Protist Classification the Saga Continues
Learning Objectives Explain what a protist is. Describe how protists are related to other eukaryotes.
What Are Protists? Photosynthetic Motile Unicellular Multicellular Freshwater Marine Terrestrial Shelled
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.
Protist Classification Today Branching points
Protists and Other Eukaryotes Plants Fungi Animals
Fossil Protists Protists were the first eukaryotes. Eukaryotes evolved from prokaryotes. About 300,000 protist species exist today.
Protist Ancestors Some ancestors of today s protists gave rise to plants, animals, and fungi. Common eukaryote ancestor
Overview: The Protist Dilemma
Protist Structure and Function
Learning Objectives Describe the various methods of protist locomotion. Describe how protists reproduce.
Protists Motion: Amoeboid Movement Move by changing shape Use cytoplasmic projections called pseudopods Pseudopod
Protist Motion: Cilia Motion by cilia is like oars propelling a large rowboat forward. Cilia
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
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)
Protists Reproduction: Cell Division Amoebas and many other protists produce new individuals through mitosis (asexually replicate DNA and then divide).
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.
Protist Reproduction: Conjugation, cont. Cells exchange one micronucleus. Micronuclei fuse; macronucleus disintegrates. New macronucleus forms from micronucleus. Diploid
Oomycetes (Water Molds and Their Oomycetes Relatives) Include water molds, white rusts, and downy mildews Were once considered fungi based on morphological studies
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. 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 28.14 6 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.
Alternation of Generations: Overview Fertilization Meiosis Sexual reproduction Asexual reproduction
Alternation of Generations: Asexual Stage Flagellated spores Spores undergo mitosis. Sporangium 2N
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. 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.