modern bio ii bact,fung,prot
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TRANSCRIPT
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 = 1mm; 1000mm = 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 single-celled 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 pH at or below pH 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
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
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/openGrownTree.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
Mycorrhizae
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/