Biology Quiz: Protists Overview

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Questions and Answers

Which characteristic distinguishes protists from prokaryotes?

Prokaryotes have chloroplasts.

Most protists are multicellular.

Protists lack organelles.

Protists are mostly unicellular eukaryotes. (correct)

What type of nutrition do mixotrophic protists exhibit?

Combination of photosynthesis and heterotrophic nutrition. (correct)

Absorption of organic molecules.

Only heterotrophic ingestion.

Only photosynthesis.

What does primary endosymbiosis involve?

Absorption of nutrients from the environment.

Engulfment of a larger eukaryotic cell.

Formation of multicellular species.

Engulfment of a prokaryotic cell by a eukaryotic cell. (correct)

Which of the following is NOT a method of reproduction in protists?

Cloning through DNA replication. Signup and view all the answers

Which statement is true about the classification of protists?

Protists form a polyphyletic group. Signup and view all the answers

Which characteristic is common among members of the Clade Excavata?

Presence of a feeding groove. Signup and view all the answers

What does it mean for protists to exhibit functional diversity?

They carry out all biological functions using cellular organelles. Signup and view all the answers

Why is the previous idea of amitochondriates as the oldest lineage of eukaryotes now considered inaccurate?

Amitochondriates represent a dead-end in evolution. Signup and view all the answers

What type of mitochondria do diplomonads possess?

Mitosomes Signup and view all the answers

Which of the following is a characteristic of parabasalids?

They have reduced mitochondria known as hydrogenosomes. Signup and view all the answers

Which kind of organism is primarily associated with kinetoplastids?

Parasites that affect various animals Signup and view all the answers

What distinguishes euglenids from other groups?

They possess one or two flagella that emerge from a specific pocket. Signup and view all the answers

What type of nutritional mode can many euglenids perform?

Mixotrophy Signup and view all the answers

What is the supposed origin of the clade Chromalveolata?

Secondary endosymbiosis with a red alga Signup and view all the answers

What do members of the clade Alveolata possess?

Membrane-bounded sacs called alveoli Signup and view all the answers

Which of the following diseases is caused by a kinetoplastid?

Sleeping sickness Signup and view all the answers

Which characteristic distinguishes heteromorphic generations in the alternation of generations?

They are structurally different. Signup and view all the answers

What is a common ecological role of oomycetes?

Decomposers or parasites of algae and fish. Signup and view all the answers

What is the primary component that forms the internal skeleton of radiolarians?

Silica. Signup and view all the answers

What pigment gives red algae their characteristic color?

Phycoerythrin. Signup and view all the answers

In the context of Rhizarians, what is the primary function of pseudopodia?

To facilitate nutrient uptake and movement. Signup and view all the answers

Which group includes organisms that were formerly classified as fungi?

Oomycetes. Signup and view all the answers

Which of the following correctly describes foraminiferans (forams)?

Their pseudopodia extend through the pores in their tests. Signup and view all the answers

What is the significance of Archaeplastida in terms of plant evolution?

It encompasses the ancestors of all land plants. Signup and view all the answers

What is a reason why the kingdom Protista is no longer considered a legitimate taxon?

It is a polyphyletic clade. Signup and view all the answers

Which process explains the evolution of plastids and mitochondria?

Endosymbiosis Signup and view all the answers

What distinguishes primary endosymbiosis from secondary endosymbiosis?

Secondary endosymbiosis involves the engulfment of a eukaryotic cell. Signup and view all the answers

Which of the following best describes the life cycle of the apicomplexan Plasmodium?

It involves multiple hosts and sexual reproduction. Signup and view all the answers

What is an important role of protists in aquatic environments?

They contribute significantly as important producers. Signup and view all the answers

Which of the following statements about protist reproduction is true?

Protists can reproduce both asexually and sexually. Signup and view all the answers

What type of generations do heteromorphic alternation of generations refer to?

Structurally different generations. Signup and view all the answers

Which organism demonstrates isomorphic generations in its life cycle?

