31.0 Introduction

1. Kingdom Protista Is Very Diverse
1. Most Are Small, Single-Celled Organisms fig 31.1
2. Kingdom Is an Artificial Group
1. Many different and distantly related groups lumped together
2. Classification does not represent evolutionary relationships

31.1 The kingdom Protista is by far the most diverse of any kingdom

1. The Challenge of Classifying the Protists
1. Knowledge of Protists in Greatest State of Flux
1. Substantial research in progress
2. May lead to additional kingdoms

2. Popular Presentation of Six Kingdoms
1. Before 1969 organisms that photosynthesized or absorbed food were considered plants
2. Protists that ingested food were considered animals
3. Early classification schemes were misleading
4. Protist relationships are becoming more evident fig 31.2

2. General Biology of the Protists
1. Unity Due to Negative Characteristic
1. Not classified as plant, animal or fungus
2. Are mostly unicellular and microscopic fig 31.3
1. May be colonial or multicellular
2. Some as large as trees

2. The Cell Surface
1. Amoebas are surrounded only by plasma membranes
2. Algae and molds encased in strong cell walls
3. Diatoms and forams secrete glassy shells of silica

3. Locomotor Organelles
1. Many move by flagellar motions
1. Some have one or more flagella
2. Others have banks of multiple flagella called cilia that create water currents

2. Others exhibit pseudopodial movement
1. Pseudopodia in amoeba are large blunt extensions of cell body called lobopodia
2. Thin branching pseudopods are called filopodia
3. Long, extremely thin pseudopods are called axopodia
1. Supported by axial rods of microtubules
2. Can be extended or retracted
3. Tips can adhere to adjacent surfaces
4. Cell moves by a rolling motion

4. Cyst Formation
1. Cysts formed to survive inhospitable conditions
1. Dormant form of cell with resistant outer covering
2. Cell metabolism is nearly completely shut down

2. Important in forms that cycle between hosts
1. Colpoda survive boiling water or liquid air
2. Parasitic amoeba resistant to gastric juices, but cannot survive drying or heat

5. Nutrition
1. Phototrophs are photosynthetic autotrophs
2. Heterotrophs obtain energy from organic molecules
1. Phagotrophs or holozoic feeders ingest visible particles of food
2. Osmotrophs or saprozoic feeders ingest food in soluble form

3. Phagotrophs produce intracellular vesicles: Food vacuoles or phagosomes
1. Fuse with lysosomes containing digestive enzymes
2. Digested molecules absorbed across vacuole membrane
3. Food vacuole decreases in size
4. Undigested material passed outside via exocytosis

6. Reproduction
1. Generally reproduce asexually
2. Sexual reproduction occurs only in time of stress
3. Asexual reproduction involved mitosis, but may be quite different from that of animals
1. Nuclear membrane may persist throughout mitosis
2. Microtubular spindle forms within nucleus

4. Asexual reproduction may involve spore formation or fission
1. Most common kind of fission is binary fission, production of two equal cells
2. Called budding if one is larger "parent" and other is small and grows to adult size

5. Multiple fission is called schizogony
1. Fission preceded by several nuclear divisions
2. Produces several individuals simultaneously

6. Sexual reproduction may include gametic meiosis
1. Includes ciliates and some flagellates
2. Occurs just before gamete formation

7. Zygotic meiosis occurs in sporozoans
1. Occurs directly after fertilization
2. All individuals are haploid until next zygote is formed

8. Intermediate meiosis occurs in algae
1. Produces alternation of generation similar to plants
2. Significant portions of life cycle spent as haploid and diploid

31.2 Protists are grouped into fifteen very distinctive phyla

1. Seven Groups of Protists
1. Fifteen Distinct Phyla
1. Historical, traditional artificial arrangement
1. Photosynthesizers = algae
2. Heterotrophs = protozoa
3. Absorbers = fungi-like protists

2. Present protists in seven groups according to major shared characteristics tbl 31.1
1. Presence or absence of cilia or flagella
2. Presence and kinds of pigments
3. Type of mitosis
4. Kinds of cristae present in mitochondria
5. Molecular genetics of ribosomal "S" subunit
6. Presence and kinds of inclusions
7. Overall body form
8. Presence of shell, test or other body armor
9. Modes of nutrition and movement

2. Other Classification Schemes Are Possible
1. Molecular analysis presents clearer picture
2. More suitable groupings will arise with further research
3. Major characteristics of seven groups tbl 31.2

