A buffer system guards against changes in ________
a. all of the choices
b. salinity
c. pH
d. temperature
c
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Its defoliant effects were first noticed when it leaked from gas lights; later found to be produced by plants themselves.
Choose the letter of the best: A. abscisic acid B. auxin C. ethylene D. cytokinin E. gibberellin
A small group of islanders leave "island A" and travel to "island B." After several generations on island B, a researcher finds that a large percentage of the population is left-handed. Left-handedness is a relatively rare trait on island A. A genetic event that explains this is
A) a population bottleneck. B) genetic load. C) a founder effect. D) natural selection.
For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate
They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work? A) There is no radioactive isotope of nitrogen. B) Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long. C) Although there are more nitrogens in a nucleotide, labeled phosphates actually have sixteen extra neutrons; therefore, they are more radioactive. D) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.
The ancestors of land plants were aquatic algae. Which of the following is not an evolutionary adaptation to life on land?
A) C? photosynthesis B) a waxy cuticle C) root hairs D) xylem and phloem E) guard cells