Since photosynthesis primarily takes place in the leaves, it is essential that glucose can be transported out of the cell to other parts of the plant. The selectively permeable plasma membrane only allows certain molecules to
cross freely through the phospholipid bilayer.
Is glucose a molecule that is allowed to cross the selectively permeable membrane freely?

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?