Which of the following has been a major source of ozone destruction over the past 50 years?
A) cellular respiration
B) ethylene glycol
C) chlorofluorocarbons
D) chemiosmosis
E) carbon dioxide
Answer: C) chlorofluorocarbons
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Why are some xenobiotics biodegraded slower than crude oil and petroleum products?
A) Xenobiotics were designed to inhibit microbial growth. B) Some xenobiotics are novel compounds that differ from naturally occurring chemicals, thus microorganisms have not yet evolved to effectively degrade them. C) Only cometabolic microbial processes degrade xenobiotics. D) Chlorinated compounds are so toxic that biodegradation is not possible.
Describe what it means to tare or zero an electronic balance. What purpose does this function serve?
What will be an ideal response?
Why was it necessary to culture E. coli for multiple generations in the 14N-rich medium to rule out the dispersive model?
a. Nitrogen is frequently lost by cells during meiosis, so multiple generations were required to ensure that residual-free 15N in the cytoplasm was replaced by 14N from the new medium. b. Multiple generations were required to ensure that the samples did not contain significant quantities of DNA from other organisms, which would confound the analysis of E. coli DNA. c. After only a single generation, it was expected that the DNA extracted from E. coli would contain equal proportions of 15N and 14N in both the semi-conservative and dispersive models. d. Multiple generations of replication in the 14N-rich medium were required to rule out the possibility that the changes to the DNA mass were not the result of inevitable statistical noise.
In this depiction of transcription, the ____
strand is ____ because it ____. a. upper; RNA; is single-stranded. b. lower; RNA; contains uracil. c. lower; RNA; contains thymine. d. upper; RNA; has no uracil (U). e. lower; DNA; contains adenine (A).