Chapter 21 Protists

I. Characteristics of Protists A. Diversity 1. Characteristics Various ways of metabolizing food a. photosynthetic b. ingest food c. absorb food

Some move by flagella or cilia Found almost everywhere there is water Many have mechanisms responding to stimuli in their environment. Many have structures called eyespots.

2. The First Eukaryotes Evolved about 1.5 billion years ago Two important eukaryotic features evolved among protists a. sexual reproduction b. multicellularity

B. Reproduction 1. Asexual reproduction in unicellular protists A mature haploid (n) cell divides by mitosis Haploid cells called zoospores are produced and remain within the wall of the parent cell Zoospores then break out of the parent cell

2. Sexual reproduction in unicellular protists A haploid (n) cell divides by mitosis to produce haploid gametes A pair of gametes fuse The pair sheds their cell walls and fuse into a diploid (2n) zygote with a think protective wall called a zygospore In favorable environmental conditions meiosis within the zygospore produces haploid (n) cells that break out of the zygospore

3. Sexual reproduction in multicellular protists a. Alteration of generations Characterized by two distinct multicellular processes i. sporophyte generation - diploid, spore-producing phase ii. Gametophyte generation - haploid, gamete-producing phase

Step 1: Adult sporophyte’s (2n) reproductive cells, sporangia, produce haploid (n) spores by meiosis Step: 2 Spores grown into multicellular haploid gametophytes Step 3: The mature gametophyte produces haploid gametes Step 4 Haploid gametes fuse into diploid zygotes Step 5: Diploid zygotes divide by mitosis to form new diploid sporophytes

Gametophyte generation Diploid (2n) Sporophyte Generation Haploid (n) Gametophyte generation Diploid (2n) Sporophyte Generation mitosis

b. Conjugation Two protists temporarily unite to exchange nuclear material The nucleus of one cell passes through the bridge made by the fusion into the adjacent cell

Unicellular heterotrophs Amoebas II. Amoebas and Forams Unicellular heterotrophs Amoebas Protists that move by using flexible, cytoplasmic extensions called pseudopodia In a process called ameboid movement, a pseudopodium bulges form the cell, stretches outward, and anchors itself to a nearby surface Live in both fresh and salt water Reproduce by fission, dividing into two cells Concept Map Protist Diversity http://www.youtube.com/watch?v=aWItglvTiLc&feature=related

B. Foraminifera Typically live in marine sand or attach themselves to other organisms or rocks Characterized by their porous shells, or tests, made of calcium carbonate

III. Algae Strict phototrophs A. Green Algae Freshwater unicellular and multicellular organisms Contain the same pigments found in the chloroplasts of plants most have sexual and asexual reproductive stages

B. Red Algae Multicellular organisms found in warm ocean waters - contributes to the great coral reefs Red pigment is efficient at absorbing the light that penetrates deep waters Life cycle involves alternation of generations

C. Brown Algae Multicellular organisms found mostly in marine environments Kelp is among the largest organisms on Earth Reproduce by alternation of generations

IV. Diatoms Photosynthetic Unicellular Unique double shells made of silica Found in oceans and lakes Important producers in the food chain

Diploid (2n) individuals that reproduce asexually - the two halves of the shell separate, and each half regenerates another matching half - tend to get smaller and smaller with each generation - when an individual gets too small it slips out of its shell, grows to full size, and regenerates a new shell

V. Flagellates Move using flagella A. Dinoflagellates Unicellular phototrophs Most are marine and make up plankton Have a protective coat made of cellulose

Most have two flagella 1. one encircles the body like a belt 2. the other beats perpendicular to it causing it to spin through water like a top Reproduce asexually by mitosis Some produce powerful toxins that are associated with the poisonous “red tides”

B. Euglenoids Live in freshwater Unicellular, asexual 1/3 contain chloroplasts and are photosynthetic Others lack chloroplasts, ingest their food, and are heterotrophic A light-sensitive organ called the eyespot helps orient the organisms movements towards light

C. Kinetoplasts Unicellular Heterotrophs Most reproduce asexually Some live symbiotically in the guts of termites, where they provide the enzymes that digest wood Others cause diseases such as African sleeping sickness

D. Ciliates Most complex of the protists Have large numbers of cilia used for movement Unicellular Heterotrophs Most form vacuoles for ingesting nutrients and regulating their water balance

Most have two types of nuclei 1. micronuclei - contain normal chromosomes that divide by mitosis 2. macronuclei - contain small pieces of DNA derived from the micronuclei Most reproduce by mitosis, with the body splitting in half Engage in sexual reproduction through conjugation

VI. Protistan Molds Heterotrophs Cell walls contain different carbohydrates than fungal cell walls

A. Cellular slime molds Individual organisms behave as separate amoebas in soil In the event of environmental stress, they gather together and form multicellular colonies called slugs - each slug develops a base, a stalk, and a swollen tip that develops spores - each spore releases and becomes a new individual

B. Plasmodial Slime Molds A group of organisms that move along as a mass of cytoplasm, or plasmodium Engulf bacteria and other organic material as they move Contains many nuclei that are not separated by cell walls

Under stress, the plasmodium divides into smaller mounds - each mound produces a stalk tipped with a capsule in which haploid spores develop - in favorable conditions, the spores germinate and become haploid cells - the haploid cells fuse into diploid zygotes that undergo mitosis and form a new plasmodium

C. Oomycetes Water molds, white rusts, an downy mildews in fresh water Either parasites or feed on dead organic matter

VII. Sporozoans Parasitic in hosts Form spores during their reproduction cycle Nonmotile Unicellular Life cycle involves both asexual and sexual reproduction - sexual reproduction between a male and female gamete results in a zygote with a think-walled structure that makes it resistant to unfavorable conditions

VIII. Protists and Health A. Beneficial protists Single largest group of photosynthesizers on the planet - help to support food chains Live in the digestive tracts of humans and animals - cattle could not digest the cellulose in the hay and grass they eat without the aid of protists

B. Malaria 3 million people die from malaria each year - die of anemia, kidney failure, or brain damage 1. Malaria Life Cycle Spread by the bite of certain mosquitoes

Three stages a. sporozoite A mosquito injects saliva containing about 1,000 protists into a human These sporozoites infect the liver where they divide and reproduce

b. Merozoite The second generation cells from the liver infect red blood cells and divide Red blood cells rupture, releasing the merozoites and toxic substances that prevents the blood from clotting

c. Gametes Some merozoites develop into gametes When eaten by a mosquito, male and female gametes fuse into a zygote The zygotes divide in the mosquito and form sporozoites

Active Reading p. 11