Protist Classification the Saga Continues

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1 Protist Classification the Saga Continues

2 Learning Objectives Explain what a protist is. Describe how protists are related to other eukaryotes.

3 What Are Protists? Photosynthetic Motile Unicellular Multicellular Freshwater Marine Terrestrial Shelled

4 Challenges of Protist Classification Protists are eukaryotes; not members of the plant, animal, or fungi kingdoms. Some protists are more like members of other kingdoms.

5 Protist Classification Today Branching points

6 Protists and Other Eukaryotes Plants Fungi Animals

7 Fossil Protists Protists were the first eukaryotes. Eukaryotes evolved from prokaryotes. About 300,000 protist species exist today.

8 Protist Ancestors Some ancestors of today s protists gave rise to plants, animals, and fungi. Common eukaryote ancestor

9 Overview: The Protist Dilemma

10 Protist Structure and Function

11 Learning Objectives Describe the various methods of protist locomotion. Describe how protists reproduce.

12 Protists Motion: Amoeboid Movement Move by changing shape Use cytoplasmic projections called pseudopods Pseudopod

13 Protist Motion: Cilia Motion by cilia is like oars propelling a large rowboat forward. Cilia

14 Protist Motion: Flagella Motion by some flagella is like the back-and-forth movement of a single long oar at the back of a boat, propelling it forward. Flagellum

15 Protist Motion: Passive Nonmotile Form reproductive structures called spores Can enter the cells of other living things and function as a parasite (e.g., Plasmodium)

16 Protists Reproduction: Cell Division Amoebas and many other protists produce new individuals through mitosis (asexually replicate DNA and then divide).

17 Protist Reproduction: Conjugation Micronucleus: reserve copy of every gene in the cell (2n) Micronucleus undergoes meiosis. Macronucleus: multiple copies of the genes cell uses every day Remaining micronucleus undergoes mitosis. Three micronuclei disintegrate.

18 Protist Reproduction: Conjugation, cont. Cells exchange one micronucleus. Micronuclei fuse; macronucleus disintegrates. New macronucleus forms from micronucleus. Diploid

19 Oomycetes (Water Molds and Their Oomycetes Relatives) Include water molds, white rusts, and downy mildews Were once considered fungi based on morphological studies

20 Most oomycetes Are decomposers or parasites Have filaments (hyphae) that facilitate nutrient uptake

The life cycle of a water mold 1 Encysted zoospores land on a substrate and germinate, growing into a tufted body of hyphae. 2 Several days later, the hyphae begin to form sexual structures.

21 The life cycle of a water mold 1 Encysted zoospores land on a substrate and germinate, growing into a tufted body of hyphae. 2 Several days later, the hyphae begin to form sexual structures. 3 Meiosis produces eggs within oogonia (singular, oogonium). Germ tube Cyst 9 Each zoosporangium produces about 30 biflagellated zoospores asexually. MEIOSIS ASEXUAL REPRODUCTION Zoospore (2n) 8 The ends of hyphae form tubular zoosporangia. Zoosporangium (2n) 4 On separate branches of the same or different individuals, meiosis produces several haploid sperm nuclei contained within antheridial hyphae. Oogonium Egg nucleus (n) Antheridial hypha with sperm nuclei (n) SEXUAL FERTILIZATION Zygote REPRODUCTION germination Zygotes (oospores) (2n) Key Haploid (n) Diploid (2n) 7 The zygotes germinate and form hyphae, and the cycle is completed. Figure A dormant period follows, during which the oogonium wall usually disintegrates. 5 Antheridial hyphae grow like hooks around the oogonium and deposit their nuclei through fertilization tubes that lead to the eggs. Following fertilization, the zygotes (oospores) may develop resistant walls but are also protected within the wall of the oogonium.

22 Alternation of Generations: Overview Fertilization Meiosis Sexual reproduction Asexual reproduction

23 Alternation of Generations: Asexual Stage Flagellated spores Spores undergo mitosis. Sporangium 2N

24 Alternation of Generations: Sexual Stage Male nuclei Male reproductive structure Egg cell Fertilization Zygotes Meiosis Female reproductive structure 2N

Overview: Locomotion and Reproduction Locomotion Reproduction Amoeboid movement 1. Passive movement 2. Use of cilia 3. 4.

25 Overview: Locomotion and Reproduction Locomotion Reproduction Amoeboid movement 1. Passive movement 2. Use of cilia Use of flagella Many protists undergo mitosis to produce genetically identical offspring. In alternation of generations, an organism goes through a sexual and an asexual stage.

Biology. Slide 1of 34. End Show. Copyright Pearson Prentice Hall

Biology. Slide 1of 34. End Show. Copyright Pearson Prentice Hall Biology 1of 34 20 5 Funguslike Protists 2of 34 20 5 Funguslike Protists Similarities and differences between funguslike protists and fungi Like fungi, g, funguslike protists are heterotrophs that absorb