Telomeres, tandem repeat sequences at the ends of chromosomes, generally get shorter after every cell division. The resulting mechanism involves a protein called p53, which ________
A) puts the cell into a permanently nondividing state
B) causes the cell to enter cell senescence
C) may induce the cell to undergo programmed cell death
D) All of the above.
D
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Nitrification
a. converts ammonia into nitrates. b. reduces nitrates to nitrites. c. converts nitrogenous compounds into free nitrogen. d. converts atmospheric nitrogen to ammonia. e. reduces ammonia to ammonium.
The extraembryonic membrane that is the first site of blood cell formation in mammals is the _____________
Fill in the blank(s) with the appropriate word(s)
Seth ordered lobster at a restaurant and realized that the outer shell was made of a tough carbohydrate similar to that used to make the carapace of a cockroach. What do you think the outer shell of the lobster is made of?
A. Cellulose B. Glycogen C. Fibrin D. Chitin E. Amylopectin
Which of the following best reflects what we know about how the flu virus moves between species?
A) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected. B) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans. C) An influenza virus gains new sequences of DNA from another virus, such as a herpesvirus; this enables it to be transmitted to a human host. D) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates, the virus is passed to a new species such as a bird, and the virus mutates again and can now be transmitted to humans.