Microbiology: A Microbiology: A Systems Approach, 2Systems Approach, 2ndnd

ed.ed.Chapter 5: Eukaryotic Cells and Chapter 5: Eukaryotic Cells and

MicroorganismsMicroorganisms

5.1 The History of Eukaryotes5.1 The History of Eukaryotes First eukaryotic cells on earth approximately 2 First eukaryotic cells on earth approximately 2

billion years agobillion years ago Evidence points to these eukaryotic cells evolving Evidence points to these eukaryotic cells evolving

from prokaryotic organisms through intracellular from prokaryotic organisms through intracellular symbiosissymbiosis Eukaryotic Eukaryotic organellesorganelles originated from prokaryotic originated from prokaryotic

cells trapped inside of themcells trapped inside of them First primitive eukaryotes- probably single-celled and First primitive eukaryotes- probably single-celled and

independentindependent Eventually formed coloniesEventually formed colonies Cells within colonies became specializedCells within colonies became specialized Evolved in to multicellular organismsEvolved in to multicellular organisms

Eukaryotes have many levels of cellular Eukaryotes have many levels of cellular complexitycomplexity

5.2 Form and Function of the 5.2 Form and Function of the Eukaryotic Cell: External StructuresEukaryotic Cell: External Structures

Figure 5.2

Locomotor Appendages: Cilia and Locomotor Appendages: Cilia and FlagellaFlagella

Eukaryotic flagella are much different from Eukaryotic flagella are much different from those of prokaryotesthose of prokaryotes 10X thicker10X thicker Structurally more complexStructurally more complex Covered by an extension of the cell Covered by an extension of the cell

membranemembrane A single flagellum contains regularly A single flagellum contains regularly

spaced microtubules along its lengthspaced microtubules along its length 9 pairs surrounding a single pair9 pairs surrounding a single pair The 9 + 2 arrangementThe 9 + 2 arrangement

Figure 5.3

Cilia- similar to flagella but some Cilia- similar to flagella but some differencesdifferences ShorterShorter More numerousMore numerous Can also function as feeding and filtering Can also function as feeding and filtering

structuresstructures

The GlycocalyxThe Glycocalyx Most eukaryotic cells have this outermost Most eukaryotic cells have this outermost

boundary that comes into direct contact with the boundary that comes into direct contact with the environmentenvironment

Usually composed of polysaccharides Usually composed of polysaccharides Appears as a network of fibers, a slime layer, or a Appears as a network of fibers, a slime layer, or a

capsulecapsule FunctionsFunctions

ProtectionProtection AdhesionAdhesion Reception of signalsReception of signals

The layer beneath the glycocalyx varies among The layer beneath the glycocalyx varies among eukaryoteseukaryotes Fungi and most algae have a thick, rigid cell wallFungi and most algae have a thick, rigid cell wall Protozoa and animal cells do not have this cell wallProtozoa and animal cells do not have this cell wall

Form and Function of the Eukaryotic Form and Function of the Eukaryotic Cell: Boundary StructuresCell: Boundary Structures

Cell WallCell Wall RigidRigid Provide support and shapeProvide support and shape Different chemically from prokaryotic cell wallsDifferent chemically from prokaryotic cell walls FungiFungi

• Thick, inner layer of chitin or celluloseThick, inner layer of chitin or cellulose• Thin outer layer of mixed glycansThin outer layer of mixed glycans

AlgaeAlgae• Varied in chemical compositionVaried in chemical composition• May contain cellulose, pectin, mannans, and May contain cellulose, pectin, mannans, and

mineralsminerals

Figure 5.5

Cytoplasmic MembraneCytoplasmic Membrane Bilayer of phospholipids with protein Bilayer of phospholipids with protein

molecules embeddedmolecules embedded Also contain sterolsAlso contain sterols

• Gives stabilityGives stability• Especially important in cells without a cell wallEspecially important in cells without a cell wall

Selectively permeableSelectively permeable

5.3 Form and Function of the 5.3 Form and Function of the Eukaryotic Cell: Internal StructuresEukaryotic Cell: Internal Structures

The Nucleus: The Control CenterThe Nucleus: The Control Center Separated from the cytoplasm by a nuclear Separated from the cytoplasm by a nuclear

envelopeenvelope• Two parallel membranes separated by a narrow spaceTwo parallel membranes separated by a narrow space• Perforated with nuclear poresPerforated with nuclear pores

Filled with nucleoplasmFilled with nucleoplasm Contains the Contains the nucleolusnucleolus

• rRNA synthesisrRNA synthesis• Colelction area for ribosomal subunitsColelction area for ribosomal subunits

ChromatinChromatin• Comprises the Comprises the chromosomeschromosomes

Long, linear DNA moleculesLong, linear DNA molecules Bound to Bound to histonehistone proteins proteins Visible during Visible during mitosismitosis

Figure 5.6

Figure 5.7

Endoplasmic Reticulum (ER)Endoplasmic Reticulum (ER): A : A Passageway in the CellPassageway in the Cell

Microscopic series of tunnelsMicroscopic series of tunnels Used in transport and storageUsed in transport and storage Two kindsTwo kinds

Rough endoplasmic reticulum (RER)Rough endoplasmic reticulum (RER)• Originates from the outer membrane of the nuclear Originates from the outer membrane of the nuclear

envelopeenvelope• Extends through the cytoplasmExtends through the cytoplasm• Spaces in the RER- cisternae- transport materials from Spaces in the RER- cisternae- transport materials from

the nucleus to the cytoplasmthe nucleus to the cytoplasm• ““Rough” because of ribosomes attached to its surfaceRough” because of ribosomes attached to its surface• Proteins synthesized on the ribosomes shunted into the Proteins synthesized on the ribosomes shunted into the

cavity of the RER and held for later packaging and cavity of the RER and held for later packaging and transporttransport

Figure 5.8

Smooth endoplasmic reticulum (SER)Smooth endoplasmic reticulum (SER) Closed tubular networkClosed tubular network No ribosomesNo ribosomes Functions Functions

• Nutrient processingNutrient processing• Synthesis and storage of nonprotein Synthesis and storage of nonprotein

macromoleculesmacromolecules

Golgi ApparatusGolgi Apparatus: A Packaging : A Packaging MachineMachine

Where proteins are modified and sent to their final Where proteins are modified and sent to their final destinationsdestinations

A stack of cisternaeA stack of cisternae Do not form a continuous networkDo not form a continuous network Closely associated with ER both in location and Closely associated with ER both in location and

functionfunction The ER buds off transitional vesicles (packets of The ER buds off transitional vesicles (packets of

protein) where it meets the Golgi apparatusprotein) where it meets the Golgi apparatus The Golgi apparatus picks up the transitional vesiclesThe Golgi apparatus picks up the transitional vesicles The proteins are often modified by addition of The proteins are often modified by addition of

polysaccharides and lipidspolysaccharides and lipids Then the apparatus pinches off condensing vesiclesThen the apparatus pinches off condensing vesicles

• Sent to Sent to lysosomeslysosomes• Or transported outside the cellOr transported outside the cell

Figure 5.9

Figure 5.10

Figure 5.11

MitochondriaMitochondria: Energy : Energy GeneratorsGenerators

Cellular activities require a constant supply of Cellular activities require a constant supply of energyenergy

The bulk of this energy generated by mitochondriaThe bulk of this energy generated by mitochondria Smooth, continuous outer membraneSmooth, continuous outer membrane Inner folded membrane (folds are Inner folded membrane (folds are cristaecristae))

Cristae hold enzymes and electron carriers of aerobic Cristae hold enzymes and electron carriers of aerobic respirationrespiration

Spaces around cristae filled with a Spaces around cristae filled with a matrixmatrix• RibosomesRibosomes• DNADNA• Enzymes and other compounds involved I the metabolic Enzymes and other compounds involved I the metabolic

cyclecycle Divide independently of the cellDivide independently of the cell Contain circular strands of DNAContain circular strands of DNA Contain prokaryotic-sized 70S ribosomesContain prokaryotic-sized 70S ribosomes

