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Biology 20

Biology 20 · Worksheets

Mixed review · Biosphere and ecosystems

Ten questions of mixed difficulty, covering Ecosystems and change, the biosphere. Print it, or work through it on screen — the answer key starts on its own page.

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Mixed review · Biosphere and ecosystems

Biology 20 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. Decomposers are essential to nutrient cycles because they

    1. a) fix nitrogen from the atmosphere
    2. b) produce oxygen for consumers
    3. c) break organic matter down into inorganic forms producers can take up again
    4. d) store carbon permanently in the soil

  2. Primary succession begins

    1. a) in an abandoned farm field
    2. b) after a forest fire
    3. c) only in the Arctic
    4. d) on bare rock or other ground with no soil

  3. The carrying capacity of an environment is

    1. a) the number of species present
    2. b) the largest population it can sustain indefinitely
    3. c) the largest population ever recorded there
    4. d) the rate at which a population grows

  4. Burning fossil fuels raises atmospheric CO₂ because it

    1. a) stops plants from photosynthesizing
    2. b) prevents carbon from dissolving in the oceans
    3. c) releases carbon from a long-term store faster than natural processes can remove it
    4. d) creates new carbon atoms

  5. In a predator–prey cycle, the predator population peaks

    1. a) at exactly the same time
    2. b) shortly before the prey population peaks
    3. c) independently of the prey
    4. d) shortly after the prey population peaks

  6. Nitrogen fixation is the conversion of

    1. a) nitrate back into N₂ gas
    2. b) ammonium into nitrate by plants
    3. c) protein into ammonia by decomposers
    4. d) atmospheric N₂ into ammonia or ammonium, largely by bacteria

  7. In a population of insects sprayed repeatedly with the same insecticide, resistance becomes common because

    1. a) the insecticide caused the insects to develop resistance
    2. b) resistant insects immigrated from elsewhere
    3. c) a few individuals were already resistant and survived to reproduce
    4. d) the insects learned to avoid the spray

  8. Carbon enters the living part of an ecosystem mainly by

    1. a) decomposition
    2. b) respiration
    3. c) combustion
    4. d) photosynthesis

  9. A climax community is one that

    1. a) never changes at all
    2. b) contains only one species
    3. c) has the fewest species of any stage
    4. d) remains relatively stable until a major disturbance

  10. The two abiotic factors that most determine which biome develops in a region are

    1. a) day length and oxygen level
    2. b) temperature and precipitation
    3. c) soil pH and wind
    4. d) latitude and altitude

Answer key · Mixed review · Biosphere and ecosystems

Biology 20 · maddyhelps.com

  1. c) break organic matter down into inorganic forms producers can take up again — Without decomposition, nutrients would stay locked in dead tissue and the cycles would stop. Decomposers are heterotrophs, but they are the step that returns matter to the abiotic pool.
  2. d) on bare rock or other ground with no soil — Primary succession starts where there is no soil at all, such as new lava or land exposed by a retreating glacier. Secondary succession starts where a community was destroyed but the soil survived.
  3. b) the largest population it can sustain indefinitely — Carrying capacity is set by whatever runs short first — food, water, nesting sites. A population can briefly overshoot it, but not for long, and usually at a cost.
  4. c) releases carbon from a long-term store faster than natural processes can remove it — Fossil fuels are carbon that was taken out of circulation over millions of years. Burning them returns it in a couple of centuries, and photosynthesis and ocean uptake cannot absorb it at that rate.
  5. d) shortly after the prey population peaks — Predators need time to convert abundant prey into offspring, so their peak lags behind. The lag is what makes the two populations oscillate instead of settling at a fixed pair of numbers.
  6. d) atmospheric N₂ into ammonia or ammonium, largely by bacteria — Atmospheric nitrogen is nearly 80% of the air but is locked in a triple bond that most organisms cannot break. Nitrogen-fixing bacteria, many of them living in legume root nodules, do the breaking.
  7. c) a few individuals were already resistant and survived to reproduce — The spray does not create resistance; it selects for whatever resistance already existed by chance. This is why partial treatment and repeated use are such effective ways to breed a resistant pest.
  8. d) photosynthesis — Photosynthesis takes inorganic CO₂ from the air and fixes it into organic molecules. Respiration, combustion and decomposition all send carbon the other way, back into the atmosphere.
  9. d) remains relatively stable until a major disturbance — It is the stage that persists because the species present can reproduce under the conditions they themselves create. Stable does not mean frozen — individuals are still replaced constantly.
  10. b) temperature and precipitation — Latitude and altitude matter because of what they do to temperature and rainfall. Plotting average temperature against annual precipitation predicts the biome remarkably well.