Which type of molecule will require some amount of energy to cross the cell membrane?
A. glycerol
B. polar
C. non-polar molecules
D. carbon dioxide
E. oxygen
Ans: B. polar
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As many as 60% of people in malaria-infected regions of Africa have the sickle-cell allele, but only about 10% of the U.S. population of African ancestry carries the allele. Malaria remains a major disease in central Africa but has not been a serious problem in the U.S. for many generations. What is/are the reason(s) for the difference in the percentages and what is a reasonable statement about future percentages?
A. The presence of malaria in Africa maintains the advantage of the heterozygous sickle-cell trait, and the prevalence of malaria will likely continue to preserve the 60% rate. B. Lack of widespread malaria in the United States would have resulted in both homozygous and heterozygous carriers of sickle cell undergoing several generations of negative selection. We should expect this to continue unless innovative therapies give all individuals an equal chance of surviving and reproducing. C. The U.S. percentage may have always been somewhat lower due to immigration from nonmalaria regions, but changes in sites and rates of immigration could occur. D. All of the choices are reasonable.
Equilibrium theories of species diversity have been applied to islands and to larger, continental regions. Which of the following processes is likely to play a greater role in the determination of equilibrium diversity in a continental region?
A) extinction of species B) immigration of species from elsewhere C) formation of new species
Compared with modern humans, Neanderthals had all the following features except:
A. Tall, thin body B. Stockier build C. Thicker bones D. Bulkier muscles E. Shorter stature
An extraterrestrial organism (ET) is discovered whose basic cell biology seems pretty much the same as that of terrestrial organisms except that it uses a different genetic code to translate RNA into protein
You set out to break the code by translation experiments using RNAs of known sequence and cell-free extracts of ET cells to supply the necessary protein-synthesizing machinery. In experiments using the RNAs below, the following results were obtained when the 20 possible amino acids were added either singly or in different combinations of two or three: RNA 1: 5?-GCGCGCGCGCGCGCGCGCGCGCGCGCGC-3? RNA 2: 5?-GCCGCCGCCGCCGCCGCCGCCGCCGCCGCC-3? Using RNA 1, a polypeptide was produced only if alanine and valine were added to the reaction mixture. Using RNA 2, a polypeptide was produced only if leucine and serine and cysteine were added to the reaction mixture. Assuming that protein synthesis can start anywhere on the template, that the ET genetic code is nonoverlapping and linear, and that each codon is the same length (like the terrestrial triplet code), how many nucleotides does an ET codon contain? (a) 2 (b) 3 (c) 4 (d) 5 (e) 6