After studying this chapter you will be able to understand: Structural, functional, and genetic adaptations contribute to prokaryotic success; a great diversity of nutritional and metabolic adaptations have evolved in prokaryotes; molecular systematics is illuminating prokaryotic phylogeny; prokaryotes play crucial roles in the biosphere; prokaryotes have both harmful and beneficial impacts on humans. | Chapter 27 Prokaryotes Overview: They’re (Almost) Everywhere! Most prokaryotes are microscopic But what they lack in size they more than make up for in numbers The number of prokaryotes in a single handful of fertile soil Is greater than the number of people who have ever lived Prokaryotes thrive almost everywhere Including places too acidic, too salty, too cold, or too hot for most other organisms Figure Biologists are discovering That these organisms have an astonishing genetic diversity Concept : Structural, functional, and genetic adaptations contribute to prokaryotic success Most prokaryotes are unicellular Although some species form colonies Prokaryotic cells have a variety of shapes The three most common of which are spheres (cocci), rods (bacilli), and spirals 1 m 2 m 5 m (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral Figure –c Cell-Surface Structures One of the most important features of nearly all prokaryotic cells Is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment Using a technique called the Gram stain Scientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gram-negative (a) Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye, which masks the added red dye. (b) Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between the plasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added. Figure , b Peptidoglycan layer Cell wall Plasma membrane Protein Gram- positive bacteria 20 m Outer membrane Peptidoglycan layer Plasma membrane Cell wall Lipopolysaccharide Protein Gram- negative bacteria The cell wall of many . | Chapter 27 Prokaryotes Overview: They’re (Almost) Everywhere! Most prokaryotes are microscopic But what they lack in size they more than make up for in numbers The number of prokaryotes in a single handful of fertile soil Is greater than the number of people who have ever lived Prokaryotes thrive almost everywhere Including places too acidic, too salty, too cold, or too hot for most other organisms Figure Biologists are discovering That these organisms have an astonishing genetic diversity Concept : Structural, functional, and genetic adaptations contribute to prokaryotic success Most prokaryotes are unicellular Although some species form colonies Prokaryotic cells have a variety of shapes The three most common of which are spheres (cocci), rods (bacilli), and spirals 1 m 2 m 5 m (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral Figure –c Cell-Surface Structures One of the most important features of nearly all prokaryotic cells Is their cell wall, which .
