Skip to content
Study Hall
← Unit 2: Sustainable Ecosystems & Climate Change

SNC1W · Unit 2 test review

Sustainable Ecosystems & Climate Change: Test Review

Everything for the Unit 2 test on one page: the key facts from all 7 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

Earth's Spheres and Ecosystem Components

  • The four spheres are the atmosphere (air), hydrosphere (water), lithosphere (rock and soil) and biosphere (life); they overlap and constantly interact.
  • Biotic factors are the living parts of an ecosystem; abiotic factors are the non-living parts such as sunlight, temperature, water, soil and pH.
  • Levels of organization: organism → population (one species) → community (many species) → ecosystem (community + abiotic factors) → biosphere.
  • A change in one sphere usually causes changes in the others.
  • Ecosystem services are benefits nature provides, such as clean water, pollination, carbon storage and soil formation.

Energy Flow: Food Chains, Food Webs and Trophic Levels

  • Producers make their own food (mostly by photosynthesis); consumers eat other organisms; decomposers break down dead matter and recycle nutrients.
  • Food-chain and food-web arrows point from the food to the eater: the direction energy flows.
  • Trophic levels: 1st = producers, 2nd = primary consumers, 3rd = secondary consumers, 4th = tertiary consumers.
  • 10% rule: about 10% (roughly 5% to 20%) of the energy at one level is passed to the next; .
  • The rest of the energy is used for life processes such as movement and body heat, lost as heat, or never eaten or digested.
  • Energy flows one way through an ecosystem and must be constantly resupplied by the Sun; matter is recycled.

Photosynthesis and Cellular Respiration

  • Photosynthesis: in chloroplasts, using chlorophyll to absorb light.
  • Cellular respiration: in mitochondria.
  • Photosynthesis stores light energy as chemical energy in glucose; respiration releases it as ATP and heat.
  • Plants carry out both processes; animals and fungi carry out only respiration.
  • The products of each process are the reactants of the other, so they are complementary: matter cycles, energy flows through.

Cycling of Matter: Carbon, Nitrogen and Water Cycles

  • Matter cycles; energy flows. Earth's atoms are reused over and over among the four spheres.
  • Water cycle: evaporation, transpiration, condensation, precipitation, runoff and infiltration, driven by the Sun and gravity.
  • Carbon is removed from the air by photosynthesis and returned by respiration, decomposition and combustion; a sink stores more carbon than it releases, a source releases more than it stores.
  • Nitrogen cycle: fixation (bacteria, lightning) → nitrification (to nitrates) → plant uptake → animals → decomposition → denitrification back to nitrogen gas.
  • Dynamic equilibrium: inputs and outputs of a reservoir balance, so the amount stays about steady even though matter keeps moving.
  • Human activity has raised atmospheric carbon dioxide from about 280 ppm before industrialization to over 420 ppm, and greatly increased fixed nitrogen through fertilizer.

Biodiversity, Succession and Ecosystem Sustainability

  • Biodiversity has three levels: genetic, species and ecosystem diversity; higher biodiversity usually means a more resilient ecosystem.
  • Population change
  • Carrying capacity is the largest population an ecosystem can support over the long term; limiting factors such as food, space, disease and predators keep populations near it.
  • Primary succession starts on bare rock with no soil (pioneer species: lichens, mosses); secondary succession starts where soil remains after a disturbance and is faster.
  • Indicator species (lichens, frogs, mayfly larvae) reveal air quality, water quality and ecosystem health.
  • A sustainable ecosystem keeps functioning over the long term in dynamic equilibrium: populations, nutrients and conditions fluctuate around a balance.

Human Impacts on Ecosystems

  • Habitat loss and fragmentation are the biggest threats to biodiversity; wildlife corridors and protected areas help.
  • Invasive species spread fast and harm native species because they lack natural predators and diseases in their new home (Ontario examples: zebra mussel, emerald ash borer, purple loosestrife).
  • Eutrophication: excess nutrients → algal bloom → algae die → decomposers use up dissolved oxygen → fish die (dead zones).
  • Biomagnification: persistent toxins (mercury, DDT, PCBs) become more concentrated at each higher trophic level, so top predators are most affected.
  • Overharvesting takes a species faster than it can reproduce (passenger pigeon, northern cod).
  • Sustainable farming practices include cover crops, crop rotation, no-till, precision agriculture, integrated pest management and vertical farming.

