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Kingdom Protista Protists
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Even a low-power microscope
Can reveal an astonishing menagerie of organisms in a drop of pond water 50 m
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Protist Diversity Protists are more diverse than all other eukaryotes
And are no longer classified in a single kingdom Most protists are unicellular And some are colonial or multi-cellular
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Protist Diversity Organisms that range in size from single cells to complex structures more than 100 meters long. They show a variety of reproductive and nutritional strategies.
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Protist Diversity Protists, the most nutritionally diverse of all eukaryotes, include Photoautotrophs, which contain chloroplasts Heterotrophs, which absorb organic molecules or ingest larger food particles Mixotrophs, which combine photosynthesis and heterotrophic nutrition
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Protists are also diverse in habitat
Including freshwater and marine species 100 m 4 cm 500 m The freshwater ciliate Stentor, a unicellular protozoan (LM) Ceratium tripos, a unicellular marine dinoflagellate (LM) Delesseria sanguinea, a multicellular marine red alga Spirogyra, a filamentous freshwater green alga (inset LM) (a) (b) (c) (d)
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ProtistA Evolution There is now considerable evidence
That much of protist diversity has its origins in endosymbiosis
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ProtistA Evolution The plastid-bearing lineage of protists
Evolved into red algae and green algae On several occasions during eukaryotic evolution Red algae and green algae underwent secondary endosymbiosis, in which they themselves were ingested
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2˚ Endosymbiosis Plastid Dinoflagellates Alveolates Apicomplexans
Cyanobacterium Heterotrophic eukaryote Primary endosymbiosis Red algae Green algae Secondary Plastid Dinoflagellates Apicomplexans Ciliates Stramenopiles Euglenids Chlorarachniophytes Alveolates
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Diplomonadida and parabasala
Have modified mitochondria Are adapted to anaerobic environments Lack plastids Have mitochondria that lack DNA, an electron transport chain, or citric-acid cycle enzymes A tentative phylogeny of eukaryotes Divides eukaryotes into many clades
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(a) Giardia intestinalis, a diplomonad (colorized SEM)
Diplomonads Have two nuclei and multiple flagella 5 µm (a) Giardia intestinalis, a diplomonad (colorized SEM)
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Zooflagellates · Move by flagella · They may enter into symbiotic
relationships with other organisms.
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Parabasalids -include trichomonads
Which move by means of flagella and an undulating part of the plasma membrane
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Euglenozoa Have flagella with a unique internal structure
Euglenozoa is a diverse clade that includes Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites 2 Types Kinetoplastids & Euglenids
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Euglenozoa The main feature that distinguishes protists in this clade
Is the presence of a spiral or crystalline rod of unknown function inside their flagella Flagella 0.2 µm Crystalline rod Ring of microtubules
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Kinetoplastids Have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems
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Tsetse fly Trypanosoma Causes sleeping sickness in humans 9 m
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Euglenids Figure 28.8 Long flagellum Eyespot: pigmented
Short flagellum Nucleus Plasma membrane Paramylon granule Chloroplast Contractile vacuole Light detector: swelling near the base of the long flagellum; detects light that is not blocked by the eyespot; as a result, Euglena moves toward light of appropriate intensity, an important adaptation that enhances photosynthesis Eyespot: pigmented organelle that functions as a light shield, allowing light from only a certain direction to strike the light detector Pellicle: protein bands beneath the plasma membrane that provide strength and flexibility (Euglena lacks a cell wall) Euglena (LM) 5 µm
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Euglenids
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Euglenids Only one third of the species of Euglenoids are
photosynthetic. · Euglena stores glucose in a polymer called Paramylon · An eyespot with a photoreceptor is capable of detecting the presence of light. Reproduction is asexual.
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Alveolates Members of the clade Alveolata
Have membrane-bounded sacs (alveoli) just under the plasma membrane Flagellum Alveoli 0.2 µm Includes: Dinoflagellates Apicomplexans Ciliates
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Dinoflagellates Two flagella
Are a diverse group of aquatic photoautotrophs and heterotrophs Are abundant components of both marine and freshwater phytoplankton Shape is reinforced by internal plates of cellulose Two flagella Make them spin as they move through the water
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Dinoflagellates Some species are responsible for red tides that kill fish and shellfish Toxins released can kill aquatic & terrestrial animals (aerosols)
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Apicomplexans Are parasites of animals and some cause serious human diseases Are so named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues Have a non-photosynthetic plastid, the apicoplast
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Apicomplexans Most apicomplexans have intricate life cycles
With both sexual and asexual stages that often require two or more different host species for completion Plasmodium causes malaria
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Plasmodium Anopheles mosquito
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Sporozoans Parasitic Complicated life cycle that usually involves the formation of infective spores. e.g. malaria - The parasite is injected into a human by a mosquito. The parasite then invades red blood cells and ruptures them.
