ProkaryotesProkaryotes

(Bacteria)(Bacteria)

Everythingelse

Prokaryotic cells have a Prokaryotic cells have a variety of shapesvariety of shapes

The three most common of which The three most common of which are spheres (cocci), rods (bacilli), are spheres (cocci), rods (bacilli), and spiralsand spirals

1 m 2 m 5 m(a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

Cell-Surface StructuresCell-Surface Structures

One of the most important features One of the most important features of nearly all prokaryotic cellsof nearly all prokaryotic cells Is their cell wall, which maintains cell Is their cell wall, which maintains cell

shape, provides physical protection, shape, provides physical protection, and prevents the cell from bursting in and prevents the cell from bursting in a hypotonic environmenta hypotonic environment

24.2

Using a technique Using a technique called the Gram staincalled the Gram stain

Scientists can classify many bacterial Scientists can classify many bacterial species into two groups based on cell wall species into two groups based on cell wall composition, Gram-positive and Gram-composition, Gram-positive and Gram-negativenegative

Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye,which masks the added red dye.

Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between theplasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added.

PeptidoglycanlayerCell wall

Plasma membrane

Protein

Gram-positivebacteria

20 m

Outermembrane

Peptidoglycanlayer

Plasma membrane

Cell wall

Lipopolysaccharide

Protein

Gram-negativebacteria

24.2/3

The cell wall of many The cell wall of many prokaryotesprokaryotes

Is covered by a Is covered by a capsulecapsule, a sticky layer , a sticky layer of polysaccharide or proteinof polysaccharide or protein

200 nm

Capsule

24.1

Some prokaryotes have Some prokaryotes have fimbriaefimbriae and and sex pilisex pili

FimbriaeFimbriae allow them to stick to their allow them to stick to their substrate or other individuals in a colonysubstrate or other individuals in a colony

Sex piliSex pili allow two bacteria to join and allow two bacteria to join and exchange DNA during conjugationexchange DNA during conjugation

200 nm

Fimbriae

24.1

MotilityMotility Most motile bacteria propel themselves Most motile bacteria propel themselves

by by flagellaflagella Which are structurally and functionally Which are structurally and functionally

different from eukaryotic flagelladifferent from eukaryotic flagellaFlagellum

Filament

HookCell wall

Plasmamembrane

Basal apparatus

50 nm

24.1

The typical prokaryotic The typical prokaryotic genomegenome

Is a ring of DNA that is not surrounded Is a ring of DNA that is not surrounded by a membrane and that is located in a by a membrane and that is located in a nucleoidnucleoid region region

1 m

Chromosome

24.1

Many prokaryotes form Many prokaryotes form endosporesendospores

Which can remain viable in harsh Which can remain viable in harsh conditions for centuriesconditions for centuries

Endospore

0.3 m

24.1

Major nutritional modes in Major nutritional modes in prokaryotesprokaryotes

24.4

Prokaryotic metabolismProkaryotic metabolismalso varies with respect to also varies with respect to

oxygenoxygen

Three types of oxygen metabolismThree types of oxygen metabolism Obligate aerobesObligate aerobes

Require oxygenRequire oxygen Facultative anaerobesFacultative anaerobes

Can survive with or without oxygenCan survive with or without oxygen Obligate anaerobesObligate anaerobes

Are poisoned by oxygenAre poisoned by oxygen

24.5

Protists

Single-celled Eukaryotes (mostly)

Overview: A World in a Drop of Water

• Even a low-power microscope– Can reveal an astonishing menagerie of

organisms in a drop of pond water

Figure 28.150 m

Protists, the most nutritionally diverse of all eukaryotes, include

– Photoautotrophs, which contain chloroplasts– Heterotrophs, which absorb organic molecules

or ingest larger food particles– Mixotrophs, which combine photosynthesis

and heterotrophic nutrition

Chlorohyta phacus24.6

Protist habitats are also diverse in habitat

• And including freshwater and marine species

There is now considerable evidence

• That much of protist diversity has its origins in endosymbiosis

Diversity of plastids produced by secondary endosymbiosis

Objectives 24.7 and 24.8 will be covered in a class project

Plasmodial Slime Molds• Many species of plasmodial slime molds

– Are brightly pigmented, usually yellow or orange

4 cm

24.9

At one point in the life cycle– They form a mass called a plasmodium

Feedingplasmodium

Matureplasmodium(preparing to fruit)

