Chapter Summary

1. Kingdoms Bacteria and Archaea consist of prokaryotic organisms (bacteria). The bacteria occur as single cells, in colonies, or in the form of chains or filaments. Some cells may be motile, or they may exhibit a gliding motion; most are nonmotile.

2. Bacterial nutrition is primarily by absorption of food in solution through the cell wall, but some are photosynthetic or chemosynthetic.

3. Reproduction is asexual by means of fission; some genetic recombination occurs by means of pili between cells.

4. Bacteria are mostly less than 2 or 3 micrometers in diameter. They occur as spheres (cocci), rods (bacilli), and in spiral forms (spirilla); they are further classified on the basis of several visible features such as sheaths, appendages, and motion. They are also classified by their chemistry and as gram-positive or gram-negative.

5. Prokaryotic cells have no nuclear envelopes or organelles. Each cell has a single, closed loop of double-stranded DNA and sometimes up to 30 or 40 small, circular DNA molecules called plasmids, which replicate independently of the large DNA molecule or chromosome.

6. Neither meiosis nor mitosis occurs, but fission takes place with the development of a transverse wall that forms near the middle of the cell; gametes and zygotes are not produced. Conjugation facilitates genetic recombination. Transformation involves the incorporation of fragments of DNA released by dead cells; transduction involves the viral transfer of fragments of DNA from one cell to another.

7. Heterotrophic bacteria are saprobes or parasites. Autotrophic bacteria are photosynthetic but do not produce oxygen; chemoautotrophic bacteria obtain their energy through oxidation of reduced inorganic groups.

8. Any nonliving organic material will eventually be decomposed to compost by bacteria and fungi. Compost is definitely good for the soil but has limited value as a fertilizer.

9. Bacteria cause huge losses through plant diseases and food spoilage and many serious diseases in animals and humans. They gain access to their hosts by various means.

10. Koch formulated postulates (rules) for proving that a particular microorganism is the cause of a particular disease.

11. Bacteria useful to humans include Bacillus thuringiensis, Bacillus thuringiensis var. israelensis, and Bacillus popilliae. Bacteria also play a major role in the manufacture of dairy products, such as yogurt, sour cream, kefir, and cheese.

12. Bacteria are used in the manufacture of industrial chemicals, vitamins, flavorings, food stabilizers, and a blood plasma substitute; they play a role in the curing of vanilla, cocoa beans, coffee, and tea and in the production of vinegar and sauerkraut; they aid in the extraction of linen fibers from flax stems, in the production of ensilage for cattle feed, and in the production of several important amino acids.

13. Cyanobacteria are virtually ubiquitous in their occurrence.

14. The cells of cyanobacteria occur in a variety of forms. They are distinguished from other bacteria in having chlorophyll a, in producing oxygen, and in having blue and red phycobilin pigments. They produce cyanophycin, a nitrogenous food reserve.

15. Cyanobacteria have no flagella, but some species have gliding movements. Fragmentation may occur at heterocysts. Akinetes may also be produced.

16. Cyanobacterial cells may have been the origin of chloroplasts, since they divide as chloroplasts do when their host cells divide.

17. Cyanobacteria may become very abundant in bodies of polluted fresh water. Toxic substances are produced when the bacteria die and are decomposed. At least 40 species of cyanobacteria are known to fix nitrogen.

18. Prochlorobacteria are similar in form to cyanobacteria but have pigmentation similar to that of higher plants and lack phycobilins.

19. Vaccination was first performed by Jesty and Jenner in connection with smallpox. Smallpox is believed to have been eradicated but may reappear as an agent of bioterrorism.

20. Viruses, which have no cellular structure, are about the size of large molecules. Some can be isolated, purified, and crystalized, yet remain virulent. They cannot grow or increase in size and cannot be replicated outside of a living cell. They depend upon DNA for their raw materials.

21. Viruses consist of a core of nucleic acid surrounded by a protein coat. They are classified on the basis of the DNA or RNA in their core, their size and shape, the number of identical structural units in their cores, and the nature of their protein coats.

22. Bacteriophages are viruses that attack bacteria. In replicating, they become attached to a susceptible cell, which they penetrate, with their DNA or RNA directing the synthesis of new virus molecules from host material; the assembled new viruses are released when the host cell dies.

23. Cells of higher animals being invaded by viruses produce interferon, a protein that causes cells to produce a protective substance that inhibits replication of viruses and also inhibits the capacity of viruses to transform normal cells into tumor cells.

24. Viral diseases, such as chicken pox, measles, mumps, and yellow fever, have declined since immunizations against the diseases have become widespread. Mass-produced viruses are used to infect insects and other pests of both plants and animals. Some viruses cause losses in creamery vats.

25. Viroids and prions are disease-causing particles that are smaller than viruses.