Questions and Answers
What is the current understanding of the relationships among protist groups?
What is the proposed origin of mitochondria?
Which of the following protist groups is no longer considered the oldest lineage of eukaryotes?
What is a characteristic of diplomonads?
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Which of the following protist groups includes the pathogen that causes yeast infections in human females?
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How are all eukaryotes, including protists, divided according to one hypothesis?
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What is the distinguishing feature of Euglenozoa?
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Which of the following is a characteristic of kinetoplastids?
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What is the proposed mechanism of origin for the supergroup SAR?
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What is the function of the alveoli in alveolates?
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Which of the following is an example of a parasitic protist?
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What is the characteristic feature of dinoflagellates?
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Which of the following eukaryotic supergroups includes the alveolates and the stramenopiles?
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What is the term for the organized mass of DNA found in the mitochondria of kinetoplastids?
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What is the primary function of the complex of organelles at the apex of apicomplexans?
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Which group of protists is characterized by the presence of cilia for movement and feeding?
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What is the function of micronuclei in ciliates?
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Which of the following is a characteristic of Stramenopiles?
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What is the primary mode of reproduction in diatoms?
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What is the composition of diatomaceous earth?
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Which protist group is responsible for causing malaria?
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What is the current focus of research efforts related to Plasmodium?
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What is the primary characteristic that distinguishes protists from other eukaryotic organisms?
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What is the metabolic process that allows some protists to produce their own food?
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What is the term for the process in which some protists can switch between autotrophic and heterotrophic metabolism?
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What is the type of reproduction that involves meiosis and fertilization in some protists?
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How are protists classified according to their evolutionary relationships?
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What is the process by which one organism consumes another and forms a symbiotic relationship, leading to the formation of organelles?
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What is the characteristic of protists that distinguishes them from other eukaryotic organisms?
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What is the term for the process by which some protists exhibit alternation of generations, where two distinct generations of individuals are needed to complete a life cycle?
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What is the characteristic feature of Excavates?
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Which subgroup of Excavates has a reduced number of mitochondria and is anaerobic?
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What is the function of kinetic plastids in Euglenozoa?
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What is the characteristic of Neoglenida?
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Which subgroup of Excavates is characterized by having two nuclei and multiple flagella?
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What is the example of a parasitic protist in the subgroup Euglenozoa?
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What is unique about the silica test in diatoms?
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What is the primary function of the flagella in golden algae?
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What is the main characteristic of the life cycle of brown algae?
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What is the term for the process by which brown algae exhibit alternation of generations?
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What is the function of the holdfasts in brown algae?
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What is the characteristic of the gametophyte generation in brown algae?
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What is the primary function of the alveoli in Alveolates?
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Which group of protists is characterized by the presence of a hairy flagellum?
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What is the primary mode of nutrition for some Stramenopiles?
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Which group of protists is responsible for causing red tides?
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What is the characteristic feature of the life cycle of Apicomplexans?
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What is the primary function of cilia in Ciliates?
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What is the ecological role of Diatoms?
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What is the characteristic feature of the SAR clade?
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What is the primary function of the stipe in brown algae?
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What is the characteristic of the diploid generation in the life cycle of brown algae?
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What is the primary characteristic of Stramenopiles?
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What is the primary function of the blades in brown algae?
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What is the characteristic of the haploid generation in the life cycle of brown algae?
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What is the primary difference between green algae and red algae?
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What is the function of the holdfast in brown algae?
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What is the characteristic of the life cycle of brown algae?
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What is the main characteristic of the pseudopodia in Radialarians?
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Which of the following Uniconta protists is known for causing amoebic dysentery?
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What is the composition of the protective structure in Foramenifera?
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Which of the following is a characteristic of acellular slime molds?
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What is the primary function of pseudopodia in Ryze area protists?
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Which group of Uniconta protists includes animals and fungi?
