Presentation on theme: "Unicellular Eukaryotes Chapter 11. Emergence of Eukaryotes First evidence of life dates to 3.5 billion years ago. First cells were bacteria-like."— Presentation transcript:
Unicellular Eukaryotes Chapter 11
Emergence of Eukaryotes First evidence of life dates to 3.5 billion years ago. First cells were bacteria-like.
Emergence of Eukaryotes Origin of complex eukaryote cells Most likely symbiosis among prokaryotic cells. Modification of engulfed prokaryote into an organelle: Primary endosymbiosis. Aerobic bacteria engulfed by bacteria. May have become mitochondria found in most modern eukaryotic cells. Engulfed photosynthetic bacteria evolved into chloroplasts. Descendants in green algae lineage gave rise to multicellular plants.
Emergence of Eukaryotes Other groups apparently originated by secondary endosymbiosis. One eukaryotic cell engulfed another eukaryotic cell and the latter became transformed into an organelle.
Protozoans Protozoans are an extremely diverse assortment of unicellular eukaryotes.
Protozoans Protozoa Lack a cell wall Have at least one motile stage in life cycle Most ingest their food Carry on all life activities within a single cell. Can survive only within narrow environmental ranges. Very important ecologically. At least 10,000 species of protozoa are symbiotic in or on other plants or animals. Relationships may be mutualistic, commensalistic, or parasitic.
Protozoans Protozoans are more diverse than all other eukaryotes. No longer classified in a single kingdom. Recently shown that there are at least seven or more clades. May be more than 60 monophyletic eukaryotic clades. “Protozoa” is now used informally without implying phyletic relationship.
Cladogram of the Major Divisions of Organisms
Nutrition in Protozoans Autotrophs - contain chloroplasts. Heterotrophs - absorb organic molecules or ingest larger food particles. Phagocytosis Mixotrophs - combine photosynthesis and heterotrophic nutrition.
Protozoans Occur in Diverse Habitats Freshwater and marine species. Require moisture Free-living and symbiotic species. Mutualistic – benefits both. Commensalistic – one benefits, the other is neutral. Parasitic – one benefits at a cost to the other.
Locomotion in Protozoans Protists have three main methods of locomotion. Some protists, like this Euglena, have one or two long flagella that they can whip around an propel themselves through the water.
Locomotion in Protozoans Some, like this Tetrahymena, are covered with numerous, but shorter, cilia that facilitate movement and/or feeding.
Locomotion in Protozoans Others use ameboid movement to get around. A pseudopod is extended forward, followed by the rest of the organism.
Form & Function - Locomotion Cilia and flagella share an internal structure of the axoneme (extending beyond the cell) consisting of 9 pairs of microtubules surrounding a central pair. Inside the cell, the kinetosome consists of 9 triplets of microtubules just like centrioles.
Form & Function - Locomotion Pseudopodia are extensions of the cell cytoplasm used for locomotion.
Form & Function - Locomotion Lobopodia – large blunt extensions of the cell body. Filopodia – are thin extensions, usually branching. Reticulopodia – repeatedly rejoin to form a netlike mesh.
Form & Function - Locomotion Axopodia – long thin pseudopodia supported by axial rods of microtubules.
Functional Components – Specialized Organelles Nucleus – contains DNA. Mitochondria – organelle used in energy production. Golgi – part of the secretory system of the ER. Plastids – organelles containing photosynthetic pigments. Extrusomes – organelles that extrude something from the cell.
Nutrition Holozoic feeders, or phagotrophs, ingest particles of food. Food vacuole – the membrane-bound vesicle containing the food. Food vacuoles fuse with lysosomes containing digestive enzymes.
Nutrition Often, the site of phagocytosis is a definite mouth structure, the cytostome.
Nutrition Saprozoic feeding (ingestion of soluble food) may be by pinocytosis or by transport of solutes across the cell membrane.
Excretion and Osmoregulation Contractile vacuoles fill with fluid and then expel the fluid outside the cell. Function in osmoregulation. More common in freshwater species.
Reproduction Fission is the cell multiplication process in protozoa. Binary fission – one individual splits into two equal sized individuals. Budding – progeny cell much smaller than parent. Multiple fission – multiple nuclear divisions followed by multiple cytoplasmic divisions producing several offspring.
Reproduction All of above accompanied by some form of mitosis. Mitosis in protozoa divisions varies from metazoan mitosis. Nuclear membrane often persists. Spindle may form within the nuclear membrane. Centrioles not observed in ciliates. Macronucleus of ciliates elongates, constricts, and divides without mitosis (amitosis).
Reproduction Many types of protists reproduce sexually as well as asexually. Isogametes – all look alike. Anisogametes – two different types. Syngamy – gametes from two individuals fuse to form the zygote. Autogamy – gametes from one individual fuse. Conjugation – gametic nuclei are exchanged.
Cysts Many protists are able to survive harsh conditions through the formation of cysts, dormant forms with resistant outer coverings and a shutdown of metabolism.
