The structure of DNA was discovered in
A. 1921.
B. 1953.
C. 1999.
D. 2003.
B. 1953.
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Which of the following choices is an example of a positive feedback mechanism?
a. ceasing exercise when tired b. sweating when hot c. contractions in childbirth increasing production of oxytocin d. eating when hungry and stopping when full
The movement of nutrient in the form of a gas takes place in which cycle?
a. global water cycle b. atmospheric cycles c. sedimentary cycles d. solar-plant cycle e. all of these
Each ________ on the hemoglobin subunit is capable of binding an oxygen molecule, thereby allowing ________ oxygen to bind with one hemoglobin molecule.
A) globin : four B) heme : four C) globin : three D) heme : three E) free iron : one
Which of the following is true about antibiotics?
a. In some cases, antibiotics are able to kill pathogenic microbes without harming human cells. b. Although some antibiotic resistance has been reported, it is not considered a real problem in medicine today. c. Antibiotics are effective against viruses. d. Antibiotics are unaffected by enzymes.