Chapter 27: Protists

Primary producers

- they are photosynthetic and form the base of aquatic food chains (in conjunction with the cyanobacteria we discussed in the previous chapter). -organisms that acquire their energy from sunlight and materials from nonliving sources.

Ciliates

-Alveolata -Unicellular -Parasetic -Move by cilia -Have two nuclei: macronucleus & micronucleus -Contain vesicles called alveoli that support the plasma membrane -In freshwater, marine, and wet soil environments

Apicomplexans

-Alveolata -Unicellular -Parasetic -Some move by amoebid motion -Contain vesicles called alveoli that support the plasma membrane -Responsible for several diseases: Species like Plamodium cause malaria and Toxoplasma is an important opportunistic pathogen in people infected with HIV

Dinoflagellates

-Alveolata -Unicellular -Photosynthetic -Primary producer -Cell wall of cellulose -Move by flagella -Contain vesicles called alveoli that support the plasma membrane -Marine and freshwater plankton -Some are bioluminescent -Responsible for harmful algal blooms

Protists

-Eukaryotes -Paraphyletic group -Extremely diverse

Euglenids

-Exacavata -Photosynthetic -Unicellular -No cell wall -Move by flagella -Excavated feeding groove on side of cell -Abundant in freshwater plankton -Has chloroplasts from unicellular green algae by the way of secondary endosymbiosis

WHO Malaria Fact Sheet

-In 2018, there were an estimated 228 million cases of malaria. -Malaria deaths reached 405,000 in 2018; 67% were children under 5 years of age. -The WHO African Region carries a disproportionately high share of the global malaria burden. In 2018, the region was home to 93% of malaria cases and 94% of malaria deaths. -Total funding for malaria control and elimination reached an estimated US$ 2.7 billion in 2018.

Endosymbiosis Theory

-Photosynthetic protists evolved chloroplasts via primary and secondary endosymbiosis.

Red algae

-Plantae -Unicellular, multicellular, or colonial -Primary producer -Has chloroplasts -Has cell walls composed of cellulose -Lack flagella -Agar developed from the cell walls of red algae

Green algae

-Plantae -Unicellular, multicellular, or colonial -Primary producer -Has chloroplasts -Has flagella -Has cell walls composed of cellulose -Most green algae are aquatic

Protist Motility

-Protists include motile and non-motile (sessile) species -Many protists move actively via amoeboid motion, flagella, or cilia

Why study protists?

-Some protists are pathogenic.

Brown algae

-Stramenopila -Multicellular -Primary producer -Has chloroplasts -Photosynthetic -Has cell wall composed of cellulose -Has flagella with hollow projections

Diatoms

-Stramenopila -Unicellular -Primary producer in salt/fresh water -Has chloroplasts -Has flagella with hollow projections -Photosynthetic -Silica in cell walls -Form ornate glass-like shells -Responsible for algal blooms

Water molds

-Stremenopila -Unicellular or multicellular -Decompose, some are parasetic -Has flagella that are covered with distinctive hollow "hairs" -Has cell wall composed of cellulose -Mature individuals are sessile -Parasetic Phytopthora infestans caused the Irish Potato famine.

Plantae

All members have cells containing chloroplasts with a double membrane (the result of primary endosymbiosis).

Life Cycles

Alternation of Generations -Major haploid and diploid phases -Haploid adult is the gametophyte -Diploid adult is the sporophyte

Which group of protists from Part II includes the parasites that cause malaria (Plasmodium) and toxoplasmosis (Toxoplasma)?

Apicomplexans

Endosymbiosis theory

Bacterial characteristics of mitochondria and chloroplasts -Circular genomes with prokaryotic-like sequences -Bacterial-like ribosomes -Replicate by binary fission -Size

There are also human protist pathogens - trypanosoma and malaria.

Both of these are serious diseases that can be fatal if untreated, and both are spread via insect bites (the protists have complex life cycles with two hosts - human and insect)

Both mitochondria and chloroplasts also retain a lot of bacterial characteristics. The most convincing involves their DNA and ribosomes. Both organelles actually have their own genomes and can produce some of their own proteins (separate DNA from the main chromosome). When scientists sequenced those genes they discovered that they are very closely related to those of bacteria, not to eukaryotic genes.

