Biologists classify organisms into three basic Domains Bacteria and Archaea which are the two...

Biologists classify organisms into three basic Domains

Bacteria and Archaea which are the two domains of the Prokaryotic group

Eukarya which contains all the eukaryotes like plants, fungi, animals and protists

Introduction: How Ancient Bacteria Changed the World

Copyright © 2009 Pearson Education, Inc.

Virtually all metabolic pathways on Earth evolved in prokaryotic cells, before the evolution of eukaryotes

The products generated by prokaryotic metabolism changed the Earth’s atmosphere and rocks

Fossilized stromatolites from 3 billion years ago contain the fossils of photosynthetic cyanobacteria

– These bacteria produced O2 and made Earth’s atmosphere aerobic

Prokaryotes (simple cells that do not have a nucleus like bacteria) lived alone on Earth for over 1 billion years

– They remain the most numerous and widespread organisms on Earth

Most prokaryotes are 1–5 µm in diameter (vs. 10–100 µm for eukaryotic cells)

There are ten times as many prokaryotes living in and on your body as the number of cells in your body

16.1 Prokaryotes are diverse and widespread


Prokaryotes live in cold, hot, salty, acidic, and alkaline habitats

Although some bacteria are pathogenic and cause disease, most bacteria on our bodies are benign or beneficial

– Several hundred species of bacteria live in and on our bodies, decomposing dead skin cells, supplying essential vitamins, and guarding against pathogenic organisms

Prokaryotes in soil decompose dead organisms, sustaining chemical cycles


16.1 Prokaryotes are diverse and widespread

The two prokaryotic domains, Bacteria and Archaea, diverged soon after life on Earth arose

Present day Archaea and Eukarya evolved from a common ancestor, complicated by gene transfer between prokaryotic lineages

Some genes of Archaea are similar to bacterial genes, some are similar to eukaryotic genes, and some are unique to Archaea

16.2 Bacteria and archaea are the two main branches of prokaryotic evolution


CO2

Organiccompounds

Energy source

Chemical

ChemoautotrophsPhotoautotrophs

ChemoheterotrophsPhotoheterotrophs

Light

Carbonsource

Prokaryotes are key participants in chemical cycles, making nitrogen available to plants and thus animals

They also decompose organic wastes and dead organisms to inorganic chemicals

Bioremediation is the use of organisms to remove pollutants from soil, air, or water

– Prokaryotes are decomposers in sewage treatment and can clean up oil spills and toxic mine wastes

16.10 CONNECTION: Prokaryotes help recycle chemicals and clean up the environment


PROTISTS Protists are eukaryotes, many are unicellular but some are also multicellular.

Some eukaryotic features that all protists share

– Membrane-bound nucleus

– Flagella or cilia with 9 + 2 pattern of microtubules

Some protists have a very high level of cellular complexity


Protists constitute several kingdoms within the domain Eukarya

The taxonomy of protists remains a work in progress

– The names, boundaries, and placement of clades will continue to change as genomes of more protists are sequenced and compared

16.11 Protists are an extremely diverse assortment of eukaryotes


Diplomonads

Water molds

Parabasalids

Euglenozoans

Dinoflagellates

Apicomplexans

Ciliates

Brown algae

Diatoms

Forams

Radiolarians

Red algae

Chlorophytes

Charophytes

Land plants

Gre

en

alg

ae

Amoebas

Slime molds

Fungi

Choanoflagellates

Animals

Alv

eo

late

sA

mo

eb

ozo

an

sS

tram

en

op

iles

Protists obtain their nutrition in a variety of ways

– Algae are autotrophic protists

– Protozoans like amoeba, paramecium are heterotrophic protists, eating bacteria and other protists

– Fungus-like protists (oomycetes) obtain organic molecules by absorption

– Protists are also parasites and pathogenic (Plasmodium, Trypanosome)

– Or they can be Symbionts (living in the host without any a harm)

Symbiosis is a close association between organisms of two or more species

– Endosymbiosis—living within another

– Termite endosymbionts digest cellulose in the wood eaten by the host

– The protists have endosymbiotic prokaryotes that metabolize the cellulose


16.11 Protists are an extremely diverse assortment of eukaryotes

What is the origin of the enormous diversity of protists?

– Complex eukaryotic cells evolved when prokaryotes took up residence within larger prokaryotes

16.12 EVOLUTION CONNECTION: Secondary endosymbiosis is the key to protist diversity


Nucleus

Primaryendosymbiosis

Cyanobacterium

Heterotrophiceukaryote

Evolved intochloroplast

Nucleus


Cyanobacterium



Autotrophiceukaryotes

Nucleus

NucleusChloroplast

Green alga

ChloroplastRed alga

Nucleus


Cyanobacterium




Nucleus

NucleusChloroplast

Green alga

ChloroplastRed alga

Heterotrophiceukaryotes

Nucleus


Cyanobacterium




Nucleus

NucleusChloroplast

Green alga

ChloroplastRed alga


Secondaryendosymbiosis


Nucleus


Cyanobacterium




Nucleus

NucleusChloroplast

Green alga

ChloroplastRed alga




Remnant ofgreen alga

Euglenozoans

Remnant ofred alga

Dinoflagellates

Apicomplexans

Stramenopiles

Diplomonads may be the most ancient surviving lineage of eukaryotes

– They have modified mitochondria without DNA or electron transport chains

– Most are anaerobic

Parabasalids are heterotrophic protists with modified mitochondria that generate some energy anaerobically

– The parasite Trichomonas vaginalis is sexually transmitted, feeding on white blood cells and bacteria living in the cells lining the vagina

16.14 Diplomonads and parabasalids have modified mitochondria


Undulatingmembrane

Flagella

Euglenozoans are a diverse clade of protists

– Their common feature is a crystalline rod of unknown function inside their flagella

Euglenozoans include heterotrophs, photosynthetic autotrophs, and pathogenic parasites

16.15 Euglenozoans have flagella with a unique internal structure


Video: Euglena Motion

Video: Euglena

Alveolates have membrane-enclosed sacs or alveoli beneath the plasma membrane

Dinoflagellates are important members of marine and freshwater phytoplankton

– Some live within coral animals, feeding coral reef communities

– Dinoflagellate blooms cause red tides

Ciliates use cilia to move and feed.

Apicomplexans are animal parasites such as Plasmodium, which causes malaria

16.16 Alveolates have sacs beneath the plasma membrane



16.16 Alveolates have sacs beneath the plasma membrane

Video: Dinoflagellate

Video: Paramecium Cilia

Video: Paramecium Vacuole

Video: Vorticella Cilia

Video: Vorticella Detail

Video: Vorticella Habitat

Stramenopiles are named for their “hairy” flagellum, usually paired with a “smooth” flagellum

– Water molds are fungus-like and decompose dead organisms in freshwater habitats

– Diatoms are unicellular, with silicate cell walls

– Brown algae are large, complex algae called seaweeds; all are multicellular and most are marine

16.17 Stramenopiles have “hairy” and smooth flagella


Video: Water Mold Oogonium

Video: Water Mold Zoospores

Video: Diatoms Moving

Video: Various Diatoms

Amoebas move and feed by means of pseudopodia

Members of the clade amoebozoans include many free-living amoebas, some parasitic amoebas, and slime molds

– All have lobe-shaped pseudopodia

16.18 Amoebozoans have lobe-shaped pseudopodia


Video: Plasmodial Slime Mold Streaming

Video: Plasmodial Slime Mold Zoom

Video: Amoeba

Video: Amoeba Pseudopodia

A plasmodial slime mold is an amoebozoan that forms a plasmodium, a multinucleate mass of cytoplasm

– The plasmodium extends pseudopodia through soil and rotting logs, engulfing food by phagocytosis as it grows

– Under adverse conditions, the plasmodium forms reproductive structures that produce spores

Cellular slime molds live as solitary amoeboid cells

– When food is scarce, the amoeboid cells swarm together, forming a slug-like aggregate that migrates, before forming a fruiting body borne on a stalkCopyright © 2009 Pearson Education, Inc.

16.18 Amoebozoans have lobe-shaped pseudopodia

Foraminiferans and radiolarians move and feed by means of threadlike pseudopodia

Foraminiferans live in marine and freshwater

– They have porous tests composed of calcium carbonate, with small pores through which pseudopodia extend

Radiolarians produce an internal silicate skeleton

– The test is composed of organic materials

16.19 Foraminiferans and radiolarians have threadlike pseudopodia


Red algae are typically soft-bodied, but some have cell walls encrusted with hard, chalky deposits

Green algae split into two groups, the chlorophytes and the charophytes

– The charophytes are the closest living relatives of land plants

16.20 Red algae and green algae are the closest relatives of land plants




Video: Chlamydomonas

Video: Volvox Colony

Video: Volvox Daughter

Video: Volvox Female Spheroid

Video: Volvox Falgella

Video: Volvox Inversion 1

Video: Volvox Sperm and Female

Video: Volvox Inversion 2

Volvoxcolonies

Chlamydomonas

General Biology of the Protists

Most protists practice both asexual and sexual reproduction; some groups practice only asexual.

Asexual reproductive processes in the protists include binary fission, multiple fission, budding, and the formation of spores.

Sexual reproduction in the protists also takes various forms.

The life cycles of most green algae involve the alternation of generations, in which a haploid (n) gametophyte alternates with a diploid (2n) sporophyte generation



Femalegametophyte

Gametes

Key

Fusion ofgametes

Malegametophyte

Meiosis

Spores

Mitosis

SporophyteZygote

Mitosis

Mitosis

Haploid (n)Diploid (2n)

Multicellularity evolved in several different lineages, probably by specialization of the cells of colonial protists.

Multicellular life arose over a billion years ago.

By 543 million years ago, diverse animals and multicellular algae lived in aquatic environments; plants and fungi colonized land 500 million years ago

16.21 EVOLUTION CONNECTION:Multicellularity evolved several times in eukaryotes


Unicellularprotist

Colony

1

Unicellularprotist

Colony

1

Locomotorcells

Early multicellular organismwith specialized, interdepen-dent cells

Food-synthesizingcells

2

Unicellularprotist

Colony

1

Locomotorcells

Early multicellular organismwith specialized, interdepen-dent cells

Food-synthesizingcells

2

Later organism thatproduces gametes

Somaticcells

Gamete

3

Biologists classify organisms into three basic Domains Bacteria and Archaea which are the two...

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