Biology 102

Study Notes Exam 1

 

Chapter 20: Classification of Living Things

 

Taxonomy: the branch of biology concerned with identifying and naming organisms

-       a natural system of classification reflects the evolutionary history of organisms

-       naming and identifying organisms began with the Greeks and Romans

-       in the middle ages, organisms were described using long Latin descriptions

-       much later, John Ray, a British naturalist argued that each organism should have a set name

 

The Binomial System

-       the number of known organisms expanded greatly in mid-eighteenth century due to European travel

-       common names vary with different languages, & the same name may refer to different organisms in different regions

-       Carolus Linnaeus developed the binomial system to name species

-       the binomial system of nomenclature names organisms using a two-part Latin name

o      first part is the genus; closely related species are assigned to the same genus

o      second part is the specific epithet; it usually provides something descriptive about an organism

o      a scientific name consists of both genus and specific epithet (e.g., Panthera tigris and Panthera leo)

o      both names are italicized or underlined; the first letter of only the genus name is capitalized

o      the genus can be abbreviated when used with a specific epithet if the full name was given before (H. sapiens)

-       the classification of organisms is an ongoing process

o      there are estimated to be between 3 and 30 million species living on earth

o      we have currently named one million species of animals and a half million plant and microorganismic species

o      some groups, such as birds, are nearly all known; some insect groups are mostly unknown

 

Identification of a Species

-       Linnaeus considered each species to have a unique structure that made it distinct

o      distinguishing species on structure can be a problem because variations occur among members of the same species

o      males and females may have a different form, as well as juveniles and adults

-       the biological definition of a species: a group of organisms that interbreed and share the same gene pool

o      distinguishing species on the basis of reproductive isolation can be a problem

o      some species do not reproduce sexually

o      some species hybridize where their ranges overlap

-       when a species has a wide geographic range,they may tend to interbreed where they overlap; these populations may be named as subspecies

o      the rat snakes Elaphe obsoleta obsoleta and Elaphe obsoleta bairdi are subspecies of Elaphe obsoleta

o      including the subspecies makes this a trinomial, or three-part, name

-       in this chapter, a classification approach is taken to the definition of species

o      the term "species" is used for a taxonomic category below the rank of genus

o      species share a more recent common ancestor with species in same genus than with those in other taxa

o      a taxon is a group of organisms in a classification category; Rosa or Felis are taxa at the genus level

o      a common ancestor is an ancestor held in common by at least two lines of descent

 

Classification Categories

-       Aristotle classified life into 14 groups (e.g., mammals, birds, etc.), and subdivided them by size

-       Ray grouped animals and plants according to how he thought they were related

-       Linnaeus grouped plants by flower parts; his categories were published in Systema Naturae in 1735

-       today, we use a minimum of 7 categories of classification:

o      kingdom, phylum (or division for plants), class, order, family, genus & species

o      a higher category, the domain, has been proposed to be added to these 7 categories

o      the higher the category, the more inclusive it is

o      members of a kingdom share general characters; members of a species share quite specific characters

o      characters are any structural, chromosomal, or molecular feature that distinguishes groups

o      additional levels of classification can be added by adding super-, sub-, or infra- (e.g., suborder)

 

Phylogenetic Trees

-       Systematics is the study of the diversity of organisms using information from cellular to population levels

o      classification reflects phylogeny; one goal of systematics is to create phylogenetic trees

o      phylogeny is the evolutionary history of a group of organisms

o      a phylogenetic tree indicates common ancestors and lines of descent or lineages

o      a primitive character is a trait that is present in a common ancestor and all members of a group

o      a derived character is present only in a specific line of descent

o      different lineages diverging from a common ancestor may have different derived characters