Both organelles also contain their own ribosomes, which are structurally similar to bacterial-type ribosomes rather than those of eukaryotes. Both organelles replicate via a process that resembles binary fission and their size is also comparable to bacteria.

Which group of protists from Part II forms the large kelp forests that are common off the Pacific coast of North America?

Brown algae

Which group of protists from Part II have two nuclei in each cell, designated the macronucleus and micronucleus?

Ciliates

Which group of protists have "glass-like" cell walls?

Diatoms

In regard to morphology, some protists have cells walls while other do not. For those that do, there's a variety of materials that are used to produce this structure.

Diatoms use silica (silicon dioxide), a mineral that's similar to glass. Others produce shells with a different mineral called calcium carbonate, the same thing found in chalk and limestone. Others may use organic materials like cellulose (same polysaccharide found in plant cell walls).

Which group of protists swim in a whirling or spinning motion due to the position of their two flagella?

Dinoflagellates

Which groups of protists are capable of producing harmful algal blooms that may release toxins?

Dinoflagellates and diatoms

Life Cycles

Diploid Life Cycles -Dominated by diploid phase

Why study protists?

Ecologically important -Primary producers -Plankton and seaweeds

Why study protists?

Economically important

This explanation for the origin of mitochondria and chloroplasts is called

Endosymbiosis Theory. It was proposed as far back as the early 1900s but didn't gain scientific acceptance until ~1980s when scientists gathered additional genetic and molecular evidence to support it.

Amoebozoa

Engulf food; move with amoeboid motion via large pseudopodia; no cell wall present.

Protist Morphology

Evolution of eukaryotic structures -Nucleus -Endoplasmic reticulum

True or False The photosynthetic protists make up a single monophyletic group.

False If you look at diagram, you can see that photosynthetic protists are all over the place and scattered, like dinoflagellates, diatoms, brown algae, and euglenids. They do not make a single monophyletic branch.

True or False The motile protists make up a single monophyletic group.

False The motile protists do not make up a single monophyletic group. There are lobose amoebae, ciliates, and dinoflagelletes as examples on diagram.

For this diploid life cycle, meiosis occurs on the adult organism. Genetically distinct haploid gametes are produced from the diploid adult.

For protists, those gametes are then typically released to the environment where they can combine with another to form a new zygote (new organism) and the process repeats itself.

The haploid adult phase is called the gametophyte, while the diploid adult is called the sporophyte.

Gametophytes will produce gametes, while sporophytes produce spores, a different type of reproductive cell that does NOT fuse with another cell to form an adult.

Which group of protists from Part II are the closest relatives of land plants?

Green algae

There are several groups of protists. A list of them with their common names:

Green algae Red algae Brown Algae Diatoms Water molds Ciliates Dinoflagellates Apicomplexans Euglenids

Which groups of protists from Part II are important primary producers in aquatic ecosystems? (Hint - there's more than one answer for this one).

Green algae, red algae, brown algae, diatoms, dinoflagellates, and some euglenids.

Stramenopila

Group name comes from their distinctive flagella, which are covered with short hairs.

Life Cycles

Haploid Life Cycle -Dominated by haploid phase

In addition to the parasites, some protists can cause disease by producing toxins.

Harmful algal blooms can be composed of both protist and certain cyanobacterial species.

The only haploid phase of this life cycle are the gametes. Since everything else is diploid, and the adult organism is diploid, we call this the diploid life cycle.

Here's an illustration (LOOK AT HANDOUT) of this type of cycle from the protist group (a diatom in this example). Note that in this species both sexual and asexual reproduction are possible, with asexual cells produced solely via mitosis.

Eventually, the bacteria lost the ability to survive independently of the host and became permanently incorporated into the host species, being passed down over generations and eventually becoming the mitochondria that we know today.

How do we know this happened? First think about the morphology of the mitochondria. It has a double membrane (as do chloroplasts). This supports the idea that it started out as a bacterium engulfed by another cell. The inner membrane represents the original bacterial cell membrane while the outer membrane came from the host cell.

We'll start with fertilization again. (LOOK AT LECTURE FOR ILLUSTRATION MADE) Two haploid gametes fuse to form a diploid zygote. (Again, this bit is the same for all three cycles).

