Trypanosomes are effective parasites of humans because they evade the immune system by __________.
a. colonizing the exterior, rather than the interior, of the body
b. entering cells of the immune system itself
c. sequentially changing surface proteins
d. only spending a short period of time in the body before moving on to another host
e. producing highly specialized cells that together make up an integrated, multicellular organism
Answer: c. sequentially changing surface proteins
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Enteric bacteria such as Salmonella spp., Shigella spp., and Escherichia spp. most often contaminate and spoil
A) meat. B) fruits. C) grains. D) milk and milk products.
Vincent Sarich and Allan Wilson estimated that humans diverged from their closest living primate relatives about 5 million years ago. What line of evidence did they use initially?
A) cladistic analysis of DNA sequences from living primates B) chromosomal banding patterns, fusions, and fissions C) radiometric dating of fossils D) DNA denaturation and re-annealing temperatures E) reactions between primate serum proteins and antibodies to human serum
Plants are raised under artificial lights turned off and on by an electric clock. Some are given long periods of light, others short periods. This is an example of:
A. deductive reasoning B. a hypothesis C. an experiment D. inductive reasoning E. a theory
In the lac operon, what occurs in the presence of lactose?
The same thing occurs in the presence and absence of lactose in the lac operon. Lactose binds to the repressor protein, allowing RNA polymerase to bind to the operator, and transcription occurs. Lactose binds to RNA polymerase and transcription cannot occur. Lactose binds to RNA polymerase, RNA polymerase becomes activated, and transcription occurs. A repressor protein competes with lactose for a position on the operator, thus making transcription a competitive process.