Crosscutting Concept 3: Flow and Conservation of Matter and Energy



According the law of conservation of matter, matter can be transformed from one form to another, but it cannot be created or destroyed. Similarly, according to the first law of thermodynamics, energy can be transformed from one form to another, but it cannot be created or destroyed. The concept of flow and conservation of matter and energy can be informative in understanding systems in all science domains, such as life science, physical science, and earth science. Thus, tracking the transfers of matter and energy has important implications for developing interdisciplinary understanding. Conservation is a particularly important principle to apply to all phenomena involving matter and energy, yet students often fail to apply or use it appropriately.

For example, when it comes to matter, students often fail to recognize that matter is conserved during a chemical reaction or a phase change that results in the production of a gas. In such cases, many students believe that what they cannot see simply disappears from existence in the universe, when in fact the opposite is true. Students should be able to track or account for energy and matter in terms of inputs, outputs, flows, or transfers within a system or process (NRC, 2012). With the proper understanding and application of the flow of matter and energy, students in middle school should, for example, be able to recognize that a plant or animal cannot grow properly without a sufficient input of matter and energy, and students should be able to account for where the matter is coming from and where it ends up as it is transformed inside of organisms. The conservation of matter is also central to the learning progression we have developed for matter (in particular, change and conservation in matter) and therefore is very much relevant to this crosscutting concept and is another reason why we include it in our competency model.

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