Ulva Signup and view all the answers

What is the primary use of the red alga Porphyra?

Traditional Japanese food Signup and view all the answers

Which group includes unicellular, colonial, and multicellular forms?

Chlorophytes Signup and view all the answers

What distinguishes plasmodial slime molds from cellular slime molds?

Plasmodial slime molds form a coherent mass called a plasmodium. Signup and view all the answers

What role do dinoflagellates play in ecological relationships?

They provide nourishment to coral polyps. Signup and view all the answers

Which organism is known to cause amoebic dysentery in humans?

Entamoeba histolytica Signup and view all the answers

What is a primary distinguishing feature of gymnamoebas?

They actively seek and consume bacteria. Signup and view all the answers

In which environments are most chlorophytes typically found?

Freshwater and many marine environments Signup and view all the answers

What encompasses the Unikonta supergroup?

Animals, fungi, and some protists Signup and view all the answers

What does the term 'phagocytosis' refer to in the context of plasmodial slime molds?

Engulfing food particles. Signup and view all the answers

Which of the following organisms are involved in harmful ecological relationships as parasites?

Entamoeba histolytica and Plasmodium Signup and view all the answers

Study Notes

Overview: Living Small

Even a low-power microscope reveals a diverse range of organisms in a drop of pond water
Protists are mostly unicellular eukaryotes, containing organelles
Protists were once classified as a kingdom but are now considered polyphyletic, because their evolutionary history is not rooted in a single ancestor

Protists/ Protozoans

Protists are eukaryotes and have organelles, making them more complex than prokaryotes
Most protists are unicellular, but some are colonial and multicellular
Protists exhibit more structural and functional diversity than any other group of eukaryotes
Single-celled protists are complex, performing all biological functions within each cell

Protists

Nutrition: Protists display diverse nutritional strategies:
- Photoautotrophs: Contain chloroplasts for photosynthesis
- Heterotrophs: Obtain nutrients by absorbing organic molecules or ingesting larger food particles
- Mixotrophs: Combine photosynthesis and heterotrophic nutrition
Reproduction: Protists reproduce both asexually and sexually:
- Asexual reproduction involves simple cell division
- Sexual reproduction involves processes of meiosis and fertilization

Endosymbiosis in Eukaryotic Evolution

Much protist diversity originates from endosymbiosis, where a eukaryotic cell engulfs another living cell:
- Primary endosymbiosis: Occurs when a eukaryotic cell engulfs a prokaryotic cell, leading to organelles like chloroplasts and mitochondria
- Secondary endosymbiosis: A eukaryotic cell engulfs another eukaryote that has already undergone primary endosymbiosis

Five Supergroups of Eukaryotes

The relationships among protist groups are constantly evolving
One hypothesis proposes five supergroups for all eukaryotes, including protists

Clade Excavata

Excavata contains protists with modified mitochondria and unique flagella
Most members are asymmetrical and single-celled, with some exceptions like slime molds with limited multicellularity
Some possess a feeding groove "excavated" from one side of their cell (Diplomonads and Parabasalids)
Diplomonads and Parabasalids live in anaerobic environments, lack plastids, and have modified mitochondria
- Diplomonads possess modified mitochondria called mitosomes
- Diplomonads are often parasites, for example, Giardia intestinalis
Parabasalids have reduced mitochondria called hydrogenosomes that generate some energy anaerobically, releasing hydrogen gas as a by-product
- Parabasalids include Trichomonas vaginalis, a parasite that causes the sexually transmitted infection Trichomoniasis
Euglenozoa is a diverse group within Excavata:
- It includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites
- The main characteristic of this clade is a spiral or crystalline rod within their flagella, with unknown function
- This clade includes the orders Kinetoplastids and Euglenids

Kinetoplastids

Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast
They are widespread, flagellated parasites of all animal groups, plants and insects
Free-living Kinetoplastids feed on bacteria in aquatic, marine and terrestrial environments
Kinetoplastids include Trypanosoma, which causes sleeping sickness in humans
Another pathogenic trypanosome causes Chagas’ disease

