Mineral & Soil Resources — Practice · Grade 12 Science

Chapter: Energy, Water & Material Resources

What this practice covers

By the end of Mineral & Soil Resources you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: ore, soil horizon, soil degradation, reclamation.

Problem 1

An ore is best defined as...
  1. any rock at all, no matter what is in it
  2. a rock or deposit rich enough in a valuable mineral to be worth mining
  3. a type of fertile soil
  4. a renewable energy source
Answer and explanation

a rock or deposit rich enough in a valuable mineral to be worth mining

An ore is a rock or deposit that holds enough of a valuable metal or mineral that it is worth the cost of mining it.

Problem 2

Which soil layer is the fertile topsoil where most crops grow?
  1. The C horizon (weathered parent rock)
  2. The bedrock at the bottom
  3. The A horizon (topsoil)
  4. The deepest layer of the profile
Answer and explanation

The A horizon (topsoil)

The A horizon is the dark, fertile topsoil rich in humus where most plant roots grow.

Problem 3

Recycling aluminum uses only about 5% of the energy needed to make it from raw ore. If making new aluminum from ore takes 100 units of energy, how many units are SAVED by recycling the same amount of aluminum instead?
Answer and explanation

95 units

Recycling uses 5% of 100 = 5 units, so it saves 100 - 5 = 95 units of energy.

Problem 4

The 1930 s Dust Bowl showed how quickly soil can be lost when...
  1. farmers plant too many cover crops
  2. land is left as undisturbed native prairie
  3. metals are recycled instead of mined
  4. native grasses are plowed up, exposing bare topsoil to wind erosion
Answer and explanation

native grasses are plowed up, exposing bare topsoil to wind erosion

Plowing up the deep-rooted prairie grasses left bare topsoil that blew away in huge dust storms once drought hit.

Problem 5

Which farming practice best conserves soil?
  1. Planting cover crops and using no-till methods
  2. Plowing straight up and down steep slopes
  3. Removing all crop residue and leaving the soil bare
  4. Growing the same crop every year until the nutrients run out
Answer and explanation

Planting cover crops and using no-till methods

Cover crops and no-till farming keep roots in the ground and the surface covered, holding soil in place and protecting its nutrients.

Problem 6

Soil is technically a renewable resource, yet environmental scientists often treat it like a nonrenewable one. Explain this apparent contradiction.
Answer and explanation

Soil does form naturally from weathering rock and decaying organisms, so it is technically renewable. But it forms extraordinarily slowly — often hundreds of years to build a single inch — while erosion from plowing, deforestation, or overgrazing can strip that same inch away in only a few decades. Because we can lose it far faster than nature rebuilds it, in human terms soil behaves like a nonrenewable resource that must be conserved.

Problem 7

A mine recovers 3 tonnes of metal from 100 tonnes ore. Find recovered mass fraction. Show the reasoning, not just the conclusion.
Hints

Distinguish a rate from total soil inventory.

Answer and explanation

3/100=0.03, or 3%.

Problem 8

Why does recycling not completely remove the need for resource accounting?
Hints

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

Answer and explanation

Collection losses, quality, energy requirements, growing demand and unrecovered material remain relevant.

Problem 9

Soil function depends on structure, organisms and formationSoil function depends on structure, organisms and formationOrganic-rich surface: roots / organismsMinerals + pores holding air and waterParent material / deeper horizonsSoil is a structured living system, not only loose mineral grains.
Original generic soil-horizon cross-section; horizon depths and colors are illustrative.
Interpret the supplied visual. Why can compaction matter even if the soil’s total mineral mass hardly changes?
Answer and explanation

It can alter pore space and connectivity, affecting infiltration, aeration and root growth.

Soil contains mineral particles, organic matter, water, air and organisms arranged in a structure. Pores allow storage and movement of air/water; roots and microbial processes interact with aggregation and nutrients. Horizons develop through weathering, transport and biological activity over time. Rapid erosion can remove a productive surface layer much faster than it forms. A schematic layer drawing is not a guarantee that every local soil has the same depths or composition.

It can alter pore space and connectivity, affecting infiltration, aeration and root growth.

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 10

A 2000 kg ore batch has 3% target metal and 75% recovery. Find contained, recovered and unrecovered target metal, then name a separate soil-quality measure.
Answer and explanation

Contained=60 kg; recovered=45 kg; unrecovered target=15 kg. Infiltration, organic matter, pore structure or measured erosion can characterize soil quality separately from mineral yield.

Contained=60 kg; recovered=45 kg; unrecovered target=15 kg.

Infiltration, organic matter, pore structure or measured erosion can characterize soil quality separately from mineral yield.

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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