27. Protists

Protist Lineages

Slime Moulds - Cellular

No. Dinoflagellates are infamous for red tides.

No. The answer is a type of algae, but not golden algae.

No. The answer is a type of algae, but not green algae.

No. Diatoms have cell walls composed of silica, and they do not contain algin.

Algin is used as a thickening agent.

Which of the following organisms is commercially harvested to extract algin from their cell walls?

Which of the following members of the SAR supergroup is incorrectly paired with its clade?
a. stramenopiles—brown algae
b. alveolates—parasites such as Plasmodium
c. alveolates—dinoflagellates
d. Rhizaria—diatoms

Suppose a friend says that we don’t need to worry about the rising temperatures associated with global climate change. She claims that increased temperatures will make planktonic algae grow faster and that carbon dioxide (CO2) will be removed from the atmosphere faster. According to her, this carbon will be buried at the bottom of the ocean in calcium carbonate shells. As a result, the amount of carbon dioxide in the atmosphere will decrease and global warming will decline. Comment.

Ciliates

No. Chlamydomonas is an example of a single-celled green alga.

No. Laminaria is a brown alga, which in Japan is used in soups.

No. Entamoeba is a parasite that infects all classes of vertebrates as well as some invertebrates.

No. Dictyostelium discoideum is a common cellular slime mold found on forest floors.

The answer is a type of stramenopile.

__________ is a protist that causes late blight of potatoes and was responsible for the Irish potato famine of the 19th century.

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Develop simple experiments to test whether Physarum prefers (1) brightly lit or dark environments; (2) dry or moist conditions; (3) oats or sugar as a food source.

Protists - Unikonta | BIALIGY.com

Protists - SAR Clade III | BIALIGY.com

Protists

Consider the following:

Plasmodium has an unusual organelle called an apicoplast. Recent research has shown that apicoplasts are derived from chloroplasts via secondary endosymbiosis and have a large number of genes related to chloroplast DNA.

Glyphosate is one of the most widely used herbicides. It works by poisoning an enzyme located in chloroplasts.

Biologists are testing the hypothesis that glyphosate could be used as an antimalarial drug in humans.

How are these observations connected?

No. Their cell walls are composed of cellulose and gel-forming polysaccharides that help cushion them against wave agitation and reduce drying when they are exposed.

Absorbing iodine and carbon dioxide from seawater

No. All parts of seaweeds accomplish these functions.

How deeply does sunlight penetrate water?

What is the purpose of the "floats" in some brown algae?

No. Dinoflagellates do not fit this description.

No. Euglenoids do not fit this description.

No. Ciliates do not fit this description.

Think about the type of protist that causes malaria.

Which of these groups includes parasitic unicellular organisms with a complex of organelles specialized for penetrating host cells and tissues?

How can dinoflagellates be harmful to humans?
a. They are transmitted by mosquitoes and cause malaria.
b. They produce toxins that can be absorbed by clams and other shellfish which, when eaten by people, can lead to paralytic shellfish poisoning.
c. They cause amoebic dysentery which leads to severe diarrhea and dehydration.
d. They are transmitted by tsetse flies and cause “sleeping sickness.”

The most important primary producers in marine ecosystems are                .

Short Video: Euglena

Apicomplexans

Protists - SAR Clade II | BIALIGY.com

No. Diatoms are not responsible for red tides.

No. Radiolarians are not responsible for red tides.

No. Euglenids are not responsible for red tides.

The red color comes from plastids within the organism.

Which organisms are capable of producing a "red tide"?

they have life cycles with both sexual and asexual stages

No. Many protists from many groups have sexual and asexual stages.

No. Many protists in other groups are also parasitic.

Both the first and third responses are correct.

No. Apicomplexans are placed in the SAR clade on the basis of a plastid that appears to be of red algal origin.

the apicoplast, a modified plastid, appears to be of red algal origin

Remember the rather controversial characteristic that is found in many members of the SAR clade.

Apicomplexans are currently assigned to the SAR clade because __________.

their red pigments readily absorb red light

their cell walls are adapted to withstand bright light

No. The deeper the water, the less the light.

they grow long stalks with floats on the ends to hold the blades near the surface

No. The answer has to do with the type of light they can absorb.

No. Only one of the other choices is correct.

their photosynthetic pigments efficiently absorb blue and green light

Consider which of the choices would promote survival in deep waters.

Many species of red algae are adapted to deeper water due to the fact that __________.

The text claims that the evolutionary history of protists can be understood as a series of morphological innovations that established seven distinct lineages, each of which subsequently diversified based on innovative ways of feeding, moving, and reproducing. Explain how the Alveolata support this claim.

Short Video: Paramecium Cilia

No. There are similarities between brown algae and land plants, but the similarities evolved independently (they are analogous).

No. Plants are not as closely related to red algae as they are to another type of algae.

No. Golden algae are stramenopiles and are not closely related to plants.

Colors may be helpful here.

Which of the following groups of algae is/are most closely related to land plants?

