Chapter 21 Protists The Simplest Eukaryotes
Protists Eukaryotes that are not fungi, plants, or animals Structurally less complex Play important ecological roles as producers or predators of microorganisms Mostly free-living. No single trait is unique to the protists, so this collection of organisms is not a monophyletic group.
Collection of Lineages No single trait unique to protists Most protists single-celled Some are colonial or multicellular Colonial organism Live in groups and behave in an integrated fashion, but remain self-sufficient Multicellular organism Cells have a division of labor and depend on one another for survival
A Collection of Lineages Protists have a huge ecological impact Example activities: Decomposing organic material Producing oxygen Taking up carbon dioxide Building organic compounds
Diverse Life Cycles Most protists reproduce asexually when conditions favor growth Switch to sexual reproduction when conditions unfavorable
Flagellated Protozoans-general characteristics Protozoans Single-celled heterotrophic protists Flagellated protozoans Single, unwalled cells with flagella Pellicle Plasma membrane lined with thin layer of elastic proteins Functions: cell protection, shape retention
Anaerobic Flagellates Live without oxygen Diplomonads and parabasalids Have multiple flagella Live in oxygen-poor waters Use hydrogenosomes instead of mitochondria to make ATP and release hydrogen gas Some live in deep seas and lakes Some live in animal hosts
Anaerobic Flagellates Example of diplomonad infecting a host Giardia lamblia attaches to intestinal lining and sucks up nutrients Causes giardiasis in humans Example of parabasalid infecting a host Trichomonas vaginalis infects the human reproductive tract Causes trichomoniasis in humans 6 million people in the United States are infected Males typically show no symptoms
Trypanosomes and Other Kinetoplastids Kinetoplastids Flagellated protozoans with a single large mitochondrion Some eat bacteria in fresh water and seas Trypanosomes: largest subgroup Parasitic Tsetse flies spread Trypanosoma brucei Causes African sleeping sickness
Euglenoids Flagellated protists Closely related to kinetoplastids Many live in fresh water None are human pathogens Can use photosynthesis or heterotrophic nutrition Light-sensitive organelle near base of flagellum Hypertonic relative to fresh water Contractile vacuoles expel water to the outside
Shelled Cells: Foraminifera and Radiolarians Two related lineages of primarily heterotrophic single-celled protists Both groups secrete a sieve-like cell Foraminifera Shell made of calcium carbonate Most live on the seafloor Others are members of marine plankton Drift or swim in open waters Take up carbon dioxide Allows the sea to absorb more carbon dioxide
Foraminifera and Radiolarians Radiolaria Secrete a glassy silica shell Consist of two cytoplasmic layers Inner layer holds typical organelles Outer layer contains gas-filled vacuoles Planktonic Abundant in nutrient-rich tropical waters Remains of both forminafera and radiolaria transformed over time to chalk and limestone
Alveolates Alveolates group Have sacs of unknown function under their plasma membrane. Ciliates Dinoflagellates Apicomplexans
Ciliates Some ciliates live in the animal gut Help grazers break down cellulose in plants Hunt bacteria and other protists Paramecium
Ciliates Balantidium coli Only ciliate known human pathogen Can live in gut of humans and pigs All ciliates reproduce asexually Some also reproduce sexually Macronucleus controls cell s daily function One or more small micronuclei Involved in sexual reproduction
Dinoflagellates Typically have two flagella One extends from the base of the cell One wraps around the middle of the cell Cell motion is rotational as it moves forward Most are photosynthetic Contain chloroplasts
Dinoflagellates-bioluminescence
Dinoflagellates Algal bloom Great increases in population size due to nutrient-rich waters Can suffocate aquatic animals
Apicomplexans Parasitic alveolates Hosts include vertebrate and invertebrate animals Plasmodium Agent of malaria Fatal to the host if untreated Toxoplasma gondii Causes the disease toxoplasmosis Can be fatal in immune-suppressed people Risk to pregnant women
