Ecology, Populations & Biodiversity — Chapter quiz · Physics & Environmental Science, Grade 12

Use food webs, population models, habitat patterns, and representative sampling.

Problem 1

Which process lets producers capture the energy that powers most ecosystems?
  1. Decomposition
  2. Predation
  3. Cellular respiration
  4. Photosynthesis
Answer and explanation

Photosynthesis

Producers use photosynthesis to fix solar energy into chemical energy that flows through the rest of the ecosystem.

Problem 2

A grassland's producers have a GPP of 16,000 kcal/m²/yr and spend 6,000 kcal/m²/yr on respiration. What is the net primary productivity (NPP)?
Answer and explanation

10000 kcal/m²/yr

NPP = GPP - respiration = 16,000 - 6,000 = 10,000 kcal/m²/yr.

Problem 3

Explain, using the 10% rule, why only a small amount of the sun's energy captured by producers ever reaches a top predator.
Answer and explanation

Only about 10% of the energy at each trophic level is stored as biomass the next level can eat; the rest is lost to respiration, heat, movement, and undigested material. After several such steps up to a top predator, only a tiny fraction of the producers' original energy remains.

Problem 4

The variety of alleles within a single population is called
  1. genetic diversity
  2. ecosystem diversity
  3. species richness
  4. species evenness
Answer and explanation

genetic diversity

Variation within one population or species is genetic diversity, the raw material for adaptation.

Problem 5

A sample has two species with 20 and 80 individuals (N = 100). Using Simpson's Diversity Index, D = 1 - Σ(n/N)², find D.
Answer and explanation

0.32

(0.20)² + (0.80)² = 0.04 + 0.64 = 0.68; D = 1 - 0.68 = 0.32.

Problem 6

A species whose removal causes an ecosystem's diversity to collapse, far out of proportion to how abundant it is, is called
  1. a decomposer
  2. a keystone species
  3. an invasive species
  4. a producer
Answer and explanation

a keystone species

A keystone species has an outsized effect on its community relative to its abundance.

Problem 7

In the continuous logistic model dN/dt=rN(1−N/K), N=400, r=.3/year, K=2000. Find the instantaneous growth rate in individuals/year.
Answer and explanation

96 individuals/yr

.3×400×(1−400/2000)=96 individuals/year at that instant, not an exact integrated one-year increase.

Problem 8

Contrast exponential and logistic growth, and explain the role of carrying capacity.
Answer and explanation

Exponential growth (a J-curve) happens when resources are unlimited, so the population accelerates without limit. Logistic growth (an S-curve) slows as the population grows because density-dependent limiting factors take hold, and it levels off at the carrying capacity, K — the maximum size the environment can sustain long-term.

Problem 9

Which terrestrial biome has the highest biodiversity and net primary productivity?
  1. Tundra
  2. Hot desert
  3. Tropical rainforest
  4. Temperate grassland
Answer and explanation

Tropical rainforest

Warm temperatures and abundant year-round rainfall make the tropical rainforest the most productive and biodiverse land biome.

Problem 10

Estuaries and wetlands are considered especially valuable ecosystems. Give one ecological service each provides and explain why it matters.
Answer and explanation

Estuaries serve as nurseries where many fish and shellfish species breed and grow, supporting fisheries far beyond the estuary itself. Wetlands filter pollutants from water and absorb floodwaters, protecting downstream water quality and reducing flood damage. Both are highly productive and support large amounts of biodiversity.

Problem 11

Explain the following claim and supply a valid example or counterexample: The 10% transfer rule is an approximate teaching model, not a universal measured constant.
Answer and explanation

First 1000, second 100 units. State that the given efficiency is modeled and energy is not recycled like matter. The 10% transfer rule is an approximate teaching model, not a universal measured constant.