It does not account for "amitochondriate" protists.

No. Protists with missing or reduced mitochondria can be classified using this scheme.

It does not take into account the importance of endosymbiosis.

No. In fact, some organisms are grouped according to the hypothesis that they all descended from an organism that engulfed an endosymbiont.

It does not explain the extra membranes found in some plastids.

No. The extra membranes found in some plastids are evidence for endosymbiosis, which is taken into account in this classification scheme.

It postulates that photosynthetic protists arose by way of endosymbiosis.

No. This is not a weakness of this hypothesis. There is abundant evidence that photosynthetic protists arose by endosymbiosis.

It shows all four supergroups diverging simultaneously from a common ancestor.

Review current classification of protists, and consider basic taxonomic principles.

Which of the following is one of the main weaknesses of the proposed classification scheme in which all eukaryotes are divided into four supergroups?

Ciliates | Animal Like Protists | Kingdom Protista

Stramenopila and Alveolata

Short Video: Amoeba Pseudopodia

The distinct cells that make up the plasmodium do not cooperate, so they do not represent a truly multicellular organism.

No. Consider the characteristics of the membrane and nuclei to figure out the answer.

Plasmodial slime molds are not able to reproduce sexually; therefore, they are not truly multicellular.

Multicellular organisms are seen only in the kingdoms Animalia and Plantae.

The nuclei found in the plasmodium of a plasmodial slime mold are diploid.

No. The ploidy of a nucleus does not, by itself, provide a sufficient basis for distinguishing between unicellular and multicellular organisms.

The plasmodium is undivided by membranes and contains many diploid nuclei; therefore, it is not technically multicellular.

Contrast multicellular with multinucleate.

In lab class, a plasmodial slime mold is used as a demonstration organism. One of the students does not understand why this organism is not considered multicellular. How would you explain it to her?

Protists - SAR Clade I | BIALIGY.com

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Which of the following best describes movement in Physarum?
a. Cilia propel the slime mold.
b. Flagella propel the slime mold.
c. The slime mold moves by amoeboid motion.
d. The slime mold moves by gliding motility.

Which pair of protists has support structures composed of silica?
a. dinoflagellates and diatoms
b. diatoms and radiolarians
c. radiolarians and forams
d. forams and amoebozoans

Animation: Life Cycle of a Malaria Parasite

No. This is not characteristic of diatoms.

No. This is not characteristic of dinoflagellates.

No. This is not characteristic of euglenids.

No. This is not characteristic of apicomplexans.

Think about sexual reproduction in Paramecia.

Which of these groups is characterized by cells that have more than one nucleus?

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Propose an experiment that would test whether the coating of extracellular slime changed the speed at which the slime mold moved across the substrate.

Which group is incorrectly paired with its description?
a. diatoms—important producers in aquatic communities
b. red algae—eukaryotes that acquired plastids by secondary endosymbiosis
c. apicomplexans—unicellular parasites with intricate life cycles
d. diplomonads—unicellular eukaryotes with modified mitochondria

Rhizarians and Amoebozoa

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Researchers have proposed that slime molds could be used to help to plan the paths of future roadways and railways. Justify this statement.

Protists - Excavata II | BIALIGY.com

Slime Moulds - Acellular

According to the phylogeny presented in this chapter, which protists are in the same eukaryotic supergroup as plants?
a. green algae
b. dinoflagellates
c. red algae
d. both A and C

They reproduce so fast that they can compensate for the death rate caused by the immune system.

No. They manage to evade the immune system.

They live only in the cerebrospinal fluid, where the immune system can't reach them.

No. They have other methods of evading the immune system.

The molecular composition of their surface changes continually.

What is one thing the immune system relies on to identify pathogens?

How do trypanosomes withstand the attack of a host's immune system?

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Does an organism without a brain have the ability to use an externalized “memory”—a spatial “slime map” that the organism uses to avoid moving to regions where it has been before? Researchers addressed this question by placing a U-shaped trap between Physarum and its food (see diagram that follows). Twenty-three out of 24 slime molds reached the food when plain agar was used as the growth substrate. However, when the agar was coated with extracellular slime, only 8 of 24 found the food. The mean time in hours that it took the successful slime molds to reach the food when placed on plain agar or agar pre-coated with extracellular slime was compared (P=0.012). Use the P value provided to determine if the difference is significant or not. What conclusion can be drawn from the graph shown here? <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/e7ecb77d5a0cae57-1677306736177.jpg" style="width: 300px;">

Protists - SAR Clade IV | BIALIGY.com

What is An Amoeba | Biology | Extraclass.com

Short Video: Stentor Ciliate Movement

No. The fossilized tests of forams do make up a large part of marine sediment, but they do not accumulate in an ooze.

The gel-forming polysaccharides secreted by brown and red algae

No. The tests of radiolarians make up this ooze.

No. Although plasmodial slime molds do form colonies, they would not be found on the seafloor.

It consists largely of silica, which may explain why it is not generally consumed by other organisms.