zygote gametocytes in gut 4 gametocytes 1 A mosquito bites a human. Haploid sporozoites enter blood, which carries them to the liver. 5 6 sporozoites in salivary glands 1 sporozoites 3 asexual blood cycle merozoites 2 Sporozoites reproduce asexually in liver cells, then mature into merozoites. Merozoites leave the liver and infect red blood cells. 3 Merozoites reproduce asexually in some red blood cells. 4 In other red blood cells, merozoites become gametocytes. 5 A mosquito bites and sucks blood from the infected person. mosquito takes up gametocytes or injects sporozoites liver stage 2 Gametocytes in blood enter its gut and mature into gametes, which fuse to form diploid zygotes. 6 Meiosis of zygotes produces cells that develop into sporozoites. The sporozoites migrate to the mosquito s salivary glands. 2016 Cengage Learning
Stramenopiles Group name means straw-haired Anterior flagellum has short, hairlike extensions Most are autotrophs Contain chloroplasts Diatoms Diploid, photosynthetic, single-celled or colonial protists Live in lakes, seas, and damp soils
Stramenopiles Diatoms Most abundant members of the phytoplankton in temperate and polar waters Shell remains known as diatomaceous earth Used in filters, cleaners, and as an insecticide Cells contain a large amount of oil Helps cells float in sunlit waters Also stores energy
Brown Algae Multicelled protists Live mainly in cool coastal waters Not related to red algae, green algae, or land plants 1500 species Range from microscopic filaments to 100 foot tall kelp Harvested for commercial use Nutritional supplements, food thickeners
Brown algae
Water Molds Heterotrophs forming a mesh of filaments Absorb nutrients Consist of diploid cells with cellulose cell walls Some are aquatic parasites Others are decomposers
Water molds Saprolegnia Phytophthora Destroyed Ireland s potato crop in the 1800s Causes five billion dollars in crop losses yearly
Red Algae and Green Algae Two related groups of primarily aquatic photosynthetic protists. Red algae Photosynthetic Typically multi-celled Live in clear, warm seas Thin sheets or branching patterns of growth Chloroplasts contain chlorophyll a and red pigments (phycobilins) Can thrive at greater depths than other algae
Red Algae and Green Algae Agar and carrageenan Gelatinous polysaccharides extracted from red algae Nori Used as thickeners or stabilizers in foods and personal care products Edible seaweed used to wrap sushi A red algae
Life cycle of red alga 4 spore-forming body (2n) zygote 3 Fertilization 2 male gametes diploid stage haploid stage germinating spore ( n) Meiosis 5 1 The haploid gamete-forming body is sheetlike. 2 Gametes form at its edges. 3 Fertilization produces a diploid zygote 4 The zygote develops into a diploid spore-forming body. 5 Haploid spores form by meiosis and are released. 6 Spores germinate and develop into a new gamete-forming body. female gametes 6 1 gamete-forming body ( n)
Green Algae Informal name for 7,000 photosynthetic species Size ranges from microscopic to more than a meter long Contain chloroplasts and chlorophylls a and b Chlorophyte algae Most diverse lineage of green algae
Green Algae Chlorella Used by Marvin Calvin to study photosynthesis Used in the experimental production of biofuel Chlamydomonas Single-celled green algae common in ponds Volvox Colonial fresh water species
Amoebozones and Choanoflagellates Amoebozones Do not have a cell wall or stiff pellicle Continually change shape Amoebas Single cells Most are predators in freshwater habitats Some live inside animals A few can cause human disease
Amoebozones and Choanoflagellates Slime molds Sometimes called social amoebas Two types: cellular and plasmodial Cellular slime molds Spend most of their time as individual haploid amoeba-like cells Example: Dictyostelium discoideum
5 Spores give rise to amoeboid cells. 4 A fruiting body forms with resting spores atop a stalk. Mature fruiting body 1 Cells feed and multiply by mitosis. 2 When food is scarce, cells aggregate. Migrating slug stage 3 The cells form a slug. It may start to develop as a fruiting body right away, or migrate about. In the slug, cells become prestalk (red) and prespore (tan) cells. Stepped Art
Amoebozones and Choanoflagellates Plasmodial slime molds Spend most of life cycle as multinucleated mass (plasmodium) When food supplies dwindle, a plasmodium develops into spore-bearing fruiting bodies.
Amoebozones and Choanoflagellates Choanoflagellates Closest known protistan animal relatives Most live as single cells Some form colonies Cells stay together after mitosis due to adhesion proteins