Ecosystems & Conservation Decisions — Chapter quiz · Life Science: Biology, Grade 10

Analyze populations, food webs, cycles, disturbance, and evidence for conservation designs.

Problem 1

A population growing along a logistic (S-shaped) curve eventually levels off at
  1. twice its carrying capacity
  2. an ever-increasing number
  3. zero
  4. its carrying capacity
Answer and explanation

its carrying capacity

Logistic growth flattens out at the carrying capacity (K), where limiting factors bring births and deaths into balance.

Problem 2

A population of 50 organisms grows exponentially, doubling every year. If nothing limits it, how many organisms are there after 3 years?
Answer and explanation

400 organisms

N = 50 × 2³ = 50 × 8 = 400.

Problem 3

Which organism is an autotroph?
  1. Grass
  2. A wolf
  3. A mushroom
  4. A hawk
Answer and explanation

Grass

Grass makes its own food through photosynthesis, so it is an autotroph (producer). The others must consume other organisms.

Problem 4

Producers in a field store 40,000 kcal of energy. Using the 10% rule, how many kcal are available to the primary consumers?
Answer and explanation

4000 kcal

40,000 × 0.10 = 4,000 kcal.

Problem 5

Using the same field (producers store 40,000 kcal), how many kcal reach the secondary consumers, two trophic levels above the producers?
Answer and explanation

400 kcal

40,000 × 0.10 × 0.10 = 400 kcal.

Problem 6

Which process removes carbon dioxide from the atmosphere?
  1. Cellular respiration
  2. Photosynthesis
  3. Combustion of fossil fuels
  4. Decomposition
Answer and explanation

Photosynthesis

Photosynthesis pulls carbon dioxide out of the air and stores its carbon in sugars; the other three release carbon dioxide.

Problem 7

Explain the key difference between how matter and energy move through an ecosystem.
Answer and explanation

Matter, such as carbon, nitrogen, and water, is recycled — the same atoms cycle again and again between living things, the air, water, and soil. Energy, by contrast, flows through an ecosystem only once: it enters from the Sun, is passed along trophic levels while about 90% is lost as heat at each step, and eventually leaves the ecosystem for good as heat. Matter cycles; energy flows through and dissipates.

Problem 8

Worldwide, the single greatest cause of biodiversity loss is
  1. nitrogen fixation by bacteria
  2. the water cycle
  3. habitat loss and fragmentation
  4. the presence of decomposers
Answer and explanation

habitat loss and fragmentation

Clearing, draining, and fragmenting habitat removes the places species need to live, making it the leading driver of extinctions.

Problem 9

A pollutant is present at 0.05 ppm in algae and biomagnifies about 10 times at each trophic level. What is its concentration, in ppm, in a fish two trophic levels above the algae?
Answer and explanation

5 ppm

0.05 × 10 × 10 = 5 ppm — biomagnification concentrates the toxin as it moves up the food web.

Problem 10

Name one human activity that threatens biodiversity, and describe one conservation or sustainability strategy that could reduce its impact.
Answer and explanation

Burning fossil fuels releases greenhouse gases that drive climate change, threatening species that cannot adapt quickly. A strategy to reduce this is shifting to renewable energy sources like solar and wind, which meet human energy needs while cutting greenhouse gas emissions. (Other valid pairs: clearing forests for farmland — protect and restore habitat or create wildlife corridors; overfishing — set sustainable catch limits; pollution — reduce, reuse, and recycle.)

Problem 11

A population exceeds its carrying capacity. The most likely immediate consequence is
  1. an increase in carrying capacity
  2. a decline in population through starvation, disease, or emigration
  3. a permanent higher population
  4. no change
Answer and explanation

a decline in population through starvation, disease, or emigration

Resources cannot support the excess, so density-dependent factors reduce the population back toward or below carrying capacity.

Problem 12

Explain why a species' niche is not the same as its habitat, and why the distinction matters when two species are introduced to the same place.
Answer and explanation

A habitat is the place an organism lives; a niche is the full set of conditions and resources it uses and the role it plays, including what it eats, when it is active, and what it requires to reproduce. Two species can share a habitat without sharing a niche if they use different resources or are active at different times. The distinction matters because competition depends on niche overlap, not on shared address: species in the same habitat with distinct niches may coexist indefinitely, while those with highly overlapping niches cannot unless one diverges.

Response criteria

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

Problem 13

Independent chapter check: A population starts at 80, with 20 births, 12 deaths, 9 immigrants and 5 emigrants. Find final count, change and percentage change.
Answer and explanation

Final count is 80+20−12+9−5 = 92. Change is +12, or 12/80×100 = 15%, under the stated boundary and interval.

Final count is 80+20−12+9−5 = 92. Change is +12, or 12/80×100 = 15%, under the stated boundary and interval.

Response criteria

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

Problem 14

Most of the energy at one trophic level does not reach the next because it is
  1. converted into matter
  2. used in respiration and released as heat, or not consumed
  3. stored permanently
  4. returned to the sun
Answer and explanation

used in respiration and released as heat, or not consumed

Organisms respire most of the energy they obtain, releasing it as heat, and a further portion of each level is never eaten.

Problem 15

Explain why producing one kilogram of meat requires more plant material than producing one kilogram of plant food, using trophic transfer.
Answer and explanation

Meat comes from an animal at the second trophic level, which retains only about a tenth of the energy in the plants it eats, the rest going to its own respiration, heat, and uneaten material. Producing a kilogram of animal tissue therefore requires roughly ten kilograms of plant tissue, while a kilogram of plant food requires only itself. The difference is a consequence of transfer efficiency, and it is why the same area of land supports more people on a plant-based diet than on a meat-based one. The ratio varies substantially between animals and farming systems, so ten to one is an approximation rather than a constant.