-       Fossil Record

o      because fossils can be dated, fossils can establish the age of a species

o      it can be difficult to associate fossils with currently living groups; a new view of turtle fossils could place them closer to crocodiles

o      the fossil record is often incomplete because soft-bodied organisms do not fossilize well

o      most organisms decay and the chances of becoming a fossil are low

-       Homology

o      homology is a character similarity that is due to having a common ancestor

o      homologous structures are related to each other through common descent but may differ in structure and function (e.g., the forelimbs of a horse and the wings of a bat)

o      analogous structures have the same function but are not derived from the same organ in a common ancestor (e.g., the wings of an insect and the wings of a bat)

o      homology helps indicate when species belong to a related group

o      convergent evolution may make it difficult to distinguish homologous from analogous structures

o      convergent evolution is acquisition of similar traits in distantly related lines of descent as a result of adaptation to similar environmental conditions

       both spurges and cacti are adapted to a hot, dry environment and are both similar, but details of flower structure indicate these two groups are not closely related

o      parallel evolution produces similar characters in related lineages without occurring in a common ancestor

-       Molecular Data

o      speciation occurs when mutations bring about changes in base pair sequences of DNA

o      each distinct lineage accumulates changes in DNA base pair sequences and amino acid sequences in proteins over time

o      Protein Comparisons

       earlier studies used immunological reactions to antibodies, made by injecting a rabbit with cells of one species, to determine the relatedness of two species

       we now use amino acid sequences to determine the differences in proteins between two species

       cytochrome c is a protein found in all aerobic organisms; the amino acid differences in cytochrome c between chickens and humans is 13 but between chickens and ducks is only 3

       since the number of universal proteins is limited, most new studies use RNA and DNA.

-       RNA and DNA Comparisons

o      all cells have ribosomes for protein synthesis; comparing rRNA sequences provides a reliable indicator of similarity

o      DNA-DNA hybridization separates the DNA strands of two species and combines the strands; the more closely related the two species, the more the DNA strands stick together

o      Chimpanzees and Humans

       DNA hybridization shows chimpanzees closer to humans than to other apes

       yet humans are kept in a separate family and chimpanzees are with the ape family because humans are markedly different in adaptation to the environment

o      Mitochondria DNA (mtDNA) changes ten times faster than nuclear DNA

       mtDNA is often used for closely related species; North American songbirds were found to have diverged well before retreating glaciation 250,000-100,000 years ago

-       Molecular Clocks

o      nucleic acid changes are not tied to adaptation; the fairly constant changes provide a "molecular clock."

o      comparison of mtDNA sequences equated a 5.1% nucleic acid difference among songbird species to 2.5 million years

o      the fossil record can then be used to calibrate the clock and confirm the hypothesis drawn from molecular data

 

Systematics Today

-       Cladistic Systematics

o      cladistic systematics is based on work of Willi Hennig

o      cladistics analyzes primitive and derived characters and constructs cladograms on the basis of shared derived characters

o      cladogram: a diagram showing relationships among species based on shared, derived characters

o      a clade is an evolutionary branch that includes a common ancestor and all its descendent species

o      Parsimony

       cladists are guided by principle of parsimony‹the minimum number of assumptions is most logical

       this approach is vulnerable if convergent evolution produces what appears to be common ancestry

       reliability of cladograms is dependent on knowledge and skill of a particular investigator gathering data

-       Phenetic Systematics

o      phenetic systematists cluster species on the basis of the number of shared similarities, regardless of whether they might be convergent, parallel, or depend on one another

o      systematists of this school do not believe that a classification that actually reflects phylogeny can be constructed; it is better to rely strictly on a method that does away with personal prejudices

o      results of their analysis are depicted in a phenogram

o      phenograms vary for the same group of organisms, depending on how the data are collected and handled

-       Traditional Systematics

o      traditional systematics stresses common ancestry and the degree of structural difference among divergent groups in order to construct phylogenetic trees

       the traditional school accepts the tenet that mammals and birds evolved from reptilian ancestors, even though the reptile group is monophyletic‹it does not include all groups from all ancestors

       to cladists, the traditional method of determining phylogeny is arbitrary

       birds are more closely related to dinosaurs and crocodiles than they are different

o      cladists would not use "reptiles" because it does not include all organisms derived from reptiles

 

