In grades K-1, students gain fluency in using the concept of part-whole relationships. They agree on names for the parts that make up several types of whole objects, including plants and animals. They learn that objects can be easily taken apart and put back together again, while other objects cannot be taken apart and reassembled without damaging them. Removing one or more parts will usually change how the object functions. Fluency with the part-whole relationship is essential for all of the sciences and is an important building block for more sophisticated understanding of how systems operate in natural and designed environments.