Ch 23 Pt 1: Protists

protists background

• eukaryotes

• most are microscopic and unicellular

• abundant in soil, freshwater, brackish, and marine environments

• some have macroscopics cells

• some are multicellular

• some are parasites

the complexity and diversity of protists makes it difficult to classify

1. cannot be classified as plants

   1. gametes and zygotes are not protected from drying out nor do they have roots, stems, etc

2. cannot be classified as fungi

   1. do not have chitin in their cell wall

3. cannot be classified as animals

   1. do not undergo embryonic development

who was the first scientist to observe protists?

antonie van leeuwenhoek, 1674

eukaryote characteristics

• cells w/ nuclei surrounded by a nuclear envelope w/ nuclear pores

• mitochondria

• cytoskeleton of microtubules and microfilaments

• flagella and cilia

• chromosomes organized by histones

• mitosis

• sexual reproduction

• cell walls (absent in animal cells)

protist structure

• most are unicellular

• some are colonial and multicellular

• some are composed of enormous, multinucleate, single cells

• unicellular protists carry out essential functions using subcellular organelles

unique plastids came from eukaryotic, symbiotic alga cells through secondary endosymbiosis

cyanobacteria became the chloroplast, proteobacteria became mitochondria

protist cell structure

• nucleus

• endoplasmic reticulum

• golgi apparatus

• lysosomes (hydrolytic digestive enzymes)

• contractile vacuoles (pumps excess water from protist cell)

endoplasmic reticulum

• if ribosome is attached: protein synthesis

• if ribosome is not attached: lipid synthesis

true or false. protist cells may be enveloped by animal-like cell membrane or plant-like cell walls

true

protist metabolism

• exhibit many forms of nutrition

• may be aerobic or anaerobic

• photoautotrophs

• heterotrophic protists

• amoebas and some other heterotrophic protist species ingest particles by phagocytosis

• saprobes

• mixotrophs

photoautotrophs

characterized by the presence of chloroplasts and perform photosynthesis

heterotrophic protists

consume organic materials (such as other organisms) to obtain nutrition

saprobes

subtypes of heterotrophs absorb nutrients from dead organisms or their organic wastes

mixotrophs

combine photosynthesis and heterotrophic nutrition

protist motility

• majority are motile

• some have one or more flagella, which they rotate or whip

• others are covered in cilia that they beat in a coordinated manner to swim

• others from cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a substrate, and pull themselves forward

• some can move toward or away from a stimulus, called taxis

• phototaxis

phototaxis

movement toward light, accomplished by coupling their locomotion strategy w a light sensing organ

protist reproduction

asexual reproduction

• binary fission

• multiple fission

• budding

sexual reproduction

protist life-cycles

binary fission

• asexual

• produces 2 daughter cells

• can be divided into transverse or longitudinal

longitudinal binary fission

the plane of division passes along the longitudinal axis of the organism (Euglena)

transverse binary fission

the plane of division is through the transverse axis of the organism (Paramecium)

multiple fission

• asexual

• some protists such as the true slime molds exhibit multiple fission and simultaneously divide into many daughter cells

budding

• asexual

• some protists produce tiny buds that go on to divide and grow to the size of the parental protist

true or false. many protist species can switch from asexual to sexual reproduction when necessary

true

sexual reproduction

• involves meiosis and fertilization, common among protists

• often associated w periods when nutrients are depleted or environmental changes occur

• may allow the protist to recombine genes and produce new variations of progeny

protist life-cycles

• range from simple to extremely elaborate

• certain parasitic protists have complicated life cycles

• must infect different host species at different developmental stages to complete their life cycle (ex. Plasmodium → malaria)

• some protists are unicellular in the haploid (n) form and multicellular in the diploid (2n) form

• alternation of generations

alternation of generations

strategy where protists have multicellular stages in both haploid and diploid forms

• ex. Laminaria (brown alga)

cysts

• a protective, resting stage

• endospores

• depending on habitat of the species, the cysts may be particularly resistant to temp extremes, desiccation, or low pH

• allows certain protists to “wait out” stressors until their environment becomes more favorable for survival or until they are carried (such as by wind, water, or transport on a larger organism) to a different environment