Figure 5.12

ChloroplastsChloroplasts: Photosynthesis : Photosynthesis MachinesMachines

Organelles found in algae and plant cellsOrganelles found in algae and plant cells Convert energy of sunlight into chemical Convert energy of sunlight into chemical

energy through photosynthesisenergy through photosynthesis Two membranesTwo membranes

Smooth outer membraneSmooth outer membrane Inner membrane folded in to Inner membrane folded in to thylakoidsthylakoids Thylakoids stacked upon one another into Thylakoids stacked upon one another into granagrana Contain chlorophyll and sometimes other Contain chlorophyll and sometimes other

pigmentspigments StromaStroma surrounds the thylakoids surrounds the thylakoids

Figure 5.13

Ribosomes: Protein Ribosomes: Protein SynthesizersSynthesizers

Some scattered in the cytoplasm and Some scattered in the cytoplasm and cytoskeletoncytoskeleton

Others associated with REROthers associated with RER Often found in chains of polyribosomes Often found in chains of polyribosomes

(polysomes)(polysomes) Composed of large and small subunits of Composed of large and small subunits of

ribonucleoproteinribonucleoprotein Larger 80S variety, composed of 60S and Larger 80S variety, composed of 60S and

40S subunits40S subunits

The Cytoskeleton: A Support NetworkThe Cytoskeleton: A Support Network

Flexible framework of molecules criss-Flexible framework of molecules criss-crossing the cytoplasmcrossing the cytoplasm

Several functionsSeveral functions Anchoring organellesAnchoring organelles Moving RNA and vesiclesMoving RNA and vesicles Permitting shape changes and movement in Permitting shape changes and movement in

some cellssome cells Two types: Microfilaments and Two types: Microfilaments and

microtubulesmicrotubules

MicrofilamentsMicrofilaments

Thin protein strandsThin protein strands Attach to the cell membraneAttach to the cell membrane Some responsible for movements of the Some responsible for movements of the

cytoplasmcytoplasm Some active in amoeboid motionSome active in amoeboid motion

MicrotubulesMicrotubules

Long, hollow tubesLong, hollow tubes Maintain the shape of eukaryotic cells Maintain the shape of eukaryotic cells

without wallswithout walls Transport substancesTransport substances Responsible for the movement of cilia and Responsible for the movement of cilia and

flagellaflagella

Figure 5.14

5.4 The Kingdom of the 5.4 The Kingdom of the FungiFungi MyceteaeMyceteae Great variety and complexityGreat variety and complexity Approximately 100,000 speciesApproximately 100,000 species Can be divided into two groups:Can be divided into two groups:

Macroscopic fungiMacroscopic fungi Microscopic fungi:Microscopic fungi:

• YeastsYeasts Round or oval shapeRound or oval shape Unique mode of asexual reproductionUnique mode of asexual reproduction Some form pseudohyphae (false filaments)Some form pseudohyphae (false filaments)

• MoldsMolds Long, threadlike cellsLong, threadlike cells Filamentous arrangement (hyphae)Filamentous arrangement (hyphae)

• Some are dimorphic (yeast-like and filamentous forms exist)Some are dimorphic (yeast-like and filamentous forms exist) Majority are unicellular or colonialMajority are unicellular or colonial

Figure 5.15

Figure 5.16

Fungal NutritionFungal Nutrition HeterotrophicHeterotrophic Acquire nutrients from Acquire nutrients from substratessubstrates Most fungi are Most fungi are saprobessaprobes Can also be Can also be parasitesparasites General method of obtaining nutritionGeneral method of obtaining nutrition

Penetrates the substratePenetrates the substrate Secretes enzymesSecretes enzymes Breaks down the enzymes into small moleculesBreaks down the enzymes into small molecules Absorbs the moleculesAbsorbs the molecules

Can absorb a wide variety of substratesCan absorb a wide variety of substrates Large medical and agricultural importanceLarge medical and agricultural importance

