Transcript Biological Science 2/e

Tree of Life
Protists are not a monophyletic group.
Protists are especially abundant in
aquatic and marine ecosystems.
Protists are foundation
of food chain
in aquatic and
marine ecosystems.
Protists are important in human health.
Malaria; 300 million cases/year, 1 million deaths.
Here, Plasmodium infecting human red blood cells.
“Red tide” caused by high pops of dinoflagellates.
Toxins build up in shellfish and can poison people.
Origin of eukaryotes:
Endosymbiosis
An organism of one species
living inside an organism
of another species.
Early anaerobic eukaryote
took up aerobic bacterium.
Engulfed bacterium lived
inside host, obtains carbon.
Eventually became
mitochondrion.
The chloroplast is also thought to originate due
to endosymbiosis.
Some current species of protists have symbiotic
relationships with algae.
If the endosymbiosis theory is wrong,
DNA of chloroplasts and mitochondria should
group with eukaryotic DNA.
If the endosymbiosis theory is correct,
DNA of chloroplasts and mitochondria
should group with prokaryotic DNA.
Diversification of eukaryotes
Morphological diversity in protists
•Compartmentalization of functions in cells
•Evolution of multicellularity
•Structures for support and protection
•Adaptations for locomotion
•Adaptations for feeding
•Reproductive life styles
The average eukaryotic cell is 10 times larger
in diameter than the average bacterial cell.
Intracellular structures provide synthesis,transport,
and distribution of molecules.
Multicellularity
Volvox considered multicellular:
Individual cells cannot survive on their own.
Each cell has a distinct function.
Some are vegetative and others undergo meiosis.
Multicellularity arose independently several times.
Structures for support and protection
“test” = shell
Made of different substances in different lineages.
Adaptations for locomotion
Adaptations for feeding: absorptive feeding
(similar to many bacteria)
Parasites absorb food from host.
Adaptations for feeding: Photosynthesis
(similar to many bacteria)
Each pigment absorbs a unique wavelength of light.
Adaptations for feeding: Ingestive feeding
Engulfing possible because no cell wall.
Adaptations for feeding: Symbiosis
Example: A protozoan (a protist) contains a
photosynthetic green algae (a protist).
Relationships among protists still unclear.
Let’s just look at a few interesting examples,
ignoring phylogeny.
Giardia is an
intestinal parasite,
causes diarrhea.
Trichomonas causes
sexually transmitted
disease, infects about
2 million women/year
in the U.S.
Leishmania
(related to Euglena)
Leishmania promastigote (green) invading a macrophage (yellow)
http://www.icp.ucl.ac.be/trop/about/subject2.htm
Ciliates in intestinal
tract of cattle & sheep.
Help host digest grass.
Some dinoflagellates
are capable of
bioluminescence.
Diatoms most important
carbon producer in
fresh and salt water.
Tests accumulate; mined.
Foraminiferans have
holes in their shells
through which pseudopodia emerge.
Tests accumulate; chalk,
limestone or marble.
Marine algae most
prominent multi-cellular
protists.
Slime mold. One cell with many nuclei.
Decomposers, move by cell crawling.
Send out spores when food scarce.
Check out Tom Volk’s blob website at
http://botit.botany.wisc.edu/toms_fungi/june99.html
The pest that caused the Irish potato famine:
Spores can swim
in rain water.
Potato introduced into Ireland ~ 1800. Peasants had to pay rent to English landlords but
subsisted on potatoes ~ 10 lbs/person/day.
Population almost doubled 1800-1845.
In 1845, Phytophthora killed all potatoes in Ireland in a matter of weeks.
1 million Irish starved between 1845-1860.
1.5 million immigrated to east coast of U.S.
To see a video, check out http://botit.botany.wisc.edu/toms_fungi/mar2001.html