Classification Systems

-       Naming the Kingdoms

o      early biologists recognized two kingdoms: animals (kingdom Animalia) and plants (kingdom Plantae)

o      the microscope revealed unicellular organisms; in the 1880s, Ernst Haeckel proposed the kingdom Protista

o      Haeckel originally placed bacteria and cyanobacteria in Monera since they lacked a nucleus

o      in 1969, R. H. Whittaker suggested a five kingdom system based on cell type, organization, and nutrition:

       Monera: prokaryotic bacteria that obtain organic molecules by absorption or photosynthesis

       Protista: mainly unicellular eukaryotes that obtain organic molecules by absorption, ingestion, or photosynthesis; the classification of protists is debated

       Plantae: multicellular eukaryotes, autotrophic by photosynthesis

       Animalia: multicellular eukaryotes, heterotrophic by ingestion, are generally motile

       Fungi: multicellular eukaryotes, heterotrophic saprotrophs that form spores, lack flagella and have cell walls containing chitin

o      generally, protists are considered to have evolved from monerans, and the fungi, plants, and animals evolved from protists via three separate lineages

-       Three-Domain System

o      sequencing of rRNA suggests all organisms evolved along three distinct lineages: domains Bacteria, Archaea, and Eukarya

o      bacteria diverged first; archaea and eukarya are more closely related than either is to bacteria

o      the archaea live in extreme environments: methanogens in anaerobic swamps, halophiles in salt lakes, and thermoacidophiles in hot acidic environments

o      the archaea cell wall is diverse but not the same as the bacterial cell wall

o      eukarya contains unicellular to multicellular organisms, always with a membrane-bound nucleus

 

 

 

 

 

Chapter 21: Viruses, Bacteria & Archaea

 

The Viruses

-       viruses are not organisms: they are noncellular; cannot metabolize; cannot respond to stimuli; multiply only within living cells by parasitizing the synthetic machinery of the infected cell; and evolve as a result of mutation and natural selection

-       all viruses are infectious

-       in 1884, Pasteur suspected something smaller than bacteria caused rabies; he chose the Latin term for "poison."

-       in 1892, Russian biologist Dimitri Ivanowsky, working with tobacco mosaic virus, confirmed Pasteur's hypothesis that an infectious agent smaller than a bacterium existed

-       with the invention of the electron microscope, these infectious agents could be seen for the first time

-       Viral Structure

o      viruses are similar in size to a large protein, generally smaller than 200 nm in diameter

o      many viruses can be purified and crystallized, and the crystals stored for long periods of time... viral crystals become infectious when the viral particles they contain invade host cells

o      all viruses have at least two parts:

       an outer capsid is composed of protein subunits

       an inner core contains either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid), but not both

      the viral genome at most has several hundred genes; a human cell contains thousands of genes

      the viral envelope is usually partly host plasma membrane (phospholipids) with viral glycoprotein spikes

      viral particles have proteins, especially enzymes (e.g., polymerases), to produce viral DNA or RNA

-       the classification of viruses is based on: their type of nucleic acid (including whether it is single-stranded or double-stranded); their size and shape; and the presence or absence of an outer envelope

-       Parasitic Nature

o      viruses are obligate intracellular parasites that cannot multiply outside a living cell

o      animal viruses in laboratories are raised in live chick embryos or in cell tissue culture

o      viruses infect all sorts of cells, from bacteria to human cells, but are very specific (tobacco mosaic virus only infects certain plants; the rabies virus infects only mammals; the AIDS virus, HIV, infects only certain human blood cells; hepatitis virus invades only liver tissues; polio virus only reproduces in spinal nerve cells)