Response criteria

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

Problem 12

Independent chapter check: A habitat has GPP12000 kJ/m²/yr and producer respiration5000. Consumers produce840 kJ/m²/yr. Find NPP and the NPP-to-consumer production efficiency.
Answer and explanation

NPP=7000 kJ/m²/yr. Efficiency=840/7000=12%. The fraction uses NPP, not GPP, and does not imply every intermediate process has12% efficiency.

NPP=7000 kJ/m²/yr.

Efficiency=840/7000=12%.

The fraction uses NPP, not GPP, and does not imply every intermediate process has12% efficiency.

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.

Problem 13

Explain the following claim and supply a valid example or counterexample: A service value or diversity index does not represent every ecological or ethical criterion.
Answer and explanation

D=.5. State this version of the index and the sampling effort before comparing sites. A service value or diversity index does not represent every ecological or ethical criterion.

Response criteria

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

Problem 14

Independent chapter check: Counts are6,3,1 for three species. Find richness and D=1−Σpi², then state a sampling limitation.
Answer and explanation

Richness=3. Fractions0.6,0.3,0.1 give D=1−(0.36+0.09+0.01)=0.54. The sample may miss rare or hard-to-detect species; matched effort and replication matter.

Richness=3.

Fractions0.6,0.3,0.1 give D=1−(0.36+0.09+0.01)=0.54.

The sample may miss rare or hard-to-detect species; matched effort and replication matter.

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.

Problem 15

Explain the following claim and supply a valid example or counterexample: rN(1−N/K) is an instantaneous rate in the continuous model, not an exact finite-year population increase.
Answer and explanation

dN/dt=.4×500×(1−.2)=160individuals/year at that moment; future N changes the rate. rN(1−N/K) is an instantaneous rate in the continuous model, not an exact finite-year population increase.

Response criteria

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

Problem 16

Independent chapter check: For continuous logistic growth with r=0.5 yr⁻¹,K=800 and N=200, find dN/dt. Compare with N=400.
Answer and explanation

At200:0.5×200×0.75=75 individuals/year. At400:0.5×400×0.5=100/year. Total growth rises even while per-capita growth falls.

At200:0.5×200×0.75=75 individuals/year.

At400:0.5×400×0.5=100/year.

Total growth rises even while per-capita growth falls.

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.

Problem 17

Explain the following claim and supply a valid example or counterexample: Biome labels summarize patterns; productivity varies by location and area basis.
Answer and explanation

Low local nutrients can limit per-area production, but its enormous total area matters for aggregate output. Biome labels summarize patterns; productivity varies by location and area basis.

Response criteria

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

Problem 18

Independent chapter check: A well-mixed1000 L tank gains600 mg oxygen/day and loses900 mg/day with no water-volume change. Find mass and concentration changes per day; state a model limit.
Answer and explanation

Mass change=−300 mg/day; concentration change=−0.30 mg/L/day. The result assumes the stated constant volume, uniform mixing and continuing fluxes; real fluxes can respond to changing conditions.

Mass change=−300 mg/day; concentration change=−0.30 mg/L/day.

The result assumes the stated constant volume, uniform mixing and continuing fluxes; real fluxes can respond to changing conditions.

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.

Problem 19

M=40,C=50,R=10. Find simple mark–recapture estimate.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

200 individuals

40×50/10=200.

Problem 20

Name a mark–recapture assumption that can fail.
Answer and explanation

Unequal capture probability, migration, births/deaths, mark loss, or incomplete mixing can bias it.

Response criteria

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

Problem 21

Independent chapter check: Four0.50 m² quadrats contain2,4,6,4 individuals. Find pooled density and an abundance estimate for100 m² if sampling is representative; state why it is an estimate.
Answer and explanation

Total16 over2.0 m² gives8 individuals/m². Extrapolated abundance≈800. Spatial variation, finite sampling and imperfect detection make it an estimate rather than a census.

Total16 over2.0 m² gives8 individuals/m².

Extrapolated abundance≈800.

Spatial variation, finite sampling and imperfect detection make it an estimate rather than a census.

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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