Euglenids

Euglenids have one or two flagella that emerge from a pocket at one end of the cell
Many Euglenids can be both autotrophic and heterotrophic, making them mixotrophs

Chromalveolates

Chromalveolata is a monophyletic clade, likely originating from a secondary endosymbiosis event involving a red alga
Contains important oceanic organisms
Range from single-celled to complex multicellular taxa
This clade includes the Alveolates and the Stramenopiles

Alveolates

Members of the clade Alveolata contain membrane-bounded sacs (alveoli) located just under the plasma membrane
The function of the alveoli is unknown
Alveolates include the dinoflagellates, ciliates, and apicomplexans

Dinoflagellates

Dinoflagellates are mostly unicellular
Many are photosynthetic, including some that cause "red tides"
They have two flagella and cell walls made of cellulose plates
Some dinoflagellates produce toxins that can kill fish

Ciliates

Ciliates are characterized by numerous short, hair-like structures called cilia
They are heterotrophic and use cilia to move and feed

Apicomplexans

Apicomplexans are parasites that infect animals
They have a unique structure called an apical complex, which helps them penetrate host cells
Apicomplexans cause diseases such as malaria and toxoplasmosis

Stramenopiles

Stramenopiles include diatoms, golden algae, brown algae, and water molds They are characterized by the presence of hair-like structures (stramenopiles) on their flagella
Diatoms are unicellular algae that have a glassy cell wall called a frustule
Golden algae are a diverse group that includes photosynthetic, heterotrophic, and mixotrophic members
Brown algae or Phaeophytes are multicellular photosynthetic protists with a complex life cycle

Brown Algae

The pigment fucoxanthin masks the green of chlorophyll, giving brown algae their characteristic brown color
Brown algae resemble plants and form underwater "forests"
All are multicellular, and most are marine
Brown algae includes many species commonly called "seaweeds"

Alternation of Generations

Multicellular algae have evolved a variety of life cycles
The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms
Heteromorphic generations are structurally different, while isomorphic generations look similar

Oomycetes

Oomycetes include water molds, white rusts, and downy mildews
They were once considered fungi due to their morphological similarities
Most oomycetes are decomposers or parasites of algae and fish
Oomycetes have filaments called hyphae, which facilitate nutrient uptake
Oomycetes can have a significant ecological impact, as in Phytophthora infestans causing potato late blight

Rhizarians

DNA evidence supports Rhizaria as a monophyletic clade
Rhizaria organisms (referred to as amoebas) have threadlike pseudopodia
Amoebas move and feed by pseudopodia
Rhizarians include forams and radiolarians

Forams

Foraminiferans, or forams, are named for their porous shells, called tests
Pseudopodia extend through the pores in the test
Pseudopodia aid in swimming and feeding
Foram tests form an extensive fossil record and are part of marine sediments

Radiolarians

Marine protists called radiolarians have symmetrical internal skeletons made of silica
The pseudopodia of radiolarians radiate from the central body
Radiolarians use their pseudopodia to engulf microorganisms through phagocytosis

Archeaplastida

Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont
The photosynthetic descendants of this ancient protist evolved into red algae and green algae
Land plants are descended from the green algae
Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants

Red Algae (Rhodophytes)

Red algae appear reddish due to an accessory pigment called phycoerythrin, which masks the green of chlorophyll
The color varies from greenish-red in shallow water to dark red or almost black in deep water
Red algae are usually multicellular; the largest are seaweeds
Red algae are the most abundant large algae in the coastal waters of the tropics

Green Algae

Named for their grass-green chloroplasts
Plants are descended from green algae
The two main groups are chlorophytes and charophytes
Most chlorophytes live in freshwater, but many exist in marine and some terrestrial environments
Example of chlorophytes: unicellular Chlamydomonas
Some chlorophytes live in damp soil, as symbionts in lichens, or in snow

Chlorophytes

Chlorophytes include unicellular, colonial, and multicellular forms
Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages

Unikonts

The supergroup Unikonta includes animals, fungi, and some protists that are closely related to fungi and animals
This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)
The root of the eukaryotic tree remains controversial
It is unclear whether unikonts separated from other eukaryotes relatively early or late

Amoebozoans

Amoebozoans are amoebas that have lobe- or tube-shaped, rather than threadlike, pseudopodia
They include slime molds, gymnamoebas, and entamoebas

Slime Molds

Slime molds, or mycetozoans, were once thought to be fungi
Molecular systematics places slime molds in the clade Amoebozoa
Slime molds are divided into plasmodial slime molds and cellular slime molds, based on their unique life cycles

Plasmodial Slime Molds

Many plasmodial slime molds are brightly pigmented, usually yellow or orange
At one point in their life cycle, plasmodial slime molds form a mass called a plasmodium
The plasmodium is not multicellular, but a single mass of cytoplasm containing many diploid nuclei
It extends its pseudopodia through decomposing material, engulfing food by phagocytosis

Cellular Slime Molds

Cellular slime molds form multicellular aggregates where cells are separated by their membranes
Cells feed individually, but can aggregate to function as a unit when food becomes scarce
Dictyostelium discoideum is a model organism for studying the evolution of multicellularity

Gymnamoebas

Gymnamoebas are common unicellular amoebozoans present in soil, freshwater, and marine environments
Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists
Some feed on dead organic matter

Entamoebas

Entamoebas are parasites of vertebrates and some invertebrates
Entamoeba histolytica causes amoebic dysentery in humans
- Dysentery: Infection of the intestines resulting in severe diarrhea
- Spread via contaminated drinking water, food, or eating utensils

Opisthokonts

Opisthokonts include animals, fungi, and several groups of protists
These protists are more closely related to animals and fungi than they are to other protists

Protists play key roles in ecological relationships

Protists are found in diverse aquatic environments
Two important roles of protists:
- Symbiotic Protists
- Photosynthetic Protists

Symbiotic Protists

Many protists form symbiotic relationships with other species
Some protist symbionts benefit their hosts:
- Dinoflagellates nourish coral polyps, contributing to reef development
- Hypermastigotes digest cellulose in the gut of termites

Photosynthetic Protists

Many protists are important producers that obtain energy from the sun
In aquatic environments, they are primary producers alongside prokaryotes
- One-third of the world's photosynthesis is performed by diatoms, dinoflagellates, multicellular algae, etc.
The availability of nutrients can affect the concentration of protists

Domain Eukarya: Protists

Mostly unicellular eukaryotes
Protista is no longer considered a valid kingdom, as it is polyphyletic
Some protists are more closely related to plants, fungi, or animals
Unicellular (Chlamydomonas), colonial (Volvox), and multicellular species (green algae) exist
Protists can reproduce asexually and sexually

Plastids and mitochondria evolved by endosymbiosis

Primary vs secondary endosymbiosis
Red and green algae underwent secondary endosymbiosis

Different Life Cycles

Apicomplexan Plasmodium: Malaria-causing parasite
- Requires two hosts to complete its life cycle
Ciliate Paramecium
- Conjugation (sexual reproduction)
- Cytokinesis produces four daughter cells
Alternation of generations
- Alternation of multicellular haploid and diploid forms
- Heteromorphic generations: Structurally different (Brown algae)
- Isomorphic generations: Look similar (Ulva)

Importance of Protists

Form mutualistic and parasitic relationships
- E.g., malaria-causing Apicomplexan Plasmodium
Important producers in aquatic environments

You should now be able to:

Explain why the kingdom Protista is no longer considered a valid taxon
Explain the process of endosymbiosis and state what living organisms are likely relatives of mitochondria and plastids
Distinguish between endosymbiosis and secondary endosymbiosis
Name the five supergroups, list their key characteristics, and describe some representative taxa

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Description

Test your understanding of protists with this quiz, which covers their classification, structure, and nutritional strategies. Learn about unicellular eukaryotes and their diverse ways of life, including their roles in ecosystems. This quiz is essential for biology students exploring cellular organisms.