Resources & Human Decisions — Chapter Practice, Grade 9

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

Problem 1

Which of these is a renewable resource?
  1. Coal
  2. Wind
  3. Natural gas
  4. Copper ore
Answer and explanation

Wind

Wind is continuously produced by uneven heating of Earth's atmosphere, so it's renewable on a human timescale.

Problem 2

Fossil fuels are considered nonrenewable mainly because...
  1. They are found only in a few countries
  2. They take millions of years to form, far slower than we use them
  3. They cannot be burned for energy
  4. They are not found underground
Answer and explanation

They take millions of years to form, far slower than we use them

Fossil fuels form over millions of years, a pace far too slow to keep up with how quickly people use them.

Problem 3

Coal forms from the ancient remains of...
  1. Marine organisms on the seafloor
  2. Swamp plants buried and compressed over time
  3. Volcanic ash
  4. Ocean saltwater
Answer and explanation

Swamp plants buried and compressed over time

Coal comes from ancient swamp and forest plant material buried and transformed by heat and pressure.

Problem 4

Why are natural resources like oil and coal NOT evenly distributed around the world?
  1. Governments choose where to place them
  2. Their locations depend on the specific geologic processes that formed them long ago
  3. They are randomly scattered by ocean currents every year
  4. All countries actually have equal amounts, just at different depths
Answer and explanation

Their locations depend on the specific geologic processes that formed them long ago

Where a resource forms depends on what geologic processes happened at that location in the past, so deposits are unevenly distributed.

Problem 5

A town pumps groundwater from an aquifer faster than rainfall recharges it. Is groundwater still acting as a renewable resource in this situation? Explain.
Answer and explanation

Not really in practice — even though groundwater is naturally renewable, pumping it out faster than it's recharged can drain the aquifer and cause real shortages, so how the resource is managed matters as much as whether it's technically renewable.

Problem 6

A power company wants to reduce its reliance on nonrenewable energy sources. Which change would best accomplish this?
  1. Switching from natural gas power plants to wind turbines and solar panels
  2. Switching from coal to natural gas
  3. Drilling deeper wells into the same oil field
  4. Building a bigger coal storage facility
Answer and explanation

Switching from natural gas power plants to wind turbines and solar panels

Wind and solar are renewable; natural gas is still a fossil fuel — just a different nonrenewable resource.

Problem 7

A forest grows 8 units of wood per year but harvest removes 12. Find the yearly stock change in a simple model. Explain the reasoning in your own words.
Answer and explanation

The stock decreases by 4 units per year despite being renewable.

Change=growth−harvest.

8−12=−4 units/year.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 8

A stock grows 50 units/year and loses 70 to harvest. Find net annual change. Show the reasoning, not just the conclusion.
Hints

Compare use rate with replenishment and ecosystem effects.

Answer and explanation

−20 units/year, before other changes.

Problem 9

Why is fossil fuel nonrenewable on a human planning timescale?
Hints

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

Answer and explanation

Formation takes geological timescales compared with rapid extraction and use.

Problem 10

Impacts can occur before and after the operating stageImpacts can occur before and after the operating stageIllustrative life-cycle impact unitsExtraction20Manufacture + transport15Operation50End-of-life10Total within this boundary = 95; compare alternatives over the same service.
Original illustrative one-metric life-cycle accounting. These values are not a measured product footprint or a combined environmental score. A proper alternative comparison needs the same service and stage coverage, with other impacts evaluated separately.
Interpret the supplied visual model. What is missing if another option is compared using operation-only impact while this one uses the whole life cycle?
Answer and explanation

A matched boundary and service. Include comparable stages or clearly state omissions before interpreting one total as superior.

The bars share one supplied impact metric and boundary. They are not four different units being silently added.

A matched boundary and service. Include comparable stages or clearly state omissions before interpreting one total as superior.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 11

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 12

Total demand on Earth's resources depends on which two factors multiplied together?
  1. Population size and per-capita consumption
  2. Ocean temperature and rainfall
  3. Number of countries and number of languages
  4. Distance from the equator and elevation
Answer and explanation

Population size and per-capita consumption

Total resource demand equals population size multiplied by how much each person consumes on average.

Problem 13

Which best defines 'stewardship'?
  1. Extracting as many resources as possible as fast as possible
  2. Managing and using resources responsibly so future generations can meet their needs too
  3. Ignoring environmental impact to boost the economy
  4. Only ever using nonrenewable resources
Answer and explanation

Managing and using resources responsibly so future generations can meet their needs too

Stewardship means taking responsible care of resources so they remain available for the future.

Problem 14

A town's population grows from 5,000 to 15,000 people, while per-capita use stays the same. By what factor does total resource demand increase?
Answer and explanation

3 ×

15,000 ÷ 5,000 = 3, so demand triples even with the same per-capita use.

Problem 15

A city's population grows by a factor of 1.5, and per-capita electricity use grows by a factor of 2. By what overall factor does total electricity demand increase?
Answer and explanation

3 ×

Multiply the two factors together: 1.5 × 2 = 3× the total demand.