Figure 5.17

Organization of Microscopic Organization of Microscopic FungiFungi

Most grow in loose associations or coloniesMost grow in loose associations or colonies Yeasts- soft, uniform texture and appearanceYeasts- soft, uniform texture and appearance Filamentous fungal colonies- cottony, hairy, or velvety Filamentous fungal colonies- cottony, hairy, or velvety

texturestextures MyceliumMycelium- the woven, intertwining mass of hyphae that - the woven, intertwining mass of hyphae that

makes up the body or colony of a moldmakes up the body or colony of a mold Unique organizational features of hyphaeUnique organizational features of hyphae

SeptaSepta- divide the hyphae into segments (most fungi have - divide the hyphae into segments (most fungi have septate hyphae)septate hyphae)

Nonseptate hyphae- one long, continuous, multinucleate Nonseptate hyphae- one long, continuous, multinucleate cellcell

Functions of hyphaeFunctions of hyphae Vegetative hyphae (mycelia)- visible mass of growth on Vegetative hyphae (mycelia)- visible mass of growth on

the substrate surface; penetrates the substrate to digest the substrate surface; penetrates the substrate to digest and absorb nutrientsand absorb nutrients

Reproductive (fertile) hyphae- from vegetative hyphae; Reproductive (fertile) hyphae- from vegetative hyphae; responsible for the production of responsible for the production of sporesspores

Figure 5.18

Reproductive Strategies and Spore Reproductive Strategies and Spore FormationFormation

Most can propagate by growth of hyphae or Most can propagate by growth of hyphae or fragmentationfragmentation

Primary reproductive mode- the production of Primary reproductive mode- the production of sporesspores

Function of sporesFunction of spores MultiplicationMultiplication SurvivalSurvival Producing genetic variationProducing genetic variation DisseminationDissemination

Large diversity in spores among the fungiLarge diversity in spores among the fungi• General grouping of spores- asexual and sexualGeneral grouping of spores- asexual and sexual

Asexual SporesAsexual Spores

SporangiosporesSporangiospores Formed by successive cleavages within the Formed by successive cleavages within the

sporangiumsporangium Sporangium attached to the sporangiophoreSporangium attached to the sporangiophore Released when the sporangium rupturesReleased when the sporangium ruptures

ConidiosporesConidiospores Aka Aka conidiaconidia Free sporesFree spores Develop either by pinching off the tip of fertile Develop either by pinching off the tip of fertile

hypha or by segmentation of a vegetative hyphahypha or by segmentation of a vegetative hypha

Figure 5.19

Sexual SporesSexual Spores

Increases genetic variationIncreases genetic variation Majority of fungi produce sexual spores at Majority of fungi produce sexual spores at

some pointsome point

Fungal Identification and CultivationFungal Identification and Cultivation

Medical specimensMedical specimens Isolated on special types of mediaIsolated on special types of media Observed macroscopically and microscopicallyObserved macroscopically and microscopically

Usually use sexual spore-forming structures Usually use sexual spore-forming structures and sporesand spores

Other characteristics that contribute to Other characteristics that contribute to identificationidentification Hyphal typeHyphal type Colony texture and pigmentationColony texture and pigmentation Physiological characteristicsPhysiological characteristics Genetic makeupGenetic makeup

The Roles of Fungi in Nature and The Roles of Fungi in Nature and IndustryIndustry

Nearly all fungi are free-living and don’t need Nearly all fungi are free-living and don’t need a hosta host

Human infection by pathogenic fungi usually Human infection by pathogenic fungi usually occurs through accidental contactoccurs through accidental contact

Humans are generally resistant to fungal Humans are generally resistant to fungal infection, except for two main typesinfection, except for two main types Primary pathogensPrimary pathogens Opportunistic pathogensOpportunistic pathogens

Mycoses vary in the way the agent enters the Mycoses vary in the way the agent enters the body and the degree of tissue involvementbody and the degree of tissue involvement

Not only involved in infectionsNot only involved in infections AllergiesAllergies PoisoningPoisoning Agricultural damageAgricultural damage

