Rickettsia prowazekii is transmitted by
A) mites of the genus Leptotrombidium.
B) the rat flea Xenopsylla cheopis.
C) the human body louse Pediculus humanus.
D) the dog tick Dermacentor.
E) the cat flea Ctenocephalides felis.
C
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Categorize the circumstances under which the same substance (molecule) can be either an electron donor or an electron acceptor
What will be an ideal response?
Annual rings in a tree trunk result from
A. deposition of colored materials in the oldest cells. B. the variation in cell size due to different growth conditions throughout a year. C. the alternation of xylem and phloem produced in one year. D. the kinds of cells, parenchyma or sclerenchyma, produced by the cambium. E. the proportion of wood cells and cork cells in the xylem.
In the technique of artificial twinning,
a. two embryos are fused. b. an embryo is teased apart. c. two sperm are used to fertilize a single egg. d. two eggs and two sperm are used to form two embryos. e. an embryo’s nucleus is removed and replaced with an adult embryo
Darwin proposed a mechanism for how evolution occurs, which he called _______
Fill in the blank(s) with the appropriate word(s).