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Ciliates The micronuclei Conjugation is separate from reproduction
Are named for their use of cilia to move and feed Have large macronuclei and small micronuclei The micronuclei Function during conjugation, a sexual process that produces genetic variation Conjugation is separate from reproduction Which generally occurs by binary fission
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Ciliates Example - Paramecium
The outer covering of paramecium is covered with hundreds of cilia They have numerous organelles including a gullet (oral groove) and an anal pore The macronucleus controls the cell's activities. The micronucleus is involved in cell reproduction (sexual & asexual).
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CONJUGATION AND REPRODUCTION
8 7 2 MICRONUCLEAR FUSION Diploid micronucleus Haploid micronucleus MEIOSIS Compatible mates Key Conjugation Reproduction Macronucleus Meiosis of micronuclei produces four haploid micronuclei in each cell. 3 micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis The cells swap one micronucleus The cells separate Micronuclei fuse, forming a diploid micronucleus. Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells. The original macro- nucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Three rounds of mitosis without cytokinesis produce eight micronuclei.
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Paramecium
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FEEDING, WASTE REMOVAL, AND WATER BALANCE
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Stentor (Type of ciliate)
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Stramenopila Stramenopiles have “hairy” and smooth flagella
The clade Stramenopila Includes: Water molds Diatoms Golden algae Brown algae Smooth flagellum Hairy 5 µm
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Oomycetes Include water molds, white rusts, and downy mildews
Were once considered fungi based on morphological studies Are decomposers or parasites Have filaments (hyphae) that facilitate nutrient uptake Have cell walls made of cellulose
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Diatoms Are unicellular algae major component of phytoplankton
With a unique two-part, glass-like wall of hydrated silica major component of phytoplankton 3 µm
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Diatoms · Most numerous unicellular algae in the oceans
and are an important source of food and oxygen. · Also important in freshwater environments. · Glucose stored as polysaccharide laminarin (Same as golden & brown algae) · Their remains form diatomaceous earth.
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Diatoms ~ species 50 µm
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Golden Algae Or chrysophytes The cells of golden algae
25 µm Golden Algae Or chrysophytes Are named for their color, which results from their yellow & brown carotenoids The cells of golden algae Are typically bi-flagellated, with both flagella attached near one end of the cell
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Brown algae Or phaeophytes Seaweeds
Are the largest and most complex algae Are all multicellular, and most are marine Include many of the species commonly called seaweeds Seaweeds Have the most complex multi-cellular anatomy of all algae
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Brown Algae Photosynthetic & multicellular · Range in size.
Blade Stipe Holdfast Photosynthetic & multicellular · Range in size. Many are m long. · Found along rocky shores The thalus (plant like body) contains: · Holdfasts for attachment · Blades and air bladders that function in floatation · A stem-like structure that holds the blades is called a stipe. Fucus Common "seaweed" found along the rocky coast.
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Brown Algae
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Kelps, or giant seaweeds
Live in deep parts of the ocean Can grow as long as 60m Cell walls are composed of cellulose and gel forming polysaccharides which cushion the algae in the intertidal zone
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Brown Algae - Macrocystis and Nereocystis (Deep water Kelp)
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A variety of life cycles Have evolved among the multi-cellular algae
Sporophyte (2n) Zoospores Female Gametophytes (n) MEIOSIS FERTILIZATION Developing sporophyte Zygote Mature female gametophyte Egg Sperm Male Sporangia Key Haploid (n) Diploid (2n) The most complex life cycles include an alternation of generations The alternation of multi-cellular haploid and diploid forms
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Cercozoans Cercozoans and radiolarians have threadlike pseudopodia
A newly recognized clade, Cercozoa Contains a diversity of species that are among the organisms referred to as amoebas Amoebas were formerly defined as protists That move and feed by means of pseudopodia Cercozoans are distinguished from most other amoebas
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Foraminiferans, or forams
Are named for their porous, generally multichambered shells, called tests 20 µm Pseudopodia extend through the pores in the test
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Radiolarians Marine protists
Whose tests are fused into one delicate piece, which is generally made of silica Phagocytize microorganisms with their pseudopodia
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The pseudopodia of radiolarians, known as axopodia
Radiate from the central body 200 µm Axopodia
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Radiolarians Marine plankton (float in marine environments) with a skeleton composed of silica, and numerous needle-like pseudopodia.
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Amoebozoans Have lobe-shaped pseudopodia
rather than threadlike, pseudopodia Include gymnamoebas, entamoebas, and slime molds
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Protozoans · Do not have a cell wall · Heterotrophic · Usually motile
· Food vacuoles · Contractile vacuole (water elimination) Reproduction is usually asexual but many also reproduce sexually during some part of their life cycle.
