Also known as protozoa This is now considered a misnomer and refers only to the animal-like protists

Diverse group Have little in common Difficult to classify Do share several features Appeared in the fossil record 1.5 b.y.a. (more recent than bacteria) Evolutionary advancement  a discrete, membrane-bound nucleus and organelles (ex. Ribosomes, mitochondria, and lysosomes)

General Characteristics All protists are eukaryotes Probably arose from prokaryotes Membrane-bound organelles provide a more efficient method of using available nutrients and carrying out metabolism

Most are microscopic and unicellular Found in fresh or salt water (aka plankton) Source of biological energy for nearly all food webs in aquatic and, in turn, terrestrial environments Supply 67% of the global supply of oxygen Some have simple multi-cellular structure

Nutrition Some are heterotrophic Others autotrophic Some alternate from 1 to other

Divided into three groups: Plant-like protists phytoplankton = photosynthetic Animal-like protists (aka protozoans) Zooplankton = heterotrophic Fungus-like protists Slime moulds

Plant-like Protists Traditionally called “Algae” (non-taxonomic) range from seaweed to greenish film on ponds Size  microscopic to 100 m long Appeared ~550 million years ago Majority are autotrophs (contain chlorophyll) Important food source for freshwater and marine organisms Most are multicellular but do not have tissues

Plant-like Protists cont’d Classified on basis of colour: Chlorophyta (green) - commonly called phytoplankton Phaeophyta (brown) commonly called Rhodophyta (red) seaweeds Chrysophyta (golden) – commonly called diatoms Pyrrophyta (dinoflagellates) Cryptophyta (cryptomonads) Euglenophyta (euglenoids)

Normally aquatic (marine and freshwater) May also be found in soils or on lower trunks of trees and on rocks (wet/moist env’ts) Contain chlorophyll and other colored pigments for photosynthesis

Phylum Euglenophyta Unicellular algae with characteristics of both plants and animals Plant characteristics : Photosynthetic in the light Large green chloroplasts (identical to green algae and plants) Have vacuoles to collect and remove excess water Food is stored in starch granules Animal characteristics : Heterotrophic in the dark Lack cell walls; Have pellicle instead = firm but flexible layer beneath plasma membrane Move by flagellum (whip) Have an eyespot (detects light)

Euglenoid Reproduction Asexual Longitudinal fission – nuclear division followed by cell dividing lengthwise Produces growth in cell circumference while organelles are being duplicated. Forms a “resting cell” with a thick coating during unfavourable conditions

Animal-like Protists (protozoa) All are heterotrophs = move to obtain food Holozoic - engulf their food (bacteria/micro-organisms) Saprozoic – absorb predigested or soluble nutrients directly through cell membrane

Facts: Rival bacteria in both : a) population numbers b) number of species Occupy a diverse range of moist habitats Size range is very broad As small as µm (blood parasites) As large as cm (foraminiferans)

Classification Major criteria is the type of locomotion Other criteria: Types of organelles Life cycle Mode of reproduction Nutrition Whether it is free-living or parasitic

Phyla: Zoomastiginia – animal flagellates Sarcodina – pseudopods amoeboids, foraminifera, radiolarians, heliozoans Ciliophora – ciliates and suctorians Sporozoa – not self-propelling; parasitic, spore-producing

Reproduction Usually asexual = Binary Fission Under adverse conditions, may form cysts (resting cells) - emerge when conditions are favourable

Phylum Sarcodinia Most are free-living (a few are parasites) Pseudopods (fingerlike projections used for locomotion and food capture) Four groups: Amoebas Foraminiferans Radiolarians Heliozoans

Amoeba One of largest, but least complex Do not have shells Two layers of cytoplasm: Ectoplasm – thin, semi- rigid, under membrane Endoplasm – more fluid part that fills the inside of the cell Continuous mov’t of endoplasm causes amoeba to change shape as it moves

Amoeba… Feed by phagocytosis Pseudopods flow engulfing food particles Food eventually enclosed in a food vacuole where it is digested Contractile vacuoles collect extra water that enters the cell and discharges it through a pore in the membrane Reproduction – binary fission In one day, one cell splits; each daughter cell grows to full size and splits again = 4 cells produced

