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PowerPoint to accompany
CONCEPTS IN BIOLOGY
Enger • Ross • Bailey
CHAPTER 21

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What are microorganisms?
 A tiny organism that cannot be seen without a microscope.
– Live in a variety of different habitats

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Domains eubacteria and archaea
 Used to be lumped into one group, bacteria
 Eubacteria have cell walls with peptidoglycan.
 Archaea and eubacteria have chemically unique cell membranes. So different from each other necessary to classify into different
Domains of life.

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Domain eubacteria
 Identified by
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Their shape
 Can be rods, spheres or spiral-shaped
Metabolic reactions
– Chemistry of their cell walls
 Gram (+) and Gram (-)

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Bacterial cells structure

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Shapes of bacteria

Domain eubacteria
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Occupy many different ecological niches
Decomposers
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Heterotrophs that break down organic matter
Called saprophytes
 Can live on dead organic matter
Some are anaerobic. – tetanus, botulism
Others are aerobic and break down organic matter into carbon dioxide and water.
Important in recycling carbon, nitrogen, phosphorus, etc.
Could be used to break down sewage, clean up oil spills
Used in food production (blue cheese, yogurt, beer, wine, etc.)
Are responsible for food spoilage

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Decomposers in sewage

Domain eubacteria
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 Commensal bacteria
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– Bacteria that live on or in organisms without benefiting or harming the host
 Mutualistic +/+
– Normal microflora-
 Bacteria on our skin
 E. coli in our large intestine

Domain eubacteria
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 Mutualistic bacteria
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E. coli in our large intestine
 Produce antibiotics and compete for resources
– Reducing the growth of pathogenic bacteria
 They produce and release vitamin K.
Cyanobacteria and fungi in lichens
– Plants and nitrogen-fixing bacteria in their roots

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Cyanobacteria
 Photosynthetic eubacteria
– Cyanobacteria performs photosynthesis like plants.
 Chlorella
 Spirulina

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Cyanobacteria

Domain eubacteria
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 Bacteria and mineral cycles
– Nitrogen cycle
 Nitrogen-fixing bacteria transform atmospheric nitrogen into ammonia.
– Ammonia can be used by plants to make amino acids.
– Other bacteria convert ammonia waste to nitrate or nitrite.
– Other bacteria convert nitrite to atmospheric nitrogen.

Domain eubacteria
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 Disease-causing bacteria
– Also called pathogens or parasites +/-
– Some commensalistic bacteria can become pathogenic.
 If they are given the opportunity to increase in number
 If they have the opportunity to invade new tissue
 Example: S. pneumoniae

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A bacterial plant disease

Domain eubacteria
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 Control of bacterial populations
– Bacterial populations grow rapidly because
 Their generation time is so short.
– About every 20 minutes
– 1 bacteria can lead to millions in a matter of days
 They can generate resistant forms or stages.
– Spores
 They mutate rapidly.
– Can produce antibiotic resistant strains
– MRSA, VRE

Kingdom protista
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A catch-all kingdom
– Includes a diverse array of organisms
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Many are not evolutionarily related to one another.
 All are eukaryotic
Most are single celled; some are multicellular.
Divided into three groups
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Algae
 Autotrophic, unicellular
Protozoa
 Heterotrophic, unicellular
Fungus-like protists

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Relationships among members of the protista

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Algae
 Contain chlorophyll and can carry out photosynthesis
 Most are aquatic.
– Plankton float in the water.
 Phytoplankton are photosynthetic.
 Zooplankton are heterotrophic.

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Algae
 The terrestrial forms live in very moist areas.
 Most are unicellular; a few are multicellular.

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Single-celled algae
 Euglenids
 Move by flagella
 Have a flexible outer covering called a pellicle
– Gives them a shape
 Some are heterotrophs, others are autotrophs.
 Many live in freshwater.

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Single-celled algae
 Diatoms
– Found in freshwater, marine and soil environments
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Major component of phytoplankton
 A few are heterotrophs.
Brownish in color
Do not have cilia or flagella
Have cell walls made of silica
Diatomeous earth

Single-cell algae
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 Dinoflagellates
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Important primary producers in marine ecosystems
 Also occur in freshwater
Have two flagella
– Have outer covering made of cellulose
– Most are autotrophs.
 Some are heterotrophs.
 Some are parasitic.
 Red tides

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Single-cell algae
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Some produce toxins that can kill fish.
 Red tide
 Can poison humans if they eat poisoned fish
Some are bioluminescent .

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Single-celled algae

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Multicellular algae
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Commonly known as seaweed.
Red algae
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Live in warm oceans
Used to produce agar and carrageenin

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Red and brown algae

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Multicellular algae
 Brown algae
– Live in cooler marine environments
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Can grow very long
Produce alginates (food stabilizer)
 Green algae
– Found in freshwater ecosystems
– Are photosynthetic and have cellulose cell walls

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Green algae

Protozoa
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 Eukaryotic
 Heterotrophic
 Unicellular
 Lack cell walls
 Classified by their means of locomotion
– Flagellates
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Ameboid
Ciliates
– Apicomplexa

Flagellates
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 Have flagella
 Live in moist environments
 Many are mutualistic.
– Found in termite gut; digest cellulose
 Many are parasitic .
– Trichomonas vaginalis -common sexually transmitted disease
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Trypanosomes cause sleeping sickness in humans and cows.
Giardia causes intestinal distress, diarrhea, gas.

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Flagellates

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Amoeboid protozoans
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Move via pseudopods
– Cellular extensions in which cytoplasm flows
Most are free-living.
– Feed on algae, bacteria, etc.
Some are parasitic.
– Amoebic dysentery
Examples
– Amoeba

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Ameboid protozoa

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Ciliates
 Contain cilia
– Beat in an organized, rhythmic fashion to move the cell
 Ruminants have ciliates in their gut.
 Termites

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Ciliates

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The apicomplexans
 Nonmotile parasites
 Have a spore-like stage in their life cycle
 Malaria is caused by an apicomplexan.
– Transmitted by mosquitoes to humans
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Reproduces in the mosquito
Eliminating mosquitoes helps reduce the incidence of malaria.

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The life cycle of Plasmodium vivax

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Funguslike protists
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Have a motile reproductive stage
Slime molds
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Move like amoeba
Digest dead organic matter

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Multicellularity in the protista
 Volvox
– Volvox is colonial.
 The flagella of each cell moves together to move the colony.
 Some of the cells are specialized to produce sperm and egg.
 Thought to be the ancestor of multicellular organisms

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The development of multicellular green algae

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Kingdom Fungi
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Nonphotosynthetic; heterotrophic
– Secrete enzymes that digest large molecules externally
Eukaryotic
Have chitin-containing cell walls
Made up of filaments known as hypha
– Hyphae form networks called mycelium
Disperse through spores
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Cells with tough protective coating
Can be produced by sexual or asexual reproduction

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Mycelium

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Fungus taxonomy

The significance of fungi
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Fungi play many roles in ecosystems
Decomposers
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Fungi and bacteria are the major composers in ecosystems.
Recycles nitrogen, carbon and phosphorus
Can destroy clothes, wood, leather, food
Food
– Fungi and their products can be used as food.
 Mushrooms
 Soy sauce is made by fermenting an ascomycete.
 Citric acid in cola is released from a mold.
 Yeasts are used to make alcoholic beverages and bread.

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The significance of fungi
 Mycorrhizae
– Associations between fungi and the roots of plants
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One type penetrates the roots of the plant.
The other type surrounds the roots but doesn ’ t penetrate.
Found in 80-90% of all plants
Increases the root ’ s surface area for absorption of nutrients up to 10-fold

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Mycorrhizae

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Significance of fungi
 Lichens
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Symbiotic relationship between a fungus and either an alga or cyanobacterium.
 The alga or cyanobacterium is photosynthetic and provides food.
 The fungus provides a moist environment.
Do not require soil for growth
 Grow on trees or rocks
 Important in soil formation during ecological succession

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Lichens

Significance of fungi
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 Pathogenic fungi
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Can infect plants
 Caused the extinction of Chesnut trees and Dutch elm trees
 Causes wheat rust and corn smut
– Causes costly damage to crops
– Farmers have to use fungicides.
Can infect humans
 Pneumocystis is present in most people ’ s lungs.
 Can cause infection in people with compromised immune systems

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Corn smut

Significance of fungi
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 Toxic fungi
– Some fungi can produce mycotoxins
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The mushroom, Amanita spp, makes a toxin that is deadly. “ Death Angel ”
 Food contaminated with these spores can cause illness and death.
The mushroom, Psilocybe contains a hallucinogenic chemical called psilobycin.
Claviceps purpurea is a parasite on rye that generates a toxin that causes hallucinations, insanity, muscle spasms and death. Witches

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Poisonous mushrooms