On some areas of the seafloor, one could observe an "ooze" that is hundreds of meters thick. What creates this ooze?

Reproduction | Ciliate Protozoans | Paramecium

Based on the phylogenetic tree in Figure 28.2, which of the following statements is correct?
a. The most recent common ancestor of Excavata is older than that of SAR.
b. The most recent common ancestor of SAR is older than that of Unikonta.
c. The most basal (first to diverge) eukaryotic supergroup cannot be determined.
d. Excavata is the most basal eukaryotic supergroup.

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Physarum is a plasmodial slime mold, whereas Dictyostelum is a cellular slime mold. Compare and contrast movement by the migrating slug stage of Dictyostelium to the plasmodial stage of Physarum.

Diatoms release large amounts of methane, a greenhouse gas, into the atmosphere.

Diatoms release large amounts of carbon dioxide, a greenhouse gas, into the atmosphere.

No. Diatoms do release some carbon dioxide during cellular respiration, but they also remove carbon dioxide from the atmosphere during photosynthesis.

During a bloom, diatom populations increase rapidly, providing many more photosynthetic organisms to the plankton population.

No. Although the increase in photosynthesizers will remove more carbon dioxide from the atmosphere, predator populations are likely to increase as well. When the predators eat the diatoms, they return around 90% of the carbon to the atmosphere as carbon dioxide.

Diatomaceous earth can be used to filter carbon dioxide from the atmosphere.

No. Diatomaceous earth is an effective filter, but not of carbon dioxide.

During a bloom, diatom populations may increase rapidly. If many diatoms die and sink to the bottom without being eaten, they effectively pump carbon dioxide out of the atmosphere.

Photosynthesis is involved here.

What role do diatoms play in the global carbon balance affecting global warming?

Excavata and Archaeplastida (Plantae)

David Roos (U Penn) Part 1: Biology of Apicomplexan Parasites

No. Apicomplexans do not fit this description.

This particular group has an interesting assortment of both plantlike and animal-like features.

Which of these groups includes photosynthetic unicellular organisms with flagella and contractile vacuoles?

Chlamydomonas is a unicellular green alga. How does it differ from a photosynthetic bacterium, which is also single-celled? How does it differ from a protozoan, such as an amoeba? How does it differ from larger green algae, such as sea lettuce (Ulva)?

Protozoans - Ciliata

What are Ciliates?

No. Dinoflagellates have cellulose plates that reinforce the cells; however, diatoms have unique glass-like walls that consist of hydrated silica embedded in an organic matrix. Each wall has two parts that overlap like a shoebox and lid.

No. Euglenids do not have particularly strong cell walls. Diatoms, on the other hand, have unique glass-like walls that consist of hydrated silica embedded in an organic matrix. Each wall has two parts that overlap like a shoebox and lid.

No. Ciliates do not have particularly strong cell walls. Diatoms, on the other hand, have unique glass-like walls that consist of hydrated silica embedded in an organic matrix. Each wall has two parts that overlap like a shoebox and lid.

No. Apicomplexans do not have particularly strong cell walls. Diatoms, on the other hand, have unique glass-like walls that consist of hydrated silica embedded in an organic matrix. Each wall has two parts that overlap like a shoebox and lid.

Think about the structure and composition of the cell walls of different protists. Would cellulose be likely to be able to hold up an elephant?

Which of these groups includes unicellular organisms that, due to the structure of their cell walls, can withstand pressures equal to the pressure under each leg of a table supporting an elephant?

Apicomplexa

Protists - Excavata I | BIALIGY.com

Protists - Archaeplastida | BIALIGY.com

Protozoan-animal-like protists

All three are heterotrophic and autotrophic.

No. None of them forms colonies of cells.

All three are parasitic on other species of organisms.

No. Only some dinoflagellates are photosynthetic.

All three have sacs known as alveoli just beneath their plasma membranes.

Consider the name of the group to which all three belong.

What do a carnivorous dinoflagellate, a parasitic apicomplexan, and a ciliate have in common?

Paramecium Structure

Both are adapted to aerobic environments.

No. Both, rather, are adapted to anaerobic environments.

No. Their mitochondria, though very much reduced, are usually present in one form or another.

No. This is true only of the diplomonads.

Think about organelles.

Which of the listed examples is a characteristic shared by diplomonads and parabasalids?

The buildup of CO2 in the atmosphere resulting from the burning of fossil fuels is regarded as a major contributor to global warming. Diatoms and other microscopic algae in the oceans counter this buildup by using large quantities of atmospheric CO2 in photosynthesis, which requires small quantities of iron. Experts suspect that a shortage of iron may limit algal growth in the oceans. Some scientists have suggested that one way to reduce CO2 buildup might be to fertilize the oceans with iron. The iron would stimulate algal growth and thus the removal of more CO2 from the air. A single supertanker of iron dust, spread over a wide enough area, might reduce the atmospheric CO2 level significantly. Do you think this approach would be worth a try? Why or why not?

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