When glucose is present, the lac genes are not fully expressed, even in the presence of inducer. This is called catabolite repression.

a ... Why does it make biological sense to have the lactose operon under negative control by Lac repressor?

b. CAP is necessary to turn on several sugar operons (including the arabinose, lactose, maltose, and galactose operons). Cells with mutations in CAP cannot efficiently metabolize any of these sugars. On plates that contain a sugar and tetrazolium (an indicator dye), colonies are white if that sugar is metabolized and red if it is not. This kind of plate is often used to screen for cells that cannot metabolize a particular sugar. How could you use these plates to isolate CAP mutants?

It can be analyzed by means of genetic analysis in case there is a genetic failure in said cell, or even laboratory tests can be done.

Your question is a little poorly written, I think you need to connect the sentences or make them more developed.

When glucose increases in the blood, it is considered that the body enters a stage of glycemia, which activates the metabolic pathways of said compound, that is why glucose enters the cell and is used as an immediate energy source or as a reserve in the case that it is a person who does not require energy at the moment.

There are studies that prove that certain cells have an inability to assimilate and generate the glucose to enter their SCI, that is, to the intracellular fluid, which leads to constant glycemia, or hyperglycemia in some cases.

Explanation:

A very clear example within the pathophysiology of this phenomenon is the disease of diabetes myelitus.