Protists Review

Flashcards covering key concepts from lecture notes on Protists, including endosymbiosis, SAR alliance, diatoms, brown algae, dinoflagellates, apicomplexans (Plasmodium/malaria), and ciliates.

What is primary endosymbiosis and its significance?

Primary endosymbiosis is a process where a eukaryotic organism engulfs a prokaryotic organism. This is a pivotal event in evolution, notably leading to the origin of mitochondria from an ancestral aerobic bacterium and plastids (chloroplasts) from an ancestral photosynthetic cyanobacterium, forming the basis for photosynthetic life in eukaryotes.

What cellular components are believed to have originated through primary endosymbiosis?

Mitochondria, found in nearly all eukaryotes, and plastids (e.g., chloroplasts), found in photosynthetic eukaryotes, are believed to have arisen from primary endosymbiosis of an aerobic bacterium and a cyanobacterium, respectively.

What defines secondary endosymbiosis?

Secondary endosymbiosis occurs when a heterotrophic eukaryotic cell engulfs another eukaryotic cell that already contains a plastid from primary endosymbiosis. This event is significant for the diversification of photosynthetic eukaryotes, particularly in groups like the SAR alliance, where they acquired plastids from red algal ancestors.

Why is secondary endosymbiosis important for understanding protist diversity?

Secondary endosymbiosis explains the presence of plastids with multiple membranes (typically three or four) in many diverse protist lineages, indicating a complex evolutionary history where photosynthetic ability was acquired from a eukaryotic rather than directly from a prokaryotic source.

What are the general characteristics of the Excavates group?

Excavates are a diverse supergroup of protists often characterized by an 'excavated' feeding groove on one side of the cell body. They also frequently possess modified mitochondria or lack them entirely, and many have flagella.

What are two examples of organisms within the Excavates group and their key features?

Two prominent examples are Euglena, a mixotrophic flagellate often found in freshwater, capable of both photosynthesis and heterotrophy, and Trypanosome, a parasitic flagellate known for causing diseases like sleeping sickness in humans.

What is the SAR alliance?

The 'SAR' alliance is a significant supergroup of protists named for its three major clades: Stramenopiles, Alveolates, and Rhizarians. This group is widely supported by molecular data.

How did phototrophic organisms in the SAR alliance likely acquire their plastids?

Phototrophic organisms within the SAR alliance are believed to have acquired their plastids through secondary endosymbiosis, specifically by engulfing a red algal ancestor. This explains the presence of chlorophyll a and c in many of these groups, as well as plastids typically surrounded by four membranes.

What are the unifying features of the Stramenopiles group?

Stramenopiles are characterized by the presence of a 'hairy' flagellum and a 'smooth' flagellum at some point in their life cycle. This group includes ecologically important organisms like diatoms and brown algae.

What types of organisms are included in the Stramenopiles group and what is their general ecological role?

The Stramenopiles group primarily includes diatoms, major components of phytoplankton and producers, and brown algae, which are large multicellular seaweeds that form extensive marine ecosystems like kelp forests. Many are photosynthetic.

Describe the unique cell wall composition and advantages of diatoms.

Diatoms possess a unique cell wall made of hydrated silicone glass, structured like a petri dish with two overlapping halves (epithetical and hypotheca). These glass cell walls are remarkably persistent in the environment, contributing to an extensive fossil record and allowing for detailed taxonomic identification.

How do diatoms store carbon and what chlorophylls do they contain?

Diatoms store carbon as a non-starch polysaccharide, often chrysolaminarin, rather than true starch. They contain chlorophyll a and chlorophyll c for photosynthesis, along with various accessory pigments like carotenoids that give them a yellowish-brown color.

What makes brown algae unusual among protists, and what is a notable example?

Brown algae are unusual among protists because they are all multicellular, often reaching considerable sizes. Some species of kelp, a type of brown algae, are among the largest photoautotrophic organisms on the planet, forming vast underwater forests.

How do large brown algae, like kelp, manage nutrient transport, and how do they store carbon?

Large brown algae, such as kelp, possess translocation anatomy, which is a specialized conducting tissue analogous to the vascular tissues in plants, allowing them to transport photosynthetic products to deeper cells. They store carbon in a non-starch polysaccharide form, specifically beta-1,3-glucan.

What type of life history does Laminaria (a brown algae) exhibit?

Laminaria, a type of brown algae, exhibits a life history known as Alternation of Generations, which involves distinct multicellular diploid (sporophyte) and haploid (gametophyte) stages.

Explain the two main stages in the Alternation of Generations life cycle.

In alternation of generations: 1. The sporophyte is the diploid (2n) stage that produces haploid spores through meiosis. 2. The gametophyte is the haploid (n) stage that produces haploid gametes through mitosis.

What is the cell wall of brown algae primarily composed of?

The cell wall of brown algae is primarily made of cellulose, alongside other polysaccharides like alginates, which give them flexibility and strength.

What is the unifying anatomical feature of the Alveolates group?

The Alveolates group is unified by the presence of alveoli, which are flattened membrane-bound sacs (vesicles) located just beneath the plasma membrane. While their exact function varies, in aquatic forms, they are hypothesized to play a role in buoyancy or osmoregulation.

What three major groups are included in the Alveolates and what are their general characteristics?

The Alveolates include:
1. Dinoflagellates, often photosynthetic flagellates responsible for red tides.
2. Apicomplexans, obligate parasites of animals, many causing serious diseases.
3. Ciliates, protozoans characterized by cilia for locomotion and feeding, and a unique nuclear dimorphism.