• cysts exhibit virtually no cellular metabolism

endospores

an adaptive strategy against adverse environmental conditions

Giardia lamblia

a flagellate protozoan which is capable of forming cysts

eukaryotic supergroups

1. Archaeplastida

2. Amoebozoa

3. Opisthokonta

4. Rhizaria

5. Chromalveolata

6. Excavata

true or false. protists are not in all 6 eukaryotic supergroups

false

true or false. protists share common ancestors w plants, animals, and fungi

true

Red Algae

archaeplastida

• mostly marine, multicellular seaweeds

• chloroplasts include unique red phycoerythrin accessory pigment

  • helps absorb light in deeper water

• humans eat it (seaweed)

• cellulose + unique cell wall polysaccharides

  • carrageenan thickener (ice cream)

  • agar (for petri dish cultures, food, nori)

Chlorophytes

archaeplastida

• green algae (along w Charophytes)

  • chloroplasts same as in plants

• most are freshwater; many marine

• many w bi-flagellated cells

• unicellular forms:

• colonial forms

colonial forms of Chlorophytes

Scenedesmus: a simple colony of four cells

Gonium: a small colony

Volvox: a large colony w/ some specialization

Chlorophyte: unicellular form

phytoplankton (ex. Chlamydomonas)

Chlorophytes: colonial form

Volvox

Chlorophytes: multinucleate single cells, large body form

Caulerpa, an intertidal chlorophyte

Chlorophytes: multicellular forms

• freshwater algae (ex. Cladophora)

• seaweeds (ex. Ulva: edible sea lettuce)

  • vitamin C, D, and iodine

  • flattened boy, showing up w no differentiation between stem and leaves

Amoebozoans

• slime molds

• gymnamoebas

• entamoebas

Amoebozoans do amoeboid ________ (cell crawling) and ___________ using lobe-like pseudopodia (false feet) (no cell walls)

movements, phagocytosis

slime molds

Amoebozoans

• live in moist terrestrial habitats (rotting wood, etc.)

• use pseudopodia to move and ingest bacteria

  • move and live up to ingest

• ex plasmodial slime mold and cellular slime mold

plasmodial slime mold

no cytokinesis → multinucleate, single cell

cellular slime mold

• aggregating into single body/mass when starving (survival structure)

• independent cells when lacking nutrients

Gymnamoebas

Amoebozoans

• found in soil, freshwater, and marine habitats

• moves w/ fat pseudopodia, feeding on bacteria, other protists, detritus

• ex. Amoeba proteus

entamoebas

Amoebozoans

• unicellular parasites of animals

• kills and feeds on host cells

• spreads by durable cyst form (endospores)

• ex. Entamoeba histolytica

Entamoeba histolytica

causes amebic dysentery

• kill and digest intestinal lining → bloody diarrhea, fever, abcesses intestinal perforation

Excavata

• diplomonads

• parabasalids

• euglenozoans

unifying features of excavata

unicellular, flagellated, and have no cell wall

diplomonads

Excavata

• unicellular, multiple flagella, no cell wall

• anaerobic, reduced mitochondria

• most are parasitic

• ex. Giardia intestinalis

Giardia intestinalis

intestinal paraiste

• durable cysts consumed in water

parabasalids

Excavata

• unicellular, multiple flagella, no cell wall

• anaerobic, reduced mitochondria, asexual reproduction

• most are symbiotic

• ex. Trichomonas vaginalis

• parabasalids in termites contain symbiotic bacteria that help w termites digest wood

Trichomonas vaginalis

human vaginal parasite (STD)

• more likely to get HIV and cervical cancer

Euglenozoans

Excavata

• unicellular, no cell wall, flagella w crystalline rod

• ex. Euglenas

• ex. Trypanosoma

Euglenas

free living, aquatic

autotroph w green chloroplasts (2o) (acquired during secondary endosymbiosis of a green algae or heterotroph or mixotroph (switches nutrition - dependent on amt of light)

Trypanosoma

blood parasite

• “sleeping sickness” carried by tse-tse fly)

kinetoplastids

• kinetoplast mitochondrial DNA: DNA molecules interlocked together

• not photosynthetic

• not plasmids