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Protists

                                                                              

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Protista

Classifying ProtistsGeneral Biology of Protists

The Kingdom Protista is divided into four major groups, not technical divisions but instead grouped by lifestyle:

A- The protozoans.

B- The slime molds.

C- The unicellular algae.

D- The multicellular algae.

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Protista

Protists are the most diverse of the four kingdoms in the domain Eukarya.Fossil history 2.5 billion years old artificial group of convenience

single-celled eukaryotic organisms Not plant not animal not fungi

little consensus about classification

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They are first eukaryotes, having a well organized nucleus and complex membranous organelles.They are unicellular or colonial forms without distinct division of labor.

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They are autotrophic or heterotrophic showing varieties of metabolic systemsLocomotion is by pseudopodia, flagella or cilia.They show mitosis, meiosis and simplest type of sexual reproduction for the first time. Common examples are Ameba, Paramecium, Euglena, diatoms and dinoflagellates.

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Ameba

A single-celled (protozoan) organism that constantly changes shape. The word "ameba" is from the Greek "amoibe" meaning "change."

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Structure of an amoeba: unicellular animal with pseudopods that lives in fresh or saltwater.Pseudopodium: part of the amoeba used for locomotion.Ectoplasm: vitreous superficial layer of an amoeba.Endoplasm: central part of an amoeba.Cell membrane: membrane covering an amoeba.Contractile vacuole: cavity of the amoeba that is able to contract.Food vacuole: cavity of the amoeba responsible for digestion.Nucleus: central organelle for an amoeba.Digestive vacuole: cavity of the amoeba responsible for digestion.

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Classification

Protozoans include all protists that ingest their food, they live primarily in aquatic habitats, such as ponds, drops of water in soil, or the digestive tracts of animals.

A small group of protozoans function as parasites.

The second group, the slime molds, are unique in having both unicellular and multicellular stages.

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Theory of Endosymbiosis

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Evidence for the endosymbiont theory is that mitochondria and chloroplasts:

- Are appropriate size to be descendants of eubacteria. - Have inner membranes similar to those on

prokaryotic plasma membranes. - Replicate by splitting, as in prokaryotes. - DNA is circular and different from the DNA of the

cell's nucleus. - Contain their own components for DNA transcription

and translation into proteins . - Have ribosomes similar to prokaryotic ribosomes. - Molecular systematics lend evidence to support this

theory. - Many extant organisms are involved in

endosymbiotic relationships.

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Protist Classification

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General Biology of the Protists

Cell surface possess varied array of cell surfaces

Plasma membrane only, extracellular material – cells walls (diatoms –silica)

Locomotor organelles chiefly flagellar rotation or pseudopodial

movement Pseudopodia – false foot – extension of body

Cyst formation dormant form of a cell with resistant outer

covering in which metabolism is essentially shut down (harsh environments – gastric secretions)

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General Biology of the Protists Nutrition

employ all forms but chemoautotrophic phototrophs heterotrophs

phagotrophs - visible food particles osmotrophs - food in soluble form

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General Biology of the Protists Reproduction

typically reproduce asexually binary fission - equal halves budding - progeny cell smaller schizogony - multiple fission - multiple individuals simultaneously

sexual reproduction in times of stress gametic meiosis - before gametes

Diploid - haploid zygotic meiosis - after fertilization

Individuals are Haploid until diploid zygote is produces intermediary meiosis – alternating (alternation of generation) haploid

and diploid undergo mitosis

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Protists

Six identified lineages: Euglenozoa Alveolata Stramenopila Rhodophyta Chlorophyta Choanoflagellida

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Euglenozoa

Euglenoids most are freshwater about one-third are autotrophic, rest

heterotrophic pellicle (interlocking proteinaceous strips in

helical pattern (flexibility) lies within plasma membrane stigma - light sensitive organ that aids in orienting

toward light Euglena

two flagella attached to reservoir contain numerous chloroplasts

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Euglenoids

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EuglenozoaKinetoplastids - 2nd group within Euglenozoa unique, single mitochondrion in each trypanosome

(2 types of DNA) mini-circles and maxi-circles Trypanosomes are kinetoplastids that cause many serious

human diseases. Usually tropical African sleeping sickness Chagas

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AlveolataDinoflagellates Most are photosynthetic Fresh and Saltwater Encased in cellulose/silica plates distinctive

flagella -single spins as it moves, protective coats (cellulose/silica plates), and

biochemistry –chlorophyll a and c and carotenoids

reproduce primarily by asexual cell division responsible for “red tides” – poisonous toxins

inhibit diaphragm and cause respiratory failure in many vertebrates

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AlveolataApicomplexes spore-forming animal parasites

unique arrangement of fibrils, microtubules, vacuoles, and other cell organelles

Most famous - malarial parasite - Plasmodium malaria eradication

eliminating mosquito vectors poison parasites inside human body - Quiinine develop vaccines

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Plasmodium Life Cycle

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AlveolataCiliates most feature large numbers of cilia

usually arranged in longitudinal rows or spirals around the body

form vacuoles to ingest food and regulate water balance

waste emptied through cytoproct

Paramecium

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Paramecium

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Stramenopila and RhodophytaStramenopila includes brown algae,

diatoms, and oomycetes brown algae - conspicuous

seaweeds alternation of generations

diatoms (phylum Chrysophyta) - photosynthetic, unicellular organisms with double shells of opaline silica

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Brown Algae

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Stramenopila and RhodophytaStramenopila oomycetes (water molds) - parasites or

saprobes. comprise water molds, white rusts, and downy

mildews motile zoospores bear two unequal flagella life cycles characterized by gametic meiosis and

a diploid phase

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Stramenopila and RhodophytaRhodophyta Red algae range in size from

microscopic to very large. origin a source of controversy

tentatively treated as a sister clade of green algae (Chlorophyta)

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Chlorophyta

Green algae are the ancestors of the plant kingdom. extensive fossil record dating back

900 million years mostly aquatic Chlamydomonas well-known genus

probably represents primitive state Chlorophyta did not give rise to land

plants.

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Chlamydomonas Life Cycle

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Choanoflagellida

Choanoflagellates are most like the common ancestor of the sponges and all animals. contain a single emergent flagellum

surrounded by a funnel-shaped, contractile collar

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Amoebas

contain pseudopods that can form at any point on the cell body and can move in any direction Phylum Actinopoda (radiolarians)

secrete glassy exoskeletons of silica.

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Foraminifera

heterotrophic marine protists with pore-studded shells complex life cycle with alternation

between haploid and diploid generations

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Slime MoldsSlime molds originated at least three distinct times. plasmodial slime molds

stream along as a non-walled, multinucleate mass of cytoplasm, plasmodium

produces sporangium during times of resource shortage

forms spores that quickly undergo meiosis

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Slime MoldsCellular slime molds individual organisms behave as separate

amoebas, moving through soil or other substrate and ingesting bacteria individual organisms aggregate and form

moving mass “slug” when food becomes scarce

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Cellular Slime Mold Development

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SummaryEndosymbiosisClassifying ProtistsGeneral Biology of ProtistsSix Lineages Euglenozoa Alveolata Stramenopila Rhodophyta Chlorophyta Choanoflagellida

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