In alternation of generations, the diploid zygote develops into a diploid adult via mitosis. This diploid adult is called the sporophyte. Once mature, the sporophyte will produce spores via the process of meiosis. So again, meiosis is occurring at a different part of the cycle than what we've seen in the previous two, and gametes are not produces via meiosis, the spores are.

The first thing to note about protist reproduction is that many can reproduce via asexual as well as sexual reproduction. It depends on the species and environmental conditions as to which strategy is more likely to occur.

In both cases, new organisms are being made.

While mitochondria evolved from aerobic bacteria, chloroplasts evolved from the photosynthetic cyanobacteria (their DNA is very similar).

In the case of chloroplasts, this process of endosymbiotic engulfment actually happened more than once. Some protists gained their chloroplasts via primary endosymbiosis, which was the engulfment of a cyanobacterium by a heterotrophic ancestral eukaryote. The cyanobacterium was retained and become the chloroplast, allowing the cell to become autotrophic and produce its own food.

The third and final cycle is called alternation of generations.

In this cycle there are two major phases - one haploid and one diploid, with "adult" versions of each phase.

Sexual reproduction involves the formation of gametes and the process meiosis.

It contributes to greater genetic diversity in the population and is only seen in eukaryotes (prokaryotes do not undergo sexual reproduction). While sexual reproduction typically takes more energy, the greater genetic diversity is advantageous to the population, particularly in changing environments.

Modern classifications of eukaryotes divide this Domain into seven different lineages.

Learn those lineages and their characteristics from the worksheet given. As well as learn some of the common protistan organisms. With our lecture we'll focus on the major themes of diversity and eukaryotic evolution, and we'll begin by discussing why protists are an important group to study

Here are two alternation of generations examples. In some cases the two phases can look identical, as in the top picture. In other species, the gametophyte phase may look very different from the sporophyte. (LOOK AT LECTURE HANDOUT)

Like some protists, plants also undergo an alternation of generations life cycle. Learning these cycles here is very important to understanding plant reproduction in our next chapter. Fungi undergo a modified haploid life cycle, so that one will also be important as we discuss that group later. I recommend that you practice drawing the cycles, first using your text/notes and then from memory. The more comfortable you get with these cycles, the easier the plant and fungal chapters will be. Study this section in your textbook and complete the practice worksheet, and let me know if you have questions.

Protists also differ in their cellularity.

Many are single-celled, like this Euglena or organisms like amoebas and paramecia. Others are large and multicellular, like Fucus and other seaweeds. Multicellular organisms contain specialized cell types and tissues that perform different functions, and each cell is dependent on the others for survival.

Endosymbiosis occurs when one species lives inside another, and we typically use it to describe a cell living inside of another cell.

Many endosymbiotic species exist today. This picture shows bacterial endosymbionts living inside of an amoeba. One of the paramecia you'll study in lab also contains endosymbiotic algae. These relationships evolve when a host cell either engulfs or is invaded by a smaller cell of a different species, and that smaller cell stays alive. The two cells form a partnership, often mutualistic, and when the host cell reproduces it may pass its endosymbiont down to its offspring, passing the relationship to the next generation. Some modern day bacteria only exist as endosymbionts inside of other cells; they can't live independently

Protist Morphology

Many possess cell walls or other structural supports

Now for some good things about protists... Protists have very important roles within the ecosystem.

Many protists are what's called primary producers

Endosymbiosis Theory

Mitochondria and chloroplasts evolved as prokaryotic endosymbionts.

The third feeding strategy are those that ingest their food (these are like us!). These organisms take in whole organisms or parts of other organisms and digest them internally.

Most of these protists are single-celled, so they ingest via phagocytosis - the engulfment of a cell or cell fragments by another cell. These protists are also typically motile - they are hunters so they need to move around to find their food. They include amoebas, ciliates and some euglenids.

Protist Reproduction

Most protists can reproduce asexually -Daughter cells/organisms genetically identical to parent Some protists also undergo sexual reproduction -Involves meiosis & gamete fusion -Produces more genetic diversity

Can all photosynthetic protists be placed in a single monophyletic group?

No

It depends on the species as the how long each adult phase lives. Some species may have a long-lived sporophyte and short-lived gametophyte or vice versa, so they may spend equal time in each. Sporophytes will always be diploid and gametophytes are always haploid, and sporophytes produce spores, while gametophytes produce gametes.