Youngsporangium

Maturesporangium

Spores(n)

Germinatingspore

Amoeboid cells(n)

Zygote(2n)

1 mm

Key

Haploid (n)Diploid (2n)

MEIOSIS

SYNGAMY

StalkFlagellated cells(n)

The feeding stageis a multinucleateplasmodium that liveson organic refuse.

1 The plasmodiumtakes a weblike form.2

The plasmodium erectsstalked fruiting bodies (sporangia)when conditions become harsh.

3

Within the bulboustips of the sporangia,meiosis produces haploidspores.

4 These cells areeither amoeboid orflagellated; the twoforms readily convertfrom one to the other.

6 The cells unitein pairs (flagellatedwith flagellatedand amoeboid withamoeboid), formingdiploid zygotes.

7 The resistant spores dispersethrough the air to new locationsand germinate, becoming activehaploid cells when conditionsare favorable.

5

24.9

Cellular Slime Molds

• Cellular slime molds form multicellular aggregates– In which the cells remain separated by

their membranes

24.9

• The life cycle of Dictyostelium, a cellular slime mold

Spores(n)

Emergingamoeba

Solitary amoebas(feeding stage)

ASEXUALREPRODUCTIONFruiting

bodies

Aggregatedamoebas

Migratingaggregate

SYNGAMY

MEIOSIS

SEXUALREPRODUCTION

Zygote(2n)

Amoebas

600 µm

200 µm

Key

Haploid (n)Diploid (2n)

In the feedingstage of the lifecycle, solitary haploidamoebas engulf bacteria.

1 During sexual repro-duction, two haploidamoebas fuse andform a zygote.

2

The zygotebecomes a giantcell (not shown)by consuminghaploid amoebas.After developing aresistant wall, thegiant cell undergoesmeiosis followed byseveral mitoticdivisions.

3

The resistantwall ruptures,releasing newhaploid amoebas.

4

When food is depleted,hundreds of amoebascongregate in response to achemical attractant and forma sluglike aggregate (photobelow left). Aggregateformation is the beginningof asexual reproduction.

5

The aggregate migrates for awhile and then stops. Some of the

cells dry up after forming a stalk thatsupports an asexual fruiting body.

6

Othercells crawl

up the stalkand developinto spores.

7

Sporesare released.

8

In a favorableenvironment, amoebasemerge from the sporecoats and begin feeding.

9

24.9

FungiFungi

Also pronounced “fun guy”Also pronounced “fun guy”

Mighty MushroomsMighty MushroomsFungiFungi

Are diverse and widespreadAre diverse and widespread Are essential for the well-being of most Are essential for the well-being of most

terrestrial ecosystems because they break terrestrial ecosystems because they break down organic material and recycle vital down organic material and recycle vital nutrientsnutrients

The Origin of FungiThe Origin of Fungi Molecular evidenceMolecular evidence

Supports the hypothesis that fungi and animals diverged from a Supports the hypothesis that fungi and animals diverged from a common ancestor common ancestor

Fungi probably evolvedFungi probably evolved Before the colonization of land by multicellular organismsBefore the colonization of land by multicellular organisms

Fossil EvidenceFossil Evidence The oldest undisputed fossils of fungiThe oldest undisputed fossils of fungi

Are only about 460 million years oldAre only about 460 million years old

Nutrition and Fungal Nutrition and Fungal LifestylesLifestyles

Fungi are heterotrophs (consumers)Fungi are heterotrophs (consumers) But do not ingest their foodBut do not ingest their food

Fungi secrete Fungi secrete exoenzymes that break down complex exoenzymes that break down complex

molecules and then they absorb the remaining molecules and then they absorb the remaining smaller compounds as nutrients.smaller compounds as nutrients.

