The function of IgD on the surface of B cells is to:

a) present antigen to helper T cells.

b) present antigen to cytotoxic T cells.

c) bind antigen so that it can be internalized by the B cell and presented to helper T cells on class II MHCs.

d) bind antigen so that it can be internalized by the B cell and presented to cytotoxic T cells on class I MHCs.

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.

answer >   yes we do, women; have three holes, urethral opening(pee hole, vagina, and the women pee/girls pee out of the urethra like the men do; only they have a single opening to pee/ejaculate.   (sorry if i'm too forward with this, but this is for a biology class, isn't it? )

hope that !         : )