Human Impact & Sustainability — Science

  1. Grade 6 — Human Impact & Conservation
  2. Grade 9 — Human Impact & Stewardship
  3. Grade 10 — Human Impact & Conservation
  4. Grade 12 — Pollution
  5. Grade 12 — Climate Change
  6. Grade 12 — Biodiversity Loss
  7. Grade 12 — Sustainability & Solutions

Apply it in a new setting

Problem 1

A lake's water holds 0.005 ppm of a persistent pesticide. It biomagnifies about 10 times at each step of the food chain: water → algae → shrimp → smelt → osprey. About what concentration, in ppm, ends up in the osprey?
Hints

Count the number of steps UP the chain from water to the osprey.

Water → algae → shrimp → smelt → osprey is 4 steps, each multiplying by 10.

Multiply 0.005 by 10 four times (that is × 10,000).

Answer and explanation

50 ppm

There are 4 steps up the chain (water→algae, algae→shrimp, shrimp→smelt, smelt→osprey), each a tenfold jump.

Total magnification = 10 × 10 × 10 × 10 = 10,000, so 0.005 ppm × 10,000.

0.005 × 10,000 = 50 ppm in the osprey.

Problem 2

A 3,200-hectare forest is cleared and developed until only five isolated 128-hectare patches remain. What percentage of the original forest area has been LOST?
Hints

First find the total area still forested across the five patches.

Remaining = 5 × 128 hectares; then lost = original − remaining.

Percent lost = (area lost ÷ 3,200) × 100.

Answer and explanation

80 %

Remaining forest = 5 × 128 = 640 hectares.

Area lost = 3,200 − 640 = 2,560 hectares; fraction lost = 2,560 ÷ 3,200 = 0.80.

0.80 × 100 = 80% lost (and the surviving 20% is fragmented, so the harm is even greater).

Problem 3

Before the Industrial Revolution, atmospheric CO_2 was about 280 ppm. A climate model projects it could reach 490 ppm by the year 2100. By what percentage would CO_2 have increased from its pre-industrial level?
Hints

Percent increase = (increase ÷ original) × 100, using the pre-industrial value as the baseline.

Increase = 490 − 280 = 210 ppm.

Divide 210 by the original 280, then multiply by 100.

Answer and explanation

75 %

Increase = 490 − 280 = 210 ppm.

Fraction increase = 210 ÷ 280 = 0.75.

0.75 × 100 = 75% above the pre-industrial level.

Problem 4

Across a farming region, thousands of farms upstream sharply increase their fertilizer use. Predict the most likely consequence downstream in the bay, and name the source type.
  1. Point-source pollution from a single pipe, which raises the bay's dissolved oxygen
  2. The extra fertilizer sinks harmlessly to the seafloor with no downstream effect
  3. Nonpoint-source runoff raises nutrient levels, feeding algal blooms whose decomposition strips oxygen from the water and creates a dead zone
  4. Nonpoint runoff cools the bay, which makes the fish population grow
Hints

Runoff from thousands of scattered farms — is that a single point source or a diffuse nonpoint source?

Extra nutrients in water trigger a chain: algal bloom → die-off → decomposition.

Decomposers using up the oxygen is the key step.

Answer and explanation

Nonpoint-source runoff raises nutrient levels, feeding algal blooms whose decomposition strips oxygen from the water and creates a dead zone

Runoff spread across thousands of farms is nonpoint-source pollution, not a single pipe.

The added nutrients fuel algal blooms; when the algae die, decomposers consume the dissolved oxygen (eutrophication), suffocating fish and forming a dead zone — so oxygen falls, not rises.

Nonpoint runoff causing an oxygen-starved dead zone is correct — C.

Problem 5

Which observation is the STRONGEST evidence of long-term climate change, rather than just day-to-day weather?
  1. A four-decade rise in global average temperature, together with shrinking ice sheets and rising sea level
  2. One unusually hot week in a single city
  3. A single record-cold winter day in one town
  4. A cloudy afternoon that felt cooler than the day before
Hints

Climate is the long-term average of weather over decades and across the whole globe.

A single day or week in one place is weather, not climate.

Look for the option spanning many years and multiple independent measurements.

Answer and explanation

A four-decade rise in global average temperature, together with shrinking ice sheets and rising sea level

Weather is short-term and local; climate is the decades-long, global average, shown by many independent lines of evidence.

A single hot week, cold day, or cloudy afternoon is just weather, but a 40-year temperature rise alongside shrinking ice and rising seas is a genuine climate signal.

The multi-decade, multi-measurement trend is the strongest evidence — A.

Problem 6

Scientists estimate species are going extinct roughly 100 to 1,000 times faster than the natural 'background' rate. Which conclusion does this best support?
  1. New species are appearing just as fast, so total biodiversity stays constant
  2. A faster extinction rate must mean the total number of species is rising
  3. Extinction has never happened before in Earth's history, so any at all is alarming
  4. Extinctions are outrunning the rate at which evolution produces new species, so total biodiversity is falling and the losses are permanent
Hints

Extinction is natural, but compare its current SPEED to how fast new species evolve.

New species form very slowly; is evolution keeping up with 100–1,000× extinction?

Remember extinction is irreversible.

Answer and explanation

Extinctions are outrunning the rate at which evolution produces new species, so total biodiversity is falling and the losses are permanent

Extinction itself is natural, but new species evolve slowly, far below 100–1,000× the background rate.

So losses outpace replacements, biodiversity falls, and because extinction is permanent the drop cannot be undone — the other options wrongly claim species are rising or constant.

Losses outrunning evolution, permanently lowering biodiversity, is correct — D.

Problem 7

A city wants to cut the plastic and CO_2 tied to its waste as effectively as possible. Which strategy best reflects sustainability principles?
  1. Send all waste to one much larger landfill, since buried trash has no further effect
  2. Reduce and reuse first, cutting waste at the source, then recycle what remains — rather than relying only on burying or burning it
  3. Burn all the plastic, because combustion removes it with no emissions
  4. Do nothing, since ecosystems can absorb an unlimited amount of waste
Hints

Recall the waste hierarchy — which comes first, reduce or recycle?

Preventing waste at the source beats cleaning it up afterward.

Watch for false claims: landfills leak, burning plastic emits CO_2, ecosystems are not limitless.

Answer and explanation

Reduce and reuse first, cutting waste at the source, then recycle what remains — rather than relying only on burying or burning it

Sustainability prioritizes preventing waste at the source: reduce and reuse first, then recycle what's left.

Landfills still leak and emit methane, burning plastic releases CO_2 and pollutants, and ecosystems cannot absorb unlimited waste — so those options fail.

Reduce and reuse first, then recycle, is the best strategy — B.

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