Note that in each of these cycles, meiosis always reduces the chromosome # from diploid to haploid (and this is also where genetically unique cells are produced). Mitotic division occurs at any place we go from haploid to haploid or diploid to diploid.

Here's a diagram (LOOK AT LECTURE HANDOUT) of the haploid cycle, illustrated with a dinoflagellate. Again you can see that asexual reproduction can also occur.

Note that in this cycle, the only diploid phase is the zygote. Everything else is haploid. That's why we call this the haploid life cycle.

Phytoplankton are photosynthetic organisms - the primary producers.

Other protists are part of the zooplankton - primary consumers that eat the phytoplankton. Those small zooplankton then serve as food sources for fish and other animals (secondary consumers).

Much of the plankton within marine environments are protists.

Plankton are small, often microscopic organisms that drift with ocean currents (the word plankton is Greek for "drifter" or "wanderer").

There are seven major eukaryotic lineages that comprise of protists:

Plantae Stramenopila Alveolata Excavata Amoebozoa Rhizaria Opisthokonta

Trypanosoma species cause sleeping sickness, which is spread by tsetse flies in Africa.

Plasmodium species cause malaria, which is spread by mosquitos and is common in Africa, Central & South America, southern Asia and other tropical and subtropical climates.

Other protists gained their chloroplasts via secondary endosymbiosis, which is the engulfment o a photosynthetic protist by another cell.

Primary endosymbiosis resulted in a chloroplast with a double membrane (inner membrane from cyanobacteria and outer membrane from host cell). Chloroplasts that have evolved via secondary endosymbiosis often have three or four membranes.

Which photosynthetic group of protists contain a pigment called phycoerythrin, which gives them a reddish color?

Red algae

Which of the following groups of protists belong to the same lineage as land plants, and contain chloroplasts with a double membrane?

Red algae and green algae

Which protists obtained chloroplasts via primary endosymbiosis? by secondary endosymbiosis? What evidence do scientists have to support those answers?

Red algae and green algae evolved by engulfing cyanobacterium (primary endosymbiosis). Dinoflagellates, apicomplexans, and stremenopiles gained chloroplasts by engulfing red alga (secondary endosymbiosis) while euglenids and chlorarachionphytes gained theirs by engulfing a green alga (secondary endosymbiosis). The evidence is that cyanobacterium are autotrophic and produce their own food. Other protists gained their chloroplasts via secondary endosymbiosis, which is the engulfment of a photosynthetic protist by another cell. Primary endosymbiosis resulted in a chloroplast with a double membrane cyanobacteria and outer membrane from host. Chloroplasts that have evolved via secondary endosymbiosis often have three or four membranes.

Opisthokonta

Reproductive cells contain a single rear flagellum; this lineage includes fungi and animals.

Rhizaria

Similar to amoebas but pseudopodia are more slender; cells are covered with a shell-like structure composed of silica or calcium carbonate.

Protist Morphology

Single-celled, colonial, or multicellular

Protists were the first eukaryotes to evolve, and they evolved from the prokaryotes whose cells lack nuclei and most organelles.

So how did these structures come about? For the nucleus and endoplasmic reticulum, the current hypothesis is that these structures developed as infoldings of the plasma membrane. Infolding of the membrane is not unusual in prokaryotes, and we can actually see some internal folding within certain groups of prokaryotes today (next slide)...Keep in mind that all internal membranes are phospholipid bilayers - the same structure that composes the plasma membrane.

For example, some aerobic prokaryotes have folded respiratory membranes that allow more surface area for cellular respiration.

Some photosynthetic prokaryotes have internal thylakoid membranes.

Protist Feeding Strategies

Some protists are heterotrophic via absorption -Saprotrophs feed on dead matter -water molds, apicomplexan parasites, etc.

Protist Feeding Strategies

Some protists are heterotrophic via ingestion -Phagocytosis - engulfment of cell or cell fragments by another cell -Amoebas, ciliates, some euglenids, etc.

Like with feeding strategies, there's also a lot of diversity in protist motility (movement).

Some protists are motile (they can move/swim) and other are not. Nonmotile species are also called sessile. SESSILE

Protist Feeding Strategies

Some protists are photosynthetic -Algae (green, red, brown), diatoms, some dinoflagellates, some euglenids Primary producers in aquatic ecosystems

Why study protists?

