When first used in medicine in the 1940s, penicillin was uniformly effective in killing the bacterium Staphyloccocus aureus. Today, ____________________ has led to an increase in antibiotic-resistant alleles, and humans are increasingly at risk from untreatable Staphyloccocus aureus infections.
a) uncleanliness in hospitals
b) natural selection in Staphyloccocus aureus populations
c) natural selection in human populations
d) the substitution of methicillin for penicillin
e) molecular genetics
Ans: b) natural selection in Staphyloccocus aureus populations
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Identical twins occur when ________
A) two eggs are released and are fertilized by two different sperm B) two eggs are released and are fertilized by the same sperm C) one egg is released and is fertilized by one sperm, and the pre-embryo later splits into two D) one egg is released and is fertilized by one sperm, and the fetus later splits into two
Which of the three gasses is the easiest to break apart: nitrogen gas (N2), oxygen gas (O2), or hydrogen gas (H2)? Which is the most difficult to break apart? What accounts for the differences?
What will be an ideal response?
True or False: A researcher hopes to estimate the size of an E. coli population in a liter of seawater. To do this, he can count the number of E. coli bacteria in a milliliter of seawater and multiply this number by 1000
A. true B. false
If cytokinesis did NOT happen at the end of a cell's mitotic division what would be the result ?
A) Four cells B) A single cells with one nucleus C) A single, multinucleated cell D) Two cells