-       Virus Evolution

o      viruses are likely to have originated from the very cells that they infect

       if so, viral nucleic acids originated from the host cell genome, & viruses evolved after cells came into existence; so new viruses are probably evolving now

o      viruses often mutate; therefore, it is correct to say that they evolve

o      viral mutation can be troublesome: a vaccine effective today may not be effective tomorrow

o      influenza (flu) viruses mutate regularly

-       Viral Reproduction

o      viruses gain entry into and are specific to a particular host cell because portions of the capsid (or spikes of the envelope) adhere to specific receptor sites on host cell surface

o      viral nucleic acid then enters a cell, where the viral genome codes for production of protein units in the capsid

o      a virus may have genes for a few special enzymes needed for the virus to reproduce and exit from a host cell

o      the virus relies on host cell enzymes, ribosomes, transfer RNA (tRNA), and ATP for its own replication

o      the virus takes over the metabolic machinery of the host cell when it reproduces

-       Replication of Bacteriophages

o      bacteriophages (phages) are viruses that parasitize a bacterial cell

o      lytic cycle: a bacteriophage "life" cycle of five stages where a virus takes over operation of the bacterium immediately upon entering it and then destroys the bacterium

       attachment: portions of the capsid bind with receptors on the bacterial cell wall

       penetration: a viral enzyme digests part of cell wall; the viral DNA is injected into a bacterial cell

       biosynthesis: synthesis of viral components - begins after the virus brings about inactivation of host genes not necessary to viral replication

       maturation: viral DNA and capsids are assembled to produce several hundred viral particles and lysozyme, coded by the virus, is produced

       release: when lysozyme disrupts the cell wall (breaks down peptidoglycan), the viral particles are released and the bacterial cell dies (lysis)

o      lysogenic cycle: a cycle where the virus incorporates its DNA into the bacterium but only later does it produce phage

       following attachment and penetration, viral DNA becomes integrated into bacterial DNA with no destruction of host DNA

       at this point the phage is latent and the viral DNA is called a prophage

       a prophage is replicated along with host DNA; all subsequent cells (lysogenic cells) carry a copy

       certain environmental factors (e.g., ultraviolet radiation) induce a prophage to enter the biosynthesis stage of the lytic cycle, followed by maturation and release

-       Reproduction of Animal Viruses

o      animal viruses replicate similarly to bacteriophages but there are modifications

o      if the virus has an envelope, glycoprotein spikes allow it to adhere to plasma membrane receptors

o      the virus genome covered by the capsid penetrates the host cell

o      once inside, the virus is uncoated as the envelope and capsid are removed

o      free of its covering, the viral genome (DNA or RNA) proceeds with biosynthesis

o      newly assembled viral particles are released by budding

o      components of viral envelopes (i.e., lipids, proteins, and carbohydrates) are obtained from the plasma or nuclear membrane of the host cell as viruses leave

o      retrovirus: an RNA animal virus with a DNA stage

       retroviruses contain reverse transcriptase that carries out reverse transcription producing cDNA from RNA

       viral cDNA is integrated into host DNA and is replicated as host DNA replicates

       viral DNA is transcribed; new viruses are produced by biosynthesis, maturation and release by budding.

-       Viral Infections

o      viruses cause infectious diseases in plants and animals, including humans

o      some animal viruses are specific to human cells: papillomavirus, herpes virus, hepatitis virus, and adenoviruses, which can cause specific cancers

o      retroviruses include the AIDS viruses (e.g., HIV) and also cause certain forms of cancer

o      some viruses are cancer-producing because they bring with them oncogenes, normal genes transformed so they can cause the cell to undergo repeated cell divisions

o      in humans, viral diseases are controlled by preventing transmission, administering vaccines, and only recently by the administration of antiviral drugs

o      antibiotics do not cure viral infections because viruses use host cell enzymes, not their own enzymes; interfering with the enzyme kills the host cell

o      over 1,000 plant viruses cause diseases; virus infections are difficult to distinguish from nutrient deficiencies and plants are propagated to stay free of virus infection

o      viroids are naked strands of RNA, a dozen of which cause crop diseases

o      prions are newly discovered disease agents that vary from viruses and bacteria

       prions are proteins with a wrongly shaped tertiary structure that cause other proteins to distort

       Creutzfeldt-Jakob disease in humans and scrapie and mad cow disease (BSE) in cattle are due to prions

