Valves in veins are formed of the tunica media. cause venous blood flow to go in only one direction. are found only in the largest veins. make the use of a skeletal muscle pump unnecessary for venous blood flow. are the leading cause of high blood pressure.

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?

Give an example of a trait that is controlled by more than one gene.

Which best describes the nucleus of an atom a. it is where all of the particle s of the atom are located b. it is the negatively charged part of the atom c. it is where the electrons and the protons are located d. it is the part of the atom with the greatest mass