Why might we get a negative result when testing a food item when we know the molecules we're testing for are present?

Which of these best describes wde by replicating the chromosomes c) the cytoplasm is divided between the two new daughter cells d) the nucleus opens to allow the chromosomes to enter the cytoplasm

Apopulation of black bears depends on salmon from a stream for food. if a drought causes the stream to run dry one year, how will this likely impact the black bear population?

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?