 

 

 

 

 

 

 

 

 

 

The Prokaryotes - the bacteria and archaea

-       Antonie van Leeuwenhoek (Dutch naturalist, 17th century) discovered bacteria while examining scrapings from his teeth

-       the organisms Leeuwenhoek observed were thought to arise spontaneously from inanimate matter

-       ~ 1850, Pasteur devised an experiment showing that the bacteria present in air contaminated the media

-       a single spoonful of soil contains 1010 prokaryotes; these are the most numerous life forms

-       Structure of Prokaryotes

o      prokaryote means "before a nucleus" and their cells lack a eukaryotic nucleus

o      prokaryotic fossils date back to 3.5 billion years ago... fossils indicate prokaryotes were alone on earth for 2 billion years - they adapted & evolved very diverse metabolic capabilities

o      prokaryotes range in size from 1-10 µm in length and from 0.7-1.5 µm in width

o      most prokaryotes have a rigid cell wall (made from peptidoglycan in bacteria) outside the plasma membrane that keeps the cell from bursting or collapsing due to osmotic changes

o      glycocalyx surrounding the cell wall can be an organized capsule &/or a loose gelatinous sheath called a slime layer; in parasitic forms, these outer coverings protect the cell from host defenses

o      flagella: structure outside cell used for locomotion by some prokaryotes

       the flagellum is a filament composed of three strands of the protein flagellin wound in a helix and inserted into a hook that is anchored by a basal body; it's capable of 360° rotation which causes the cell to spin and move forward

o      fimbriae: short hairlike filaments extending from the surface that allow many prokaryotes adhere to surfaces

       the fimbriae of Neisseria gonorrhoeae allow it to attach to host cells and cause gonorrhea

o      prokaryotic cells lack the membranous organelles of eukaryotic cells

o      metabolic pathways are located on the plasma membrane

o      nucleoid: a dense area in prokaryotes where the chromosome is located; it is a single circular strand of DNA

o      plasmids: accessory rings of DNA found in some prokaryotes; they can be extracted and used as vectors to carry foreign DNA into bacteria during genetic engineering procedures

o      protein synthesis in prokaryotic cells is carried out by thousands of ribosomes, which are smaller than eukaryotic ribosomes

-       Reproduction in Prokaryotes

o      binary fission is a splitting of a parent cell into two daughter cells; it is asexual reproduction in prokaryotes

       the single circular chromosome replicates; the two copies separate as the cell enlarges... newly formed plasma membrane and cell wall separate the cell into two cells

       mitosis, which involves formation of a spindle apparatus, does not occur in prokaryotes

o      because prokaryotes have a short generation time, mutations are generated and distributed through a population more rapidly

o      in bacteria, genetic recombination can occur in three ways:

       conjugation: a bacterium passes DNA to a second bacterium through a tube (sex pilus) that temporarily joins two cells; this occurs only between bacteria in the same or closely related species

       transformation: bacteria take up free pieces of DNA secreted by live bacteria or released by dead bacteria

       transduction: a bacteriophage transfers portions of bacterial DNA from one cell to another

o      plasmids can carry genes for resistance to antibiotics and transfer them between bacteria by any of these processes

-       Endospore Formation

o      some bacteria form resistant endospores in response to unfavorable environmental conditions

o      the chromosome & some cytoplasm dehydrate and are encased by three heavy, protective spore coats... the rest of the bacterial cell deteriorates and the endospore is released

o      endospores survive in the harshest of environments: desert heat and dehydration, boiling temperatures, polar ice, and extreme ultraviolet radiation

o      endospores also survive very long periods of time; anthrax spores 1,300 years old can cause disease

o      when environmental conditions are again suitable, the endospore absorbs water and grows out of spore coat... in a few hours, newly emerged cells become typical bacteria capable of reproducing by binary fission

o      endospore formation is not reproduction but it is a means of survival and dispersal to new locations.