24.10/11

Fungi exhibit diverse lifestylesFungi exhibit diverse lifestyles DecomposersDecomposers ParasitesParasites Mutualistic symbiontsMutualistic symbionts

24.10/11

BasidiomycetesBasidiomycetes

DecomposersDecomposers Breakdown organic Breakdown organic

material using material using enzymes to obtain enzymes to obtain nutrientsnutrients

(a) Fly agaric (Amanita muscaria), acommon species in conifer forests in the northern hemisphere

(b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat

(c) Shelf fungi, important decomposers of wood

(d) Puffballs emitting spores

24.10-1124.14

PathogensPathogens

About 30% of known fungal speciesAbout 30% of known fungal species Are parasites, mostly on or in plantsAre parasites, mostly on or in plants

(a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye

24.10-1124.14

Lichens Lichens (mutualistic)(mutualistic)

Are a symbiotic association of millions of Are a symbiotic association of millions of photosynthetic microorganisms held in a photosynthetic microorganisms held in a mass of fungal hyphaemass of fungal hyphae

(a) A fruticose (shrub-like) lichen

(b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens

24.10-1124.14

Body StructureBody Structure The morphology of multicellular fungiThe morphology of multicellular fungi

Enhances their ability to absorb nutrients Enhances their ability to absorb nutrients from their surroundingsfrom their surroundings

Hyphae. The mushroom and its

subterranean mycelium are a continuous

network of hyphae.

Reproductive structure.

The mushroom produces

tiny cells called spores.

Spore-producing

structures

20 m

Mycelium

24.12

Fungi consist ofFungi consist of Mycelia, networks of branched hyphae Mycelia, networks of branched hyphae

adapted for absorptionadapted for absorption Most fungi have cell walls made of chitin Most fungi have cell walls made of chitin

(polysaccharide - also found in the exoskeleton of many insects and (polysaccharide - also found in the exoskeleton of many insects and arthropods)arthropods)

24.12 Network of Hyphae

Fungi propagate themselvesFungi propagate themselves By producing vast numbers of spores, either sexually By producing vast numbers of spores, either sexually

or asexuallyor asexually

24.13

LIFE CYCLE

Many fungi that can reproduce Many fungi that can reproduce asexuallyasexually Grow as mold, sometimes on fruit, bread, Grow as mold, sometimes on fruit, bread,

and other foodsand other foods

2.5 m

Orange

24.13/14

Other asexual fungi are yeastsOther asexual fungi are yeasts

That inhabit moist environmentsThat inhabit moist environments Which reproduce by simple cell divisionWhich reproduce by simple cell division

10 m

Parent cell

Bud

24.14

Fungus-Animal SymbiosisFungus-Animal Symbiosis

Some fungi share their digestive services Some fungi share their digestive services with animalswith animals Helping break down plant material in the Helping break down plant material in the

guts of cows and other grazing mammalsguts of cows and other grazing mammals

24.14

Practical Uses of FungiPractical Uses of Fungi Humans eat many Humans eat many

fungifungi And use others to And use others to

make cheeses, make cheeses, alcoholic alcoholic beverages, and beverages, and breadbread

The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards.

Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open.

24.15

Antibiotics produced by fungiAntibiotics produced by fungi Treat bacterial infectionsTreat bacterial infections

Staphylococcus

Penicillium

Zone of inhibited growth

24.15

Fairy RingsFairy Rings Folklore holds that fairy rings are doors into the fairies' Folklore holds that fairy rings are doors into the fairies'

world, transporting people to other places or making world, transporting people to other places or making

people appear in the same place in a different time.people appear in the same place in a different time.

Extra Credit – write 1/2 page describing how fairy rings form