Ecologists typically model patterns among trophic levels by drawing pyramids. the general name for these pyramids are ecological or trophic pyramids. one more specific type of pyramid is called the pyramid of biomass. this pyramid shows all the biomass at different trophic levels at one point in time. because this ecosystem has only two trophic levels (algae and catfish), it can be represented with a two-tiered pyramid. what ideas do you have about the structure of the biomass pyramid in this pool based on what you already know?

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?