What allows the cell membrane to control the substances that enter leave the cell

Which of these statements best describes the st. lawrence seaway? the st. lawrence seaway connects the st. lawrence river with the arctic ocean. the st. lawrence seaway provides an important trading route between the u.s. and mexico. the st. lawrence seaway provides an important trading route for the u.s, but has little value for canada. the st. lawrence seaway connects the great lakes, the st. lawrence river, and the atlantic ocean.

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.

What will happen if two of the base pairs of the stand of the dna are switched