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Gymnamoebas Most are heterotrophic
Are common unicellular amoebozoans in soil as well as freshwater and marine environments Pseudopodia 40 µm Most are heterotrophic And actively seek and consume bacteria and other protists
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Entamoeba Are parasites of vertebrates and some invertebrates
Entamoeba histolytica Causes amebic dysentery in humans
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Amoeboids Amoeba Move by cytoplasmic extensions called pseudopodia.
Feed by phagocytizing (engulfing) their prey. Most amoeboids are marine organisms; Amoeba proteus is found in freshwater
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Amoeboids
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Slime molds, or mycetozoans
Were once thought to be fungi Molecular systematics Places slime molds in the clade Amoebozoa Plasmodial & Cellular types
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The plasmodium Is undivided by membranes and contains many diploid nuclei Extends pseudopodia through decomposing material, engulfing food by phagocytosis
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Protists that are Decomposers (Saprotrophs)
· Slime molds play an ecological role similar to that of fungi. · They are decomposers, feeding on dead organic material. · They differ from fungi in that slime molds ingest their food. · Slime molds are masses that creep along the substrate and phagocytize dead organic material and microorganisms. · The mass is one large cell referred to as a plasmodium. · Spores are resistant to environmental extremes (Food and moisture) and germinate when environmental conditions become favorable · Saprotrophic; they live off of dead organic matter.
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Slime Molds
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Plasmodial Slime mold life cycle
Feeding plasmodium Mature (preparing to fruit) Young sporangium Spores (n) Germinating spore Amoeboid cells Zygote (2n) 1 mm Key Haploid (n) Diploid (2n) MEIOSIS SYNGAMY Stalk Flagellated cells
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Cellular slime molds Form multicellular aggregates
In which the cells remain separated by their membranes Has become an experimental model for studying the evolution of multi-cellularity
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Cellular Slime Mold Life Cycle
Spores (n) Emerging amoeba Solitary amoebas (feeding stage) ASEXUAL REPRODUCTION Fruiting bodies Aggregated amoebas Migrating aggregate SYNGAMY MEIOSIS SEXUAL Zygote (2n) Amoebas 600 µm 200 µm Key Haploid (n) Diploid (2n)
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Algae The word algae refers to aquatic (freshwater or marine) protists. Algae photosynthesize like plants. They produce much of the oxygen in the atmosphere. · Algae provide food for aquatic food chains.
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Red & Green Algae Are the closest relatives of land plants
Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont And the photosynthetic descendants of this ancient protist evolved into red algae and green algae
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Red Algae Are reddish in color
Due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll
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Red Algae Red algae are found mainly in warmer, tropical oceans.
Accessory photosynthetic pigments are called phycobilins which allow some species to survive in deep waters where blue and green light predominates. Some species are filamentous but most have a complex pattern of branching. Some coralline forms deposit calcium carbonate in their cell walls, making coral reefs.
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Green Algae Are named for their grass-green chloroplasts
Are divided into two main groups: chlorophytes and charophyceans Are closely related to land plants
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Green Algae Single-celled and multicellular forms. ·
· Ancestors of the first plants, both have the following characteristics in common: They have a cell wall that contains cellulose. They have chlorophyll They store their food as starch inside the chloroplast.
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Chlorophytes (green algae)
Include: Unicellular, colonial, and multi-cellular forms (a) ) 20 µm 50 µm
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Ulva Multicellular with a leaf-like body that is two cells thick but up to one meter long Common name: Sea lettuce
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Volvox · Colonial green algae
· They divide asexually to produce a daughter colony. Notice the daughter colonies within the larger colonies.
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Volvox Some cells are specialized to produce sperm and eggs for sexual reproduction which is a characteristic of multicellular organisms. Considered to be a colony because it appears to be intermediate between a group of individual cells and a multicellular organism.
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Spirogyra · Filamentous form of green algae.
· Has a ribbonlike spiral-shaped chloroplast. · Sexual reproduction occurs by conjugation. · The zygote is resistant and overwinters.
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Spirogyra Conjugation
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Chlorophyte Life Cycle
Harsh environmental conditions Flagella Cell wall Nucleus Regions of single chloroplast Zoospores ASEXUAL REPRODUCTION Mature cell (n) SYNGAMY SEXUAL Zygote (2n) MEIOSIS 1 µm Key Haploid (n) Diploid (2n) + Normal environmental conditions
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Protists Compared to Plants, Animals, and Fungi
Characteristics resemble plants, animals, or fungi. Photosynthetic protists differ from plants in that they do not have structures that protect the gametes or zygote. Plants and animals undergo a period of embryonic development but protists do not. Fungi have cell walls composed of chitin; protists do not have chitin in their cell walls Fungi do not have cilia or flagella. Many kinds of protists have cilia or flagella.
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Trophic Levels Autotrophs: · green algae · brown algae · red algae
· diatoms · dinoflagellates · euglenoids Heterotrophs: · amoeboids · ciliates · zooflagellates · sporozoans · slime molds
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