CAIE Checkpoint Science – Biology: Classification and Variation — covers major invertebrate groups (coelenterates, flatworms, nematodes, annelids, arthropods, molluscs, echinoderms) and arthropod classes (myriapods, insects, arachnids, crustaceans), vertebrate classes (mammals, birds, reptiles, amphibians, fish), plant groups (algae, mosses, ferns, conifers, flowering plants), and types of variation (continuous and discontinuous) with examples and environmental influences.