The Carbon Cycle · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The Carbon Cycle

Science · Ecosystems & Habitats · ages 12-13
Name ______________________   Date ____________

  1. A carbon cycle diagram has boxes for atmosphere, plants, animals, and dead matter. An arrow points from 'dead matter' to 'atmosphere'. Which process does that arrow show?

    AtmospherePlantsAnimalsDead matter
    • Photosynthesis
    • Decomposition
    • Feeding

  2. Which process takes carbon dioxide out of the air and turns it into sugar inside a plant?

    • Photosynthesis
    • Respiration
    • Decomposition

  3. True or false: respiration, combustion, and decomposition all release carbon dioxide back into the air.

    Circle one:   True   False

  4. A cow eats grass, then breathes out. Which process is happening when the cow breathes out carbon dioxide?

    • Respiration
    • Photosynthesis
    • Decomposition

  5. Carbon that was floating in the air becomes part of a tree's wood. Which process moved that carbon into the tree?

    • Respiration
    • Combustion
    • Photosynthesis

  6. How does burning fossil fuels affect the carbon cycle?

    • It removes carbon dioxide from the air
    • It adds extra CO2 to the air
    • It has no effect on the carbon cycle

  7. The carbon in a wooden table originally came from carbon dioxide in the air. Which path did it take to get there?

    • CO2 in air, absorbed by a tree through photosynthesis, built into wood
    • CO2 in air, eaten by an animal, passed into the tree
    • CO2 in air, released by decomposition, absorbed by the tree

  8. A student says cutting down forests only matters because animals lose their homes. What carbon cycle role are they missing?

    • Forests release CO2 through decomposition
    • Forests have no role in the carbon cycle
    • Forests store carbon and remove CO2
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Answer key

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

The Carbon Cycle W1-mt_Be1A88GUpu-s1

  1. Decomposition · Decomposers break down dead matter and release the stored carbon back into the air as CO2.
  2. Photosynthesis · Photosynthesis uses CO2 from the air and builds it into sugar inside the plant.
  3. True · All three break down carbon-containing material and release CO2 as a result.
  4. Respiration · Respiration breaks down food for energy and releases CO2 as a waste product.
  5. Photosynthesis · Photosynthesis is the only process here that pulls CO2 from the air into the plant.
  6. It adds extra CO2 to the air · Fossil fuels store carbon that took millions of years to lock away, so burning them adds it back much faster than plants can take it out again.
  7. CO2 in air, absorbed by a tree through photosynthesis, built into wood · The tree absorbed the CO2 directly through photosynthesis and used the carbon to build its wood.
  8. Forests store carbon and remove CO2 · Fewer trees means less CO2 pulled from the air, so deforestation adds to the carbon buildup even without any burning.
Worksheet · LightMySky