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A. Systems
By the end of 8th grade, students should know that:
- A system can include processes as well as things.
- Thinking about things as systems means looking for how every part relates to others.
- Any system is usually connected to other systems, both internally and externally.
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B. Models
By the end of 8th grade, students should know that:
- Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly, or that are too vast to be changed deliberately, or that are potentially dangerous.
- Mathematical models can be displayed on a computer and then modified to see what happens.
- Different models can be used to represent the same thing.
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C. Constancy and Change
By the end of 8th grade, students should know that:
- Physical and biological systems tend to change until they become stable and then remain that way unless their surroundings change.
- A system may stay the same because nothing is happening or because things are happening but exactly counterbalance one another.
- Many systems contain feedback mechanisms that serve to keep changes within specified limits.
- Symbolic equations can be used to summarize how the quantity of something changes over time or in response to other changes.
- Symmetry (or the lack of it) may determine properties of many objects, from molecules and crystals to organisms and designed structures.
- Cycles, such as the seasons or body temperature, can be described by their cycle length or frequency, what their highest and lowest values are, and when these values occur.
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D. Scale
By the end of 8th grade, students should know that:
- Properties of systems that depend on volume, such as capacity and weight, change out of proportion to properties that depend on area, such as strength or surface processes.
- As the complexity of any system increases, gaining an understanding of it depends increasingly on summaries, such as averages and ranges, and on descriptions of typical examples of that system.
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