- Slides: 55
Three Domains of Life Protists
Three Domains of Life
Changes in Classification • The ‘old school’ method of classification included 5 Kingdoms (what I learned in school) – Monera – Protista – Fungi – Plantae – Animalia • Today, advances in molecular technology expanded our understanding (and interpretation) of systematics
Modern Systematics • Three Domain classification of life • Numerous, virtually countless Kingdoms • Bacteria and Archaea are now 2 distinct Domains (once included together in Kingdom Monera) • Protista, Fungi, Plantae, and Animalia remain classified as distinct Kingdoms, although classification of the kingdom Protista has been met with complications
Prokaryotes • Includes the kingdoms Archaea & Bacteria • Oldest, structurally-simplest, and most abundant forms of life • Photosynthesis Bacterial and Eukaryotic Diversity • Important decomposers and symbionts
Prokaryotes • Unicellular • Typically 1μm or less (1000 μm = 1 mm; 1000 mm = 1 meter) • No membrane-bound nucleus; instead a single circular chromosome made of DNA • Asexual reproduction by binary fission • Photosynthetic bacteria utilize oxygen or chemical compounds, such as sulfur
Prokaryotic Cell Structure • Three basic forms: – Bacillus – rod-shaped – Coccus - sphercal or ovoid-shaped – Spirillum – spiral or helical
Prokaryotic Cell Structure • Prokaryotes have a tough cell wall and other external structures • Cell wall consists of peptidoglycan; a rigid network of polysaccharide strands cross-linked by peptide side chains; unique to Bacteria • Maintains the shape of the cell and protects it from swelling and rupturing
• Prokaryotes can have 1 or more flagella (much less complex than in Eukaryotes) • Some Prokaryotes possess pilli, which helps fasten cell to host membrane
Domain Archaea • Once considered a subdivision of the Kingdom Monera, now its own domain • Like all prokaryotes, Archaea are singlecelled microorganisms that lack a nucleus and membrane-bound organelles • Best known for the “extremophiles” – Archaea which thrive in extremely harsh environments
Archea - Extremophiles • Thermophiles – thrive at 60 -80°C (>176°F!) • Acidophiles – thrive at p. H at or below p. H 3 • Xerophiles – grow in extremely dry conditions • Halophiles – require extremely high concentrations of salt http: //www. dpchallenge. com/image. php? IMAGE_ID=448561
Archaea - Extremophiles • Evidence for evolution of life on Earth? • Many of the harsh conditions which extremophiles require to survive were characteristic of our early Earth • Likely that extremophiles evolved to dwell in such conditions billions of years ago and retained ability to survive today in specific environments
• Archaea differ from Bacteria in numerous ways – Plasma membranes are made of different kinds of lipids – RNA and ribosomal proteins more like those of Eukaryotes – Mostly anaerobic Photosynthetic
Domain Bacteria • Two types: – Gram-positive – Gram negative • Refers to the Gram Stain (purple dye) • Gram-positive bacteria – possess a thicker peptidoglycan cell wall; retain stain • Gram-negative bacteria – contain less peptidoglycan; do not retain stain
Gram-positive and negative
Bacterial Conjugation • Transfer of genetic material • Horizontal gene transfer • NOT sexually (no gametes)
Eukaryotic origin • The nucleus and endoplasmic reticulum arose from infolding of the prokaryotic cell membrane
Eukaryotic origin • Eukaryotic organelles arose from a consortium of symbiotic prokaryotes – Mitochondria were aerobic heterotrophic prokaryotes – Chloroplasts (for photosynthesis) were photosynthetic prokaryotes
Endosymbiotic theory • Evidence? – Mitochondria have their own independent DNA, and a double membrane – Chloroplasts resemble cyanobacteria; also have their own independent DNA and a double membrane
Kingdom Protista (the trouble-maker) • Kingdom Protista is NOT monophyletic Paraphyletic – includes common ancestor but not all descendents
Kingdom Protista • Eukaryotic (must be! Domain Eukarya) • Largely unicellular with some multi-cellular ‘exceptions’ (e. g. , kelps, seaweed) • May be autotrophic or heterotrophic • Debate over classification – – Are some protists members of other kingdoms? – Would protists best be considered as several different kingdoms?