2. The Sarcodines
1. Rhizopoda: The Amoebas
1. Fresh and salt water specimens, abundant in soil, parasites of animals
2. Reproduction by fission, direct division into two cells
3. Lack cell walls, flagella, meiosis and sexual reproduction
4. Undergo mitosis, have typical eukaryotic spindle apparatus
5. Locomotion via pseudopods fig 31.4
1. Cytoplasmic projections that also engulf food particles
2. Involved with microfilaments of actin and myosin

6. Parasitic species may form resistant cysts fig 31.24
1. Entamoeba histolytica : Causes amoebic dysentery
2. Cysts resist digestion by host
3. Mitotic divisions occur in cysts, release four, eight or more amoebas
4. Cysts dispersed in feces, transmitted via food, water, flies, direct contact
5. Spread of disease limited by proper sanitation and hygiene

7. Actinosphaerum is an unusual kind of amoeba fig 31.5
1. Member of phylum Actinopodia
2. Have glassy skeletons with needlelike pseudopods

2. A Possible Missing Link
1. Pelomyxa palustris may represent early stage of eukaryotes fig 31.6
1. Stage before mitochondrial symbiotic event and evolution of mitosis
2. Lacks mitochondria, does not undergo mitosis

2. Nuclei divide by simple pinching apart into two nuclei, like bacteria
3. Larger than bacteria, visible to naked eye
4. Possess two special symbionts that play same role as mitochondria
5. Assigned to own phylum, Caryoblastea

3. Foraminifera: Forams
1. Heterotrophic, marine organisms
2. Variable in size
3. Possess pore-studded shells called tests
1. Organic matter reinforced with inorganic material
2. Use sand grains, echinoderm plates, spicules from sponges
3. Shells may appear quite different from one another

4. Most live in sand or attach to other organisms, two families are free-floating, planktonic
1. Tests are usually multichambered, often spiral shaped
2. Cytoplasmic extensions called podia extrude through pores in test fig 31.7
3. Podia used for swimming, gathering material for test, feeding
4. Eat a wide variety of organisms

5. Complex life cycles with sporic meiosis
6. Provides extensive fossil record
1. Used as geological markers
2. Used as guide to oil-bearing strata

7. Form limestone structures like White Cliffs of Dover fig 31.8

3. The Algae
1. Chlorophyta: The Green Algae
1. Ancestors of all plants were multicellular green algae
1. Have to similar chloroplasts
2. Contain chlorophylls a and b, carotinoids

2. Varied group
1. Represented by aquatic and semiterrestrial habitats
2. Unicellular and multicellular forms
3. Generally microscopic with few macroscopic forms like Ulva fig 28.12b

3. Well-known genus is Chlamydomonas fig 31.9
1. Microscopic, unicellular and biflagellated
2. Light sensitive eye spot orients cell for swimming
3. Most individuals are haploid
4. Reproduces asexually by cell division
5. In sexual reproduction two fuse to form diploid zygote with four flagella
1. Zygote forms resting stage called zygospore
2. Meiosis occurs at end of resting stage, produces four haploid cells

4. Evolutionary specialization in Chlamydomonas-like cells
1. Nonflagellated Chlorella
1. Reproduces only asexually
2. Possible use as food source for humans and other animals

2. Motile, colonial forms leading to Volvox fig 31.1
1. Specialized reproductive cells give rise to new colonies
2. Have definite anterior and posterior ends
3. Flagella beat to rotate colony clockwise
4. Division of labor among different types of cells in colony

5. Other growth forms
1. Filamentous algae: Spirogyra
1. Differ substantial from rest of green algae
2. Sometimes placed in separate phylum, new research very revealing

2. Sheet-like algae: Ulva fig 28.12b
1. Attaches to substrate with basal cell protuberances
2. Exhibits sporic meiosis and alternation of generations fig 29.7c
3. Haploid gametophytes and diploid sporophytes resemble one another

3. Stoneworts: Chara and Nitella fig 31.10
1. Complex forms, have whorled branches
2. Reproductive gametangia are complex and multicellular
3. Abundant in brackish water, common fossils

2. Rhodophyta: The Red Algae
1. Most common coastal seaweeds
2. Chloroplasts related to cyanobacteria
1. Possess phycoerythrin, phycobilin pigment
2. Chlorophyll a and phycobilins, like cyanobacteria
3. Cyanobacteria were likely candidates for symbiotic events

3. Primarily multicellular fig 28.12c
1. More common in warm water than brown algae
2. Efficiently absorb green, violet and blue lights
3. Able to grow at greater depths than green or brown algae

4. Body form composed of complex, interwoven filaments
1. Coralline algae deposit calcium carbonate in cell walls fig 31.11
2. Others incorporate sulfated polysaccharides like agar, carrageenan

