The 3rd Grade Performance Expectations (PEs) are organized into four different bundles of PEs in this model, using a topical arrangement. Bundle 1 focuses on traits of organisms. Bundle 2 builds on Bundle 1 to focus on relationships between organism traits and survival in a habitat. Bundle 3 extends this study to focus on how the climate affects organisms over long periods of time. Bundle 4 shifts focus to the physical sciences, with a study of forces and motion.