chapter 18: the protists

the protists

-historically, least precise Eukaryotic kingdom

-any eukaryote that's not an animal, plant or fungus

classification of protists

-Historically classified as protozoa, algae, slime molds, water molds based on mode of nutrition

-Currently, eukaryotes with the taxonomic classification in flux

-New classification evolving based on molecular differences (18s rRNA genes & others)

kingdom protista

-over 65,000 different eukaryotes

-Most are unicellular, some colonial, some multicellular

-Most free living, some symbionts

-Some parasites of animals

Multicellular protists

lack the level of tissue organization present in higher eukaryotes, although some of the largest approach it

nutrition in protists

-Protozoa and slime molds are chemoorganoheterotrophic protists

-Mostly saprophytes

-Algae are photolithoautotrophic protists

saprophytes

nutrients obtained from dead organic matter through release of digestive enzymes

oxygen requirements in protists

Strict aerobes, use photosystems I and II for oxygenic photosynthesis

protist cell membrane

structure similar to multicellular plants/animals

protist cytoplasm

subdivided into compartments/organelles

protist proteinacious pellicle

provides structural support for protists that lack walls (most protzoans)

nearly all algae have...

cell walls of varying composition

protist vacuoles

-Vacuoles commonly present in protists

-contractile vacuoles help maintain osmoregulation

-phagocytic vacuoles allow some protists to ingest food

energy production in protists

-through mitochondria in aerobic chemoorganoheterotrophic protists

-through chloroplasts and mitochondria in photosynthetic protists

encystment

-dormant form with thick cell wall and very low metabolic activity

-some protists can change into cysts at certain times

function of cysts

-protects against environmental changes

-serve as a means of host to host transfer for parasitic species

-germinates back to vegetative form when environment favorable again

group 1

Excavata

Excavata

Microaerophilic protist members are flagellated and lack mitochondria

Giardia have mitosomes

mitochondria-like double-membrane bounded organelles

most Excavata are harmless symbionts with the following exceptions

Giardia - causes diarrhea

Hexamida salmonis - fish parasite

Euglenozoa Excavata

-Commonly found in fresh water

-Alternate nutritional lifestyles

-Contain chloroplasts

-Euglena is the representative phototrophpellicle

-chlorophylls a and b, carotenoids

-contractile vacuole and flagella

Euglenozoa Excavata alternate nutritional lifestyles

both chemotrophic and phototrophic

Euglenozoa Excavata contain chloroplasts

-used when living in light

-in dark environments lose chloroplast can exist as chemoorganotrophs

Euglena is the representative phototrophpellicle

proteinaceous strips, microtubules

Pathogenic Euglenozoa

-Trypanosomes parasites of plants and animals

-T. gambiense and T. rhodesiense cause African sleeping sickness

-Transmitted by bite of fly (vector)

Super-Group 2

Amoebozoa

Amoeboid motility

use of pseudopodia for locomotion and feeding

Naked amoebae

are surrounded only by a plasma membrane

Testate amoebae

plasma membrane covered by material made by amoebe or obtained from the environment

slime molds

2 main groups

plasmodial slime mold

-vegetative form is a plasmodium

-plasmodium lacks cell membrane

-contain up to 10,000 diving nuclei

streaming masses of colorful protoplasm...

creep along in amoeboid fashion

plasmodial slime mold functions

-degrade rotting organic matter and feed by endocytosis

-develop fruiting bodies to produce spores

-spores germinate in good environments

plasmodium

is a multinucleate mass of streaming cytoplasm

cellular slime mold

-vegetative form is a single cell

-vegetative form - Unicellular and amoeboid

-Endocytosis to feed on bacteria and yeast

-Several stages in life cycle

-Multicellularity in some portions of life cycle

cellular slime mold life cycle

-Amoeboid cells - unicellular, vegetative form

-Cell aggregation due to chemical signals

-Cell aggregate and fuse to form slug phase (motile)

-Sporangia develops out of slug phase

-Spores released

-Spores germinate in suitable environment to form amoeboid cells

Group 3

Rhizaria-Foraminifera

Foraminiferans

-have filopodia (thin pseudopods) arranged in branching network

-have characteristics tests arranged in multiple chambers that are sequentially added as organism grows

-Found in marine and estuarine habitats

-Foram tests make up most modern-day chalk, limestone, and marble

Group 4

Alveolata

Alveolate

-All have structure on inside cell in cytoplasm just under cell membrane that looks like an alveolus (from mammal lungs)

-Exact function uncertain

Alveolata - Dinoflagellates

-Dinoflagellates - large group found in marine plankton

-Some cause toxic blooms in seawater

-Called Red Tides

-Nutritionally complex

-Symbiotic forms

Dinoflagellates are nutritionally complex

most photolithoautotrophs; some also facultative chemoorganoheterotrophs

Dinoflagellates have symbiotic forms

(zooxanthellae) live in association with reef building corals

Alveolata- Ciliophora

-Chemoorganoheterotrophic

-Found in water and wet soil

-Use many cilia as locomotory and feeding organelles

-Two nuclei - binucleate

ciliaphora reproduction

Reproduction asexual by transverse binary fission

-sexual by conjugation

-micronucleus diploid, normal somatic number of chromosomes

-Controls sexual reproduction

-macronucleus controls normal cell functions and asexual reproduction

Alveolata- Diatoms

-Chlorophylls and accessory pigments

-Cell wall of silica unique, beautiful patterns

-Important in global carbon cycling

-marine planktonic diatoms produce 40-50% of organic ocean carbon

Alveolata- Apicomplexans

-Apicomplexans are obligate parasites of animals

-cause severe diseases such as malaria, toxoplasmosis, and coccidiosis

-produce life cycle stage called sporozoites

-function in transmission of the parasite to a new host

more about apicomplexans

-Contain unipolar apical complex

-Parasitic with complex life cycles

-life cycle has both sexual and asexual phases

-clonal and sexual stages are haploid, except for zygotes

-Most important member is Plasmodium, the cause of malaria