Question

Exotoxins are ______.

Select one:

a. antiphagocytic factors

b. lipopolysaccharides

c. proteins secreted by living bacterial cells

d. secretions that always target nervous tissue

e. only released after a cell is damaged or lysed

B cell receptors differ from T cell receptors in that

Select one:

a. B cell receptors are comprised of four polypeptides, whereas T cell receptors have only two polypeptides in their quaternary structure.

b. B cell receptors have two antigen binding sites, whereas T cell receptors have only one antigen binding site.

c. B cell receptors are immunoglobulin in nature, whereas T cell receptors are not immunoglobulin molecules.

d. B cell receptor immunoglobulins can be secreted as antibodies, whereas T cell receptors are never secreted.

e. All of the choices represent differences between B cell and T cell receptors.

Since the 1970s, approximately 40 new infectious disease agents have been discovered, including SARS, chikungunya and zika. The ability of these agents to spread rapidly and cause global concern is due to all of the following except

Select one:

a. communities are becoming more densely populated.

b. communities are becoming more sparsely populated.

c. individuals are traveling more frequently and farther distances than in the previous half-century.

d. communities are spreading into rural areas/wildlife habitats.