Suppose a mutation arises in a population of sunflowers that results in xylem vessels twice as large in diameter as the wild-type vessels. These mutant xylem vessels will have water transport capacity, and will be susceptible to cavitation from freezing. higher; more higher; less lower; less lower; more

Superantigens produce intense immune responses by stimulating lymphocytes to produce cytokines.

Explanation:

Superantigens are a group of bifunctional proteins that interact with at least two receptors expressed on different cells.  The superantigen´s receptors in lymphocyte T is located in the same place where the lymphocyte interacts with a conventional antigen, RCT. The capability of these superantigens to join their receptors in many T cells, shoots a series of processes that conduce to cellular activation, differentiation, proliferation, and great production and release of cytokine.    

Superantigens constitute the most potent natural immunostimulators known.