The four bundles in this 1st Grade model are tied together with a theme relating to light. The first bundle focuses on seeing objects, and includes the foundational and challenging idea that light is necessary for us to see. The need for light is true whether viewing objects on Earth or in the sky. Bundle 2 extends the study of light to include its interaction with various materials, and applies ideas about light and sound to solve a problem. Bundle 3 is tied to organisms and sunlight, as part of a study of the structure and function of the external parts of plants and animals. In bundle 4, while students study plants and animals with a focus on the traits of parents and their offspring and behaviors of parents and offspring, the study of light is brought back in by looking back over student observations of the amount of daylight over the past year.