Major Protozoan Taxa After the eukaryotic cell evolved, diversification followed, resulting in many clades. Opisthokonta is a very large clade characterized by a combination of flattened mitochondrial cristae and one posterior flagellum on flagellated cells. Includes animals, fungi, chaonoflagellates and microsporidians.
Stramenopila The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae. Most stramenopiles have a “hairy” flagellum paired with a “smooth” flagellum.
Stramenopila Water molds, diatoms, golden algae, brown algae.
Viridiplantae The clade Viridiplantae contains unicellular and multicellular green algae, bryophytes and vascular plants. Phylum Chlorophyta – single celled algae colonial forms.
Viridiplantae Volvox is a colonial organism that shows a division of labor where most cells are somatic cells concerned with nutrition & locomotion, but a few germ cells are responsible for reproduction.
Euglenozoa Phylum Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites. Kinetoplastids & Euglenids. Persistence of nucleoli during mitosis. Cell membrane contains microtubules to stiffen it into a pellicle.
Euglenids Subphylum Euglenida have one or two flagella that emerge from a pocket at one end of the cell. Contain chloroplasts surrounded by a double membrane – may have arisen by secondary endosymbiosis.
Kinetoplastids Subphylum Kinetoplasta have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast. Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems. Others are parasitic. Trypanosoma
Retortamonads Phylum Retortamonada includes commensal and parasitic unicells. Lack mitochondria & Golgi
Diplomonads Phylum Retortamonada: Diplomonads: Are adapted to anaerobic environments. Lack plastids. Lack mitochondria but may have mitochondrial genes in the nucleus. Diplomonads have two nuclei and multiple flagella. Giardia
Parabasalids Parabasalids move by means of flagella and an undulating part of the plasma membrane. This clade may have diverged from the main eukaryotic clade very early. Trichomonas
Alveolata Members of the clade (superphylum) Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane. Dinoflagellates, apicomplexans, ciliates.
Alveolata - Ciliates Members of the phylum Ciliophora use cilia to move and feed. Ciliates have large macronuclei and small micronuclei.
Alveolata - Ciliates Ciliates are a large, varied group of protists.
Alveolata - Ciliates Ciliates are structurally complex. All ciliates have a kinety system made up of the cilia, kinetosomes and other fibrils. Many have structures that can be expelled such as trichocysts and toxicysts. Defensive function
Alveolata – Types of Ciliates Suctorians – ciliates that lose cilia as adults, grow a stalk and become sessile. Use tubelike tentacles for feeding. Symbiotic ciliates – some commensal, others parasitic. Free-living ciliates – may be swimmers, or sessile. Stentor, Vorticella, Paramecium
Alveolata – Reproduction in Paramecium Paramecium, as well as many other protists, reproduce asexually by binary fission.
Alveolata – Reproduction in Paramecium Conjugation is a sexual process that produces genetic variation. Conjugation is separate from reproduction which generally occurs by binary fission.
Alveolata – Dinoflagellates Phylum Dinoflagellata is a diverse group of aquatic photoautotrophs and heterotrophs. Abundant in both marine and freshwater phytoplankton.
Alveolata – Dinoflagellates Each has a characteristic shape that in many species is reinforced by internal plates of cellulose. Two flagella make them spin as they move through the water.
Alveolata – Dinoflagellates Rapid growth of some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans. California Noctiluca Bloom
Alveolata – Dinoflagellates Some dinoflagellates are bioluminescent. Others live symbiotically with corals (zooxanthellae).
Alveolata – Apicomplexans Apicomplexans are parasites of animals and some cause serious human diseases. Named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues. Have a non- photosynthetic plastid, the apicoplast.
Alveolata – Apicomplexans Most apicomplexans have intricate life cycles w ith both sexual and asexual stages that often require two or more different host species for completion.
Amoebozoa Amebas are found in fresh and salt water as well as moist soil. An ameba feeds by wrapping a pseudopod around its food – phagocytosis.
Entamoebas Entamoebas are parasites of vertebrates and some invertebrates. Entamoeba histolytica causes amebic dysentery in humans.
Foraminifera This Phylum has slender pseudopodia that extend through openings in the test, then branch and run together forming a net (reticulopodia). Foraminiferans, or forams are named for their porous, generally multichambered shells, called tests.
Foraminifera Pseudopodia extend through the pores in the test. Foram tests in marine sediments form an extensive fossil record.
Radiolaria Radiolaria refers to marine testate ameba with intricate skeletons. They have very diverse and beautiful forms. Useful for determining the age of rock strata.
Radiolaria The pseudopodia of radiolarians, known as axopodia radiate from the central body.
Phylogeny and Adaptive Diversification Phylum Retortamonada Phylum Diplomonadea Phylum Parabasala Order Trichomonadida Phylum Euglenozoa Subphylum Euglenida Class Euglenoidea Subphylum Kinetoplasta Class Trypanosomatidea Phylum Stramenopiles Phylum Ciliophora Phylum Dinoflagellata Phylum Apicomplexa Class Gregarinea Class Coccidea Phylum Foraminifera Phylum Radiololaria Phylum Viridiplantae Phylum Amoebozoa Phylum Opisthokonta