Problem 16

Which of these is the BEST example of a stewardship strategy?
  1. Setting fishing quotas so fish populations can regrow before more are caught
  2. Draining a wetland to build a parking lot
  3. Pumping groundwater as fast as possible for a new water park
  4. Burning coal without any pollution controls
Answer and explanation

Setting fishing quotas so fish populations can regrow before more are caught

Fishing quotas let a population regrow, which is a sustainable, responsible way to manage a resource.

Problem 17

Explain, using the idea of per-capita consumption, why a small increase in population combined with a big increase in per-person resource use can strain Earth's systems even more than a huge population increase with no change in per-person use.
Answer and explanation

Because total demand is population multiplied by per-capita use, a big jump in per-capita consumption multiplies across the whole population, so even a modest population increase combined with people each using much more can produce a bigger total increase in demand than population alone growing a lot while individual use stays the same.

Problem 18

A stream becomes clearer after planting a buffer, but rainfall also fell. What limits the causal claim? Explain the reasoning in your own words.
Answer and explanation

The result is consistent with improvement but does not isolate the buffer's effect.

Both planting and rainfall changes could affect sediment.

Compare similar untreated areas and repeated measurements under comparable weather.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 19

Why can fertilizer runoff affect dissolved oxygen? Show the reasoning, not just the conclusion.
Hints

A before–after change alone is not a controlled causal test.

Answer and explanation

Nutrients can stimulate growth, followed by decomposition that consumes oxygen, depending on conditions.

Problem 20

A clean-energy project reduces emissions but damages habitat. What should evaluation include?
Hints

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

Answer and explanation

Both climate benefit and habitat impact, with alternatives, equivalent service, uncertainty and monitoring.

Problem 21

Preventing input and restoring function are distinct goalsPreventing input and restoring function are distinct goalsSeparate supplied outcome indicesInitial pollutant input100After prevention70Reduction pathway75Later restorationindicator60Specify which input, exposure or ecosystem function each action targets.
Original conceptual intervention-outcome indices, not a measured restoration trial or one-unit ranking of alternatives. The distinct indices are not additive and cannot establish total ecological benefit without defined criteria and a common comparison basis.
Interpret the supplied visual model. Why is the number of planted trees insufficient evidence that an ecosystem has recovered?
Answer and explanation

It measures an action. Survival, appropriate species, biodiversity, soil/habitat functions and other goal-linked outcomes need monitoring over time.

Read the bars as separately defined illustrative indicators, not identical physical quantities. Their labels identify which part of the intervention chain is being assessed.

It measures an action. Survival, appropriate species, biodiversity, soil/habitat functions and other goal-linked outcomes need monitoring over time.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 22

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 23

Energy demand falls from 200 to 160 units. Find percent reduction.
Answer and explanation

20 %

40 ÷ 200 × 100 = 20.

Problem 24

Which is a constraint?
  1. Reduce runoff as much as possible
  2. Stay within a $5,000 budget
  3. Measure water use
  4. Compare two designs
Answer and explanation

Stay within a $5,000 budget

The budget limits feasible solutions.

Problem 25

Why should a design be monitored after implementation?
Answer and explanation

Actual outcomes and maintenance can differ from predictions; evidence can guide revision.

Problem 26

Design A reduces modeled runoff from 100 to 70 mL; B reduces it to 55 mL. Compare percentage reductions and name missing evidence. Explain the reasoning in your own words.
Answer and explanation

A gives 30% and B 45% in this model; that alone does not establish the best real design.

A reduction is (100−70)/100×100=30%.

B gives 45%; costs, maintenance, habitat and real-scale behavior are still unknown.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 27

A system saves 3 units/day for 200 days. Estimate annual savings for those operating days. Show the reasoning, not just the conclusion.
Hints

Equivalent outcomes and boundaries make comparisons meaningful.

Answer and explanation

3×200=600 units, assuming the daily saving holds.

Problem 28

What makes a design recommendation scientifically revisable?
Hints

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

Answer and explanation

Measurable success criteria, monitoring and a plan to update choices when observed outcomes differ.

Problem 29

A local improvement can move costs or impacts to another stageA local improvement can move costs or impacts to another stageOne supplied life-cycle metric (units)Manufacture impact35Installed local impact15Maintenance impact20End-of-life impact10Reduced local impact can coexist with other impacts elsewhere.
Original one-metric life-cycle stage example, not an actual product assessment or a hidden multi-criterion score. Values can be added only within that supplied metric/boundary; they do not establish ecological tradeoffs without the other relevant indicators.
Interpret the supplied visual model. Why should a design report include maintenance and later water release rather than only initial runoff capture?
Answer and explanation

Performance and impacts can change over time, and stored water or material effects can shift elsewhere. A boundary ending at capture omits consequential stages of the service.

The four bars share one illustrative impact metric; a complete decision would also compare runoff, cost, accessibility and maintenance separately.

Performance and impacts can change over time, and stored water or material effects can shift elsewhere. A boundary ending at capture omits consequential stages of the service.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 30

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.

Browse all courses