5. Economic importance
1. Agar used as laboratory medium, base for cosmetics
2. Prevent baked goods from drying out, temporary preservative for meat and fish
3. Carrageenan stabilizes paints, cosmetics and ice cream
4. Nori cultivated for human consumption

6. Complex life cycles involve alternation of generations, sporic meiosis
7. Completely lack flagella and centrioles at all stages
8. May be one of most ancient groups of eukaryotes, along with fungi

3. Phaeophyta: The Brown Algae
1. Mostly multicellular marine organisms
2. Conspicuous seaweeds, include kelps
1. Fast growing and photosynthetically productive
2. Possess flattened blade, stalks and anchoring base
3. Provide food for numerous animal forms fig 31.12

3. Largest specimens in genera like Macrocystis
1. Some specimens grow as large as 100 meters in length
2. Flattened blades help kelp float on top of water
3. Base anchored tens of meters below
4. Sargassum also ecologically important
5. Exhibit complex internal differentiation of conducting tissues

4. Possess chlorophyll a and c chloroplasts, like diatoms and dinoflagellates
5. Exhibit alternation of generations
1. Diploid sporophyte: Large, conspicuous kelp-like form
2. Haploid gametophyte: Small, filamentous form
3. Sporophytes produce sporangia, after meiosis produces spores
4. Spores divide by mitosis, give rise to gametophytes
5. Two different gametophytes, produce either male or female gametes
6. Gametes fuse producing a zygote that becomes the sporophyte

6. Economic importance for sodium and potassium salts, iodine and alginates
7. Potential for farming as source of fuel

4. The Diatoms
1. Chrysophyta: The Diatoms
1. Produce unique carbohydrate called chrysolaminarin
2. Include diatoms and golden algae
3. Diatoms are photosynthetic, unicellular organisms
1. Double shells of opaline silica
2. Resemble box with lid

4. Chloroplasts resemble that of dinoflagellates and brown algae
1. Chlorophylls a and b, carotinoids
2. Groups are dissimilar, probably do not share immediate common ancestor

5. Well-represented in living and fossil specimens
1. Fossils produce thick sediments of diatomaceous earth
2. Used as abrasive or paint additive

6. Occur in plankton and attached to submerged objects in shallow water
7. Some move by secretions produced from groove along each shell
8. Grouped by radial or bilateral symmetry fig 31.13
1. Shells are rigid
2. Asexual reproduction separates shell halves
3. Each half produces new shell within old one
4. Organisms and shells get smaller with each consecutive division
5. When size is too small, cell slips shell and grows to full size, makes new shell

9. Individuals are diploid, meiosis occurs more frequently under starving conditions
1. Marine diatoms produce multiple sperm or single egg
2. Freshwater diatom gametes are amoeboid and similar in appearance

2. The Golden Algae
1. Named for yellow and brown carotenoid pigments, xanthophyll accessory pigments
2. Unicellular, often colonial, found in freshwater
3. Have two flagella, both attached to same end of cell
4. Form resistant cysts when ponds dry out in summer, viable cells emerge when wetter

5. The Flagellates
1. Pyrrhophyta: The Dinoflagellates
1. Unicellular, photosynthetic, mostly marine
2. Some planktonic forms are luminescent
3. Distinctive flagella and coat, not directly related to other protists
1. Two flagella beat in grooves cause a spinning motion
2. Protective coat composed of stiff cellulose plates fig 31.14

4. Most have chlorophyll a and c along with carotinoids
1. Resemble diatoms and brown algae
2. May have ingested them and acquired their chloroplasts

5. Some forms are symbionts in animals
1. Sea anemones, mollusks and corals fig 31.15a
2. Called zooxanthellae, lack characteristic cellulose plates fig 31.15b,c
3. Primary factor for high productivity of corals in nutrient poor water

6. Periodic mass reproduction causes blooms and red tides
1. Pigments responsible for color of water
2. Produce toxins harmful to many vertebrates
3. Toxins accumulated by shellfish can poison humans, other consumers

7. Reproduce primary by longitudinal cell division
1. Sexual reproduction does occur
2. Mitosis is unique as it occurs within nucleus
1. Chromosomes are permanently condensed
2. Are distributed along sides of channels containing bundles of microtubules

2. Euglenophyta: The Euglenoids
1. Mostly fresh water organisms
2. Group has characteristics of plants and animals
1. Some specimens have chloroplasts and are photosynthetic
2. Others lack chloroplasts and are heterotrophic
3. Some can transform from autotrophs to heterotrophs and back, depending on light