Benefits of fungiBenefits of fungi Decomposing organic matter and returning Decomposing organic matter and returning

essential minerals to the soilessential minerals to the soil Mycorrhizae increase the ability of plant roots to Mycorrhizae increase the ability of plant roots to

absorb water and nutrientsabsorb water and nutrients Production ofProduction of

• AntibioticsAntibiotics• AlcoholAlcohol• Organic acidsOrganic acids• VitaminsVitamins

Food flavoringsFood flavorings

5.5 The Protists5.5 The Protists

Traditionally contains the algae and Traditionally contains the algae and protozoaprotozoa

Two major taxonomic categoriesTwo major taxonomic categories Subkingdom AlgaeSubkingdom Algae Subkingdom ProtozoaSubkingdom Protozoa

Any unicellular or colonial organism that Any unicellular or colonial organism that lacks true tissueslacks true tissues

The The AlgaeAlgae: Photosynthetic : Photosynthetic protistsprotists

Vary in length from a few micrometers to 100 Vary in length from a few micrometers to 100 metersmeters

Unicellular, colonial, and filamentous formsUnicellular, colonial, and filamentous forms Larger forms can possess tissues and simple Larger forms can possess tissues and simple

organsorgans Exhibit all eukaryotic organellesExhibit all eukaryotic organelles Chloroplasts contain chlorophyll as well as other Chloroplasts contain chlorophyll as well as other

pigmentspigments One of the main components of One of the main components of planktonplankton Rarely infectiousRarely infectious Primary medical threat: shellfish exposed to red Primary medical threat: shellfish exposed to red

tidetide

Figure 5.21

Biology of the ProtozoaBiology of the Protozoa

About 65,000 speciesAbout 65,000 species Most are harmless, free-living inhabitants Most are harmless, free-living inhabitants

of water and soilof water and soil Few are parasitesFew are parasites

Protozoan Form and FunctionProtozoan Form and Function Most are single cellsMost are single cells Contain major eukaryotic organelles except Contain major eukaryotic organelles except

chloroplastschloroplasts Cytoplasm usually dividedCytoplasm usually divided

EctoplasmEctoplasm: clear outer layer involved in locomotion, : clear outer layer involved in locomotion, feeding, and protectionfeeding, and protection

Endoplasm: granular inner region housing the nucleus, Endoplasm: granular inner region housing the nucleus, mitochondria, and food and contractile vacuolesmitochondria, and food and contractile vacuoles

Some ciliates and flagellates have organelles working Some ciliates and flagellates have organelles working like a primitive nervous systemlike a primitive nervous system

No cell wall- so some flexibilityNo cell wall- so some flexibility Cell shape can remain constant or can change Cell shape can remain constant or can change

constantly (amoebas)constantly (amoebas) Size between 3 to 300 µmSize between 3 to 300 µm

Nutritional and Habitat RangeNutritional and Habitat Range HeterotrophicHeterotrophic Usually require their food in a complex organic formUsually require their food in a complex organic form Free-living species scavenge or grazeFree-living species scavenge or graze Some have special feeding structures such as oral Some have special feeding structures such as oral

grooves; some absorb food directly through the cell grooves; some absorb food directly through the cell membranemembrane

Parasitic species live on the fluids of their host; or can Parasitic species live on the fluids of their host; or can actively feed on tissuesactively feed on tissues

Predominant habitatsPredominant habitats Fresh and marine waterFresh and marine water SoilSoil Plants Plants AnimalsAnimals

Many can convert to a resistant, dormant stage called Many can convert to a resistant, dormant stage called a cysta cyst

Styles of LocomotionStyles of Locomotion All but the Apicomplexa are motile by means of All but the Apicomplexa are motile by means of

pseudopodspseudopods, , flagellaflagella, or , or ciliacilia Some unusual species move by gliding or twistingSome unusual species move by gliding or twisting PseudopodsPseudopods

Amoeboid motionAmoeboid motion Can serve as feeding structuresCan serve as feeding structures

FlagellaFlagella From one to severalFrom one to several Some attached along the length of the cell by the Some attached along the length of the cell by the

undulating membraneundulating membrane CiliaCilia

Mostly distributed over the entire surface of the cellMostly distributed over the entire surface of the cell Form characteristic patternsForm characteristic patterns

