Eukaryotic Evolution and Diversity Lesson 4. Introduction to Protists
Learning Goals • Understand theory of endosymbiosis in the evolution of eukaryotes • Provide evidence for the theory of endosymbiosis • Distinguish between the 3 groups of protists (animal; fungus; plant-like)
Origin of Eukaryotes • First eukaryotic organism thought to have evolved about 1.5 billion years ago. Prokaryotes are as old as 4 billion years • Protozoans (protists) possibly evolved from the 1st eukaryotes by Endosymbiosis • Endosymbiosis –theory that explains how eukaryotic cells evolved from the symbiotic relationship between two or more prokaryotic cells; often one prokaryote lives inside another becoming dependent upon each other
Endosymbiotic Theory • First postulated by Lynn Margulis in 1967 • Although now accepted as a well-supported theory, both she and the theory were ridiculed by mainstream biologists for a number of years. Thanks to her persistence, and the large volumes of data that support this hypothesis gathered by her and many other scientists over the last 30 years, biology can now offer a plausible explanation for the evolution of eukaryotes.
Endosymbiosis wha??? • Endo = "within“ • Endocytosis = (cyto = cell) a process of 'cell eating' - cells are engulfed, but then usually digested as food.... • Endosymbiosis = cells are engulfed, but not digested...cells live together in a mutually benefiting relationship, or symbiosis
Origin of Eukaryotes • Eukaryotic cells more complex than prokaryotic cells: • Membrane-bound nucleus and organelles • Many chromosomes that occur in pairs. • Protists, fungi, plants & animals are composed of eukaryotic cells.
Eukaryotic Animal Cell Typical Animal Cell
Eukaryotic Plant Cell Typical Plant Cell
Origin of Eukaryotes Endomembrane infolding Infolding of membrane system forming nucleus and ER
Origin of Eukaryotes: Cholorplasts and Mitochondria • Mitochondria and chloroplasts (endosymbionts) were prokaryotes that invaded larger cells (host cell) • Mitochondria provided energy for the host cell and chloroplasts converted solar energy into molecular energy • Endosymbiont, ancestral mitochondria: • Aerobic, heterotrophic & prokaryotic • Endosymbiont ancestral chloroplasts: • Anaerobic, autotrophic and prokaryotic
Origin of Eukaryotes • Ancestral chloroplasts were photosynthetic, prokaryotes that became endosymbionts (cyanobacteria) • Relationship began as parasitic or undigested prey • Assumed here that endomembrane infolding evolved first, i.e., cell already evolved nucleus, ER, …
N Endosymbiosis Hypothesis A A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote A C B D Cyanobacteria Aerobic bacteria Chloroplasts Mitochondria N N Plant cell Prokaryote N Animal Cell
N Endosymbiosis Hypothesis B Over a long period of time the aerobes became mitochondria, no longer able to live on their own A C B D Cyanobacteria Aerobic bacteria Chloroplasts Mitochondria N N Plant cell Prokaryote N Animal Cell
N Endosymbiosis Hypothesis C Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments A C B D Cyanobacteria Aerobic bacteria Chloroplasts Mitochondria N N Plant cell Prokaryote N Animal Cell
N Endosymbiosis Hypothesis D Cyanobacteria became chloroplasts, unable to live on their own A C B D Cyanobacteria Aerobic bacteria Chloroplasts Mitochondria N N Plant cell Prokaryote N Animal Cell
Scientific Evidence for Theory of Endosymbiosis • Membranes of chloroplasts and mitochondria are similar to those of living prokaryotes • The ribosomes found in these organelles are more similar to prokaryotic ribosomes than to ribosomes found in eukaryotes • These organelles reproduces by binary fission within the cell • Each organelle contains a circular chromosome and gene sequences match those of living prokaryotes
Multicellularity • Endosymbiosis does not explain multicellularity, another eukaryotic advance • First multicellular organisms existed 1.2 to 1.5 billion years ago (or half as long as unicellular organisms) Red Algae • Large complex eukaryotes fist developed 550 million years ago Red Algae fossils
Life Cycles and Reproduction • Eukaryotes also have more diverse life cycles than prokaryotes • In prokaryotes cell division and reproduction are the same thing: Asexual • In multicellular eukaryotes cell division ≠ reproduction • In sexual reproduction, two individuals make eggs and sperm knows as gametes • Gametes are haploid (one set of chormosomes, ha=half) compared to cells of the rest of the organism; diploid (both sets of chromosomes, di=2)
All prokaryotes Some eukaryotes (yeast) Asexual Life Cycle
Organism is diploid Produces haploid gametes which are fertilized (zygote) Zyogote undergoes mitosis (cell division) to become organism Humans Gametic Sexual Life Cycle
Organism is haploid Produces haploid gametes that upon fertilization form diploid zygote Zygote undergoes meiosis to produce haploid spores that develop into organism Most fungi Some protists (malaria parasite Zygotic Sexual Life Cycle
Organism lives in 2 stages: diploid and haploid Haploid organism produces haploid gamete Zygote undergoes mitosis to become diploid organism Diploid organism produces haploid spores Haploid spores become haploid organism Sporic Sexual Life Cycle
General Characteristics All are eukaryotic, mostly single-celled microscopic organisms Come in all shapes, sizes and colours Some have cell walls, some are motile Classified together because they do not fit into other kingdoms, rather than because they are similar or closely related to one another Most diverse group of eukaryotes, but not as diverse as the bacteria or archaea 3 main groups of protists, characterized by how they get their nutrients.
