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Chapter 26: Protozoa. 26-1 Overview of Protozoa. 26-2 Protozoan Diversity. 26-1 Overview of Protozoa. I. Protists. A diversity of protozoa, algae, slime molds, and water molds that lack tissue differentiation and are eukaryotes. (A-L, P-L, F-L). II. Characteristics of Protozoa.
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Chapter 26: Protozoa 26-1 Overview of Protozoa 26-2 Protozoan Diversity
26-1 Overview of Protozoa I. Protists • A diversity of protozoa, algae, slime molds, and water molds that lack tissue differentiation and are eukaryotes. (A-L, P-L, F-L)
II. Characteristics of Protozoa • Approximately 65,000 microscopic species have been identified (half extinct), can have inhabited the marine, freshwater, and terrestrial habitats. (1) Protozoa • Unicellular and heterotrophic (most species), can be either free-living or parasitic, requiring multiple hosts.
Critical Thinking (1) Some protozoan parasites are very difficult to grow in test tubes because they lose the ability to produce certain key enzymes or growth factors when outside their host. How could this host-parasite relationship be similar to that described in the Endosymbiosis Hypothesis? How could it be different?
(2) Food Vacuoles • Membrane-bound chambers containing digestive enzymes that break down small food molecules ingested by heterotrophic protozoans. (3) Zooplankton • Population of organisms that is made up by numerous protozoan species; a critical trophic level in aquatic ecosystems.
(A) Reproduction • All protozoa are capable of binary fission (asexual), where one divides into two identical offspring; however some are capable of sexual reproduction as well. (1) Multiple Fission (asexual) • A form of asexual reproduction where a number (>2) of identical offspring are yielded. (2) Conjugation (sexual) • Individuals from opposite “mating-strains” pair up and exchange genetic material (slightly more complex than conjugation in bacteria).
Critical Thinking (2) The process of conjugation is complex, requiring an expenditure of energy and resources. How can you relate the high biological cost of conjugation to the adaptive advantage of exchanging genetic material?
(B) Classification • Protozoa belong to Kingdom Protista and are further classified into four phyla, distinguished by form of locomotion: (1) Phylum Sarcodina (2) Phylum Ciliophora (3) Phylum Zoomastigina (4) Phylum Sporozoa
(C) Adaptations • Many species of protozoa have physiological mechanisms for monitoring conditions/noxious chemicals in their environment. (1) Eyespot • Localized region of pigment that can detect changes in the amount of sunlight (dark or light).
(2) Cyst • A dormant form characterized by a hardened external covering in which metabolic activity ceases. NOTE: Stressors include drought, nutrient deficiency, decreased oxygen levels, or pH/temperature changes. Emergence occurs when conditions become favorable once again.
Critical Thinking (3)Many parasitic protozoa, such as Entamoeba histolytica, are able to form cysts whenever they pass out of a host. Why would cyst formation represent an advantage to a parasitic protozoan?
(D) Evolution (~1.5 b.y.a.) • Descended from the earliest eukaryotic cells, followed prokaryotes (bacteria) possibly due to endosymbiosis.
26-2 Protozoan Diversity I. Phylum Sarcodina (40,000 species of sarcodines) • Include amoebas, which inhabit fresh water, saltwater, and soil, and are characterized by cytoplasmic extensions called pseudopodia and flexible cell membranes.
(1) Pseudopodia • Large, rounded cytoplasmic extensions that function in movement. (2) Endoplasm • Inner portion of the cytoplasm that pushes against the ectoplasm. (3) Ectoplasm • Outer layer of cytoplasm that is pushed outward to create a blunt, armlike extension.
Critical Thinking (4) Many species of protozoa feed by means of pseudopodia. What do you believe could be the stimulus that might cause these cytoplasmic extensions to form?
(4) Ameboid Movement • The simultaneous extension and contraction of the pseudopodia to initiate movement (powered by cytoplasmic streaming). (5) Cytoplasmic Streaming • Internal flowing of a cell’s cytoplasm; includes ameboid movement (6) Contractile Vacuole • Organelle that expels fluid from the cell in order to maintain homeostasis (i.e., freshwater protists are usually hypertonic relative to their habitat).
(A) Ecological Role • Calcium-rich layer of sediment deposited at the bottoms of oceans from the tests of dead foraminifera. (1) Test • A protective but porous CaCO3 shell (slender pseudopodia extend through these openings) that covers the delicate cell membrane of some sarcodines, including foraminifera. (2) Foraminifera • Ancient group of shelled sarcodines found primarily in oceans with chambered tests. (3) Radiolarians • Oldest of foraminifera, inhabit shallow waters and usually have a radial arrangement of spines that extend through their test.
(B) Human Diseases • Although the majority of amoebas are free-living, some parasitize the large intestines of humans or other animals. (1) Amebic Dysentery (Entamoeba histolytica) • Amoeba enter through the consumption of contaminated food or water and as the amoeba grow, enzymes are secreted that agitate the intestinal lining resulting in painful ulcers.
II. Phylum Ciliophora (8,000 species of ciliates) • Swim by cilia and are abundant in ponds and slow-moving streams containing bacteria, algae, and decaying organic matter. (e.g., Paramecium Caudatum)
(A) Internal Structure • Ciliates have the most elaborate organelles of any protozoa and are multinucleate. (1) Pellicle & Oral Groove • A clear, elastic layer of protein surrounding the cell membrane (pellicle); the pellicle contains a funnel-like tube lined with cilia (oral groove)
(2) Mouth Pore & Gullet • Beating cilia sweep in food particles into the mouth pore, of which opens into the gullet where food vacuoles are formed and circulated. (3) Anal Pore • Vacuoles of indigestible materials are moved to the anal pore where they are expelled into the surroundings.
(4) Macronucleus (larger) • Contains multiple copies of DNA and is responsible for metabolic, developmental, and asexual reproductive functions. (5) Micronucleus (smaller) • Participates in the exchange of genetic material between individual ciliates during conjugation.
(B) Reproduction (asexual and sexual) • Asexually via binary fission and sexually via conjugation. NOTE: Following conjugation, each paramecium divides, producing a total of four genetically identical paramecia. Because genetic material is exchanged between the two original paramecia, the four offspring paramecia are genetically different from either original paramecium.
Critical Thinking (5) Many biologists suggest that paramecia are more complex than amoebas. What adaptations in paramecia would justify this claim?