Life Cycles and ReproductionLife Cycles and Reproduction

Figure 5.22

Vary from simple to complexVary from simple to complex Some exist only in Some exist only in trophozoitetrophozoite stage stage Others alternate between trophozoite and Others alternate between trophozoite and

cystcyst Life cycle of a parasitic protozoan Life cycle of a parasitic protozoan

determines the mode of transmission to determines the mode of transmission to hostshosts

All reproduce by asexual methodsAll reproduce by asexual methods Usually mitotic cell divisionUsually mitotic cell division Some by multiple fissionSome by multiple fission

Sexual reproduction occurs during the life Sexual reproduction occurs during the life cycle of most protozoacycle of most protozoa Ciliates participate in Ciliates participate in conjugationconjugation

Classification of Selected Medically Classification of Selected Medically Important ProtozoaImportant Protozoa

• Four groupsFour groups• Based on:Based on:

• Method of motilityMethod of motility• Mode of reproductionMode of reproduction• Stages in the lifecycleStages in the lifecycle

MastigophoraMastigophora (Flagellated) (Flagellated) Motility primarily by flagellaMotility primarily by flagella Single nucleusSingle nucleus Sexual reproduction by syngamySexual reproduction by syngamy Division by longitudinal fissionDivision by longitudinal fission Parasitic forms tend to lack mitochondria and Parasitic forms tend to lack mitochondria and

Golgi apparatusGolgi apparatus Most form cysts and are free-livingMost form cysts and are free-living Most are solitaryMost are solitary ExamplesExamples

TrypanosomaTrypanosoma LeishmaniaLeishmania GiardiaGiardia TrichomonasTrichomonas

Figure 5.23

SarcodinaSarcodina (Amoebas) (Amoebas) PseudopodsPseudopods Some have flagellated reproductive statesSome have flagellated reproductive states Asexual reproduction by fissionAsexual reproduction by fission Two groups have an external shellTwo groups have an external shell Mostly uninucleateMostly uninucleate Usually encystUsually encyst Most free-livingMost free-living ExamplesExamples

EntamoebaEntamoeba ForaminiferaForaminifera RadiolariansRadiolarians

Figure 5.24

CiliophoraCiliophora (Ciliated) (Ciliated)

Trophozoites mobile by ciliaTrophozoites mobile by cilia Some have cilia in tufts for feeding and Some have cilia in tufts for feeding and

attachmentattachment Most develop cystsMost develop cysts Both macronuclei and micronucleiBoth macronuclei and micronuclei Division by transverse fissionDivision by transverse fission Most have definite mouth and feeding Most have definite mouth and feeding

organelleorganelle Show relatively advanced behaviorShow relatively advanced behavior Majority are free-living and harmlessMajority are free-living and harmless

Figure 5.25

ApicomplexaApicomplexa (Sporozoa) (Sporozoa)

Most not motile except male gametesMost not motile except male gametes Complex life cyclesComplex life cycles Produce Produce sporozoitessporozoites following sexual following sexual

reproductionreproduction Important in transmission of infectionsImportant in transmission of infections Most form oocystsMost form oocysts Entire group is parasiticEntire group is parasitic ExamplesExamples

PlasmodiumPlasmodium Toxoplasma gondiiToxoplasma gondii

Figure 5.26

Protozoan Identification and Protozoan Identification and CultivationCultivation

Shape and size of cellShape and size of cell Type, number, and distribution of Type, number, and distribution of

locomotor structureslocomotor structures Presence of special organelles or cystsPresence of special organelles or cysts Number of nucleiNumber of nuclei Can be cultivated on artificial media or in Can be cultivated on artificial media or in

laboratory animalslaboratory animals

Important Protozoan PathogensImportant Protozoan Pathogens

Pathogenic Flagellates: Pathogenic Flagellates: TrypanosomesTrypanosomes

Genus Genus TrypanosomaTrypanosoma T. bruceiT. brucei causes sleeping sickness causes sleeping sickness T. cruziT. cruzi causes Chagas disease causes Chagas disease