Describe the distinguishing features of dinoflagellates.

Dinoflagellates are planktonic protists characterized by two flagella: one that wraps around their mid-section in a transverse groove (cingulum) and another that trails posteriorly. Many are covered by armored plates of cellulose within their cell membranes.

How do dinoflagellates store carbon, what chlorophylls do they possess, and what environmental phenomena are they known for?

Dinoflagellates store carbon as a starch-like polysaccharide. They typically contain chlorophyll a and chlorophyll c. They are widely known for causing 'red tides,' which are harmful algal blooms involving rapid population explosions that can color the water reddish-brown due to concentrated carotenoid pigments.

What environmental and health issues can arise from dinoflagellate blooms?

Dinoflagellate blooms, or red tides, can lead to severe oxygen depletion in the water as vast numbers of dead cells are decomposed by bacteria. Furthermore, some species produce potent toxins that can cause Paralytic Shellfish Poisoning (PSP) in humans who consume shellfish (like mussels or clams) that have filtered and accumulated these toxins, leading to neurological symptoms or even death.

What is a distinguishing characteristic of all Apicomplexans?

A primary distinguishing characteristic of all Apicomplexans is that they are obligate parasites of animals. They possess an apical complex, a specialized set of organelles at one end of the cell, which is crucial for penetrating host cells.

Describe the apicoplast found in Apicomplexans, including its origin and function.

The apicoplast is a unique, non-photosynthetic organelle found in Apicomplexans. It is highly reduced and descended from red algal plastids through secondary endosymbiosis. Although non-photosynthetic, it is believed to play a vital role in essential metabolic pathways, such as lipid synthesis and heme biosynthesis, making it a target for anti-parasitic drugs.

What organism is responsible for causing malaria?

The organism responsible for causing malaria, a severe parasitic disease, is Plasmodium, an Apicomplexan.

What are the two hosts in the typical life cycle of Plasmodium, and how does transmission occur?

The typical life cycle of Plasmodium involves two hosts: a human and a mosquito (specifically, a female Anopheles mosquito). Female mosquitoes acquire protein for their offspring by taking a blood meal, during which they can inject Plasmodium sporozoites into a human host, transmitting the parasite.

Outline the initial stages of Plasmodium infection in a human host.

Upon injection by a mosquito, the first cell type of Plasmodium, sporozoites, rapidly travels to and initially infects liver cells. Within the liver cells, they undergo asexual reproduction to produce thousands of merozoites.

Explain the next stage of Plasmodium infection and why it causes severe symptoms.

After maturing in the liver, Plasmodium merozoites burst out of liver cells and infect red blood cells. Inside red blood cells, they multiply asexually, causing the cells to burst. The synchronized bursting of infected red blood cells and the massive release of merozoites into the bloodstream cause the periodic, severe symptoms of malaria, including fever, chills, and anemia.

How does Plasmodium ensure its transmission back to the mosquito?

Some merozoites that infect red blood cells develop into gametocytes, which are the sexual stages of the parasite. When a mosquito takes another blood meal from an infected human, it ingests these gametocytes.

Where does sexual reproduction of Plasmodium occur, and what is its only diploid stage?

Fertilization of Plasmodium gametes occurs in the mosquito's digestive tract, forming a zygote. The zygote is the only diploid (2n) stage in the entire complex life cycle of Plasmodium; all other stages in both human and mosquito hosts are haploid (n).

What is the primary characteristic that gives ciliates their name, and what is their function?

Ciliates are named for being covered with numerous short, hair-like appendages called cilia. These cilia are structurally identical to flagella but are shorter and more numerous, primarily used for locomotion (propelling the cell) and for generating feeding currents to sweep food particles (like bacteria and detritus) into an oral groove.

What unique nuclear arrangement do ciliates possess, and what are their functions?

Ciliates are characterized by being dikaryotic, meaning they possess two functionally distinct types of nuclei: a large, polyploid macronucleus and one or more small, diploid micronuclei. The macronucleus controls daily cell functions and gene expression, while the micronuclei are primarily involved in sexual reproduction (genetic exchange) and serve as a germline reservoir.

How do ciliates (e.g., Paramecium) store carbon and manage water balance in freshwater?

Ciliates like Paramecium store carbon in the polysaccharide form of starch. In freshwater environments, they utilize specialized organelles called contractile vacuoles. These vacuoles actively pump out excess water that constantly diffuses into the cell due to osmosis, thereby preventing the cell from bursting (lysis).

How do ciliates engage in a form of 'sexual' reproduction?

Ciliates engage in a unique form of genetic recombination called conjugation. During conjugation, two ciliate cells pair up and exchange micronuclei. This process involves meiosis and mitosis, leading to the exchange of genetic material and the formation of new macronuclei, but it does not result in an increase in cell number (it's genetic recombination, not reproduction in the numerical sense).

What are the general characteristics of the Rhizarians group?

Rhizarians are a diverse group of protists that are typically amoeboid and move and feed using slender, thread-like pseudopods (filose pseudopods). Many species in this group are encased in intricate shells or skeletons.

What are two prominent subgroups within Rhizarians, and what are their distinguishing features?

Two prominent subgroups within Rhizarians are:
1. Foraminiferans (Forams): Characterized by porous shells (tests) made of calcium carbonate, through which their pseudopods extend. They are excellent index fossils.
2. Radiolarians: Possess exquisite, intricately symmetrical internal skeletons typically made of silica. They are primarily marine planktonic organisms.