Storage change — Science definition
Inputs minus outputs across a stated boundary; a store can grow or shrink while matter is conserved overall.
Where it is taught
- Carbon, Water & Cycling Matter — Ecosystems, Matter & Energy, Life Science & Scientific Inquiry, Grade 7
In use
To follow matter through any of this you draw a boundary, count what crosses in and out, and work out the storage change — which is what the pond model at the end of this unit does.
Carbon, Water & Cycling Matter
Questions using storage change
Problem 1
Illustrative pond interval: rain adds 40 L; runoff adds 20 L; evaporation removes 25 L; outflow removes 15 L. Other pathways are excluded.
Calculate storage change, label inputs and outputs, and explain the conservation distinction.
Answer and explanation
The modeled pond gains 20 L. Rain and runoff are inputs, while evaporation and outflow cross outward. The changing pond amount is consistent with matter conservation because the pond is only one boundary. The result assumes the stated pathways are complete for the interval and does not predict future weather or every real pond exchange.
Inputs: 40+20=60 L.
Outputs: 25+15=40 L.
Change: 60−40=+20 L.
Response criteria
- Explain the relevant biological process accurately.
- Use the supplied evidence and show calculation steps with units where needed.
- Connect a labeled model or mechanism with the claim.
- State an assumption, evidence limitation, or useful next observation.
Problem 2
A water store receives 30 L and loses 18 L in one stated interval. Find storage change.
Answer and explanation
12 L
30−18=+12 L under the stated complete budget.