1. Protists
Chapter 28

2. Outline
Endosymbiosis
Classifying Protists
General Biology of Protists
Six Lineages
Euglenozoa
Alveolata
Stramenopila
Rhodophyta
Chlorophyta
Choanoflagellida

3. Endosymbiosis
Theory of endosymbiosis proposes that mitochondria originated as symbiotic, aerobic bacteria.
Each mitochondrion has its own genome in a circular, closed molecule of DNA.
divide by simple fission
directed by nuclear genes

4. Theory of Endosymbiosis

5. Classifying Protists
Protists are the most diverse of the four kingdoms in the domain Eukarya.
artificial group of convenience
single-celled organisms
little consensus about classification

6. Protist Classification

7. General Biology of the Protists
Cell surface
possess varied array of cell surfaces
Locomotor organelles
chiefly flagellar rotation or pseudopodial movement
Cyst formation
dormant form of a cell with resistant outer covering in which metabolism is essentially shut down

8. General Biology of the Protists
Nutrition
employ all forms but chemoautotrophic
phototrophs
heterotrophs
phagotrophs - visible food particles
osmotrophs - food in soluble form

9. General Biology of the Protists
Reproduction
typically reproduce asexually
binary fission - equal halves
budding - progeny cell smaller
schizogony - multiple fission
sexual reproduction in times of stress
gametic meiosis - before gametes
zygotic meiosis - after fertilization
intermediary meiosis - alternating

10. Protists
Six identified lineages:
Euglenozoa
Alveolata
Stramenopila
Rhodophyta
Chlorophyta
Choanoflagellida

11. Euglenozoa
Euglenoids
most are freshwater
about one-third are autotrophic
pellicle lies within membrane
stigma - light sensitive organ that aids in orienting toward light
Euglena
two flagella attached to reservoir
contain numerous chloroplasts

12. Euglenoids

13. Euglenozoa
Kinetoplastids
unique, single mitochondrion in each trypanosome
Trypanosomes are kinetoplastids that cause many serious human diseases.
African sleeping sickness
Chagas

14. Alveolata
Dinoflagellates
distinctive flagella, protective coats, and biochemistry
reproduce primarily by asexual cell division
responsible for “red tides”

15. Alveolata
Apicomplexes
spore-forming animal parasites
unique arrangement of fibrils, microtubules, vacuoles, and other cell organelles
malarial parasite - Plasmodium
malaria eradication
eliminating mosquito vectors
poison parasites inside human body
develop vaccines

16. Plasmodium Life Cycle

17. Alveolata
Ciliates
most feature large numbers of cilia
usually arranged in longitudinal rows or spirals around the body
form vacuoles to ingest food and regulate water balance
waste emptied through cytoproct
Paramecium

18. Paramecium

19. Stramenopila and Rhodophyta
includes brown algae, diatoms, and oomycetes
brown algae - conspicuous seaweeds
alternation of generations
diatoms (phylum Chrysophyta) - photosynthetic, unicellular organisms with double shells of opaline silica

20. Brown Algae

21. Stramenopila and Rhodophyta
oomycetes (water molds) - parasites or saprobes.
comprise water molds, white rusts, and downy mildews
motile zoospores bear two unequal flagella
life cycles characterized by gametic meiosis and a diploid phase

22. Stramenopila and Rhodophyta
Red algae range in size from microscopic to very large.
origin a source of controversy
tentatively treated as a sister clade of green algae (Chlorophyta)

23. Chlorophyta
Green algae are the ancestors of the plant kingdom.
extensive fossil record dating back 900 million years
mostly aquatic
Chlamydomonas well-known genus
probably represents primitive state
Chlorophyta did not give rise to land plants.

24. Chlamydomonas Life Cycle

25. Choanoflagellida
Choanoflagellates are most like the common ancestor of the sponges.
contain a single emergent flagellum surrounded by a funnel-shaped, contractile collar

26. Amoebas
contain pseudopods that can form at any point on the cell body and can move in any direction
Phylum Actinopoda (radiolarians) secrete glassy exoskeletons of silica.

27. Foraminifera
heterotrophic marine protists with pore-studded shells
complex life cycle with alternation between haploid and diploid generations

28. Slime Molds
Slime molds originated at least three distinct times.
plasmodial slime molds
stream along as a non-walled, multinucleate mass of cytoplasm, plasmodium
produces sporangium during times of resource shortage
forms spores that quickly undergo meiosis

29. Slime Molds
Cellular slime molds
individual organisms behave as separate amoebas, moving through soil or other substrate and ingesting bacteria
individual organisms aggregate and form moving mass “slug” when food becomes scarce

30. Cellular Slime Mold Development

31. Summary
Endosymbiosis
Classifying Protists
General Biology of Protists
Six Lineages
Euglenozoa
Alveolata
Stramenopila
Rhodophyta
Chlorophyta
Choanoflagellida