Week 9
The Classification of Organisms
Carolus Linnaeus devised the system of binomial identification – every species has a
distinct genus and species name…including extinct animals…
A scientific name consists of genus and a specific epithet. The yellow perch is
properly called Perca flavescans. Names are derived from latin or greek and are intended
to be descriptive, often named for people or places
Taxa are taxonomic groupings and range from the broad groupings (kingdoms) to species
and subspecies.
Kingdoms
Phyla
Classes
Orders
Families
Genera
Species (the only one that actually exists in
nature, all others are artificial constructs. No operational definition exists for a genus,
family or phylum)
Page 362 –0 Fig 20-1 Classifying the family cat (Felis catus)…
Kindom – Animalia
Phyla – Chordata
Class – Mammalia
Order – Carnivora
Family – Felidae
Genus – Felis
Specific epithet – Catus
Figure 20-5, page 367 – sjhows comparison of mammals and bony fish.
Species have a biological basis for separation , members can interbreed and are
reproductively isolated from other species.
Speciation takes place over long periods of time ---see figure 20-2 on page 364
Lumping when taxonomists ignore minor differences and put organisms into already
existing taxa.. Consistent variations among members of a species sometimes classified as
a subspecies
Species have a reproductive isolation from other species but are tied to other species
through evolutionary ties.
Systematics is based on phylogeny (evolutionary history). Systematists arrange taxa in
monophyletic groupings. Species in a monophyletic group share common ancestors.
(see Figure 20-3, page 365) If all subgroups share a common ancestor they are said to be
monphyletic (one branch). Monophyletic groups are natural groups as they reprsent one
line of evolutionary relationships.
A taxon containing all of the taxa descending from one ancestor is called a clade.
Polyphyletic groups include organisms with similar characteristics but not common
ancestors. Systematists analyze homologous structures, compare ancestral and derived
structures and molecular similaritites.
Homologous structures, physiology, behavorial and molecular traits used to place
organisms. Homologous structures indicate common parentage.
Ancestral characters are traits that the ancestor had that remain unchanged
Derived characters are traits that have evolved sine the ancestor.
Deciding what are the most important traits is important (duck billed platypus has some
traits shared with birds others with mammals, which are the most important?)
Fur vs feathers (do all birds have feathers, do all mammals have fur?) READ
DISCUSSION ON PAGE 368 – no mammal has feathers, no birds have
fur…taxonomists look for an the best classification…considering all of the facts and the
relative importance or generalness of the facts.
Usually weighted on a combination of traits…
Molecular Biology – by comparing the macromolecules of organisms scientists can
determine in which order the molecules evolved, which form mutated from which
previous form... Nature article discussed on pg 369...fungus more closely related to
animals than to plants...!
3 APPROACHES - phenetics, cladistics, classical evolutionary taxonomy
Phenetics is a numerical system which evaluates the number of shared characteristics,
whereas cladistics use phylogenetic evidence to classify organisms. Classical
evolutionary taxonomy uses both evolutionary branching and divergence to classify
organisms.
Phenetic uses numeric system called phenotypic system based on number of similar
characteristics
Cladistics relies on cladograms…each branch represents an evolutionary divergence or
splitting…examples of turtles and crocodiles sharing a common ancestor. See page 370
Classical evolutionary taxonomy uses a phylogenetic tree. See page 372
Chapter 21 Microorganisms
VIRUSES
Structure
Nucleic Acid core and protien coat (capsid)
May have outer membrane
Contain DNA or RNA
Shape of capsid: rod shaped and/or polyhedral
Not truly living …not true cells, cannot reporduce or carry out metabolic
functions on their own
Origin of viruses –maybe bits of DNA or RNA that escaped from a parent
cell which may have plant, animal or bacteria. This could explain the
specificity of viruses to host cells
Bacteriophages - infect bacteria, typically DNA viruses in polyhedral
head. Cultured in labs, used in biotechnology.
Lytic bacteriophages – destroy the host cell.
Stages of infection:
Attachment
Penetratiob – nucleic acid injected into
bacterium, capsid remians attached to the cell wall.
Replicationof new bacteriophage molecules
using bacteria’s ribosomes, enzymes, etc.
Release of bacteriophages by bacterial lysis
Temperate bacteriophages – do not destroy the cell, integrate their DNA in
the host DNA, replicate together, may turn intoas lytic cycle however
Viruses infecting animal cells – spread between plants by plant feeding
insects like aphids, may also be spread by seeds or asexual propoagation of plants, pass
between plant cells via plasmodesmata. Most are RNA viruses, attach to plant
ribosomes and are then translated…su\ymptoms of viral infection: spots on leaves, lower
yields…cures are not well known
BACTERIA
Bacteria :
Characteristics:
Single-celled, contain ribosomes, lack membrane-bound organelles
DNA not surrounded by a nuclear membrane, is circular, accessory
DNA rings known as plasmids
Have a cell wall exterior to cell membrane
Typically composed of peptidoglycan; sugars linked with peptides
May have a capsule exterior to cell wall which aids in protection
from dessication and adds to its ability to cause disease.