-       Prokaryotic Nutrition:

o      bacteria differ in the need for, and tolerance of, oxygen (O2)

       obligate anaerobes are unable to grow in the presence of O2 (anaerobic bacteria that cause botulism, gas gangrene, and tetanus)

       facultative anaerobes are able to grow in either the presence or absence of gaseous O2

       aerobic organisms (including animals and most prokaryotes) require a constant supply of O2 to carry out cellular respiration

o      autotrophic prokaryotes

       photoautotrophs are photosynthetic and use light energy to assemble the organic molecules they require

      primitive photosynthesizing bacteria (e.g., green sulfur bacteria and purple sulfur bacteria) use only photosystem I that contains bacteriochlorophyll; they do not give off O2 because hydrogen sulfide (H2S) is used as an electron and H + donor instead of H2O

      advanced photosynthesizing bacteria (e.g., cyanobacteria) use both photosystem I and II that contain the same types of chlorophylls found in plants; they do give off O2 because H2O is used as an electron and H + donor

       chemoautotrophs make organic molecules by using energy derived from the oxidation of inorganic compounds in the environment

      deep ocean hydrothermal vents provide H2S to form of chemosynthetic bacteria

      methanogens are chemosynthetic bacteria that produce methane (CH4) from hydrogen gas and CO2; ATP synthesis and CO2 reduction are linked to this reaction and methanogens can decompose animal wastes to produce electricity as an ecological friendly energy source

      nitrifying bacteria oxidize ammonia (NH3) to nitrites (NO2) and nitrites to nitrates (NO3)

o      heterotrophic prokaryotes

       most free-living bacteria are chemoheterotrophs that take in pre-formed organic nutrients

       as aerobic saprotrophs, there is probably no natural organic molecule that cannot be broken down by some prokaryotic species

       decomposers are critical in recycling materials in the ecosystem; they decomposing dead organic matter and make it available to photosynthesizers

o      commercial uses

       prokaryotes produce chemicals including ethyl alcohol, acetic acid, butyl alcohol, and acetones

       prokaryotic action produces butter, cheese, sauerkraut, rubber, cotton, silk, coffee and cocoa

       antibiotics are produced by some bacteria

o      some chemoheterotrophs are symbiotic, forming intimate, long-term relationships with members of other species; includes mutualistic, commensalistic, and parasitic relationships

       mutualistic nitrogen-fixing Rhizobium bacteria live in nodules on roots of soybean, clover, and alfalfa where they reduce N2 to ammonia for their host; bacteria use some of a plant's photosynthetically produced organic molecules

       mutualistic bacteria that live in the intestines of humans benefit from undigested material and release vitamins K and B12, which we use to produce blood components

       in the stomachs of cows and goats, mutualistic prokaryotes digest cellulose (produce cellulase)

       commensalistic bacteria live in or on organisms of other species and cause them no harm

       parasitic bacteria are responsible for a wide variety of infectious plant, animal and human diseases

 

The Bacteria

-       Gram Stain and Shape

o      the Gram stain procedure (developed in the late 1880s by Hans Christian Gram) differentiates bacteria

       Gram-positive bacteria have a thick peptidoglycan cell wall & stain purple

       Gram-negative bacteria have a thin cell wall & stain pink

o      bacteria and archaea have three basic shapes: spirillum (spiral-shaped), bacillus (elongated or rod-shaped bacteria) and coccus (spherical bacteria)

o      cocci and bacilli tend to form clusters and chains of a length typical of the particular species

-       Types of Bacteria

o      earlier classification of bacteria was based on metabolism, nutrition, etc.

o      work by Carl Woese since 1980 has revised bacterial taxonomy based on similarity of 16S rRNA

o      12 groups are now recognized based on bacterial 16S ribosomal RNA sequences

