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Prokaryotic and Eucaryotic
Cell Structures
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Morphology of Bacteria
A. Size- bacterial cells vary in size depending on the species,but most are approximately 0.5 to 1 um in diameter or
width
e.g. Staphylococci and streptococci (D=0.75 to 1.25 um)
cylindrical typhoid and dysentery bacteria (0.5 um to
1 um in width and 2 to 3 um in length)
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C. Arrangement
Examples:
a. Neisseria
b. Streptococcus species
which cause throat and
wound infection
c. Pediococcus
d. Staphylococcus
e. Sarcina
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Patterns of arrangement
Examples
a. Corynebacterium diphtheriae
b. Caulobacter
c. Streptobacillus
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Bacterial Cell Structure
1. Appendages flagella and pili
2. Surface Layers- capsule, cell wall and plasma
membranes, mesosomes3. Cytoplasm nuclear material, plasmids, ribosomes,
inclusions and chromatophores
4. Special structures
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Flagella (singular, flagellum)-thin, hairlike filaments extend from the cytoplasmic
membrane and through the cell wall
-propel bacteria through liquid sometimes as fast as100 um per second (= to 3000 body lengths/min)
-composed of three parts:
1. basal body
2. a short hooklike structure
3. a long helical filament
L ringP ringRod
S ringM ring
Gram-negative
(E. coli)
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Pseudomonas
Some pseudomonads
spirilla
Escherichia
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Periplasmic flagella-also known as axial filament
-special flagella that arise atthe cell poles and wind
around the cell body or
protoplasmic cylinder
beneath the outer mem-
brane of the cell wall
-responsible for the corkscrew-
like motility of the
spirochetes
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Chemotaxis
- the movement of bacteria in response to chemicals
in the environment
*attractant towards*repellant away
Polar flagellated bacteria (swim in back- and- forth fashion)
-reverse their direction by reversing the direction offlagellar rotation
Peritrichous flagellated bacteria swim in a very complicated
manner (the cell swims along a relatively straight
track called a run, when the flagellar motors reverse,the bundleof flagella flies apart and the cell tumbleswildly)
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http://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.mov
Movie of motile Rhodobacter spheroideswith fluorescent labelled-flagella
http://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.movhttp://www.rowland.org/labs/bacteria/movies/rsphe_f_swim_1.mov7/30/2019 Bio 127 lec3
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Fimbriae and Pili
- found in gram-negative bacteria
-shorter, straighter and more numerous than
flagella
-not for motility
-are hollow like flagella but nonhelical
-thinner (3 to 10 nm in diam)
Fimbria
- belong to a class of proteins called lectins
which recognize and bind to specific sugar resi-dues in cell surface polysaccharides)
-frequently called adhesins (bacteria
possessing fimbriae have a tendency to adhere
to each other as well as to animal cells)
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N. gonorrhoeae and enterotoxigenic E.coli
-ability of certain organisms to cause
disease is associated with the possessionof fimbriae (loss of fimbriae is accompanied
by a loss of virulence)
Pilus or Pili-morphologically and chemically similar to
fimbriae
-involved in sexual reproduction of bacteria
(F pilus)*those with F pilus are donor cells and
those without it are recipient cells
(genetic materials are transferred during
bacterial conjugation)
Gl l
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Glycocalyx
- a layer of viscous material that surrounds
some bacterial cells
- special stains are used to show this layersuch as India ink (appears halo under a light
microscope)
-composed of polymers
a. Capsule if the glycocalyx is organizedinto a defined structure and is attached
firmly to the cell wall
b. Slime layer- if the glycocalyx is disorganized
and without any definite shape-attached loosely to the wall
-tends to be soluble in water
-medium becomes highly viscous
-produce stringiness in milk
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Capsules maybe:
1. Homopolysaccharide
-single kind of sugar-synthesis of glucan from sucrose by
Streptococcus mutans-to adherefirmly to smooth tooth
surfaces and cause dental caries orcavities (without the sticky glucan, the
microorganisms might be swept away
by flowing saliva)
2. Heteropolysaccharide-more than one kind of sugar
-capsule ofS. pneumoniae , type VI,consists of galactose, glucose &
rhamnose
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4. Capsules may prevent attachment and
lysis of cells by bacteriophages(viruses
that attack bacteria)5. Capsules protect pathogenic from being
engulfed by the white blood cells that
defend the mammalian body
6. Nuisance to industry (responsible for
accumulation of slime in manufacturing
equipment that can clog filters and coat
pipes affecting the quality of the finalproduct)
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The Cell Wall of Prokaryotes:
Peptidoglycan and RelatedMolecules
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Bacterial cell wall
- fundamental differences in ultrastructure ofthe cell wall are responsible for the reaction
(+ or -) of bacteria towards the Gram stain.
- In both types of cell,the cytoplasmicmembrane issurrounded and supported bya cell wall, which provides strength, rigidity
and shape. (prevents cell from expanding
and eventually bursting bec of water
uptake)
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-Usually essential for cells to grow and divide
(cells whose walls have been removed in thelaboratory are incapable of normal growth and
division)
-Account for as much as 10 to 40% of the dry
weight of the cell depending on the species
and the cultural conditions
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This material consists of strands ofalternating repeats ofN-acetylglucosamineandN-acetylmuramic acid, with the latter
cross-linked between strands by shortpeptides. Many sheets of peptidoglycan canbe present, depending on the organism.
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Each peptidoglycan repeating subunit iscomposed of four amino acids (L-alanine, D-alanine, D-glutamic acid, and either lysine ordiaminopimelic acid) and twoN-acetyl-glucose-like sugars
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peptidoglycan
Cytoplasmic
membrane
Outer membrane
peptidoglycan
Gram + Gram -
Cytoplasmic
membrane
Cell wallCell wall
15-80 nm
7-8 nm
7-8 nm
2-3 nm
Schematic cross sections of bacterial cell wall
Typical lipid-protein bilayer
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Peptidoglycans Alias murein or mucopeptide
Present in almost all bacteria (exceptions: wall-
less mycoplasmas; archaebacteria)
Unique to bacteria Essential function
(physical support of thecytoplasmic membrane)
Common architecture
but variations in
structural detail Ideal target forselective toxicitycontains3 kinds of
building blocks
1 2
3(tetrapeptide)
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Gram-positive
Relatively thick and featureless (electronmicroscope)
Major component (~50%) is peptidoglycan
No lipid and often no protein
Accessory polymers (teichoic acid and/orteichuronic acid) covalently linked toPeptidoglycan or to cell membrane
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2 major forms ofteichoic acid
1. polymers of ribitol phosphates
2. polymers of glycerol-aid in the transport of positive ions in
and out of cell
-aid in the storage of phosphorus
-highly antigenic(i.e. They will induce a
host to make specific antibodies); provide the
antigenic determinants used in the serological
identification of many groups and species ofgram-positive bacteria
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Lipopolysaccharides (LPSs)
-characteristic of gram negative bacteria(gram+ bacteria ,cell wall has no LPS)
-composed of 3 covalently linked
segments:
1. Lipid A - firmly embedded in themembrane
-extremelyimportant bec of itstoxicity to animals (also)
known as an endotoxinand can
act as a poison-causing fever,
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*the outer membrane is selectively permeable to
molecules on the basis of their electric charge
and molecular size
Porinsdiffusion channels formed by special proteins
where molecules pass
The general designation foroutermembraneproteinsincluding porins and receptors isOmp.
Removal of peptidoglycan layer in the presence of 10-20% sucrose , the cell
with CM is
called: spheroplast - Gram-negative bacteria
protoplast Gram-positive bacteria
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Cell Wall
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-it secretes extracellular hydrolytic
enzymes
- it ensures the segregation of nuclear matl
(DNA) to daughter cells during division
- it controls the transport of mostcompounds entering and leaving the cell
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Structure and Chemical Composition of CM
-approx 7.5 nm thick
-composed of phospholipid (20-30%) andproteins (50-70%)
-fluid-mosaic model
-semipermeable
-contains specific proteins called permeases
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diff sion and osmosis occ rs across the c toplasmic
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-diffusion and osmosis occurs across the cytoplasmic
membrane
Internal Cell Structures
-material contained wiithin the cytoplasmic membranemay be divided into:
1. the cytoplasmic area the fluid portion contg. dissol-
ved substances and particles such as ribosomes
2. nuclear material or nucleoidrich in the geneticmaterial DNA
Cytoplasmic area-consists of of about 80% water
-aside from water, NA, proteins, CHO, lipids, inorganicions, many low-mol weight cpds and particles w/
various functions
- no evidence that it has cytoskeleton unlike in
eukaryotes
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Cytoplasmic inclusions Where found Composition Function
Table 8. Some inclusions in bacterial cells.
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y p p
glycogenmany bacteria e.g. E.coli
polyglucosereserve carbon andenergy source
polybetahydroxyutyricacid (PHB)
many bacteria e.g.Pseudomonas
polymerized hydroxybutyrate
reserve carbon andenergy source
polyphosphate (volutingranules)
many bacteria e.g.Corynebacterium
linear or cyclicalpolymers of PO4
reserve phosphate;possibly a reserve ofhigh energy phosphate
sulfur globules
phototrophic purpleand green sulfurbacteria andlithotrophic colorlesssulfur bacteria
elemental sulfur
reserve of electrons(reducing source) inphototrophs; reserveenergy source inlithotrophs
gas vesiclesaquatic bacteriaespeciallycyanobacteria
protein hulls or shellsinflated with gases
buoyancy (floatation)in the vertical watercolumn
parasporal crystalsendospore-formingbacilli (genus Bacillus)
proteinunknown but toxic tocertain insects
magnetosomes certain aquatic bacteriamagnetite (iron oxide)Fe3O4
orienting andmigrating along geo-
magnetic field lines
carboxysomesmany autotrophicbacteria
enzymes forautotrophic CO2fixation
site of CO2 fixation
phycobilisomes cyanobacteria phycobiliproteinslight-harvestingpigments
chlorosomes Green bacterialipid and protein and
bacteriochlorophyll
light-harvesting
pigments and antennae
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c. Sulfur globules found in H2S-oxidizing bacteria
d. Volutin granules (metachromatic granules)-made of
polyphosphates
-reddish color when stained with methylene
blue
-appear round
Chromatophores-special membrane system found in certain
photosyhnthetic bacteria and cyanobacteria
-lacks chloroplasts
Nuclear area
-lacks nucleus
-nuclear matl in a bacterial cell occupies a position
near the center of the cell
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Figure 3. A variety of bacterial inclusions. a. PHB
granules; b. a parasporal BT crystal in the sporangium ofBacillus thuringiensis; c. carboxysomes inAnabaenaviriabilis, showing their polyhedral shape; d. sulfurglobules in the cytoplasm ofBeggiatoa.
seems to be attached to the mesosome cytoplasmic
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-seems to be attached to the mesosome-cytoplasmic
membrane system
-total nuclear material called the nucleoid consists of a
single, circular chromosome
Plasmids
-relatively small, circular pieces of double-stranded
DNAwhich exist separately from the bacterial
chromosome
- capable of autonomous replication and encode
for many auxiliary functions (antibiotic resistance) not
necessary for bacterial growth
-can be transferred from 1 bacterium to another thruconjugation or thru lab manipulation. (recombinant
DNA technology)
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Dormant Forms of Prokaryotic Microorganisms
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Dormant Forms of Prokaryotic Microorganisms
-some species of bacteria produce dormant forms
called: spores and cysts
-can survive unfavorable conditions such as dryingor heat
-resting forms (metabolically inactive) but in favora-
ble conditions they can germinate and become
metabolically active vegetative cells (grow andmultiply)
Spores
-only two genera of medical importance, Bacillusand
Clostridium have the ability to developed specialized struc-tures called endospore.
-form within the cell
-thick-walled, highly refractile and highly resistant to
environmental changes
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Gross Morphological Characteristics of
Eukaryotic Microorganisms
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Molds
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-multicellular organisms that look like filaments under low
magnification
-with high magnification, they look like tiny jungles-the body (thallus)
-consists of the mycelium (mycelia) and dormant
spores
-each mycelium is a mass of filaments called hyphae
Hypha
-about 5-10 um in width and is formed by joining to-
gether of many cells
-rigid walls of hyphae are made of chitins, celluloses
and glucans-maybe classified as
1. coenocyticdo not have septa(crosswalls bet the
cells that make up a long filament)
-contains many nuclei
2 septate have septa that divide the filaments into
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2. septate have septa that divide the filaments intodistinct cells containing nuclei
*there is a pore in each septum that allows cytoplasm andnuclei to migrate between cells
A hypha grows by elongation at its tip and each fragment
that contains nuclei is capable of growing into a new
organism
-some hyphae are embedded in solid media such asbread or soil to give the thallus support and nourishment
(rhizoids-specialized hyphae since they are rootlike)
Reproductive hyphae may grow upward into the air to disse-minate the spores they produce.
Vegetative hyphae- hyphae with no specialized division of
labor may simply grow along the surface of the substrate
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Germ tube
-a short, hyphalike
extension that soon
Grows into a thallus
th h h b i d i t l t t
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-other hyphae can become organized into large structures
to form the so called fleshy fungi, such as mushrooms,
puffballs, and bracket fungi.
Many fungi exhibit dimorphism (existing either in a unice-
llular, yeastlike form or in a filamentous form)
Present when the
organism is parasiteWhen the organism is a
saprophyte in its natural
habitat (such as soil) or onlab media incubated at rm T
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Morphology of Algae
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- are of many sizes and shapes
-species range from single microscopic cells to orgs
hundreds of feet long
-Singlecelled species may be:
1. spherical
2. rod-shaped
3. club-shaped
4. spindle-shaped-some maybe motile
-Multicellular
-some organized as filaments of cells attached end to end
-in some species these filaments intertwine into microscopicplantlike bodies
-occur in colonies, some of which are simple aggregations of
single cells, while others contain different cell types with
special functions
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-structurally and functionally more complex
th ti fl ll d ili
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than procaryotic flagella and cilia
-composed of thin, hairlike
microtubules: 9 + 2 arrangement (9 pairsof these tubules encircle a central pair )
-shaft formed by the microtubules
Is wrapped in a membrane
Differences bet eucaryotic and procaryo
-tic flagella1. movement is powered by the
hydrolysis of the chemical cpd
ATP for the eucaryotes while for
procaryotic flagella, the energy tomove it comes from the proton
motive force(the movement of
hydrogen ions across the CM)
2. Differ also in the way they move the cell
*eucaryotic flagellum-propels the cell by acting
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eucaryotic flagellum propels the cell by acting
like a whip, bending and twisting against the
liquid environment
*procaryotic flagellum-moves the cell by rotatinglike a corkscrew
Pseudopodia
-specialized structures as mode of locomotion by
some protozoans
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-a pseudopodium is a temporary projection of part of
th t l d t l i b hi h i d
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the cytoplasm and cytoplasmic membrane which is caused
by cytoplasmic streaming
-characteristics of amoebas
-maybe used to capture food particles
Cell Walls
-plants, algae and fungi have cell walls
-maintains the shape of cells and prevents them frombursting through osmotic pressure
-cell walls of plants, algae, and fungi differ from one
another and from bacterial cell walls in chemical
composition and physical structure-protozoa lack cell wall but some are surrounded by
a layer of shell-like matl (may fit tightly or form a
loose chamber in which the organism moves)
*scales or spines may be present
Table 4. Differences in the cell wall compositions of eucaryotes
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Organism Chem. composition
Plant Rigid; mainly polysaccharides
(cellulose and pectin)
Filamentous fungi Chitin and cellulose
Unicellular yeast Polysaccharide mannan (polymer of
the monosaccharide mannose)
algae Varying amounts of cellulose, other
polysaccharides and calcium
carbonate
-the walls of diatoms (algae)
*impregnated with silica making them thick & rigid
*surfaces often delicately sculptured with intricate
designs characterictic of the species
Cytoplasmic membrane
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-eucaryotes CM have sterols while that of
procaryotes generally does not
Cellular Organelles
-inside the the CM is the protoplasm
Protoplasm is divided into:
a. Karyoplasm- the material inside the nuclear
membrane
b. Cytoplasm- the material between the nuclear
membrane and CM.
-where organelles are found
-has cytoskeleton (network of microtubulesand proteins)
*provides shape and support
*serves as framework along which
organelles move thru the cytoplasm
Nucleus
- many protozoan have multiple nuclei thruout the
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many protozoan have multiple nuclei thruout the
greater part of their life cyle.
- in ciliated microorganisms, there are two nuclei:
1. macronucleus- large nucleus- controls metabolic activities, growth and
regeneration
2. micronucleus- small nucleus
- controls reproductive activities
Chloroplast
algae have another energy generating cytoplasmic
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- algae have another energy-generating cytoplasmic
organelle
-site of photosynthetic reactions(light is used to con-
vert energy for the cell)
-a cucumber-shaped body (2 to 3 um wide, 5 to 10 um
long) surrounded by a double membrane
Stroma- the interior
- where DNA(circular, like procaryotic DNA)codes for proteins on the chloroplast
ribosomes and for the enzymes needed
to use carbon dioxide from the air.
Thylakoids- stacks of disk-shaped or ribbonlike sacswhich contain the chlorophyll and caro-
tenoid pigments that function in photo-
synthesis
Grana- each stalk is called granum
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Dormant Forms of Eucaryotic Microorganisms
-some microorganisms can produced dormant forms
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some microorganisms can produced dormant forms
called spores and cyts that can withstand unfavorable
conditions
-both fungi and protozoa use such resting structuresfor protection and reproduction
-algae also form spores but their main function is for
reproduction. Algae do not form cyts.
Spores
-fungi produce both sexual and asexual spores
A. Sexual spores
-produced as a result of the fusion of two
specialized reproductive cells called gametes
into one fertilized cell.
-produced less frequently and in smaller numbers
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B. Asexual spores
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-does not involve the fusion of gametes
-each thallus can produce hundreds of thousands of
asexual spores, produced by aerial hyphae-purpose is to dessiminate the species, and are
specially structured for dispersion from the mother
thallus
*spores of aquatic fungi-may be motile in water
*spores of soil fungi-may have thick coats to
withstand drying or may be light enough
to travel on air currents
-usually white when 1st produced but they turn a cha-
racteristic color with age.-eg. Peniciliium notatum-colonies blue-green
Aspergillus niger- black
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Cysts
-resting forms produce by many protozoa
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resting forms produce by many protozoa
- 2 possible forms of protozoan cyts:
a. Protective cyst
b. Reproductive cyst
Trophozoites
-the vegetative forms of protozoa
-synthesize protective cysts that are resistant to drying,
lack of food, lack of oxygen, or acidity in the hostsstomach. (when conditions once again become favora-
rable, cysts form trophozoites that feed and grow.
Reproductive cyst- not induced by adverse environmental
conditions-often thin-walled and lack the resistance of protective
cysts
*parasitic species of protozoa often move from host to
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parasitic species of protozoa often move from host to
host as cysts(mode of transmission)
-form in the intestinal tract and are excreted in
feces which contaminate water and food ingested
by next host.
*CYST is the only way to survive outside the host.
e.g. Giardia lamblia -causative agent of diarrhea
and abdominal cramps in humans-transmitted to humans by cysts
in water supplies contaminated with feces
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