Climate Change and Ecosystems

  • Climate is the long-term average of weather; climate change is a long-term shift in those patterns.
  • Human activities (burning fossil fuels, deforestation, livestock, fertilizer, landfills) add carbon dioxide, methane and nitrous oxide, enhancing the greenhouse effect.
  • Indicators: rising temperatures (Canada roughly 1.7 to 2× the global rate, the North more than 2×, the Arctic nearly 4×), carbon dioxide over 420 ppm, shrinking sea ice and glaciers, thawing permafrost, rising sea level, earlier springs and more extremes.
  • Ecosystem impacts include range shifts, timing mismatches, warmer lakes, sea-ice loss, more pests and more wildfire.
  • Indigenous practices such as the Three Sisters, cultural burning and seasonal harvesting reflect an understanding of dynamic equilibrium; Two-Eyed Seeing combines Indigenous and Western knowledge.
  • Mitigation reduces greenhouse gas emissions or increases sinks; adaptation adjusts to changes that are already happening.

Where marks get lost

  • Calling the biosphere a separate layer above or below the others. The biosphere overlaps all three other spheres: life is found in the air, in water and in soil and rock. (Earth's Spheres and Ecosystem Components)
  • Classifying something as biotic because living things make it or use it. Oxygen, water and minerals are abiotic even though living things depend on them. (Earth's Spheres and Ecosystem Components)
  • Mixing up population and community. A population is one species; a community is all the species in the area. (Earth's Spheres and Ecosystem Components)
  • Forgetting that an ecosystem includes the non-living parts. A list of only living things is a community, not an ecosystem. (Earth's Spheres and Ecosystem Components)
  • Thinking ecosystems are always large. A rotting log or a puddle can be an ecosystem if it has living and non-living parts interacting. (Earth's Spheres and Ecosystem Components)
  • Drawing food-chain arrows from the predator to the prey. Arrows point from the food to the eater, showing the direction energy flows. (Energy Flow: Food Chains, Food Webs and Trophic Levels)
  • Thinking the 10% rule is exact. It is an average; real transfers range from about 5% to 20%, so use the percentage given in a question. (Energy Flow: Food Chains, Food Webs and Trophic Levels)
  • Multiplying by 0.10 when working down the pyramid. Going from a higher level back toward the producers, divide by 0.10 (multiply by 10). (Energy Flow: Food Chains, Food Webs and Trophic Levels)
  • Saying the "lost" 90% of energy disappears. Energy is never destroyed; it is used for life processes and ends up as heat that leaves the ecosystem, or stays in material that was not eaten. (Energy Flow: Food Chains, Food Webs and Trophic Levels)
  • Leaving decomposers out of an ecosystem's energy story. They get energy from dead material at every trophic level and recycle the nutrients. (Energy Flow: Food Chains, Food Webs and Trophic Levels)
  • Saying plants do not carry out cellular respiration. Plants respire all the time in their mitochondria; they also photosynthesize when there is light. (Photosynthesis and Cellular Respiration)
  • Treating breathing and cellular respiration as the same thing. Breathing moves air in and out of lungs; cellular respiration is a chemical reaction inside cells. (Photosynthesis and Cellular Respiration)
  • Writing that respiration "makes" energy. Energy is not created; respiration releases chemical energy that was stored in glucose by photosynthesis. (Photosynthesis and Cellular Respiration)
  • Mixing up the reactants and products. Photosynthesis uses carbon dioxide and water; respiration produces them. (Photosynthesis and Cellular Respiration)
  • Thinking plants get their mass from the soil. Most of a plant's dry mass is built from carbon dioxide taken from the air; soil supplies water and small amounts of minerals. (Photosynthesis and Cellular Respiration)
  • Saying energy is recycled like matter. Matter cycles, but energy flows one way and leaves as heat, so ecosystems need constant sunlight. (Cycling of Matter: Carbon, Nitrogen and Water Cycles)