Three groups of protists • Animal-like protists • Fungus-like protists • Plant-like protist
Animal-like Protists • (Protozoa) – e.g. Amoebas • Consume other organisms for food • Some species are parasites
Protozoa • Means first animals • Scavengers or predators • Some are parasites. • Vary in shape and size. • Most live as single cells but others form colonies
The Cercozoans: Phylum Cercozoa • Amoebas • Cell membrane w/o cell wall, so can change shape • Can form cytoplasmic extensions called pseudopods (false feet) for feeding and movement • http://www.youtube.com/watch?v=7pR7TNzJ_pA
The Ciliates: Phylum Ciliophora • Paramecia • Have many short hair-like projections called cilia (singular cilium) • move by cilia beating in a coordinated rhythm, they also help move food into the paramecium’s gullet, which leads to a food vacuole. • http://www.youtube.com/watch?v=fh_yjLppNAg&feature=fvwrel
Flagellates: Phylum Zoomastigina • Have one or more flagella which whip from side to side to move them about • some are mutualistic: Trichonympha live in digestive systems of termites and help break down cellulose. • some are parasitic: Trypanosomia causes African sleeping Sickness • http://www.youtube.com/watch?v=9duvzqvVflw
The Sporozoans: Phylum Sporozoa • Parasites • they have spores at some point in their lifecycle • they contain a number of complex organelles at one end of their bodies to help them invade their victim. Plasmodium vivax causes one type of malaria in humans
Life Cycle of Malaria-causing Plasmodium http://highered.mcgraw-hill.com/olc/dl/120090/bio44.swf
Fungus-like Protists • – e.g. Slime moulds, water moulds • Absorb nutrients from other organisms (living or dead) • Some consume other organisms, some are parasites
Slime and Water Moulds Have the characteristics of fungi, protozoa and plants. They glide from place to place and ingest food like protozoa. They have cellulose in their cell walls like plants. They also absorb nutrients from their environment like fungi.
Plasmodial Slime Moulds (Myxomycotes) • Visible to the naked eye as tiny slug like organisms that creep over damp, decaying plant material in forests and fields. • This blob, called a plasmodium, contains many nuclei. Feed in a similar manner to amoebae. • http://www.youtube.com/watch?v=khEAZabMtOk&feature=related
Cellular Slime Moulds (Acrasiomycota): exist as individual amoeboid like cells with one nucleus each. Feed by ingesting tiny bacteria or yeast cells. When food becomes scarce, the cells release a chemical that causes them to gather together to form a pseudoplasmodium. This is a jelly-like mass, which produces a sporangia that releases spores.
Water Moulds (Oomycota): includes water moulds, white rusts and downy mildews Filamentous organisms that resemble fungi. Most live as saprotrophs (dead organic matter) some are parasitic on plants, insects and fish. They extend fungus like threads into their host where they release digestive enzymes and absorb the nutrients. Cause of the Irish Potato Famine.
Plant-like Protists • e.g. Diatoms and dinoflagellates • Make their own food by photosynthesis • Some can consume other organisms when light is unavailable
Diatoms: Phylum Chrysophyta most abundant unicellular algae in the oceans. They are one of the biggest components of plankton. Can reproduce asexually. Sexual reproduction is less common As photosynthetic organisms they are also a major source of atmospheric oxygen. They have rigid cell walls that contain silica, a common ingredient in sand and glass. The remains of diatoms stick around for a long time and they are used in filters, sound proofers, insulation and as a gentle abrasive in metal polishes and toothpastes.
Dinoflagellates: Phylum Pyrophyta Unicellular, photosynthetic and mostly marine. They have protective coats made of stiff cellulose plates. They all have two distinct flagellae They are extremely numerous and form an important base for marine food chains. Form red tides which cause toxins to built up in shellfish that eat them.
Red Tide Some bioluminescence http://www.youtube.com/watch?v=Py-J1ZazHDM&feature=fvwrel
Euglenoids Unicellular freshwater organisms with two flagellae, one usually much longer than the other. They contain chloroplasts but if there is no sunlight then they lose their chloroplasts and ingest and eat food. Have a light receptor and allows them to move towards light
Homework • Pg 69, Q 13-18 • Pg 76, Q 19-24