May have flagella, flagella pushes the cell through the medium
(eukaryotic flagella pull).
Heterotrophic bacteria – most are saprobes; gain nourishment from
dead organic matter, important as decomposers, recycle organic matter
Autotrophic bacteria are either phototrophs (photosynthetic) or
chemotrophs. (oxidize inorganic molecules as an energy source)
Reproduction by binary fission; DNA is replicated, new cell membrane and wall forms
between 2 rings of DNA, very rapid as fast as every 20 minutes, limited only by lack of
food and accumulation of wastes.
Nitorgen fixation is critical to life on earth, bacteria that have this ability take
atmospheric niotrogen and convert it to orgainc forms, which are available toplants
ARCHAEBACTERIA
Archaebacteria – prokaryotes split into two groups early on…archaebacteria tend to live
in harsh environments, they lack peptidoglycan in cell walls, and have other biochemical
differences from eubacteria. Have some characteristics in common with eukaryotes
Halophiles live in very salty environments, some are photosynthetic
Methanogens produce mthane and inhabit the digestive tracts of human and other animals
Thermophiles live in very hot often acidic environments
EUBACTERIA
Eubacteria : very diverse but with similar morphologies; 3 main shapes –bacillus,
coccus, spirillum
Mycoplasmas are tiny bacteria without a cell wall, live in soil, sewage, some are
parasites, typically not pathogenic (disease causing)
Gram positive bacteria stain violet, thick walls of peptidoglycan, penicillin works against
gram-positive bacteria
Gram-negative do not absorb stain, two layered wall - thin peptidoglycan wall and an
outer membrane…includes many pathogens (gonorrhea, syphilis, typhus, Rocky
Mountain spotted fever, bacterial meningitis…also include nitrogen fixing bacteria.
Some nitrogen fixers are free living othewrs live in and on root nodules.
Enterobacteria are decomposers, include E. coli (normally inhabit GI tract
some strains cause disease and even death
Cyanobacteria (blue-green algae) are aquatic, terrrestrial in moist area,
photosynthetic autotrophs, many also fix nitrogen
Gram-positive bacteria lactic acid bacteria produce lactic acid from fermentation of
lactose…used commercially to make yogurt, pickles and sauerkraut
Streptococci cause “strep throat”, tooth decay, pneumonia, scarlet fever and rheumatic
fever
Staphylococci nomrally live in the nose and on your skin, cause disease when immune
system is lowered, may cause boils, skin infections,food poisoning, toxic shock syndrome
Clostridia are anaerobes; cause gas gangrene, tetanuis and botulism
PROTISTS
Diverse –some plant-like some like animals, most unicellular, some colonial
Phototrophs inlcude algae
Heterotrophs include water molds and protozoans
Most are aquatic, make up part of plankton. Some live in moist terrestrial habitat or are
parasitic
Chapter 22
Fungi
Fungi have their own kingdom! Includes mushrooms, truffles, morels as well as molds
and mildew…
More than 80,000 known species. All are eukaryotes.
Fungi are lkike plants in some ways but differ enough to be in their own kingdom. Fungi
have cell walls like plants buyt the wall is composed of a different chemical. Chitin is
part of the material that comprise the cell walls of fungi. Chitin resists breakdoewn more
than cellulose foudnin plant cell walls.
Fungi lack chlorophyll and chloroplasts and are not photsynthetic.
Because they cannot maKE THEIR OWN FOOD LIKE PLANTS THEY MUST GET
FOOD FROM ANOTHER SOURCE…FUNGI ARE HETEROTROPHS, AS ARE
ANIMALS
Fungi use digestive enzymes to liquify and absorb predigested food as small organic
molecules through the cell walls. They receive their nuitrition from dead or living
organic matter…
Structural differences: from single celled yeasts to very large multicellular orgainisms
Yeasts reproduce asexually by budding or sexually by spore fromation.
Most fungi are filamentous molds…long threads of cells called hyphae. The tangled
mass formed by the hyphae are called mycellium.
Spores – released by fruting body…
No morphological differencews between mating types…no male – female referred to as +
or -…
Fungal cells usually contain haploid nuclei…when they come into contact with a hyphae
of another mating type they grow together, a young zygospore is formed and
dedvelops…it may lie dormant for sometime but when it is ready it germinates an aerial
hypha developes with a sporangium at the tip from which haploid spores are relaesed.
Only the zygote is diploid all other parts and the spores are haploid.
Read discussion on page 403
3 divisions of Fungi
Classification is based primarily on the differences between spores and fruiting bodires:
Zygomycota – reproduce sexually by forming zygospores- decomposers Note the
drawing on page 405, Figure 22-2.
Ascomycota – sac fungi…asexual reproduction…
Basidomycota – club fungi – mushrooms, bracket fungus, puffballs…name derived from
the development of basidium from which extend four basiospores (see page 408)
A fourth division is Deutermycota – no known sexual stage (the Mr rogers of Fungi)
Lichens – photsynthetic bacteria and fungus – a symbiotic relationship or controlled
parasitism?…
Ecological role saprophytes or decomposers
Mycorrihizae – mutualistic relationship