  • Thinking plants can take nitrogen gas straight from the air. Plants absorb fixed nitrogen (mainly nitrates) from the soil; only certain bacteria, lightning and human processes (fertilizer factories and high-temperature burning in engines) can fix nitrogen gas. (Cycling of Matter: Carbon, Nitrogen and Water Cycles)
  • Mixing up nitrogen fixation and denitrification. Fixation turns nitrogen gas into usable compounds; denitrification turns nitrates back into nitrogen gas. (Cycling of Matter: Carbon, Nitrogen and Water Cycles)
  • Calling the carbon dioxide from fossil fuels "natural" because fossil fuels are natural. The carbon had been locked away for millions of years; releasing it quickly adds new carbon to today's active cycle. (Cycling of Matter: Carbon, Nitrogen and Water Cycles)
  • Thinking dynamic equilibrium means nothing is changing. Matter is moving all the time; only the overall amounts in each reservoir stay steady. (Cycling of Matter: Carbon, Nitrogen and Water Cycles)
  • Thinking biodiversity just means the number of animals. It includes all organisms (plants, fungi, microorganisms) and three levels: genetic, species and ecosystem diversity. (Biodiversity, Succession and Ecosystem Sustainability)
  • Mixing up primary and secondary succession. Ask whether soil is present: no soil means primary; soil remaining after a disturbance means secondary. (Biodiversity, Succession and Ecosystem Sustainability)
  • Believing a population at carrying capacity stays exactly constant. It fluctuates up and down around the carrying capacity. (Biodiversity, Succession and Ecosystem Sustainability)
  • Forgetting immigration and emigration when calculating population change. Movement in and out matters as much as births and deaths. (Biodiversity, Succession and Ecosystem Sustainability)
  • Assuming every disturbance is harmful. Fires and floods are natural parts of many ecosystems and start secondary succession; some species, like jack pine, depend on fire. (Biodiversity, Succession and Ecosystem Sustainability)
  • Thinking any non-native species is invasive. A species is invasive only if it spreads and causes harm; many introduced crops and garden plants are not invasive. (Human Impacts on Ecosystems)
  • Mixing up bioaccumulation and biomagnification. Bioaccumulation is buildup within one organism over time; biomagnification is the increase from one trophic level to the next. (Human Impacts on Ecosystems)
  • Saying the algae themselves use up the oxygen in eutrophication. Living algae release oxygen in daylight; it is mostly decomposers breaking down dead algae that use up the dissolved oxygen. (Human Impacts on Ecosystems)
  • Believing fertilizer is always harmful. Fertilizer helps feed people; the problem is extra fertilizer that crops do not use and that washes into water. (Human Impacts on Ecosystems)
  • Assuming top predators get toxins mainly from the water. Most of a top predator's toxin load comes from the food it eats, which is why concentrations rise up the food chain. (Human Impacts on Ecosystems)
  • Mixing up weather and climate. One cold week does not disprove climate change; climate is the average over 30 or more years. (Climate Change and Ecosystems)
  • Thinking the greenhouse effect itself is bad. The natural greenhouse effect keeps Earth livable; the problem is the extra warming from added greenhouse gases. (Climate Change and Ecosystems)
  • Assuming Canada warms at the same rate as the rest of the world. Canada has warmed roughly 1.7 to 2 times as fast as the global average, and the North even faster. (Climate Change and Ecosystems)
  • Confusing mitigation and adaptation. Mitigation tackles the cause (emissions); adaptation deals with the effects. (Climate Change and Ecosystems)
  • Describing Indigenous knowledge as one single set of practices. Practices differ between nations and places, so name the community (for example, Haudenosaunee Three Sisters, Anishinaabe manoomin harvesting). (Climate Change and Ecosystems)

Practice test

21 questions from across the unit. Each one shows the lesson it comes from.

  1. Earth's Spheres and Ecosystem Components
    1
    Match each sphere to an example that belongs mainly to it.
    Atmosphere
    Hydrosphere
    Lithosphere
    Biosphere
  2. Earth's Spheres and Ecosystem Components
    2
    What term means all the members of one species living in the same area at the same time?
  3. Earth's Spheres and Ecosystem Components
    3
    A student lists "spruce trees, snowshoe hares, lynx, mosses and fungi in one forest." What has the student described?
  4. Energy Flow: Food Chains, Food Webs and Trophic Levels
    4
    Put this Ontario lake food chain in order, starting with the producer.
    1. 1Zooplankton
    2. 2Northern pike
    3. 3Yellow perch
    4. 4Algae
  5. Energy Flow: Food Chains, Food Webs and Trophic Levels
    5
    Match each organism to its main role in an ecosystem.
    Sugar maple
    White-tailed deer
    Grey wolf hunting deer
    Shelf fungus on a dead tree
  6. Energy Flow: Food Chains, Food Webs and Trophic Levels
    6
    Using the same area of farmland, why can more people be fed on a diet of grains and beans than on a diet of beef from grain-fed cattle?
  7. Photosynthesis and Cellular Respiration
    7
    Which organisms carry out cellular respiration?
  8. Photosynthesis and Cellular Respiration
    8
    A sealed jar holds a potted plant and is kept in complete darkness for two days. What happens to the carbon dioxide level in the jar?
  9. Photosynthesis and Cellular Respiration
    9
    On a sunny summer afternoon, what is the overall gas exchange of a healthy maple tree?
  10. Cycling of Matter: Carbon, Nitrogen and Water Cycles
    10
    Why can't most plants use the nitrogen gas that makes up about 78% of the air?
  11. Cycling of Matter: Carbon, Nitrogen and Water Cycles
    11
    Which of these is acting as a carbon sink?
  12. Cycling of Matter: Carbon, Nitrogen and Water Cycles
    12
    A farmer plants clover in a field one year and corn the next. Why might the corn need less nitrogen fertilizer?
  13. Biodiversity, Succession and Ecosystem Sustainability
    13
    Why is an ecosystem with high biodiversity usually more resilient?
  14. Biodiversity, Succession and Ecosystem Sustainability
    14
    Match each indicator to what it tells you.
    Many kinds of lichens on trees
    Mayfly and stonefly larvae in a stream
    Dark, crumbly soil full of earthworms
    Frog populations suddenly declining
  15. Biodiversity, Succession and Ecosystem Sustainability
    15
    Beavers build dams that create ponds used by fish, frogs, ducks and moose. Removing the beavers would change the whole ecosystem. What kind of species is the beaver?
  16. Human Impacts on Ecosystems
    16
    Put the steps of eutrophication in order.
    1. 1Fish suffocate and a dead zone forms
    2. 2Decomposers break down the dead algae, using up dissolved oxygen
    3. 3Large numbers of algae die and sink
    4. 4Fertilizer runoff adds extra nutrients to a lake
    5. 5Algae grow rapidly, forming an algal bloom
  17. Human Impacts on Ecosystems
    17
    Why did DDT harm ospreys and bald eagles much more than the insects it was sprayed on?
  18. Human Impacts on Ecosystems
    18
    A new highway is built through a large forest, splitting it into two halves. Which impact is this?
  19. Climate Change and Ecosystems
    19
    Which of these is an indicator of climate change rather than a cause?
  20. Climate Change and Ecosystems
    20
    A remote First Nation in northern Ontario depends on a winter road for fuel and building supplies. Which climate change impact most directly threatens this?
  21. Climate Change and Ecosystems
    21
    Lake trout need cold, oxygen-rich water. Why do warmer summers threaten them in many Ontario lakes?

Endless drill

Fresh numbers every time, for the calculation questions in this unit.

Endless drillnew numbers every time

Generating a problem…

Keep going