Some protists produce toxins -Harmful algal blooms

Protist Feeding Strategies

Some species have moth-like structures

That haploid adult is now the mature organism. It will produce gametes, but via the process of mitosis, not meiosis. (LOOK AT VIDEO FOR REVIEW AND ILLUSTRATION SHE MAKES)

Students typically associate meiosis with gamete production - it's the type of cell division we use to produce eggs and sperm. That's how we teach it in 1107 because it's the life cycle we're most familiar with (it's what we and other animals do). This is only true of the diploid life cycle though. For many other organisms, gametes are produced via mitosis and the meiotic division occurs at a different stage of the life. This haploid cycle is also sometimes called the zygotic meiosis cycle, since the zygote divides via meiosis.

According to endosymbiosis theory, the organelles we know as mitochondria and chloroplasts were once bacterial endosymbionts. In the case of mitochondria, these organelles evolved when an ancestral anaerobic eukaryote (an early protist) engulfed an aerobic bacterium.

The bacterium survived and established a mutualistic endosymbiotic relationship with the host cell. The bacterium benefited by gaining access to the host cell's food and the host cell benefited by being able to use some of the ATP produced by the bacteria. Remember that aerobic metabolism is more energy efficient than anaerobic (it produces more ATP), so the addition of the bacteria would have given the host cell more energy.

Some protists are colonial, which is a state sort of in-between the other two.

The cells of the colony benefit from living as a group and often form physical connections with each other, but they are still considered independent cells and will usually survive if separated from the group. Multicellularity is thought to have evolved from colonial relationships as cells became more specialized and dependent on each other.

Eukaryotic cells evolved from prokaryotes ~2.5 billion years ago, and one of the topics we'll discuss with this lecture is the evolution of this cell type.

The common name of the organism we are studying is protist.

For each of these cycles I like to start by drawing the process of fertilization, because this portion will be the same for each cycle. During fertilization two haploid gametes fuse together to form a diploid zygote. We typically think of those gametes as egg & sperm, but we don't always call them that. Gametes are defined as haploid reproductive cells that fuse together to form a zygote, and this process is called fertilization.

The diploid zygote is the first cell of the new organism. In the diploid life cycle, this zygote grows and develops into a diploid adult organism. If the adult is multicellular this process occurs via mitosis. That adult organism will then produce gametes via the process of meiosis. Recall that meiosis is a reduction division - it always involves the reduction of chromosome number as the homologous pairs of chromosomes are divided. Meiosis also introduces genetic diversity via processes like gene recombination. Each cell produced via meiosis will contain half the # of chromosomes as the parent cell and will be genetically unique - different from its parent and different from the other daughter cells.

Like the prokaryotes we discussed last week, some protist species are pathogenic - they cause disease in animals and other organisms.

The famous Irish potato famine of the 1800s was caused by the species Phytophthora infestans. This is a plant pathogen that causes potato blight.

Haploid life cycles are dominated by the haploid phase; the adult organism will contain haploid cells (only one version of each chromosome present).

The fertilization process is the same here as in the diploid cycle. Two haploid gametes fuse to form a diploid zygote. In this cycle, that diploid zygote does not develop into the adult. Instead, the zygote undergoes meiosis to produce genetically distinct haploid daughter cells. Each daughter cell is then capable of developing into the adult organism (via mitosis if the adult is multicellular).

Since spores are produced via meiosis, they are haploid and genetically distinct from each other. Each spore can then develop into a haploid adult via mitosis. (Spores are defined as haploid reproductive cells that develop into an adult without fusing with another cell. They are differentiated from gametes, which are haploid cells that DO fuse with another via fertilization).

The haploid adult phase that develops from the spore is called the gametophyte. That mature gametophyte can then produce gametes via mitosis.

The reason there is much diversity in this group is because they are not a single monophyletic lineage.

The organisms that we called protists include any eukaryote that isn't classified as a plant, fungus, or animal.

Amoeboid motion occurs in amoebas and looks like a crawling motion. The cytoskeletal filaments beneath the membrane interact to push fingers of cytoplasm forward - these finger-like projections are called pseudopodia ("false feet"). The cell crawls through its environment in search of food or a better environment.

