Why do molecules tend to move from regions of high concentration to regions of low concentration?

What are the doorways into and out of cells, attached to the membrane, and built in the rough er.

What are the three types of counseling established by marine corps policy?

Dna and rna share a number of similarities,but they also differ in certain aspects of their structure. wich nitrogenous base is found in rna but is not found in dna