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.
4. According to Figure 1 and 2, after first exposure to an antigen, the concentration of which of the following returns to its normal level the soonest?
Your Answer is
Correct Answer is F
Explanation
return to normal level indicates that the concentration (ordinate) of the cell has dropped to 0 again;
Refer to figure 1 and figure 2, it is found that the concentration of natural killer cells in figure 1 is about 3 days When the first drop to 0