Edward Jenner noticed that the milkmaids who milked cows by hand often were infected with cowpox and that their infections were mild. He also noticed that these same milkmaids did not contract smallpox, which was a much more serious disease. He presumed that the cowpox infections prevented the milkmaids from contracting the much more serious disease of smallpox. Subsequently he began vaccinating people with the pus-like material from cowpox lesions to determine if his thinking was correct. In the story above, the underlined portion is a(n)
A. hypothesis.
B. observation.
C. theory.
D. experiment.
A. hypothesis.
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During periods of stratification, transfer between surface and bottom waters is controlled by
A) mixing. B) diffusion. C) niche partitioning. D) current.
In the figure above, the animals colored green in the lower left represent:
a) the reproductive output of the dominant male elephant seal. b) the male offspring of a colony of elephant seals. c) the reproductive output of the low-ranking male elephant seals. d) are the female elephant seals that will mate with the blue males. e) the next generation of dominant male elephant seals.
Which genus is resident biota of the mouth, large intestine, and within the vagina from puberty to menopause?
A. Treponema B. Lactobacillus C. Haemophilus D. Clostridium E. Escherichia
Saliva contains salivary __________ an enzyme that begins the chemical digestion of starch.
Fill in the blank(s) with the appropriate word(s).