The pseudopodia are also used for feeding - they wrap around food particles and the cell then engulfs the food via phagocytosis.

The phylogenetic tree (in lecture notes) shows the major eukaryotic lineages; all of the orange branches (everything except plants, fungi and animals) are protists.

The term that we use for this type of grouping is paraphyletic - a common ancestor and some, but not all, of the descendants.

These images show two kinds of protists that are common in these blooms - dinoflagellates and diatoms. Not all species in these groups produce toxins, but those that do can cause neurological and respiratory issues if the toxins are ingested or breathed in.

The toxins can become concentrated in oysters, mussels and other shellfish, producing shellfish poisoning

There are three general patterns of sexual life cycles in eukaryotes, and this is where things get a bit complex.

The typical animal life cycle that we're familiar with is only one pattern of sexual reproduction. We'll review that one first and then describe the other two.

Some of these species have mouth-like structures, like the oral groove on Paramecia and Stentor.

There are some video of these guys feeding on d2l so you can see these structures in action.

Feeding strategies also vary among the protists. As we mentioned earlier, many protists are photosynthetic and are important primary producers.

These organisms include the algae, diatoms and some dinoflagellates and euglenids.

The producers also include larger multicellular seaweeds like kelp.

These species resemble plants and often form huge underwater forests that support a huge diversity of other organisms. (see video on d2l).

For our next two eukaryotic structures: mitochondria and chloroplasts.

These two organelles actually started out as bacteria - prokaryotic cells like the ones we see here that were engulfed by an ancestral eukaryote and became part of its structure. So inside each of our cells are organelles were once independent bacteria! Mitochondria evolved from aerobic prokaryotes and chloroplasts evolved from cyanobacteria.

The organisms in this chapter will be from eukaryotes.

They have larger and more complex cells than prokaryotes, with nuclei and abundant organelle.

Other protists are heterotrophic, needing to take in food from other organisms. Some of these feed via absorption.

They secrete digestive enzymes into their environment and externally digest their food before absorbing the nutrients.

These blooms occur when nutrient levels and temperatures create perfect conditions for the growth of these organisms.

This excess growth can sometimes be seen as "red tides" due to the pigments present in the algae. In addition to causing discoloration and odors, HABs can also produce various toxins that can harm wildlife and humans.

The "animal-type" sexual life cycle is called the diploid life cycle.

This is because this cycle is dominated by the diploid phase of the organism. I'm going to draw this cycle and review the major phases with you, including the ploidy of each phase. (LOOK AT LECTURE NOTES FROM VIDEO FOR REFERENCE)

Agar, which is used to make culture plates for studying microorganisms, is also extracted from seaweeds.

This picture on the left (from lecture) shows diatomaceous earth. Diatomaceous earth is essentially fossilized diatoms. Diatoms are a group of protists that have silica in their cell walls - it's similar to glass. There are so many diatoms in the ocean that as these organisms die, their remains accumulate on the seafloor and can eventually form a type of sedimentary rock that we call diatomaceous earth. There are multiple uses for this product but it's best known as a nontoxic insecticide. Because it's composed of small pieces of silica, it's essentially like tiny shards of glass. When insects crawl across it their protective exoskeleton is damaged which causes them to dry out and die.

With asexual reproduction, the new organisms are genetically identical to the parent.

This process can occur via mitosis & cytokinesis as one cell divides to produce two new cells. It can also occur via fragmentation, which is when a piece of the parent organism breaks off and forms a new individual.

Excavata

Unicellular, with an excavated feeding groove; some groups lack mitochondria.

Alveolata

Unicellular, with small sacs called alveoli under the plasma membrane.

Protists are also important for us economically, as food and other resources.

Various seaweeds are used for food and have high nutritional value - sushi, for instance is wrapped with seaweed. Many seaweeds also produce a gel-like polysaccharide called carrageenan that is used to improve the texture/flavor of dairy products like ice cream and milk.

Which group of protists from Part II includes the parasites that caused the Irish potato famine (Phytophthora)?

Water molds

Many of these species are saprotrophic, which means that they feed on dead organisms and are important decomposers within the food chain. DECOMPOSERS

Water molds and apicomplexan parasites are examples of absorptive feeders.

