Which proportion of the universe's galaxies can be seen from Earth? A. far less than 1 percent
B. nearly half
C. approximately 25 percent
D. approximately 10 percent

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.

Which of the following is caused by reproductive isolation within a species? a. a decrease in gene flow b. an increase in genetic flow c. a decrease in genetic drift d. an increase in gene flow

What term describes a doctor who becomes a specialist by meeting standards beyond those of getting a license and passing a test in the specialty area?