Environmental science · Grades 9–12
Environmental stocks, flows and system boundaries · revision notes
A stock is an amount present at a time; a flow is an amount transferred per time. Mixing their units can produce invalid comparisons.
Key ideas and conditions
Stock and flow
A stock is an amount present at a time; a flow is an amount transferred per time. Mixing their units can produce invalid comparisons.
Balance
Change in stock equals inputs minus outputs under a stated boundary and period, with transformations accounted for consistently.
Boundaries
An environmental comparison depends on which stages, locations and time horizons are included. A shifted burden outside the boundary is not necessarily eliminated.
Uncertainty
Report measurement uncertainty and assumptions. An accounting model is a tool for reasoning, not automatically a verified full lifecycle assessment.
Explain without looking
- Describe an honest comparison of two environmental options.
- A stock decreases from 80 to 60 units. Find its change final minus initial.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
AI-assisted preview; independent educational review required. Level labels describe prerequisites, not accreditation or official curriculum alignment.