Phylum Mastigophora Have one or more flagella Free-living types live mainly in freshwater or marine habitats Parasitic types live inside other organisms (even humans)

Phylum Ciliophora Possess hairlike structures called cilia which may cover the entire surface of the organism. Similar function to flagella Usually shorter and more abundant Synchronized for swimming (Paramecium) Attach the microorganism to a surface (Vorticella and Stentor )

Ciliates Most advanced of the protozoans Live in both freshwater and marine habitats Possess an oral groove with a “mouth” leading into a cavity called the gullet Specialized cilia sweep food particles into the cavity Food enters a vacuole from the gullet Food is digested in the vacuole and waste is ejected through an anal pore Contractile vacuoles help regulate water by collecting and expelling excess water.

Paramecium

Paramecium… Have two nuclei macronucleus – controls most of the cell’s activities micronucleus – involved in reproduction Reproduction is usually asexual by binary fission Periodically may undergo conjugation Pair of paramecia join to combine their genetic material then daughter cells undergo fission Defense mechanism = hundreds of poison-laden barbs (trichocysts)can be discharged either to drive away predators or to capture prey

Phylum Sporozoa Unique among protozoans due to lack of independent locomotion Have no pseudopods, cilia, or flagella Exclusively parasitic Depend entirely on body fluids of hosts for movement Have fewer organelles and specialized structures

Life cycles of Sporozoans Complex life cycles contrast the simple structure Have reproductive cells that can produce a new organism without fertilization (spores) Early stage of development, called sporozoites

Sometimes involve two or more hosts Parasite reproduces sexually in one host And asexually in the other Insects frequently transmit from one host to the next (Plasmodium = malaria)

Fungus-like Protists Phylum Gymnomycota Aka Slime Moulds Named for trail left behind as move over the ground 3 Categories: Water molds ( protostelids) plasmodial slime molds (Myxomycetes) cellular slime molds Prefer cool, shady, moist places Usually found under fallen leaves or rotting logs

All slime molds are capable of forming a structure called a sporangium. Formed when conditions are unfavorable for the growth or survival of the slime mold. A sporangium is a cluster of spores on a stalk. Each spore is a bundle of genetic information.spore Dispersal of the spores by air currents can lead to the formation of new slime molds when the spores land and germinate.

Life cycle of Fungus-like Protist Resemble protozoans for part of life cycle Become amoeba-like or have flagella Other stages produce spores like fungi Do not always remain as single-celled organisms

Single cells may converge at some point into a large slimy mass called a plasmodium not to be confused with the Phylum Sporozoan Plasmodium It is an enormous single cell that contains thousands of nuclei oozes about seeking a region of acceptable warmth /brightness can be several inches in diameter and is often vividly colored Scientists use plasmodia to study a phenomenon called cell streaming, where the contents of a cell move about; readily visible using a microscope

Dictyostelium life cycle

Slime Mould Movement The plasmodial mass creeps like a single organism It extends its slug-like form and pulls up from behind Feeds on organic matter as it goes If it runs into an object it retracts and slithers around it Movements are very slow (1 mm/hour)

Biologists recognize becoming multicellular as a tremendous advancement Individual cells begin to work together = groundwork for cell specialization In higher kingdoms, more advanced organisms use specialized cells to develop structures suited for specific tasks

Kingdom Protista - Summary Kingdom Protista contains plantlike, animal-like, and fungi-like protists The group contains organisms that do not fit into the other five kingdoms Protists are eukaryotes and obtain energy in a variety of ways Animal-like protists vary from simple one-celled forms to large multi-cellular organisms Fungi-like protists exhibit complex life cycles and exist in various cellular forms Reproduction in protists may be sexual or asexual, with many having complex reproductive cycles Algae are primary food producers and the source of biological energy for most aquatic food webs They supply about two thirds of the world’s oxygen

Additional Resources ory/files/Bio%20102/Bio%20102%20lectures/protists/p rotists.htm ory/files/Bio%20102/Bio%20102%20lectures/protists/p rotists.htm calSciences/MajorDivisions/KingdomProtista/Protists /protists.htm calSciences/MajorDivisions/KingdomProtista/Protists /protists.htm A virtual pond dip