Environmental Systems, Feedback & Risk — Practice · Grade 12 Science

Chapter: Conservation, Systems & Environmental Design

What this practice covers

By the end of Environmental Systems, Feedback & Risk you should be able to:

8 questions, numeric and written answer, each with a worked explanation.

Vocabulary used: reservoir, feedback, exposure.

Problem 1

Reservoir 600 units,outflow 30 units/year. Estimate residence time.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

20 years

600/30=20.

Problem 2

Is positive feedback necessarily desirable?
Answer and explanation

No; positive means amplifying, not good.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

Storage begins 100 units; inputs 45 and outputs 20. Find final storage.
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

125 units

100+45−20=125.

Problem 4

Why might equal expected-loss options have different consequences?
Answer and explanation

They may differ in extreme outcomes, who is exposed, reversibility, and uncertainty.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

A shortage causes groundwater pumping that further lowers groundwater levels. What loop is plausible? Show the reasoning, not just the conclusion.
Hints

Negative does not mean undesirable.

Answer and explanation

A reinforcing depletion loop if the lower levels worsen shortage and induce more pumping.

Problem 6

Why pair probability with consequence in a risk assessment?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Rare severe events and frequent minor events differ; neither likelihood nor severity alone describes risk adequately.

Problem 7

Expected loss does not summarize every aspect of riskExpected loss does not summarize every aspect of riskScenarioProbabilityConsequence unitsExpected valueA0.1010010B0.50157.5InterpretationDefined intervalComparable scaleNot worst-caseseverityExposure, vulnerability and consequence distribution also matter.
Illustrative probabilities and comparable consequence units, not a forecast or insurance estimate.
Interpret the supplied visual. Which scenario has larger expected value, and which has the larger single-event consequence?
Answer and explanation

A has expected 10 versus 7.5 for B, and its consequence 100 is also larger; other scenarios could separate those rankings.

A simple expected loss multiplies event probability by a consequence on a defined comparable scale, summing across mutually specified outcomes. Probability needs an interval and reference class. Exposure concerns who or what is in contact with the hazard; vulnerability affects the damage given that contact. Two options can have similar expected loss but different worst cases, inequality or uncertainty. Explain these dimensions rather than treating one average as the entire decision.

A has expected 10 versus 7.5 for B, and its consequence 100 is also larger; other scenarios could separate those rankings.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

Event A has probability 0.05 and consequence 200 units; B has probability 0.20 and consequence 40. Find expected losses and explain why the smaller expected value need not settle the choice.
Answer and explanation

A=10 units; B=8 units. B has lower expected loss, but worst-case severity, uncertainty, distribution, constraints and priorities still need transparent consideration.

A=10 units; B=8 units.

B has lower expected loss, but worst-case severity, uncertainty, distribution, constraints and priorities still need transparent consideration.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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