Prokaryotes and Protists

16.7 Prokaryotes have inhabited Earth for billions of years Prokaryotes are the oldest life-forms They remain the most numerous and widespread organisms on Earth today Figure 16.7

16.8 Archaea and bacteria are the two main branches of prokaryotic evolution Prokaryotes are cells that lack nuclei and other membrane-enclosed organelles

Prokaryotes are classified into two domains, based on nucleotide sequences and other features Bacteria and Archaea Table 16.8

16.9 Prokaryotes come in a variety of shapes Spheres (cocci) are the most common Rods (bacilli) Curves or spirals Figure 16.9A-C

16.10 Prokaryotes obtain nourishment in a variety of ways These E. Coli colonies are growing with only glucose as an organic nutrient Figure 16.10

Autotrophs obtain carbon from CO2 and are of two types Photoautotrophs and chemoautotrophs Heterotrophs obtain carbon from organic compounds Photo- heterotrophs and chemo- heterotrophs Table 16.10

The first cells were most likely chemoautotrophs They may have gotten their energy from sulfur and iron compounds

16.11 Archaea thrive in extreme environments—and in the ocean Archaea live in anaerobic swamps salt lakes acidic hot springs deep-sea hydrothermal vents animal digestive systems Figure 16.11A, B

Rotating flagella aid in locomotion 16.12 Diverse structural features help prokaryotes thrive almost everywhere Rotating flagella aid in locomotion Flagellum Plasma membrane Cell wall Rotary movements of each flagellum Figure 16.12A

Pili help cells cling to surfaces Figure 16.12B

Endospores allow certain bacteria to survive environmental extremes in a resting stage Figure 16.12C

Many prokaryotes grow in linear filaments Figure 16.12D