three domains of life protists. three domains of life

Three Domains of Life

Protists

Three Domains of Life

Changes in Classification• The ‘old school’ method of classification included 5

Kingdoms (what I learned in school)– Monera– Protista– Fungi– Plantae– Animalia

• Today, advances in molecular technology expanded our understanding (and interpretation) of systematics

Modern Systematics• Three Domain classification of life • Numerous, virtually countless Kingdoms• Bacteria and Archaea are now 2 distinct

Domains (once included together in Kingdom Monera)

• Protista, Fungi, Plantae, and Animalia remain classified as distinct Kingdoms, although classification of the kingdom Protista has been met with complications

Prokaryotes

• Includes the kingdoms Archaea & Bacteria • Oldest, structurally-simplest, and most

abundant forms of life• Photosynthesis Bacterial and Eukaryotic

Diversity• Important decomposers and symbionts

Prokaryotes

• Unicellular• Typically 1μm or less (1000 μm = 1mm;

1000mm = 1 meter)• No membrane-bound nucleus; instead a

single circular chromosome made of DNA• Asexual reproduction by binary fission• Photosynthetic bacteria utilize oxygen or

chemical compounds, such as sulfur

Prokaryotic Cell Structure• Three basic forms:

– Bacillus – rod-shaped– Coccus - sphercal or ovoid-shaped – Spirillum – spiral or helical

Prokaryotic Cell Structure• Prokaryotes have a tough cell wall and other

external structures• Cell wall consists of peptidoglycan; a rigid

network of polysaccharide strands cross-linked by peptide side chains; unique to Bacteria

• Maintains the shape of the cell and protects it from swelling and rupturing

• Prokaryotes can have 1 or more flagella (much less complex than in Eukaryotes)

• Some Prokaryotes possess pilli, which helps fasten cell to host membrane

Domain Archaea• Once considered a subdivision of the Kingdom

Monera, now its own domain• Like all prokaryotes, Archaea are single-celled

microorganisms that lack a nucleus and membrane-bound organelles

• Best known for the “extremophiles” – Archaea which thrive in extremely harsh environments

Archea - Extremophiles• Thermophiles – thrive at

60-80°C (>176°F!)• Acidophiles – thrive at pH

at or below pH 3• Xerophiles – grow in

extremely dry conditions• Halophiles – require

extremely high concentrations of salt

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Dr. Anastasia’s lecture starts here

13

Molecular Classification

Bacteria and Archae differ fundamentally

• Cell Wall– Bacterial cell walls are made of peptidoglycan, Archae are not

• Gene expression– Archaea may have more than one RNA polymerase (Transcription:

reads DNA to make RNA), and these enzymes more closely resemble the eukaryotic RNA polymerases than they do the single bacterial RNA polymerase

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Eukaryotic OriginsThe nucleus and

endoplasmic reticulum arose from infoldings of prokaryotic cell membrane

Endosymbiotic theory• Eukaryotic organelles

evolved from a consortium of symbiotic prokaryotes– mitochondria were

aerobic heterotrophic prokaryotes

– chloroplasts were photosynthetic prokaryotes

Kingdom Protista• Eukaryotic• Most are unicellular (there are some simple

multicellular ones)• Originally consisted of all unicellular eukaryotes• was paraphyletic• The 17 major protist phyla are grouped into six

major monophyletic groups

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Cil

iate

s

Ap

ico

mp

lex

ans

ArchaeaEubacteria Chromalveolata Rhizaria Archaeplastida Excavata Amoeboza Opisthokonta

Par

aba

sal

id

Din

ofl

ag

ella

tes

Alveolata Stramenopila Rhodophyta Chlorophytes Diplomonads Euglenozoa Choanoflagellates

An

ima

ls

Fu

ng

i

Am

oeb

ozo

a

La

nd

pla

nts

Ch

aro

ph

yte

s

Ce

rco

zoa

Fo

ram

inif

era

Ra

dio

lara

Bro

wn

alg

ae

Dia

tom

s

Oo

myc

ete

s

Fig. 29.5

Paraphyletic – includes common

ancestor but not all descendents

Characteristics Used to Classify Protists

• Mode of locomotion• mode of nutrition• overall body form• pigments• & others…

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Second flagellumStigma

Contractile vacuole

Paramylon granule

Nucleus

ChloroplastFlagellum

Pellicle

MitochondrionBasal bodies

Reservoir

b.

a. 6 µm

Fig. 29.8

a: © Andrew Syred/Photo Researchers, Inc.

A ciliated protozoan

Too diverse for one kingdom: a diatom, a unicellular "alga"

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Ptychodiscus

Noctiluca

Ceratium

Gonyaulax

Fig. 29.13

Too diverse for one kingdom: Australian bull kelp (Durvillea potatorum)

Fig. 29.24

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+

Gametangia

Gametophyte (n)

Gametes

+Gametangia

+Gametophyte (n)

Spores

Sporangia

Sporophyte (2n)

Germinatingzygote

n

2n

Zygote

MEI

OSI

S

FERTILIZATION

Fig. 29.27

© Dr. Diane S. Littler

Too diverse for one kingdom: Amoeba proteus, a unicellular "protozoan"

Too diverse for one kingdom: a slime mold (Physarum polychalum)

Kingdom Fungi

• Eukaryotes, mostly multicellular, heterotrophic, have cell walls (chitin)

• decomposers, food, some cause disease• Acquire nutrients through absorption

Mycologists believe there may be as many as 1.5 million fungal species

Fungi are classified into 5 major phyla based on mode of reproduction-Chytrids (aquatic, flagellated, ancestral)-Zygomycetes (bread molds)-Glomeromycetes (mycorrhizae)-Ascomycetes (bread yeast, truffles)-Basidiomycetes (mushrooms)

Kingdom Fungi

Table 32.1

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General Biology of the FungiMulticellular fungi consist of long, slender

filaments called hyphae

-Some hyphae are continuous

-Others are divided by septa

34

General Biology of the FungiA mass of connected hyphae is called a mycelium

-It grows through and digests its substrate

Fungal mycelia

37

Fungal Parasites and Pathogens

Largest Organism? Armillaria –a pathogenic fungus – 8 hectares

Fungi Reproduction• spores are produced either sexually or asexually• hyphae and spore nuclei are haploid

– except for a brief diploid stage that occurs during sexual reproduction

Figure 31.3 Generalized life cycle of fungi (Layer 1)

Figure 31.3 Generalized life cycle of fungi (Layer 2)

Figure 31.3 Generalized life cycle of fungi (Layer 3)

Figure 31.6 The common mold Rhizopus decomposing strawberries

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Zygomycetes

Lichens

• Mutualism between fungi and algae or cyanobacteria

• Sensitive to pollution due to absorption capabilitues

Fig. 32.15Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a. b. c.

Fruticose Lichen Crustose LichenFoliose Lichen

a: © Ken Wagner/Phototake; b: © Robert & Jean Pollock/Visuals Unlimited; c: © Robert Lee/Photo Researchers, Inc.

Fig. 32.16Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Algalcells

Fungalhyphae

40 μm © Ed Reschke

Mycorrhizae

• Mutualism between fungi and the roots of 90% of all vascular plants

• Increases absorption of phosphorous, zinc & other nutrients

Fig. 32.17Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a. b.

Root

50 µm5 µm

Arbuscular Mycorrhizae Ectomycorrhizae

a: © Eye of Science/Photo Researchers, Inc.; b: © Dr. Gerald Van Dyke/Visuals Unlimited