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C H A P T E R 3 Growth

  1. Figure 3–1 depicts a bacterial growth curve divided into phases

a, b, c, and d. In which one of the phases are antibiotics such as

penicillin most likely to kill bacteria?

(A) Phase a

(B) Phase b

(C) Phase c

(D) Phase d


  1. Some bacteria are obligate anaerobes. Which of the following

statements best explains this phenomenon?

(A) They can produce energy both by fermentation (i.e., glycolysis)

and by respiration using the Krebs cycle and cytochromes.

(B) They cannot produce their own ATP.

(C) They do not form spores.

(D) They lack superoxide dismutase and catalase.

(E) They do not have a capsule.

✅ Answers (1)

Private answer
  1. (B)

During exponential phase

The earliest studies on the mechanism of action of penicillin showed that the bactericidal

activity of /I-lactam antibiotics depends on bacterial growth (Hobby et al., 1942; Hobby &

Dawson, 1944). This is best illustrated by the inability of penicillin to kill nongrowing bacteria in

contrast to the rapid killing and lysis of the same cells during exponential growth. The

insensitivity of nongrowing cells to the bactericidal and lytic effect of antibiotics is a property

shared by all bacteria and has been termed phenotypic tolerance (Tuomanen, 1986).



  1. (D)

(D) They lack superoxide dismutase and catalase.

Obligate anaerobes lack superoxide dismutase and catalase and/or peroxidase, and therefore undergo lethal oxidations by various oxygen radicals when they are exposed to O2.

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Answered on June 24, 2020 5:02 pm

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