What prevents the lac genes in the dna of e. colin from being expressed most of the time ?

What causes temperature extremes in the desert

Urgent. the table shows the relative blood flow through some organs in the human body that is, the percentage of blood that flows through a given organ, through which organ(s) does all the blood flow? explain the effect of exercise on blood flow to skeletal muscles.

In which of the following relationships is one organism always benefited while the other organism is always harmed