"by measuring the relative abundances of two stable isotopes of oxygen - 16o and 18o - in some fossil deposit, or in an ice core, or in a coal bed, or in some sedimentary layer, what can one determine about the conditions that pertained at the time those deposits were laid down

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.

Most of the carbon on earth is stored in the form of

Match each symbol with its description.