Carbon Atom Story Quiz

Quiz · Grade 6 · Science · ngss

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Questions

• Q1. A carbon atom in carbon dioxide (CO₂) is absorbed by an oak tree during photosynthesis. What happens to that carbon atom inside the tree? (MS-LS2-3)

  • It is converted into oxygen and released back into the air.
  • It is used to build sugar molecules that store energy in the tree's cells.
  • It is immediately passed to the soil as a nutrient.
  • It is broken down into smaller atoms by the tree's roots.

  Answer: It is used to build sugar molecules that store energy in the tree's cells.

  Explanation: During photosynthesis, producers like oak trees use CO₂ and water to build glucose (sugar), incorporating the carbon atom into organic molecules. Matter is not destroyed — it changes form and becomes part of the tree's structure.

• Q2. A caterpillar eats a leaf from the oak tree, taking in the carbon atom. Which statement BEST describes what happens to most of that carbon in the caterpillar's body? (MS-LS2-3)

  • All of the carbon is stored permanently in the caterpillar's body.
  • Most of the carbon is released as CO₂ during cellular respiration, while some builds the caterpillar's body.
  • The carbon is destroyed when the caterpillar digests the leaf.
  • The carbon turns into nitrogen so the caterpillar can grow.

  Answer: Most of the carbon is released as CO₂ during cellular respiration, while some builds the caterpillar's body.

  Explanation: Consumers use organic molecules for energy through cellular respiration, releasing CO₂. Only a portion of the carbon is incorporated into the consumer's body tissues. This illustrates why energy decreases at each trophic level while matter cycles.

• Q3. The caterpillar is eaten by a robin. The carbon atom is now in the robin's muscle tissue. What crosscutting concept BEST describes the fact that the carbon atom was never created or destroyed throughout this journey? (MS-LS2-3)

  • Cause and Effect
  • Energy and Matter: Conservation of Matter
  • Structure and Function
  • Scale, Proportion, and Quantity

  Answer: Energy and Matter: Conservation of Matter

  Explanation: The crosscutting concept of Energy and Matter states that matter is conserved — it changes form and moves between organisms and the environment, but the total amount stays the same. The carbon atom changes form but is never created or destroyed.

• Q4. The robin dies and falls to the forest floor. Which organisms are MOST responsible for returning the carbon in the robin's body back to the soil and atmosphere? (MS-LS2-3)

  • Producers, such as grasses and ferns
  • Herbivores, such as deer and rabbits
  • Decomposers, such as fungi and bacteria
  • Carnivores, such as hawks and foxes

  Answer: Decomposers, such as fungi and bacteria

  Explanation: Decomposers break down dead organic matter, releasing nutrients into the soil and carbon dioxide into the atmosphere through cellular respiration. They are essential recyclers that complete the carbon cycle and make nutrients available again for producers.

• Q5. A scientist removes all decomposers from a forest ecosystem in an experiment. Which outcome would MOST LIKELY occur over time? (MS-LS2-4)

  • The forest would grow faster because there would be no competition for nutrients.
  • Dead matter would pile up and nutrients would not be returned to the soil, causing producers to decline.
  • Consumers would take over the role of decomposers and the ecosystem would stay balanced.
  • Carbon dioxide levels in the atmosphere would increase rapidly.

  Answer: Dead matter would pile up and nutrients would not be returned to the soil, causing producers to decline.

  Explanation: Without decomposers, the carbon and nutrient cycle breaks down. Dead organic matter accumulates, nutrients are locked away, and producers lose access to the raw materials they need. This cascades through the entire food web, demonstrating ecosystem interdependence (MS-LS2-4).

• Q6. Carbon moves from the atmosphere into living organisms and back again in a continuous loop. This movement of carbon through living and nonliving parts of an ecosystem is BEST described as — (MS-LS2-3)

  • energy flow
  • trophic transfer
  • the carbon cycle
  • cellular respiration only

  Answer: the carbon cycle

  Explanation: The carbon cycle describes the continuous movement of carbon atoms through the atmosphere, living organisms, soil, and water. Unlike energy, which flows in one direction and is lost as heat, matter like carbon cycles repeatedly through the ecosystem.

• Q7. Which pair of processes works TOGETHER to cycle carbon between living organisms and the atmosphere? (MS-LS2-3)

  • Photosynthesis and cellular respiration
  • Predation and competition
  • Evaporation and condensation
  • Mutation and natural selection

  Answer: Photosynthesis and cellular respiration

  Explanation: Photosynthesis pulls CO₂ from the atmosphere and fixes carbon into organic molecules. Cellular respiration releases CO₂ back into the atmosphere. Together, these two processes form the foundation of the carbon cycle in ecosystems.

• Q8. Humans burn fossil fuels, releasing carbon that was stored underground for millions of years. How does this MOST directly affect the carbon cycle? (MS-LS2-5)

  • It slows down photosynthesis by blocking sunlight.
  • It adds extra carbon dioxide to the atmosphere faster than natural cycles can absorb it.
  • It removes carbon from the food web, harming consumers.
  • It increases the rate of decomposition in forest ecosystems.

