chapter 20

Protists: Single-celled eukaryotes, collection of diverse lineages.
Not a natural group, some lineages distantly related.
Features: chloroplasts, colonial forms, multicellular forms, obligate aerobes, anaerobic types.
Nutritional modes: autotrophic (photosynthetic) and heterotrophic (absorptive).

Excavates: Include diplomonads, parabasalids, kinetoplastids, and euglenoids. Characteristics: single-celled, mostly heterotrophs, some free-living, some parasitic.
Stramenopiles: Comprising diatoms (mostly autotrophs), brown algae (multicellular, autotrophs), and water molds (heterotrophs).
Alveolates: Include ciliates (most free-living), dinoflagellates (autotrophs and heterotrophs), and apicomplexans (all parasites).
Rhizarians: Radiolaria and foraminifera, single-celled, heterotrophic marine protists with sieve-like shells.
Archaeplastida: Red and green algae, cellulose walls, chloroplasts from primary endosymbiosis.
Amoebozoans: Include amoebas and slime molds, mostly heterotrophs; exhibit unique life cycles.
Opisthokonts: Closest relatives of animals, including choanoflagellates.

Protists possess a nucleus and typical organelles.
Adaptive traits include: outer coverings, motility structures, contractile vacuoles, and chloroplasts.
Reproductive strategies: both sexual and asexual reproduction observed in various protists.

Plasmodium, an apicomplexan, causes malaria, responsible for over 500,000 deaths annually.
Transmission via mosquitoes, with life cycles involving manipulation of host behavior.

Red Algae: Mostly multicellular, marine, phycobilins for light capture, produce agar and carrageenan.
Green Algae: Closest relatives to land plants; have chlorophylls a and b, can be unicellular or multicellular.

Algal blooms resulting from nutrient overload can be harmful and toxic to wildlife and humans; pose challenges for food safety.

Protists display a vast array of forms and functions, from microbial primary producers to major human pathogens, and play critical roles in ecosystems.