"housekeeping genes" in bacteria are commonly expressed constitutively, but not all of these genes are expressed at the same level (the same number of molecules per cell). the primary mechanism responsible for variations in the level of constitutive enzymes from different genes is that:

Housekeeping genes may be defined as the genes that are constitutive genes important for the cellular functioning of the organism. The expression of housekeeping gene may or may not vary.

Some housekeeping genes are not expressed at same level because the housekeeping genes also have different promoters. The different promoters have different affinity to interact with the holoenzyme of RNA polymerase.

false because ozone (o3) depletion does not cause global warming, but both of these environmental problems have a common cause: human activities that release pollutants into the atmosphere altering it.

global warming is caused primarily by putting too much carbon dioxide into the atmosphere when coal, oil, and natural gas are burned to generate electricity or to run our cars.

explanation:

"a.) well–developed vascular system."