  Answer: It adds extra carbon dioxide to the atmosphere faster than natural cycles can absorb it.

  Explanation: Burning fossil fuels rapidly releases carbon that took millions of years to accumulate underground, overwhelming natural cycling processes. This is an example of humans accelerating part of a natural cycle with significant consequences for ecosystems and climate (MS-LS2-5).

• Q9. A student claims: 'When a log rots in the forest, the matter in it disappears.' Which response BEST uses evidence to argue against this claim? (MS-LS2-4)

  • The log does disappear, but its energy is transferred to the next consumer in the food chain.
  • Decomposers break down the log and release its carbon as CO₂ and nutrients into the soil, where they are reused by plants — matter is conserved, not destroyed.
  • The log is converted entirely into water vapor during decomposition.
  • The matter in the log is destroyed, but new matter is created by the decomposers to replace it.

  Answer: Decomposers break down the log and release its carbon as CO₂ and nutrients into the soil, where they are reused by plants — matter is conserved, not destroyed.

  Explanation: This response uses scientific evidence and the principle of conservation of matter to counter the misconception. Decomposition does not destroy matter — it transforms it into forms (CO₂, minerals, water) that re-enter the cycle and support new life (MS-LS2-4).

• Q10. Two communities are debating how to protect a local forest ecosystem. Community A wants to remove all dead trees and logs to 'keep the forest clean.' Community B wants to leave dead wood on the forest floor. Using your understanding of matter cycling, which community's plan BEST supports ecosystem health, and why? (MS-LS2-5)

  • Community A, because removing dead wood prevents disease from spreading to living trees.
  • Community B, because dead wood provides habitat for decomposers that recycle nutrients back into the soil, supporting the entire ecosystem.
  • Community A, because dead trees block sunlight from reaching producers on the forest floor.
  • Community B, because dead wood stores carbon permanently, preventing it from entering the atmosphere.

  Answer: Community B, because dead wood provides habitat for decomposers that recycle nutrients back into the soil, supporting the entire ecosystem.

  Explanation: Dead wood is a critical part of the carbon and nutrient cycle. It supports decomposers (fungi, bacteria, insects) that break down organic matter and return nutrients to the soil for producers to use. Removing it disrupts matter cycling and reduces biodiversity. This is an example of evaluating competing design solutions using evidence (MS-LS2-5).

Grade

• Grade 6

Subject

• Science

Answer Key

• Answer: It is used to build sugar molecules that store energy in the tree's cells.
• Number: 1
• Explanation: Photosynthesis incorporates atmospheric CO₂ into organic glucose molecules, building the tree's structure. Matter changes form but is conserved.
• Answer: Most of the carbon is released as CO₂ during cellular respiration, while some builds the caterpillar's body.
• Number: 2
• Explanation: Consumers release most ingested carbon as CO₂ through respiration; only a fraction is incorporated into body tissues, explaining energy loss between trophic levels.
• Answer: Energy and Matter: Conservation of Matter
• Number: 3
• Explanation: The crosscutting concept of conservation of matter explains that atoms like carbon are never created or destroyed — they change form and location as they cycle through ecosystems.
• Answer: Decomposers, such as fungi and bacteria
• Number: 4
• Explanation: Decomposers are the ecosystem's recyclers. They break down dead organic matter, releasing carbon as CO₂ and returning mineral nutrients to the soil.
• Answer: Dead matter would pile up and nutrients would not be returned to the soil, causing producers to decline.
• Number: 5
• Explanation: Removing decomposers breaks the nutrient cycle. Without recycled nutrients, producers decline, which cascades to all consumers — demonstrating ecosystem interdependence.
• Answer: the carbon cycle
• Number: 6
• Explanation: The carbon cycle describes the continuous movement of carbon atoms through atmosphere, organisms, soil, and water — a repeating loop unlike the one-directional flow of energy.
• Answer: Photosynthesis and cellular respiration
• Number: 7
• Explanation: Photosynthesis fixes atmospheric CO₂ into organic molecules; cellular respiration releases CO₂ back. Together they cycle carbon between organisms and the atmosphere.
• Answer: It adds extra carbon dioxide to the atmosphere faster than natural cycles can absorb it.
• Number: 8
• Explanation: Fossil fuel combustion releases ancient stored carbon rapidly, disrupting the balance of the carbon cycle and demonstrating how human activity can overwhelm natural processes.
• Answer: Decomposers break down the log and release its carbon as CO₂ and nutrients into the soil, where they are reused by plants — matter is conserved, not destroyed.
• Number: 9
• Explanation: This answer correctly applies conservation of matter and describes the role of decomposers in transforming, not destroying, the matter in dead organic material.
• Answer: Community B, because dead wood provides habitat for decomposers that recycle nutrients back into the soil, supporting the entire ecosystem.
• Number: 10
• Explanation: Dead wood supports decomposer communities essential to nutrient cycling. Removing it disrupts matter cycling and biodiversity. Community B's solution is supported by evidence about how ecosystems function (MS-LS2-5).

Difficulty

• Medium

Total Questions

• 10

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