3. Small size with variable form
1. Thin flexible pellicle lies within cell membrane
2. Composed of interlocking proteinaceous strips

4. Reproduction via mitotic cell division
1. Nuclear envelope remains intact through entire process
2. No known sexual reproduction

5. Model specimen is Euglena fig 31.16
1. One short, one long flagellum attached to flask-shaped reservoir
1. Long flagellum has row of short hairlike projections along one side
2. Short flagellum does not emerge from reservoir

2. Contractile vacuoles collect excess water, pump it out reservoir
3. Has light sensitive stigma
4. Has numerous small chloroplasts with chlorophylls a, b and carotinoids
1. Probable common origin of chloroplasts of euglena and green algae
2. Euglena may have acquired chloroplasts by ingesting green algae

3. Zoomastigina: The Zoomastigotes
1. Unicellular, heterotrophic, highly variable in form fig 31.17
2. Possess one to thousands of flagella
3. Free-living and parasitic forms
4. Many reproduce only asexually, some reproduce sexually
5. One group alternates between amoeboid and flagellated stages
6. Many trypanosomes are human pathogens fig 31.18
1. Cause sleeping sickness, East Coast fever, Chagas' disease
2. Spread by various insects, such as tsetse flies fig 31.21b
3. Attempts to produce vaccine via genetic engineering
1. Difficult due to constant changes in glycoprotein coat
2. Caused by gene recombination during asexual cycle

7. Other species inhabit guts of wood-eating insects fig 31.17b
1. Possess enzymes capable of digesting cellulose
2. Provide food for host

8. Choanoflagellates are likely ancestors of all animals fig 31.17a
1. Definite relationship to sponges
2. Possess single flagellum, funnel-shaped contractile collar
3. Feed on bacteria strained out by collar

4. Hiker's Diarrhea
1. Caused by Giardia lamblia, found throughout world fig 31.19
1. Occurs in water, infects wild and domesticated animals, humans
2. May appear in city water supplies, requires boiling water to kill

2. May cause nausea, cramps, bloating, vomiting, diarrhea
1. No longer thought to be harmless
2. May infect 16 million Americans

3. Lives in upper small intestine of host
1. Form is motile, cannot live outside body
2. Spreads as cysts in feces, can survive for months in cool water
3. Resistant to treatment with chlorine and iodine
4. Spread by human pollution
5. Good sanitation necessary when in wilderness
1. Dogs should be kept out of pristine areas, contract and spread disease
2. Must filter drinking water with micropore filter or boil for one minute

6. The Sporozoans
1. Apicomplexa: The Sporozoans
1. Nonmotile, spore-forming animal parasites
2. Exhibit fibrils, microtubules, vacuoles and organelles at one end
3. Have complex life cycles with sexual and asexual phases
1. Exhibit alternation of haploid and diploid generations
2. Both generations also reproduce by mitosis to increase numbers
3. Fusion of gametes produces a thick-walled cyst, the oocyst
4. Meiotic divisions in oocyst produce infective haploid spores, sporozoites

4. Common example Plasmodium causes malaria
1. Sporozoite stage carried by Anopheles mosquito fig 31.20
2. Injected into bloodstream, travel to liver, divides asexually
3. Become merozoite and reinvade liver cells or return to bloodstream
4. Invade red blood cells, cause them to rupture, releases toxic substances
5. Some merozoites develop into male or female gametocytes
6. Extracted by mosquito, produce sperm or eggs
7. Fuse, form oocysts that undergo mitosis forming sporozoites

2. Malaria
1. One of most serious diseases in the world, 500 million infected at any one time
1. Kills most children who contract it, 200 million humans die each year
2. Symptoms include chills, fever, sweating, enlarged spleen, confusion, thirst
3. Victim may die of anemia, kidney failure, brain damage
4. may be controlled by victim's immune system, drugs

2. Eradication of malaria
1. Elimination of mosquito vectors by use of DDT
1. Cannot use DDT in U.S.
2. Effectiveness is dropping
3. Potential environmental problems

2. Development of drugs to poison parasites
3. Development of vaccines

3. Large number of new cases due to drug resistant strains
4. Genetic engineering has developed antibodies to parasites

3. Vaccines Against Malaria
1. Three different stages of Plasmodium make three antigens, sensitive to three antibodies
2. Vaccine against sporozoites may not make very effective vaccine
1. Travel rapidly to liver, no longer exposed to antibodies
2. Multiply readily, even one will cause disease

