Unicellular Eukaryotes, Porifera, and Sponges PDF

1 OUTLINE Unicellular Eukaryotes (Protozoa / Protista) 1. Introduction (Classification) 2. Locomotion (Pseudopodia) 3. Nutrition, Digestion & Excretion 4. Osmoregulation 19 NUTRITION AND DIGESTION Unicellular Eukaryotes 1....

1 OUTLINE Unicellular Eukaryotes (Protozoa / Protista) 1. Introduction (Classification) 2. Locomotion (Pseudopodia) 3. Nutrition, Digestion & Excretion 4. Osmoregulation 19 NUTRITION AND DIGESTION Unicellular Eukaryotes 1. Autotrophs 2. Heterotrophs Synthesize their own food Obtain organic molecules (i.e. do not eat other organisms or synthesized by other organisms substance derived from them) Phagotroph Osmotroph [= holozoic] [= saprozoic] Ingest visible particles Absorb soluble food (phagocytosis) Endocytosis (pinocytosis) 20 NUTRITION AND DIGESTION Autotroph (Flexibility) Euglena viridis - Normally photoautotrophic, contains chloroplasts bearing chlorophyll - When kept in dark, E. viridis becomes osmotrophic (saprozoic) Chloroplasts: green pigment 21 NUTRITION AND DIGESTION Heterotrophs Phagotroph Osmotroph (Phagocytosis) (Pinocytosis) Particle No visible particles Lobopodia extend around particle 22 NUTRITION AND DIGESTION Classic Amoeboid phagocytosis Plasma membrane 1 2 3 4 Cell cytoplasm Food vacuole Digestive (phagosome) vacuole Lysosome Golgi body Cell membrane binds to food particle and encloses it to form a food vacuole 23 NUTRITION AND DIGESTION Examples of Interesting Feeding Mechanisms 1. Didinium: Free-living ciliophoran that uses a non- ciliated cytopharynx to engulf prey. A voracious predator of paramecium. 1 2 3 4 Paramecium Didinium 24 NUTRITION AND DIGESTION Examples of Interesting Feeding Mechanisms 2. Stentor (Vorticella): Free-living ciliophoran that transforms into a horn like structure. Utilizes cilia to generate feeding current towards horn. 25 NUTRITION AND DIGESTION Examples of Interesting Feeding Mechanisms 3. Suctorian: Sessile. Utilizes tentacles to snag other protozoans and suck their cytoplasm. Tentacles - tentacles are hollow. -the knobby tips of the tentacles have an opening and contain haptocysts. 26 EXCRETION EXOCYTOSIS Elimination of undigested material within digestive vacuole occurs via fusion with cell surface (i.e. ENDOCYTOSIS in reverse) PASSIVE DIFFUSION Metabolic wastes- e.g. end products of nitrogen metabolism, such as ammonia, readily diffuses across cell membrane CYTOPROCT - permanent excretory pore Waste material accumulates in a vacuole adjacent to the cytoproct and is periodically discharged (e.g. in ciliates) 27  28 OSMOREGULATION Hydromineral balance is regulated by specialized organelles called contractile vacuoles - Contractile vacuoles are commonly found in freshwater unicellular eukaryotes & generally absent in marine/parasitic forms (i) Freshwater is more dilute than the internal environment of the unicellular eukaryote (ii) Diffusive ion loss and water uptake by osmosis would result in dilution of the cytoplasm and eventual death 29 OSMOREGULATION (1) Proton pump (H+-ATPase) – Primary active transport (2) Bicarbonate (HCO3-) co-transport (3) Passive water diffusion (4) Cytoplasmic carbonic anhydrase replenishes H+ & HCO3- H2CO3 H+ + HCO3- 30 31 OSMOREGULATION Filling and expulsion rates depend on - ionic/osmotic gradient - organism size 1 OUTLINE Phylum Porifera - Sponges 1. Introduction 2. Cell types 3. Canal systems 4. Reproduction 2 INTRODUCTION - Sessile multicellular animals with no organs. - possess functionally distinct cell types. - filter feeders: system of canals through which water is pumped into the body and food particles collected. 3 CELL TYPES 1. Choanocytes Exposed end - ovoid cells that line canal systems and chambers - exposed end, a collar forming a filtering device - flagellar motion pulls water through “filter” Embedded end 4 CELL TYPES 2. Archeocytes - amoeboid cells move through gelatinous Matrix (mesohyl) in sponge. - receive and digest food particles from choanocytes. totipotent Choanocyte - give rise to all other cell types in sponge Archeocyte 5 CELL TYPES 3. Secretory Cells - Produce Spicules through secretions Mineral (calcium) Protein (collagen, spongin) 3 subtypes of secretory cells a) Sclerocytes (mineral spicules) b) Spongocytes (spongin spicules) c) Collencytes (collagen spicules) 6 CELL TYPES 4. Pinacocytes - Form protective lining (pinacoderm) that faces the external environment. - Also line some internal canals where choanocytes are not present. 5. Porocytes - only found in some sponges (Asconoid) - form channels in pinacoderm through which water flows to the inside of the sponge (ostia). 7 CELL TYPES General Arrangement of Cell Types in Sponge Body: Porocytes Archaeocytes (Ostium) Pinacocytes (Pinacoderm) Mesohyl (gelatinous matrix) Sclerocytes Choanocytes (mineral (Choanoderm) spicules)