Eukaryotic Diversity Chapter 28

Protists Protists – eukaryotes; more complex than prokaryotes. 1 st – unicellular - called protists – in 1 big kingdom (Protista) Protista - unicellular eukaryotes that are not plants, fungi, or animals.

Some heterotrophs, some autotrophs, some both. Euglena use light (if available) to produce food or find food themselves (if no light)

Protists divided into 3 categories. 1 Protozoa- ingestive, animal-like. 2 Fungus-like protists. 3 Algae -- photosynthetic, plant-like protists. Movement - flagella, cilia (some point in life cycle)

Both move cell with rhythmic power strokes, like oars of boat. Reproduction and life cycles highly varied among protists.

Asexual - can shuffle genes through syngamy (union of 2 gametes) Primarily asexual; can reproduce sexually occasionally. Many form resistant cells (cysts) - can survive harsh conditions.

Protists found where water is (oceans, ponds, lakes); also damp soil, leaf litter, moist terrestrial habitats. Protists - part of plankton, communities of organisms that drift passively or swim weakly in water.

Many protists symbionts - inhabit body fluids, tissues, or cells of hosts. Relationships could be mutualistic or parasitic.

Origin Prokaryote - limited amount of metabolic activity. Evolution of multicellular prokaryotes - cells specialized for different functions.

Groups formed that had specialty or compartments for each activity (evolution of eukaryotes) Plasma membrane infolded, creating organelle membranes in eukaryotes. Chloroplasts, mitochondria evolved from endosymbiotic relationships (Endosymbiotic theory)

Ancestors of mitochondria - aerobic heterotrophic prokaryotes. Ancestors of chloroplasts - photosynthetic prokaryotes.

Evolved mutualistic relationship. Became more interdependent. Close similarity between bacteria and chloroplasts + mitochondria of eukaryotes.

Mitosis/meiosis - result of evolution. Mitosis - could reproduce large genomes in eukaryotic nucleus. Meiosis - essential process in eukaryotic sex.

Mitochondria, plastids contain DNA - not genetically self-sufficient. Why mitochondria have own DNA.

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Secondary endosymbiosis - heterotrophic protist engulfed algae containing plastids. Led to diversification of plastids (including chloroplasts).

Domain Archaea - more closely related to eukaryotes than prokaryotes.

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Flagellates Group Diplomonads: multiple flagella, 2 separate nuclei (double celled), no mitochondria or plastids. Includes Giardia.

Euglenoids - anterior pocket from which 1 or 2 flagella emerge. Most autotrophic; can be heterotrophic or mixotrophic. Example - Euglena

Kinetoplastids - single large mitochondrion. Symbiotic; include pathogenic parasites. Trypanosoma - African sleeping sickness.

Alveolata - flagellated protists (dinoflagellates), parasites (apicomplexans), ciliated protists (ciliates).

Example – dinoflagellates - big components of phytoplankton. Each dinoflagellate species has characteristic shape, reinforced by internal plates of cellulose - hard- shelled.

Red tides caused by dinoflagellates in bloom. Color comes from pigment they produce. Produce toxins deadly to predators and humans. 1 species - carnivorous; produces toxin to stun fish, then eats flesh.

Some dinoflagellates form mutualistic symbioses with cnidarians, animals that build coral reefs. Some are bioluminescent.

5 Apicomplexans Apicomplexans - parasites of animals; some cause serious human diseases. Spores - infectious. Plasmodium - protist that causes malaria; spends part of life cycle in mosquitoes, part in humans.

6 Ciliates Named for use of cilia to move and feed. Most ciliates live as solitary cells in freshwater. Ciliates - 2 types of nuclei, large macronucleus, several tiny micronuclei.

Paramecium - cilia along oral groove draw in food engulfed by phagocytosis. Paramecium expels accumulated water from contractile vacuole.

Ciliates reproduce via conjugation - micronuclei that have gone through meiosis exchange genetic information.

7 Stramenopila Includes heterotrophic and photosynthetic protists; presence of numerous fine, hairlike projections on flagella. Heterotrophic stramenopiles – oomycotes - water molds, white rusts, downy mildews.

Water molds important decomposers, mainly in fresh water. Form cottony masses on dead fish. Some water molds parasitic, growing on skin, gills of injured fish. White rusts and downy mildews parasites of terrestrial plants.

8 Heterokont algae Diatoms (Bacillariophyta) - glasslike walls composed of hydrated silica embedded in organic matrix. Reproduce mostly asexually; form cysts during certain parts of year.

Golden algae named for pigments (yellow and brown carotene and xanthophyll) Some mixotrophic; can form cysts that will last decades.

Brown algae - largest and most complex algae. Most multicellular, unlike other members of group. Brown or olive color - accessory pigments in plastids. Found in temperate waters.

9 Seaweed Largest marine algae - brown, red, and green algae - seaweeds. Inhabit intertidal and subtidal zones of coastal waters. Body of seaweed – thallus - consists of rootlike holdfast + stemlike stipe - supports leaflike photosynthetic blades.

Some brown algae have floats to raise blades toward surface.

Algae - many uses including thickener for foods. Seaweed popular food item in Asian countries.

Multicellular brown, red, and green algae show complex life cycles with alternation of multicellular haploid and multicellular diploid forms.

Diploid individual (sporophyte) produces haploid spores (zoospores) by meiosis. Haploid individual (gametophyte) produces gametes by mitosis that fuse to form diploid zygote.

10 Rhodophyta Red algae - no flagellated stages in life cycle. Red coloration visible due to accessory pigment. Red algae (Rhodophyta) - most common seaweeds in warm coastal waters of tropical oceans.

Some species that live down deep have special pigments - allow them to absorb blue and green wavelengths (only ones that penetrate bottom). Most red algae multicellular - some reaching size large enough to be “seaweeds.”

Life cycles of red algae especially diverse. In absence of flagella, fertilization depends entirely on water currents to bring gametes together.

11 Chlorophyta Green algae (chlorophytes) named for grass-green chloroplasts - similar to plants. Most of the species chlorophytes live in freshwater. Most green algae have both sexual and asexual reproductive stages.

3 groups of protists use pseudopodia, cellular extensions, to move and feed. Most heterotrophic; some parasitic. Rhizopods (amoebas) - unicellular - use pseudopodia to move and feed.

Amoeba extends pseudopod, anchors tip, streams more cytoplasm into pseudopodium. Pseudopodia activity not random - directed toward food.

Amoebas inhabit freshwater and marine environments. Most free-living heterotrophs. Some important parasites, including dysentery in humans.

Most heliozoans (“sun animals”) live in fresh water. Skeletons made of glass. Foraminiferans, (forams) almost all marine. Shells have pores in them. Pseudopodia extend through pores for swimming, shell formation, feeding.

12 Mycetozoa Mycetozoa (slime molds or “fungus animals”) neither fungi nor animals - protists. Slime molds feed and move via pseudopodia but comparisons of protein sequences place slime molds close to fungi and animals, not amoeba.

Plasmodial slime molds (Myxogastrida) brightly pigmented, heterotrophic organisms.

Cellular slime molds (Dictyostelida) straddle line between individuality and multicellularity. Feeding stage consists of solitary cells. When food scarce, cells form aggregate (“slug”) - functions as unit. Dominant stage - haploid stage.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings