Download Protists – Chpater 22 in Starr et al. Protists can be: •Protozoans

Protists – Chpater 22 in Starr et al.
Protists
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Eukaryotic
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Bacteria
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Single-cellular and
Multi-cellular
complex cells with a true
nucleus and membranebound organelles.
Cell wall absent
Heterotrophs and Autotrophs
Sexual and asexual reproduction
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Prokaryotic
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Single-cellular
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Cell wall present
no membrane-bound
organelles, including
nucleus
Heterotrophs and
Autotrophs
Reproduction by prokaryotic
(binary) fission
Protists can be:
•Protozoans: Animal-like
•Plant-like
•Fungus-like
How Protozoans are similar to animals:
–Heterotrophic
–Motile
–Some reproduce sexually
–Composed of complex eukaryotic cells with a true nucleus and membrane-bound
organelles
Animal-like Protozoans
•Good: Many species make up zooplankton, a population of organisms that constitutes
one of the primary sources of energy in aquatic ecosystems.
•Bad: Some protozoa cause harmful human diseases such as malaria and giardia.
How Protozoans are similar to plants:
–Autotrophic (photosynthesize)
–Have chloroplasts
–Mostly aquatic in both fresh water and marine habitats
–Some can live in moist soil
–Some are symbionts with fungi to form lichen
Plant-like Protists—Major types
• Algae: Includes green, brown and red algae. Green algae are most closely related to
plants. Good—Algae is a food source for many people
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Dinoflagellates
•About ½ the species are photosynthetic—the rest are predators on bacteria, algae
and even fish.
•Good—Symbiotic with coral
•Bad—Some species produce neurotoxins and are the cause of algal blooms. Red
tides are caused by dinoflagellates
•Fungi-like protists are similar to fungus:
–Digest food externally and then absorb it
–Look like fungus
– Similar life cycle including reproduction.
They differ from fungi in having motility in parts of their life cycle.
Slime molds are found on the ground where it is moist, especially in forests.
Plasmodial slime molds are enormous single cells with thousands of nuclei. That move
by oozing like amoebas.
Good—breaks down forest litter.
Water molds are found in wet environments such as fresh water and the upper layer of
soils. A water mold was responsible for the potato blight that started the Irish famine.
Fungi – Chapter 24 of Starr et al.
Characteristics of Fungi
• Eukaryotic
• Single or multi-celled
• Heterotrophic
• Decomposers (saprophytes)
• Parasites
• Cell walls contain chitin
A Variety of Roles
• Pathogens
• Spoilers of food supplies
• Used to manufacture:
o Antibiotics
o Cheeses
o Alcohol
• Decomposers – make sure you understand how this works and how it differs from
parasitic forms.
The Mycelium: Most fungi produce a multicellular feeding structure called a mycelium
It consists of branching tubular cells called hyphae. Hyphae have a high surface-tovolume ratio.
The role of the mycelium is to break down organic compounds in their surroundings:
• Carry out extracellular digestion and absorption
• Mycelium grows into food source
• Tips of hyphae secrete digestive enzymes
• Enzymes break down organic material into simple forms that can be absorbed by
hyphae
• Plants benefit because some carbon and nutrients are released
Fungal Life Cycle: See book for illustrations of life/reproductive cycle.
• No motile stage
• Asexual and sexual spores produced
• Spores germinate after dispersal
• In multi-celled species, spores give rise to a new mycelium
Fungal spores:
Withstand extreme conditions of dryness, heat or cold.
Disperse by wind or water to distant locations.
Remain dormant until environmental conditions favor germination
Fungal classification is based on type of sexual spores
Fungal Diversity
At least 56,000 known species + a million unknown?
Major Groups and Characteristics:
1. Chytrids and microsporidians
Oldest
Flagellated spores
Intracellular parasites
Chytridiomycosis: infectious disease that affects amphibians worldwide
Increased infection of humans suffering from compromised immune symptoms (e.g.
HIV)
2. Zygote Fungi (Zygomycetes) - Bread molds
1% of known species
Successful, rapid reproducers
Produce and disperse hundreds of spores from hyphae tips
Zygomycosis- malnourished, diabetics, burns, weakened immune systems
3. Club fungi (Basidiomycota) - Mushrooms
25,000 species
Reproductive structures protrude out from mycelium
Caps with gills on surface that have spores
4. Sac Fungi (Ascomycota)
Most diverse group (30,000 species)
Produce sexual ascospores in sac-shaped cells call asci
Multicelled species form reproductive structures called ascocarps that enclose the asci
Cup-shaped, flask-shaped or globular
Example of Edible sac fungi:
Tuber melanosporum (truffles)
Morchella esculenta (morels)
Disease-causing sac fungi:
Candida albicans - yeast infections
Ophiostoma ulmi - Dutch elm disease
Useful sac fungi:
Penicillium chrysogenum - antibiotic
Saccharomyces cerevisiae - brewing & baking
Yeast metabolism
Fungal Foes
Most fungi are vital decomposers and plant symbionts
Small proportion are plant pathogens
Tiny minority adversely affect human health
Plant Pathogens
Ascomycetes are responsible for
Chestnut blight
Dutch elm disease
Apple scab
Basiomycetes cause smuts of cereal grains
Human Pathogens & Toxins
Ascomycetes cause: Candida (“yeast”) infections, Ringworm, Athlete’s foot, Ergotism
Armillaria ostoyae
Largest known single organism in the world. Occurs in NE Oregon
Covers 2,200 acres, estimated to weigh 605 tons
May have taken 2,400 years to reach this size