ADDITIONAL PROTISTS NOTES CH. 16

The eukaryotic cell probably originated as a community of prokaryotes Eukaryotic cells evolved from prokaryotic cells more than 2 billion years ago The nucleus and endomembrane system probably evolved from infoldings of the plasma membrane. Mitochondria and chloroplasts probably evolved from aerobic and photosynthetic endosymbionts, respectively.

A model of the origin of eukaryotes Cytoplasm Ancestral prokaryote Plasma membrane Endoplasmic reticulum Nucleus Nuclear envelope Cell with nucleus and endomembrane system Membrane infolding Aerobic heterotrophic prokaryote Ancestral host cell Endosymbiosis Mitochondrion Chloroplast Photosynthetic eukaryotic cell Photosynthetic prokaryote Some cells Figure 16.17

16.18 Protists are an extremely diverse assortment of eukaryotes Protist are mostly unicellular eukaryotes Diplomonads Euglenozoans Dinoflagellates Apicomplexans Ciliates Water molds Diatoms Brown algae Amoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Animals Red algae Green algae Closest algal relatives of plants Plants Alveolates Stramenopila Amoebozoa Ancestral eukaryote Figure 16.18

See other Protist notes for various groups of protists! Characteristics Examples

Life Cycle of Many Algae (Plant-like Protists) The life cycles involve the alternation of haploid gametophyte and diploid sporophyte generations Mitosis Male gametophyte Gametes Spores Meiosis Fusion of gametes Female gametophyte Zygote Sporophyte Haploid (n) Diploid (2n) Key Figure 16.24C

Probably by specialization of the cells of colonial protists 16.25 Multicellularity evolved several times in eukaryotes in several different lineages Probably by specialization of the cells of colonial protists Multicellular life arose over a billion years ago Unicellular protist Colony Early multicellular organism with specialized, interdepen- dent cells Later organism that produces gametes Food- synthesizing cells Locomotor cells Somatic cells Gamete 1 2 3 Figure 16.25