Why do different kinds of control mechanisms exist?

Cells contain a diverse set of different mechanisms for controlling gene activation. In general, the type of mechanism controlling the synthesis of a gene product depends on the product's function. If a product is involved in an catabolic pathway then gene expression will be stimulated by initial substrates of the pathway and repressed by final products of the pathway. Initial substrate molecules can either inactivate repressor proteins or induce activator proteins. Final product molecules would activate repressor proteins. Using these types of control mechanisms the genes for the pathway molecules could be turned on when there is a lot of the substrate molecules and turned off when there is a lot of the of the final product. V

An active repressor protein:
A. is a structural protein.
B. binds to the DNA molecule and promotes transcription initiation.
C. binds to the DNA molecule and prevents transcription. binds to the RNA polymerase, preventing messenger RNA synthesis.
D. binds to an inducer to activate it.

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.

Be in this im starting a with you so if you want you can get a partner for this. but basically im going to assign you guys a biome and you have to have a big sheet paper and you will turn it into 4 squares. the top right square is will be a drawing square for a drawing you will make of your biome. the top left square is about the biomes plants and drawings of them. the bottom left square is about the biomes animals. the bottem rights square is about the description of the biome. leave a comment or an answer and i will assign biomes. if your request one thats the one you get. send me a link to the project and i will grade ! im not a teacher btw.

Acell in the human nervous system whose primary function is to form myelin and the blood-brain barrier, respond to injury, remove debris, and enhance learning and memory is called a(n) cell.