The diagram on the right depicts this hypothesis. Image 1 shows the ancestral eukaryote, with a chromosome but no nuclear membrane yet. Image 2 shows infoldings beginning to form from the membrane, and Image 3 shows the final state, where those infoldings have moved into the center of the cells and converged around the DNA, forming the nucleus and well as the endoplasmic reticulum (which is still connected to the nuclear membrane in our cells today). These new structures provided an advantage for these early eukaryotes - the compartmentalization of the cells allowed them to grow larger, protected the chromosome and increased the variety of proteins that could be produced from the genes.

When we think of a typical eukaryotic cell today, we imagine a cell with a single nucleus. In reality there's a lot of diversity in nuclear structure within the protist group. Giardia for instance has two identical nuclei that look like eyespots on the cell (these are parasitic protists that causes diarrhea) Ciliates like paramecia also have two nuclei but one is larger than the other - a macronucleus and micronucleus.

When a mosquito bites an infected person, the Plasmodium gametes enter the mosquito and undergo fertilization to produce new zygotes. Those new organisms are then passed onto the next human host through the mosquito's saliva when it bites again. Once in the human the parasites infect the liver and red blood cells producing fever, headaches, fatigue and other symptoms. In severe cases this leads to kidney failure, coma and death.

You don't need to know the details of this cycle, but I want you to be aware of the importance of mosquitos in spreading disease. Controlling mosquito populations is main target of malarial prevention/control programs.

Other protists move via cilia or flagella.

a. Each of these structures is part of the cytoskeleton that projects out from the cells. Cilia are shorter and there are many per cell, while flagella are longer and there are usually only one 1-2 per cell. The ciliate groups, which includes Paramecia, swim via cilia. A variety of diverse groups swim via flagella.

For those that do move, there are three main types of movement:

amoeboid motion, or movement via flagella or cilia.

According to endosymbiosis theory, what is the origin of eukaryotic mitochondria? a. cyanobacterium b. aerobic bacterium c. infolding of the eukaryotic plasma membrane

b. aerobic bacterium The engulfment of the cyanobacterium would be the evolution of the chloroplast. The infolding of the eukaryotic plasma membrane is the process that we think lead to the development of the nuclear membrane and endoplasmic reticulum.

Which of the following statements are correct? a. All protists have cell walls b. All protists are unicellular c. All protists are photosynthetic d. All protists are motile e. None of the above

e. None of the above

The life cycle for many of these pathogens involve TWO HOSTS-

for Plasmodium those hosts are humans and mosquitos, which is why mosquitos spread the disease.

Protists

includes algae, like the brown kelp in the image shown, as well as many common pond water organisms, plankton, various parasites and more. -They are a very diverse group

Saprotrophic

is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter.

We're going to spend a little more time discussing malaria, because it is one of the most common infectious disease in the world. In 2018 there was estimated 228 million cases with over 400,000 deaths, more than half of which were children.

n. Over 90% of cases and deaths occur in Africa, where they have both a species of mosquito that is particularly effective at transmitting the disease and the species of Plasmodium that leads to more severe cases. Many of the countries affected are also poor and lack the resources of wealthier nations to combat the spread and provide effective treatment. Organizations like the WHO are continually fighting for better control, but factors like insecticide resistance in mosquitos and drug - resistant strains of the parasite have made it more difficult. (Just like bacteria that develop antibiotic resistance, many protistan parasites have also developed resistance to the drugs we use to fight them).

Primary endosymbiosis

occurs when a eukaryotic cell engulfs and absorbs a prokaryotic cell, such as a smaller cell that undergoes photosynthesis (eg. cyanobacteria).

Secondary endosymbiosis

occurs when a eukaryotic cell engulfs and absorbs another eukaryotic cell.

The endosymbiotic theory

states that some of the organelles in eukaryotic cells were once prokaryotic microbes.

Endosymbiosis Theory explains

that mitochondria and chloroplasts evolved as prokaryotic endosymbionts. We defined the term symbiosis earlier - two organisms living in a close physical relationship.

Phagocytosis

the ingestion of bacteria or other material by phagocytes and amoeboid protozoans.

Plankton

the small and microscopic organisms drifting or floating in the sea or fresh water, consisting chiefly of diatoms, protozoans, small crustaceans, and the eggs and larval stages of larger animals. Many animals are adapted to feed on plankton, especially by filtering the water.