Response criteria

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

Problem 16

Independent chapter check: A supplied chain transfers 15% of 8,000 kJ to its primary consumer level, then 8% of that to a secondary level. Calculate both outputs and explain why 10% should not replace the supplied values.
Answer and explanation

The outputs are 1,200 kJ and 96 kJ. The stated transfer fractions define this comparison; ten percent is an approximation, not a compulsory constant.

The outputs are 1,200 kJ and 96 kJ. The stated transfer fractions define this comparison; ten percent is an approximation, not a compulsory constant.

Response criteria

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

Problem 17

Denitrifying bacteria affect the nitrogen cycle by
  1. fixing atmospheric nitrogen
  2. converting nitrates back to nitrogen gas
  3. building protein
  4. producing phosphate
Answer and explanation

converting nitrates back to nitrogen gas

Denitrification returns nitrogen from soil compounds to atmospheric nitrogen gas, completing the cycle and removing usable nitrogen from the soil.

Problem 18

Fertilizer runoff adds large quantities of nitrate to a lake, and the lake later loses most of its fish. Explain the sequence and identify the step at which oxygen becomes the problem.
Answer and explanation

Added nitrate removes the nutrient limit on algal growth, so algae multiply rapidly and form a bloom. The bloom's organisms die in large numbers, and decomposers respiring that dead material consume dissolved oxygen far faster than it is replaced. Oxygen becomes the problem at the decomposition step, not during the bloom itself: once dissolved oxygen falls below what fish require, the fish die. The cause is therefore the altered nitrogen flux, but the proximate killer is oxygen depletion by decomposers.

Response criteria

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

Problem 19

Independent chapter check: A nitrogen store begins at 50 units and receives 12 while losing 9 each year for four years. Find its final amount and distinguish that result from the annual input.
Answer and explanation

The final store is 50+4×(12−9)=62 units. Twelve units/year is an input flux, not the stock or net annual gain; the net gain is three units/year.

The final store is 50+4×(12−9)=62 units. Twelve units/year is an input flux, not the stock or net annual gain; the net gain is three units/year.

Response criteria

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

Problem 20

Which measure addresses habitat fragmentation most directly?
  1. Reducing fishing quotas
  2. Establishing corridors connecting separated patches
  3. Banning a pesticide
  4. Removing an invasive plant
Answer and explanation

Establishing corridors connecting separated patches

Corridors restore movement between isolated patches, which is the specific problem fragmentation creates; the other measures address different pressures.

Problem 21

Explain why conservation decisions involve trade-offs, using one concrete example, and what distinguishes a good decision from a popular one.
Answer and explanation

Resources, land, and attention are limited, so protecting one thing usually means not protecting another or constraining some human use. Restricting a fishery protects the stock and the people who depend on it in the long term while reducing catches and income now; the costs and benefits fall on different people and at different times. A good decision states the evidence for the expected effect, names who bears the cost, specifies what will be measured to check whether it worked, and says what would count as failure. A popular decision may do none of these, and a decision that cannot be evaluated cannot be improved.

Response criteria

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

Problem 22

Independent chapter check: After restoration, observed animals rise from 40 to 60, but survey effort doubles. Explain why a 50% recovery claim is not established and suggest a better evaluation.
Answer and explanation

The raw count rises 50%, but changed detection can contribute. Use comparable effort/methods, suitable reference sites and repeated population/condition indicators; estimate detection where appropriate before attributing recovery.

The raw count rises 50%, but changed detection can contribute. Use comparable effort/methods, suitable reference sites and repeated population/condition indicators; estimate detection where appropriate before attributing recovery.

Response criteria

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

Problem 23

Cover rises from 25% to 55%. What is the increase in percentage points?
Answer and explanation

30 percentage points

55 − 25 = 30.

Problem 24

Why does restored total abundance not guarantee restored biodiversity?
Answer and explanation

The count may be concentrated in fewer species, with altered evenness, composition, genetic diversity, or ecosystem functions.

Problem 25

Independent chapter check: A supplied system loses 80% of its output during disturbance and returns to its initial output after three years. Describe resistance and recovery and explain one limit of that evidence.
Answer and explanation

It has low resistance for this disturbance/output but relatively rapid recovery over the stated interval. Output recovery alone does not establish restored species composition or every ecological function.

It has low resistance for this disturbance/output but relatively rapid recovery over the stated interval. Output recovery alone does not establish restored species composition or every ecological function.

Response criteria

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

Problem 26

A sample has nonzero counts for five species. What is its observed richness?
Answer and explanation

5 species

Richness counts observed species, not all individuals.

Problem 27

Why can equal richness conceal different community structures?
Answer and explanation

Abundance may be uneven, identities may differ, and ecological roles and other diversity levels may differ.

Problem 28

Independent chapter check: Two equal-area reserves have dimensions 100×100 m and 200×50 m. Find their perimeters and explain why shape alone cannot select the best design.
Answer and explanation

Their areas are 10,000 m² and perimeters 400 versus 500 m. Boundary exposure and width differ, but species, habitat quality, connectivity, disturbance, costs and goals determine the useful comparison.

Their areas are 10,000 m² and perimeters 400 versus 500 m. Boundary exposure and width differ, but species, habitat quality, connectivity, disturbance, costs and goals determine the useful comparison.

Response criteria

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

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