The Nitrogen Cycle and the Microbes That Drive It · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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The Nitrogen Roundabout

Science · Organisms & Life Processes · ages 17-18
Name ______________________   Date ____________

  1. What is ammonification?

    • Nitrates turning back into nitrogen gas
    • Ammonium turning into nitrites
    • Dead matter and urea to ammonium

  2. What happens during nitrogen fixation?

    • Nitrogen gas to ammonia and ammonium
    • Plants turn nitrates back into nitrogen gas
    • Lightning turns ammonium into nitrites

  3. What do nitrifying bacteria do?

    • Ammonium to nitrites then nitrates
    • Turn nitrates back into nitrogen gas
    • Turn nitrogen gas into ammonium

  4. A field floods for weeks. What happens to its soil nitrates?

    • They rise as nitrifiers work faster
    • They stay locked because all microbes stop
    • They are lost to the air as denitrification speeds up

  5. What is denitrification, and when does it thrive?

    • Nitrates to nitrogen gas, where oxygen runs short
    • Ammonium to nitrates, where oxygen is plentiful
    • Nitrogen gas to ammonia, inside root nodules

  6. How does cycled nitrogen differ from flowing energy?

    • Nitrogen flows one way while energy cycles
    • Nitrogen cycles round while energy leaves as heat
    • Both leave the ecosystem as heat

  7. A student says nitrogen, like energy, flows one way through ecosystems. This claim is true.

    Circle one:   True   False

  8. A farmer drains a waterlogged field. Which bacteria gain, and which lose?

    • Denitrifiers gain and nitrifiers lose
    • Both groups gain equally
    • Nitrifiers gain and denitrifiers lose
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Answer key

For grown-ups. Fold this page away before handing over the rest.

The Nitrogen Roundabout W1-mt__K1J47NhWj-s1

  1. Dead matter and urea to ammonium · Decomposers and ammonifying bacteria release ammonium from waste and remains.
  2. Nitrogen gas to ammonia and ammonium · Fixing bacteria turn the air's nitrogen into forms plants can use.
  3. Ammonium to nitrites then nitrates · Nitrifiers oxidise ammonium stepwise to nitrites and then nitrates, using oxygen.
  4. They are lost to the air as denitrification speeds up · Flooded soil lacks oxygen, so nitrification stalls while denitrifiers convert nitrates to gas.
  5. Nitrates to nitrogen gas, where oxygen runs short · Denitrifiers reduce nitrates back to gas, and they multiply where oxygen runs out.
  6. Nitrogen cycles round while energy leaves as heat · Nitrogen atoms are reused again and again, while energy passes through once and escapes as heat.
  7. False · Nitrogen cycles between air, soil, and living things. Only energy flows one way.
  8. Nitrifiers gain and denitrifiers lose · Air returning revives the oxygen-needing nitrifiers and suppresses the denitrifiers.
Worksheet · LightMySky