-       Cyanobacteria

o      cyanobacteria are Gram-negative bacteria with a number of unusual traits

o      they photosynthesize in same manner as plants; are responsible for introducing O2 into the primitive atmosphere

o      they were formerly mistaken for eukaryotes and classified with algae

o      they have pigments that mask chlorophyll (blue-green, red, yellow, brown, black)

o      they are relatively large (1-50 µm in width)

o      they can be unicellular, colonial, or filamentous

o      some move by gliding or oscillating

o      some possess heterocysts, thick-walled cells without a nucleoid, where nitrogen fixation occurs

o      cyanobacteria are common in fresh water, soil, on moist surfaces, and in harsh habitats (e.g., hot springs)

o      some are symbiotic with other organisms (e.g., liverworts, ferns, and corals)

o      lichens are a symbiotic relationship where the cyanobacteria provide organic nutrients to the fungus and the fungus protects and supplies inorganic nutrients

o      cyanobacteria were probably the first colonizers of land during evolution

o      cyanobacteria "bloom " when nitrates and phosphates are released as wastes into water; when they die off, decomposing bacteria use up the oxygen and cause fish kills

 

The Archaea

-       Relationship to Domain Bacteria and Domain Eukarya

o      Archaea are prokaryotes with molecular characteristics that distinguish them from bacteria and eukaryotes; their rRNA sequence is different from rRNA in bacteria

o      because archaea and some bacteria are both found in extreme environments (hot springs, thermal vents, salt basins), they may have diverged from a common ancestor

o      later, the eukarya split from the archaea; archaea and eukarya share some ribosomal proteins not found in bacteria; initiate transcription in the same manner, and have similar types of tRNAs

-       Structure and Function

o      Archaea have unusual lipids in their plasma membranes that allow them to function at high temperatures: glycerol linked to hydrocarbons rather than fatty acids

o      cell walls of archaea do not contain the peptidoglycan found in bacterial cell walls

o      only some methanogens have the ability to form methane

o      most are chemoautotrophs; none are photosynthetic; this suggests chemoautotrophy evolved first

o      some are mutualistic or commensalistic but none are parasitic‹none are known to cause disease

-       Types of Archaea

o      methanogens live under anaerobic environments (e.g., marshes) where they produce methane

       methane is produced from hydrogen gas and carbon dioxide and is coupled to formation of ATP

       methane released to the atmosphere contributes to the greenhouse effect; about 65% of methane found in our atmosphere is produced by methanogenic archaea

o      halophiles require high salt concentrations (e.g., Great Salt Lake)

       their proteins have unique chloride pumps that use halorhodopsin to synthesize ATP in presence of light

       usually they require 12-15% salt concentrations; ocean is only 3.5% salt

o      thermoacidophiles live under hot, acidic environments (e.g., geysers). a. They survive best at temperatures above 80šC; some survive above boiling

       metabolism of sulfides forms acidic sulfates; these bacteria grow best at pH of 1 to 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 22: The Protists

 

General Biology of Protists

-       Protists are classified in the domain Eukarya and the kingdom Protista

-       the endosymbiotic hypothesis explains how the eukaryotic cells arose

o      it proposes that aerobic bacteria became mitochondria & cyanobacteria became chloroplasts after being taken up by eukaryotic cells; spirochetes became flagella

-       Giardia has two nuclei but no mitochondria; the nucleus therefore came before the mitochondria

-       although unicellular to multicellular, protists are highly complex & can have complex life cycles

-       euglenoids have both flagella and chloroplasts

-       plasmodial slime molds are usually amoeboid; during drought, they produce a sporangium

-       protists use asexual reproduction and, when conditions become stressful, sexual reproduction

o      formation of spores allows free-living and parasitic protists to survive hostile environments

o      a cyst is a dormant cell with a resistant outer covering

-       amoeboids and ciliates are more complex, with organelles not seen among other eukaryotes

o      food is digested in food vacuoles & excess water is expelled by contractile vacuoles

-       ecological importance of protists:

o      some are of great medical importance in causing disease; others are ecologically important

o      plankton float near the surface and serve as food for heterotrophic protists and animals

o      plankton that photosynthesize produce much of the oxygen in the atmosphere

o      many protists enter symbiotic relationships; coral reefs rely on symbiotic photosynthetic protists

-       evolution of protists: