The is the lowest level of stimulation that a person can consciously detect 50 percent of the time the stimulation is present

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.

yes we can.   a lady urinates from her urethra.