Resources & Human Decisions — Problem set, Grade 9

Evaluate resource use and environmental solutions with quantitative evidence and trade-offs.

Review the key ideas

Natural Resources: Renewable & Nonrenewable

Renewable resources are replenished on a human timescale, but nonrenewable resources like fossil fuels take millions of years to form — and where each resource is found depends on the specific geologic processes that created it.

Human Impact & Stewardship

Total demand on Earth's resources grows with both population and per-capita consumption together, so responsible stewardship — conservation, recycling, renewable energy, and sustainable practices — is what keeps resources available for the future.

Evaluating Environmental Solutions

A defensible design choice meets stated criteria within constraints and accounts for measured trade-offs.

Problem 1

Classify each as renewable or nonrenewable: sunlight, coal, wind, oil.
Answer and explanation

Sunlight — renewable; coal — nonrenewable; wind — renewable; oil — nonrenewable.

Sunlight and wind are continuously produced by ongoing processes (the Sun shining, uneven atmospheric heating), so they're renewable on a human timescale. Coal and oil formed from ancient organic matter transformed over millions of years, far slower than we use them, so they're nonrenewable.

Problem 2

Explain why 'renewable' does not automatically mean 'unlimited,' using groundwater as your example.
Answer and explanation

Groundwater is naturally renewable, but pumping it out faster than it's recharged by rain and snowmelt can still cause shortages.

Renewable just means nature can replenish the resource on a human timescale — it doesn't mean the supply is infinite at any moment. If a community pumps groundwater out of an aquifer faster than rainfall and snowmelt can recharge it, the water table can drop and wells can run dry, even though groundwater is technically a renewable resource.

Problem 3

Two countries are the same size, but Country X has huge coal reserves and Country Y has almost none. Explain, using geologic processes, why this might be the case rather than assuming it's random chance.
Answer and explanation

Coal forms only where ancient swamp or forest environments existed and were buried and transformed over millions of years — Country X's land likely had those conditions in its geologic past, while Country Y's did not.

Coal doesn't form everywhere — it requires a specific history: ancient swamp or forest plant matter that got buried by sediment and slowly transformed by heat and pressure over millions of years. Whether a particular patch of land had that kind of environment millions of years ago (and has kept those rock layers intact since) determines whether coal is there today. Country X's territory likely sat somewhere with ancient swamp environments preserved in its rock layers, while Country Y's territory simply never had those specific geologic conditions.

Problem 4

Define stewardship in one or two sentences.
Answer and explanation

Stewardship means using and managing natural resources responsibly so that future generations can still meet their own needs.

Stewardship is about balancing today's use of resources with long-term care, which is the core idea behind sustainability — the difference between using resources up carelessly and managing them so they last.

Problem 5

A county's population grows from 40,000 to 60,000 people, while per-capita water use stays the same. By what factor does total water demand increase?
Answer and explanation

1.5× (demand increases by 50%).

Total demand = population × per-capita use. 60,000 ÷ 40,000 = 1.5, so with per-capita use unchanged, total demand increases by a factor of 1.5.

Problem 6

A region's population grows by a factor of 1.2 over ten years, while per-capita energy consumption grows by a factor of 2.5 over the same period (people are using far more electronics, air conditioning, and so on). By what overall factor does total energy demand grow, and what is one stewardship strategy that could help offset this increase?
Answer and explanation

3× (total energy demand triples); one strategy: switch to renewable energy sources and improve energy efficiency.

Total demand = population × per-capita consumption, so multiply the two growth factors: 1.2 × 2.5 = 3. Even though population only grew by 20%, the much larger growth in per-capita use means total energy demand actually triples. A stewardship strategy that helps: investing in renewable energy sources (solar, wind) and requiring more energy-efficient buildings and appliances, so rising demand doesn't have to be met entirely with more fossil fuel use.

Problem 7

A forest grows 12,000 m³ of timber a year and 15,000 m³ is harvested. What is the annual deficit in m³?
Answer and explanation

3000 m³

15,000 − 12,000 = 3,000 m³ taken from standing stock each year.

Problem 8

Explain why reserve estimates change over time even when nothing is extracted.
Answer and explanation

Reserves are the portion that can be extracted economically with current technology, not the total amount present. Better exploration finds new deposits, improved technology makes previously uneconomic deposits recoverable, and a change in price shifts the boundary in either direction. The physical quantity in the ground may be unchanged while the reported reserve rises or falls.

Response criteria

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

Problem 9

Chapter review: A locally renewable store starts at 200 units, gains 12 units/year and loses 17/year for six years. Find final stock. Explain why the renewable label and a per-use efficiency improvement alone do not guarantee preservation of the store.
Answer and explanation

Net change is −5 units/year, giving −30 over six years and final stock 170. Renewal can be exceeded, and total use depends on quantity of service as well as efficiency; check actual replenishment and withdrawal conditions.

Net change is −5 units/year, giving −30 over six years and final stock 170. Renewal can be exceeded, and total use depends on quantity of service as well as efficiency; check actual replenishment and withdrawal conditions.

Response criteria

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

Problem 10

A protected area holds 240 of a species; an unprotected comparison area falls from 200 to 160 over the same period while the protected population rises from 200 to 240. What is the percentage rise in the protected area?
Answer and explanation

20 %

(240 − 200)/200 × 100 = 20 percent, against a 20 percent fall in the comparison area.

Problem 11

Explain why a comparison area strengthens a claim that a measure worked.
Answer and explanation

Without one, a rise could be due to a favourable season, a change in counting effort, or natural fluctuation affecting the whole region. A comparison area experiences those same general conditions without the measure, so a difference between the two is far more likely to be caused by the measure itself. The comparison converts an observation into evidence.

Response criteria

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

Problem 12

Chapter review: Population rises 20% while average use/person falls 10%. Calculate the total-demand factor and explain one limit of using the average to describe impacts on all families.
Answer and explanation

1.20×0.90 = 1.08, an 8% total rise. A population average hides differences in use, access and circumstances; it does not establish identical individual consumption or responsibility.

Convert changes to factors 1.20 and 0.90.

Multiply to get 1.08, an 8% rise.

Identify the aggregation limit and ask for group-specific evidence when relevant.

Response criteria

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

Problem 13

A town can afford one project: a 30% runoff reduction with high maintenance or a 20% reduction with low maintenance. What evidence is needed to choose?
Answer and explanation

Compare baseline runoff, lifecycle costs, maintenance capacity, reliability, equity, and the stated target; the larger percentage alone does not settle the choice.

Problem 14

Chapter review: A matched storm baseline gives 120 m³ runoff. Design A gives 72 m³ at cost 85; B gives 54 m³ at cost 110. Budget limit is 100. Calculate both reductions, identify feasibility and state a further test before recommending A.
Answer and explanation

A reduces runoff by 40% and meets the cost constraint. B reduces it by 55% but exceeds the budget. Test repeated relevant storm/soil conditions, maintenance and effects elsewhere, checking all success criteria before recommending A.

A: (120−72)/120 = 0.40 = 40%.

B: (120−54)/120 = 0.55 = 55%, but cost 110 exceeds 100.

Evaluate repeated performance, life-cycle effects and maintenance within the defined service.

Response criteria

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