directed, Barbara’s symptoms resolve and she finally begins to feel like herself again. Presuming no drug
resistance to amoxicillin was involved, and given the effectiveness of azithromycin, the causative agent of
Barbara’s pneumonia is most likelyMycoplasma pneumoniae. Even though this bacterium is a prokaryotic
cell, it is not inhibited by amoxicillin because it does not have a cell wall and, therefore, does not make
peptidoglycan.
Go back to thepreviousClinical Focus box.- Explain how the cellular envelope of eukaryotic cells compares to that of prokaryotic cells.
- Explain the difference between eukaryotic and prokaryotic flagella.
Summary
3.1 Spontaneous Generation
- The theory ofspontaneous generationstates that life arose from nonliving matter. It was a long-held belief
dating back, within the written record, to Aristotle and the ancient Greeks, and persisted through the Middle
Ages. - Experimentation by Francesco Redi in the 17th century presented the first significant evidence refuting
spontaneous generation by showing that flies must have access to meat for maggots to develop on the
meat. Prominent scientists designed experiments and argued both in support of (John Needham) and against
(Lazzaro Spallanzani) spontaneous generation. - LouisPasteuriscreditedwithconclusivelyendingthecontroversyaboutthetheoryofspontaneousgeneration,
with his famous swan-neck flask experiment. He subsequently proposed that “life only comes from life.”
3.2 Foundations of Modern Cell Theory
- Although cells were first observed in the 1660s by Robert Hooke,cell theorywas not well accepted for
another 200 years. The work of scientists such as Schleiden, Schwann, Remak, and Virchow contributed to its
acceptance. - Endosymbiotic theory states that mitochondria and chloroplasts, organelles found in many types of
organisms, have their origins in bacteria. Significant structural and genetic information support this theory. - The miasma theory of disease was widely accepted until the 19th century, when it was replaced by thegerm
theory of diseasethanks to the work of Semmelweis, Snow, Pasteur, Lister, and Koch, and others.
3.3 Unique Characteristics of Prokaryotic Cells
- Prokaryotic cells differ from eukaryotic cells in that their genetic material is contained in anucleoidrather
than a membrane-bound nucleus. In addition, prokaryotic cells generally lack membrane-bound organelles. - Prokaryotic cells of the same species typically share a similarcell morphologyandcellular arrangement.
- Most prokaryotic cells have acell wallthat helps the organism maintain cellular morphology and protects it
against changes in osmotic pressure. - Outside of the nucleoid, prokaryotic cells may contain extrachromosomal DNA inplasmids.
- Prokaryoticribosomesthat are found in the cytoplasm have a size of 70S.
- Some prokaryotic cells haveinclusionsthat store nutrients or chemicals for other uses.
132 Chapter 3 | The Cell
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