In terms of number of species, the most successful terrestrial vertebrates that invaded the air are
A. insects.
B. pterosaurs.
C. birds.
D. bats.
E. flying monkeys.
C. birds.
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Smooth muscle cells are activated when Ca2+binds to:
A. calmodulin. B. troponin. C. tropomyosin. D. myosin kinase. E. myosin.
A gram-positive Bacillus, which is c-hemolytic on 5% sheep blood agar, produces a wide zone of lecithinase on egg yolk agar, is nonmotile, and was isolated from the stool of a patient with abdominal pain and watery diarrhea. Because of the patient's existing immunocompromised state, the physician administered penicillin as the antibiotic therapy. The patient's condition did not improve after 7
days of treatment. Which one of the following statements explains the reason for the antibiotic failure? a. The course was too abbreviated and should be given for 14 days. b. The patient may be allergic to penicillin and its therapeutic effects. c. Penicillin is ineffective against gram-positive organisms. d. The organism produces c-lactamase, which renders the drug inactive.
The connective tissue fibers in bone are found in the ____
a. periosteum b. growth plate c. lacuna d. matrix e. osteocytes
A stomach cell is producing pepsin, an enzyme that hydrolyzes proteins. Which of the following events suggests that gene expression of pepsin has been turned off in the cell?
A) The pepsin protein is folded properly in the cytoplasm. B) The chromosome with the pepsin gene is tightly coiled. C) The pepsin mRNA leaves the nucleus and enters the cytoplasm. D) Activators and RNA polymerases are abundant in the nucleus.