An antigen
a. is a foreign molecule that evokes a specific response by a lymphocyte
b. is a protein attacked by an invading microorganism
c. induces development of white blood cells in the bone marrow could be an invading bacterium
d. is a protein molecule that defend the body against disease

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?

How are fungi more like an animal? they have a cell wall. they are heterotrophs that absorb their food. they produce seeds and have membrane-bound nucleus. they use sunlight for photosynthesis.

Which zone within the open-ocean zone is home to the most organisms? deep zone surface zone intertidal zone transition zone