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Study Notes
Endosymbiosis and Protist Evolution
- Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then an organelle in the host cell
- Mitochondria are believed to have evolved by endosymbiosis of an aerobic prokaryote
- Plastids are believed to have evolved by endosymbiosis of a photosynthetic cyanobacterium
Diversity of Protists
- Excavates are no longer thought to be the oldest lineage of eukaryotes
- Many excavates have been shown to have mitochondria and have been reclassified
- Our understanding of the relationships among protist groups continues to change rapidly
- One hypothesis divides all eukaryotes (including protists) into four supergroups
Excavates
- Characterized by a feeding groove that appears like “excavated” from the surface
- Includes diplomonads, parabasalids, and euglenozoans
Diplomonads
- Have modified mitochondria called mitosomes
- Derive energy from anaerobic biochemical pathways
- Have two equal-sized nuclei and multiple flagella
- Are often parasites, such as Giardia intestinalis
Parabasalids
- Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically
- Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females
Euglenozoa
- A diverse clade that includes euglenids and kinetoplastids
- Some are predatory heterotrophs, photosynthetic autotrophs, and parasites
- Characterized by a spiral or crystalline rod of unknown function inside their flagella
Euglenids
- Have one or two flagella that emerge from a pocket at one end of the cell
Kinetoplastids
- Have a single mitochondrion with an organized mass of DNA called a kinetoplast
- Include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems
- Include Trypanosoma gambiense, which causes sleeping sickness in humans, and pathogenic trypanosomes that cause Chagas’ disease
SAR Supergroup
- Some data suggest that the supergroup SAR is monophyletic and originated by a secondary endosymbiosis event
- The proposed endosymbiont is a red alga
- Includes the alveolates and the stramenopiles
Alveolata
- Characterized by membrane-bounded sacs (alveoli) just under the plasma membrane
- Function of the alveoli is unknown
- Includes dinoflagellates, apicomplexans, and ciliates
Dinoflagellates
- Have two flagella and each cell is reinforced by cellulose plates
- Are abundant components of both marine and freshwater phytoplankton
- Are a diverse group of aquatic phototrophs, mixotrophs, and heterotrophs
- Toxic “red tides” are caused by dinoflagellate blooms
Apicomplexans
- Are parasites of animals, and some cause serious human diseases
- Spread through their host as infectious cells called sporozoites
- Have a complex of organelles specialized for penetrating host cells and tissues
- Most have sexual and asexual stages that require two or more different host species for completion
- Include Plasmodium, which causes malaria
Ciliates
- A large and varied group of protists, named for their use of cilia to move and feed
- Have large macronuclei and small micronuclei
- Genetic variation results from conjugation, in which two individuals exchange haploid micronuclei
Stramenopila
- Includes important phototrophs as well as several clades of heterotrophs
- Most have a “hairy” flagellum paired with a “smooth” flagellum
- Includes diatoms, golden algae, brown algae, and oomycetes
Diatoms
- Unicellular algae with a unique two-part, glass-like wall of hydrated silica
- Are a major component of phytoplankton and are highly diverse
- Fossilized diatom walls compose much of the sediments known as diatomaceous earth
- Reproduction is mainly asexual
Introduction to Protists
- Protists are a diverse group of eukaryotic organisms exhibiting a wide range of shapes, patterns, and internal structures.
Characteristics of Protists
- Protists are eukaryotic, meaning their cells contain a nucleus and numerous membrane-bound organelles.
- Most protists are single-celled (unicellular) organisms, but some live in groups (colonies) and a few are multicellular.
- Protists have diverse subcellular structures, including organelles and other internal features.
Nutrition and Metabolism
- Photoautotrophic protists produce their own food through photosynthesis using chloroplasts.
- Heterotrophic protists obtain nutrients by ingesting or absorbing them from their surroundings.
- Some protists can switch between autotrophic and heterotrophic metabolism, a process known as mixotrophy.
Reproduction and Life Cycles
- Some protists reproduce asexually, while others are capable of sexual reproduction through meiosis and fertilization.
- Some protists, like kelp, exhibit alternation of generations, where two distinct generations of individuals are needed to complete a life cycle.
Classification of Protists
- There are four supergroups of protists: Excavata, SAR, Archaeplastida, and Opisthokonta.
- Each supergroup has a hypothesized common ancestor, and the protists are considered polyphyletic, meaning they have multiple ancestors.
Endosymbiosis
- Endosymbiosis is a process where one organism consumes another and forms a symbiotic relationship, leading to the formation of organelles like mitochondria and chloroplasts.
- Scientists hypothesize that endosymbiosis played a role in the origin of certain organelles in eukaryotic cells.
Protist Super Groups
- Protist classification is based on morphological and DNA data, and they have unique characteristics such as nutritional styles and replication methods that distinguish them from other organisms.
Super Group: Excavates
- Excavates have a unique cytoskeleton with a groove-like structure resembling an excavation.
- They have modified mitochondria.
- They possess two major groups with flagella that are distinct from other organisms.
Subgroup: Diplomonads
- Diplomonads have modified mitochondria called microsomes.
- They lack an electron transport chain and use anaerobic pathways for energy production.
- They have two nuclei and multiple flagella.
- Many diplomonads are parasites, such as Giardia lamblia, which causes diarrhea and vomiting in humans.
Subgroup: Parabasalids
- Parabasalids have a reduced number of mitochondria.
- They are anaerobic and produce hydrogen gas as a byproduct.
- Example: Trichomonas vaginalis, a sexually transmitted disease causing a burning, itching sensation in women.
Subgroup: Euglenozoa
- Euglenozoa have a rod-shaped structure inside their flagella.
- They have kinetic plastids, which are single large mitochondria with a large mass of DNA.
- They are free-living parasites, such as Trypanosoma, which causes African sleeping sickness and Chagas disease.
Subgroup: Neoglenida
- Neoglenida have a pocket at one end with one or two flagella emerging.
- They are mixotrophic, able to undergo photosynthesis, ingest other organisms, or synthesize their own energy.
- Example: Euglena, a common microscopic organism found in pond water.
SAR Clade
- The SAR clade is a supergroup of protists that includes Stramenopiles, Alveolates, and Rhizarians, and is thought to be a monophyletic group.
