Which of the following is an example of biological mechanical action (or weathering? ) a. rocks breaking into smaller pieces due to growing salt crystals in their pores. b. potholes forming on roads when water inside pavement joints freezes and expands. c. the heating and cooling of minerals inside rocks, fracturing them. d. tree roots from a tree next to a sidewalk growing underneath it and uplifting and cracking the sidewalk. e. acid and rain water producing an acidic solution that disintegrates gravestones.

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.