Figure 5.27

Infective Amoebas: Infective Amoebas: EntamoebaEntamoeba

Amoebiasis caused by Amoebiasis caused by Entamoeba Entamoeba histolyticahistolytica

Fourth most common protozoan infection Fourth most common protozoan infection in the worldin the world

Aka amoebic dysentery Aka amoebic dysentery

Figure 5.28

5.6 The Parasitic Helminths5.6 The Parasitic Helminths

Tapeworms, flukes, and roundwormsTapeworms, flukes, and roundworms Adults large enough to be seen with the Adults large enough to be seen with the

naked eyenaked eye From 1 mm to 25 m in lengthFrom 1 mm to 25 m in length Microscope is necessary to identify eggs Microscope is necessary to identify eggs

and larvaeand larvae Two major groups: Flatworms and Two major groups: Flatworms and

RoundwormsRoundworms

FlatwormsFlatworms

Phylum PlatyhelminthesPhylum Platyhelminthes ThinThin Often segmentedOften segmented SubdivisionsSubdivisions

CestodesCestodes (tapeworms) (tapeworms) TrematodesTrematodes (flukes) (flukes)

Figure 5.29

RoundwormsRoundworms

Phylum AschelminthesPhylum Aschelminthes Aka Aka nematodesnematodes ElongateElongate CylindricalCylindrical UnsegmentedUnsegmented

Figure 5.30

General Worm MorphologyGeneral Worm Morphology

Most developed organs are those of the Most developed organs are those of the reproductive tractreproductive tract

Some degree of reduction in digestive, Some degree of reduction in digestive, excretory, nervous, and muscular systemsexcretory, nervous, and muscular systems

Most have thick cuticles for protection and Most have thick cuticles for protection and mouth glands for breaking down the host’s mouth glands for breaking down the host’s tissuetissue

Life Cycles and ReproductionLife Cycles and Reproduction

Fertilized egg (embryo), larval, and adult stagesFertilized egg (embryo), larval, and adult stages In most, adults derive nutrients and reproduce In most, adults derive nutrients and reproduce

sexually in a host’s bodysexually in a host’s body Nematodes- separate sexesNematodes- separate sexes Trematodes- separate sexes or Trematodes- separate sexes or hermaphroditichermaphroditic

Must complete the life cycle by transmitting an Must complete the life cycle by transmitting an infective form to the body of another hostinfective form to the body of another host Larval development- intermediate (secondary) hostLarval development- intermediate (secondary) host Adulthood and mating- Adulthood and mating- definitive (final) hostdefinitive (final) host

A Helminth Cycle: The A Helminth Cycle: The PinwormPinworm

Person swallows microscopic eggsPerson swallows microscopic eggs Picked up from another infected person by direct Picked up from another infected person by direct

contactcontact Or by touching articles an infected person has touchedOr by touching articles an infected person has touched

Eggs hatch in the intestineEggs hatch in the intestine Release larvae that mature in to adult worms (about Release larvae that mature in to adult worms (about

1 month)1 month) Male and female worms mateMale and female worms mate Female migrates out of the anus to deposit eggs Female migrates out of the anus to deposit eggs

Causes intense itchinessCauses intense itchiness Relieved by scratchingRelieved by scratching Scratching contaminates the fingers which transfer the Scratching contaminates the fingers which transfer the

eggseggs Eggs spread to others or the original host reinfects Eggs spread to others or the original host reinfects

him or herselfhim or herself

Helminth Classification and Helminth Classification and IdentificationIdentification

ShapeShape SizeSize Degree of development of various organsDegree of development of various organs Presence of hooks, suckers, or other Presence of hooks, suckers, or other

special structuresspecial structures Mode of reproductionMode of reproduction Kinds of hostsKinds of hosts Appearance of eggs and larvaeAppearance of eggs and larvae

Distribution and Importance of Distribution and Importance of Parasitic WormsParasitic Worms

About 50 species parasitize humansAbout 50 species parasitize humans Distributed in all areas of the worldDistributed in all areas of the world Yearly estimate of worldwide infections- in Yearly estimate of worldwide infections- in

the billionsthe billions