Which phylum of the animal kingdom includes all organisms which possess a spine (backbone)? chordata arthropoda annelida mollusca

Which group is noted for the independence of gametophyte and sporophyte generations from each other? a) ferns b) mosses, hornworts, and liverworts c) charophytes d) angiosperms e) gymnosperms

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?

Which of the following describes a difference when gram-positive bacteria are compared to gram-negative bacteria?