.4403

Although, every cycle includes a diploid and haploid stage, what is unique about alternation of generations4409

is that these cycles have a multicellular diploid stage and a multicellular haploid stage.4414

That is what makes alternation of generations different than the other two life cycles.4437

The other two life cycles do not have multicellular forms that are haploid and a multicellular form that is diploid, and we see this in some protist.4442

We also see it in plants.4450

Example two: match the following groups of protist to their descriptions: diatoms, green algae, euglenids and cellular slime molds.4453

Let's look for the diatoms first- flagellated photosynthetic mixotrophs with a pigmented eyespot.4464

Unicellular photosynthetic organisms that are commonly part of plankton. They have cell walls containing silica.4472

More closely related to plants than other groups of protist. Their cell walls contain cellulose, and they have chlorophyll A and B.4481

Release cyclic AMP, which acts as a signal for individual cells to aggregate. Asexual reproduction follows the formation of a stock.4488

So, starting with the diatoms, these are photosynthetic organisms, and I see that here and here.4497

And they do not contain an eyespot, so that is not correct.4503

Looking at B, they are unicellular. They are part of plankton, and they have cell walls containing silica in them.4509

B- diatoms match with B.4518

Green algae: well, green algae are photosynthetic, but they do not have a pigmented eyespot; so that is not correct.4522

More closely related to plants than other groups of protist- that is a correct statement.4531

Cell walls contain cellulose - true - and they have chlorophyll A and B.4535

That is accurate. This one is not.4540

They do not form a stock, so let's go with C.4542

Euglenids: one thing that just comes to my mind right away that is unique about them is this eyespot.4547

And they are flagellated photosynthetic mixotrophs with an eyespot, so A.4553

That leaves us with no. 4, which does fit with D- cellular slime molds can release cyclic AMP, which signals these cells to come together in a group.4559

They may eventually form a stock with spores and then, reproduce asexually once conditions are good, so B, C, A and D.4569

Example three: what are three structures that protist use for motility?4583

Well, we have seen examples of cilia.4590

Paramecium use cilia. They are type of ciliate.4596

Flagella: we saw that in the dinoflagellates, in Giardia, which is a diplomonad, in Trichomonas, so those all use flagella for motility.4600

Finally, pseudopods are used by amoebas for example, and these are cytoplasmic extensions.4609

OK, final question is label the following structures on a sketch of a Paramecium.4623

So, Parameciums are a type of ciliate, and we saw this sketch before.4630

And this is a type of ciliate, so oral groove, micronucleus, macronucleus, cilia and contractile vacuole.4637

Well, the micronucleus here is located next to the larger macronucleus, so micronucleus and here, macronucleus.4645

So, we took care of that one and that one.4661

Cilia: you can see cilia all along the outside of the cell and contractile vacuole. Well, either of these structures you could choose.4664

These are all different vacuoles, so contractile vacuole, or these could be food vacuoles.4680

It is a less specific term, but vacuoles within these protists carry a wide array of function: to remove extra water and waste, to digest food.4687

There are various vacuoles with many functions and the oral groove right here. water is swept in along this oral groove into an opening.4704

And then, food particles are digested, enter through phagocytosis and then, digested.4713

That concludes this lecture on the protist.4722

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