Kingdom Protista • Characterized by: – Mode of locomotion (e. g. , flagella, cilia) – Mode of nutrition (e. g. , autotrophic, heterotrophic) – Body form (unicellular, multicellular) – Pigmentation (e. g. , Red, Green, Brown alga) – Reproduction (asexual, sexual) • Multicellular protists are distinguished from other Kingdoms by their lack of specialized tissues
Kingdom Protista • Have you ever eaten a protist? , or should I ask, have you ever eaten seaweed? ? ? • Just to complicate matters, green algae is categorized as a plant in Kingdom Plantae…
Green Plants evolved from Green Algae • We’ll come back to this…
Kingdom Fungi • • • Unicellular and multi-cellular ~1. 5 million species Important decomposers Includes many disease-causing organisms Others are important symbionts and fermenting organisms
Kingdom Fungi • Mycology – the study of fungi • All fungi are heterotrophic – Obtain their food by secreting digestive enzymes and absorbing the nutrients released by the enzymes • Unicellular fungi may have flagella; multicellular fungi are primarily filamentous in form • Cell walls composed of chitin
Kingdom Fungi • Six phyla – Cytrids (flagellated), Zygomycetes (inc. bread molds), Glomeromycetes (mycorrhizae), Ascomycetes (inc. yeast), Bascidiomycetes (mushrooms), and Deuteromycetes (not pictured)
Kingdom Fungi • Phylogeny based on the 5 major Phyla (based on mode of sexual reproduction)
Kingdom Fungi • Multicellular fungi consist of long, slender filaments called hyphae • Some hyphae are continuous; others are divided by septa • Mycelium – a mass of connected hyphae
Kingdom Fungi • Mycelium grows through and digests its substrate • Fungi live in their food!
Kingdom Fungi • Hyphae (mycelium) form complex structures • A mushroom is a spore-bearing body of a fungus; composed of hyphae • A puffball is a spore-bearing body of certain species of fungi, including the deadly Death Cap mushroom; composed of hyphae
Kingdom Fungi • Fungi can also be monokaryotic or dikaryotic – Monokaryotic – one nucleus per cell – Dikaryotic – two nucleii per cell • Fungi reproduce sexually and asexually – During sexual reproduction in some fungi, 2 haploid nuclei fuse creating a dikaryotic (dikaryon) stage, which precedes the normal diploid nucleus
Kingdom Fungi • Some fungi produce specialized mycelial structures to house spores (e. g. , mushroom, puffballs, ‘shelf’ mcycelium on dead trees) • Spores can form as a result of sexual or asexual reproduction • Spores can withstand degradation and survive for long periods of time; because of their size, they can travel long distances
Kingdom Fungi • Chestnut Blight – a fungal disease which has virtually eliminated the American chestnut • Accidentally introduced into the U. S. on imported lumber from Asia • The roots of the tree are fairly resistant to the fungus, but the tree succumbs once it grows enough shoots to reproduce • Unknown spreading agent (the spores are everywhere!)
Kingdom Fungi http: //www. kychestnut. org/images/open. Grown. Tree. jpg
…Jack Frost nippin’ at your nose… • The American chestnut once covered large tracts of forest in the U. S. • The chestnut was a very important source of food for wildlife (and the inspiration for at least 1 Christmas song…) • At the turn of the twentieth century, one quarter of all trees in the eastern United States were chestnut!
The Chestnut Blight • Only a few mature survivors remain of the American Chestnut, which once consisted of 4 billion trees (that’s over 99. 99% gone) • If you have ever eaten a chestnut, you had a European import; only our grandparents may have ever tasted an American chestnut • The American Chestnut Foundation seeks to restore the great chestnut, but how?
The Chestnut Blight • Development of blight-resistant American chestnuts is accomplished through a process known as “backcross breeding” • Hybrids between American and Chinese chestnuts are repeatedly crossed back onto purely American specimens, yielding offspring which are blight- resistant • The resulting offspring are ~94% American (6% Chinese) and disease-resistant
Kingdom Fungi • Spores are frequently dispersed by wind, but may also be spread by insects and small animals • Chytrids are an ancestral group and retain flagella; have motile zoospores
Why did the mushroom go to the party? • Many fungi live underground, and can reach great sizes • One of the largest living organisms in the world is a fungus! • The largest known specimen covers more than 3. 4 square miles and is thousands of years old • And some species of fungi are bioluminescent!
Armillaria fungus • Connected underground by hyphae!
Fungal Ecology • Fungi often have interactions or symbioses with other organisms • Obligate symbiosis – essential for survival; fungus cannot survive without symbiont • Facultative symbiosis – fungus can survive without symbiont • Mutualistic relationships – both partners benefit • Commensal relationships – one partner benefits, but the other is unaffected
Fungal Ecology • A lichen is a symbiotic association between a fungus and a photosynthetic partner (usually green algae or cyanobacteria)
Fungal Ecology • Mycorrhizae – association between a fungus and the root of a tree • Mycorrhizae function as an extension of the plant root system; the fungus increases surface area for absorption and aids in transfer of nutrients • The plant, in return, supplies organic carbon to the fungus
Mycorrhizae • Very important! • Mycorrhizal plants are more resistant to drought and even microbrial soil-borne pathogens • Two types – Arbuscular mycorrhizae – Ectomycorrhizae
Fungal Ecology • Leaf-cutter ants – an animal symbiont with fungi! • The ants feed on special structures produced by a fungus that they have domesticated • The ants feed the fungus leaves and protect it from pests and molds • In return, the ants eat the fungus and feed it to their young
Just in case you didn’t believe me… http: //www. flickr. com/photos/kellyslittlepieces/2243322652/