If you are checking a cell for a zero value and the cell is blank, the test evaluates to true. For example, if you have the following formula in cell A1 =IF(B1=0,"zero","blank") and B1 is blank, the formula returns "zero" and not "blank" as expected.
If the range might contain a blank cell, you should use the ISBLANK function to test for a zero value, as in the following example: =IF(ISBLANK(B2),"blank",IF(B2=0,"zero","other")) Note that the above formula returns "zero" if there is a zero value in the cell, "blank" if the cell is blank, and "other" if anything else is in the cell.
You must always use the ISBLANK formula first before you test for a zero value. Otherwise you will always return a "true" for the zero value, and never get to the test for the ISBLANK formula.
Answer:
Sigma factors bind to the promoter region of a particular gene and facilitating the binding of RNA Polymerase to the promoter region (formation of the RNA polymerase holoenzyme complex) in order initiate transcription of the gene.
Put simply - Helps RNA Polymerase do it's job.
That's true. There is little variety among organisms found in pools, pounds and lakes. Despite that fact that many ponds are seasonal, lasting just a couple of month (for exemple sessile pools) while lakes can exist for more than hundred years. Lakes and ponds have limited species diversity because they are often limited from each other and from other water sources like rivers, seas and oceans.