Alveolates
- Alveolates are characterized by the presence of membrane-bound pockets called alveoli, which may serve as an extra source of oxygen in low-oxygen conditions.
- Alveolates include dinoflagellates, apicomplexans, and ciliates.
Dinoflagellates
- Dinoflagellates have two flagella, one at the terminal end and one around the central groove.
- They can be photoautotrophic, heterotrophic, or mixotrophic.
- Some dinoflagellates are responsible for red tides, which can cause gastrointestinal poisoning in humans.
Apicomplexans
- Apicomplexans have a pointy structure called an apex, which is used to penetrate host cells.
- They have a complex life cycle that involves multiple hosts and stages.
- Apicomplexans are responsible for diseases such as malaria, which kills approximately 900,000 people per year.
Ciliates
- Ciliates have organized rows of cilia, which are used for locomotion.
- They have a complex life cycle that involves sexual and asexual stages.
- Ciliates can reproduce through binary fission, but may not produce genetically identical clones.
Stramenopiles
- Stramenopiles are characterized by the presence of a hairy flagellum.
- They include diatoms, golden algae, brown algae, and oomycetes.
- Stramenopiles have a diverse range of strategies for obtaining energy and nutrition, including photoautotrophy and heterotrophy.
Diatoms
- Diatoms are single-celled or colonial organisms that can be found in freshwater and seawater.
- They are abundant in aquatic ecosystems and play a key role in the food chain.
- Diatoms have a silica test, which is made of hydrated silicon material, and is embedded in a matrix of organic molecules.
Golden Algae
- Golden algae have two flagella, one hairy and one smooth.
- They can be photoautotrophic, heterotrophic, or mixotrophic.
- Golden algae are sometimes colonial and have a yellowish color due to the presence of a specific type of photosynthetic pigment.
Brown Algae
- Brown algae have a complex life cycle and a range of morphologies.
- They are often found in the ocean and provide food and shelter for young fish.
- Brown algae can grow up to 100 meters in length and have a complex structure, including holdfasts, stipes, and blades.
Alternation of Generations
- Brown algae exhibit an alternation of generations, where a diploid sporophyte generation alternates with a haploid gametophyte generation.
- The sporophyte generation produces spores, while the gametophyte generation produces gametes.
- This alternation of generations results in a heteromorphic life cycle, where the different generations have different forms.
Brown Algae
- Brown algae are multicellular protists that resemble plants, but have distinct structures with different functions.
- Holdfast anchors the algae to rocks or substrate, but does not absorb nutrients.
- Stipe helps hold structures upright, similar to a stem or trunk.
- Blades hold photosynthetic cells, similar to leaves.
- Some brown algae have bladders that help them float upright and grow towards the surface of the water.
- Brown algae have an alternation of generations life cycle, with two generations having different numbers of chromosomes.
Life Cycle of Brown Algae
- Diploid generation produces haploid spores through meiosis.
- Haploid generation produces gametes (eggs and sperm) through mitosis.
- Fertilization of gametes produces a new diploid sporophyte, which grows into a mature sporophyte.
- Sporangia are sacs containing spores that develop into male and female gametophytes.
Characteristics of Brown Algae
- Belong to the stramenopiles group.
- Have two flagella, one smooth and one hairy.
- Sporophytes are responsible for producing spores, which develop into gametophytes.
- Gametophytes are responsible for producing gametes, which fertilize to produce a new sporophyte.
Red Algae
- Red algae have an abundance of the accessory pigment ficocyanin, which gives them a red color.
- Some red algae are edible and used in sushi rolls.
- Most red algae are multicellular and live in the ocean.
Green Algae
- Most green algae are multicellular and live in freshwater.
- They are filamentous, with cells arranged in a long chain.
- Some green algae, like sea lettuce and Caulerpa, live in the ocean.
- Green algae are important contributors to the food chain, producing energy for other organisms.
Amoeboid Protists
- Move using pseudopodia (false feet) or extensions of their cell membrane.
- Classified into two groups: Ryze area (AR) and Uniconta.
Ryze Area (AR)
- Have thin, slender extensions called pseudopodia used for locomotion and capturing prey.
- Examples include:
- Foramenifera: have a protective structure called a test made of calcium carbonate, with tiny holes (perforations) for pseudopodia to emerge.
- Radialarians: have tests made of silica, with intricate patterns and shapes.
Uniconta
- Include animals, fungi, and protists.
- Examples include:
- Slime molds:
- Acellular slime molds: many cells with no plasma membrane dividing them, forming a mass of cytoplasm with many nuclei.
- Cellular slime molds: individual amoeba cells with their own plasma membrane, forming aggregates.
- Tubulinea:
- Have amoeba-like movement, but with lobe-like pseudopodia.
- Feed on other protists, algae, and bacteria.
- Entamoeba:
- Can be parasites of the gastrointestinal system, causing amoebic dysentery.
- Entamoeba histolytica is notorious for causing severe gastrointestinal disease.
- Slime molds:
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Description
Learn about the process of endosymbiosis, mitochondria and plastid evolution, and protist diversity, including the debunking of Excavates as the oldest eukaryote lineage.