3. Compound vaccine most effective, hard to develop
4. Experimental vaccine developed in 1997 fig 31.21
5. Induces immune system to produce defenses to destroy parasite in future infections
1. Six out of seven vaccinated individuals did not get malaria when exposed

7. The Ciliates
1. Ciliophora: The Ciliates
1. Unicellular and heterotrophic
2. Have large numbers of characteristic cilia fig 31.22a
1. Arranged in longitudinal rows or spirals
2. Coordinated beating provides motility to cells
3. Often fuse to form structures modified for feeding or locomotion

3. Outer pellicle is tough but flexible
4. Two types of nuclei fig 31.22b
1. Micronuclei contain normal diploid chromosomes
1. Divide by meiosis
2. Undergo genetic recombination

2. Macronuclei contain genes for routine cellular activities
1. Derived from certain micronuclei in complex series of steps
2. Divide by elongating and constricting

3. Specialized vacuoles ingest food and regulate water fig 31.23
1. Food enters through gullet and passes into vacuoles
2. Digestion occurs, wastes empty via cytoproct
3. Contractile vacuoles function to regulate water balance, expand and contract

5. Non-sexual reproduction by transverse fission fig 31.24a
6. Sexual reproduction in Paramecium called conjugation fig 31.11b
1. Two different mating types exchange pair of haploid micronuclei
2. Macronucleus in each individual disintegrates
3. Replications of micronuclei reconstitutes macronucleus

7. Progeny undergo 50 asexual divisions before they can conjugate
1. Biological clocks are then restarted for next conjugation event
2. After 600 asexual divisions, proteins around gullet lost
3. Can no longer recognize sexual mating partner
4. Death follows 100 divisions later
5. Events unknown, associated with accumulation of a protein

8. The "Molds"
1. Acrasiomycota: The Cellular Slime Molds
1. Once thought to be related to fungi
1. Most closely related to amoebas
2. Have certain characteristics that make them distinct

2. Common in fresh water, damp soil, rotting vegetation
3. Important group for studies on differentiation fig 31.25
4. Presentation of life cycle
1. Individuals behave as individual amoebas
2. At certain phase cells aggregate into motile slug
3. Transforms into sorocarp, amoebas encyst as spores
4. Some amoebas fuse sexually forming macrocysts with diploid nuclei
5. Zygotic meiosis occurs in macrocysts after a short period
6. Other amoebas released directly to reaggregate into new slug

5. Study chemical signals in development and differentiation in Dictyostelium
1. Aggregation occurs when bacteria in area are eaten and starvation ensues
2. Induced by pulses of cyclic adenosine monophosphate (cAMP) secreted by cells
3. Spores differentiate in terminal portion of sorocarp
4. Spores released, can release new amoeba to reinitiate cycle

2. Myxomycota: The Plasmodial Slime Molds
1. Consist of streaming plasmodium fig 31.26
1. Feeding phase may be yellow, orange or other color
2. Cytoplasm exhibits conspicuous streaming
3. Engulf and digest bacteria, yeasts, bits of organic matter
4. Lack dividing cell walls, thus multinucleate

2. Nuclei undergo mitosis in synchrony, nuclear envelop breaks down in late anaphase or telophase
3. Lack centrioles
4. No strong evidence indicating they are related to cellular slime molds
5. Forms sporangium under adverse conditions fig 31.27
1. Spores may be diploid or haploid
1. If diploid, meiosis occurs within 24 hours of formation
2. Three of four nuclei disintegrate, leaving one haploid nucleus

2. Resistant spores survive years if dry
3. With favorable conditions release amoeboid or flagellated gametes (protoplasts)
4. Gametes fuse to produce diploid plasmodium

3. Oomycota
1. Include water molds, white rusts and downy mildews
2. Parasites or saprobes
3. Mistakenly classified with fungi
1. Cell walls are composed of cellulose or similar polymers
2. Fungi cell walls composed of chitin
3. Gametic meiosis produces a diploid phase (unlike fungi)
4. Exhibit normal mitosis (mitosis in fungi is unusual)

4. Possess filamentous structures called hyphae
5. Live in freshwater or soil, many are plant or animal parasites
6. Exhibit unique sexual reproduction
1. Zoospores have two unequal flagella
2. Spores produced asexually in sporangium
3. Female gametangium called oogonium with one to eight eggs
4. Male gametangium called antheridium with numerous male gametes
5. Fusion produces zygote that becomes thick-walled oospore

7. Typical water mold: Saprolegnia fig 31.28
8. Important plant pathogens
1. Downy mildew of grapes
2. Late blight of potatoes caused Irish potato famine