Chapter 24 Protists

Kingdom Protista “Simple” eukaryotes Mostly unicellular Some form colonies Some are coenocytic Multiple nuclei in one mass of cytoplasm A few are multicellular

Most protists live in aquatic environments Sixty major groups of protists Important in the biosphere Food for other organisms Photosynthetic protists supply oxygen

Locomotion Modes of nutrition Pseudopodia Flagella Cilia A few are nonmotile Modes of nutrition Autotrophs Heterotrophs

Chlamydomonas

Interactions with other organisms Free-living Mutualism Commensalism Parasitism Habitats Most live in the ocean or freshwater ponds, lakes, and streams Parasites live in host’s bodily fluids

Modes of reproduction Many protists reproduce both sexually and asexually Syngamy (union of gametes) Some protists are solely asexual

Endosymbiont theory Certain organelles arose from symbiosis with prokaryotes Mitochondria arose from aerobic eubacteria Chloroplasts arose from cyanobacteria

Primary and secondary endosymbiosis

Classifying eukaryotes Ultrastructure Fine details of cell structure Molecular data Ribosomal RNA Nuclear genes The protist kingdom is probably paraphyletic

Eight monophyletic groups of eukaryotes

Zooflagellates Mostly unicellular heterotrophs Move using flagella Now separated into several monophyletic groups Excavates Discicristates

Excavates live in oxygen-free environments Diplomonads No mitochondria No Golgi complex One or two nuclei Up to eight flagella Giardia is a parasite

Giardia

Discicristates have disc-shaped mitochondrial cristae Euglenoids About 1/3 are photosynthetic Inhabit freshwater ponds and puddles Trypanosoma causes African sleeping sickness

Euglena gracilis

Alveolates have flattened vesicles under the plasma membrane Ciliates Move by hairlike cilia Micronuclei for sexual reproduction Macronuclei control metabolism Reproduce sexually by conjugation

Paramecium, a ciliate

Alveolates Dinoflagellates Apicomplexans Mostly unicellular with two flagella Mostly photosynthetic Apicomplexans Parasitic Spore-forming Plasmodium causes malaria

Dinoflagellates

Heterokonts are motile with two different kind of flagella Water molds Mycelium absorbs organic material Reproduce asexually with biflagellate zoospores Reproduce sexually with oospores Phytophthora causes plant diseases

Mycelium around a dead insect Saprolegnia

Heterokonts Diatoms Golden algae Mostly unicellular with shells containing silica Some diatoms are part of plankton Golden algae Mostly unicellular, biflagellate algae Both freshwater and marine

Diatoms

Heterokonts Brown algae Multicellular seaweed Ecologically important in cooler ocean waters Kelps have leaflike blades, stemlike stipes, anchoring holdfasts, gas-filled bladders

Brown algae

Cercozoa are amoeboid cells that often have hard outer shells, called tests, through which cytoplasmic projections extend

Cercozoa Foraminferans Actinopods Many-chambered tests with pores Cytoplasmic extensions to move and obtain food Actinopods Mostly marine plankton Axopods to obtain food

An actinipod

Plants have chloroplasts bounded by inner and outer membranes Land plants, red algae, and green algae are monophyletic Red algae and green algae are in kingdom Protista

Red algae are mostly multicellular seaweeds Ecologically important in warm tropical waters Red algae with calcium carbonate in their cell walls are important for reef building

Red algae

Green algae are diverse in size, structural complexity, and reproduction May be the ancestors of land plants Multicellular forms do not have cells differentiated into tissues, unlike plants

Green algae

Amoebas move and obtain food using cytoplasmic extensions called pseudopodia Capture and engulf food by surrounding it and forming a vacuole around it Entamoeba histolytica causes amoebic dysentery

Plasmoidal slime mold Feeding stage is a multinucleate plasmodium that extends up to one foot in diameter In the reproductive stage, stalks called sporangia produce haploid spores

Plasmoidal slime mold

Cellular slime molds Feeding stage is individual amoeboid cells During moisture or food shortage, they aggregate into a migrating pseudoplasmodium Forms stalked fruiting body containing spores

Cellular slime mold