Passage I

Table 1 lists various components of the human immune system and some of their actions. An antigen is a foreign substance that elicits an immune response. An antibody is a molecule that binds specific antigens.

Figures 1 and 2 show the time periods during which cell and/or antibody concentrations are typically above normal during the 28 days after first exposure to an antigen.

Figure 3 shows the stages of infection in humans exposed to the human immunodeficiency virus (HIV), the virus that causes AIDS.

Table 1 and Figure 3 adapted from Neil A. Campbell, Biology, 3rd ed.

©1993 by the Benjamin/Cummings Publishing Company, Inc.

Figure 1 and 2 adapted from Peter H. Raven and George B. Johnson,

Understanding Biology. ©1988 by Times Mirror/Mosby College Publishing.

3. According to Figure 2, which of the following correctly lists the order, from first to last, in which the 3 types of T cells first appear at above-normal concentrations after first exposure to the antigen?

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

Look at the first picture of figure 2, when the ordinate is greater than 0, the concentration of the cell is higher than the normal concentration.

So it can be seen from the figure that the first ordinate greater than 0 is helper T cells, then cytotoxic T cells, and finally suppressor T cells