An introductory Day 1 biology lesson investigating how plants acquire carbon from atmospheric carbon dioxide and return it through combustion, tracking atoms to demonstrate the conservation of matter across Earth systems (BI-LS2-5 and BI-LS2-4).
4. Did the remaining 9.9 kg of matter get destroyed or converted into pure heat? Based on your knowledge of matter, what actually happened to those carbon atoms?
4
Part 4: The Atom-Counting Balance Sheet (BI-LS2-4)
Conservation of Matter
When wood fuel (represented here by glucose monomer \(\text{C}_6\text{H}_{12}\text{O}_6\)) burns in atmospheric oxygen (\(\text{O}_2\)), it undergoes complete combustion:
5. Use your findings from today to explain how carbon cycles between the Atmosphere and Biosphere. Include the roles of both photosynthesis and combustion, and explicitly state what happens to the atoms during both events.
Page 2 of 2 • Carbon Trackers Student Investigation
Combustion Solutions, Atom Inventory & Evaluation Rubric
Complete answer keys for Parts 3, 4, and 5 with standard-aligned scoring criteria.
3 Part 3: Burning the Timber (Exemplar)
3 Points
4. Where did the missing 9.9 kg of matter go? Did it turn into pure energy?
Exemplar: Matter was not destroyed or converted into pure energy. In accordance with the Law of Conservation of Mass, the 9.9 kg of solid wood reacted with atmospheric \(\text{O}_2\) to form invisible gases—primarily carbon dioxide (\(\text{CO}_2\)) and water vapor (\(\text{H}_2\text{O}\))—that escaped into the atmosphere with smoke and hot air. The 0.1 kg ash left behind consists solely of non-flammable mineral nutrients (like potassium, calcium, magnesium) the tree took up from soil.
4 Part 4: Completed Atom-Counting Table (BI-LS2-4)
Conclusion: Exactly 36 atoms enter the combustion reaction and 36 atoms emerge; matter is 100% conserved.
5 Part 5: Synthesis Model & Rubric (BI-LS2-5)
3 Points
Exemplar Model Explanation:
"Carbon flows in a continuous cycle between the atmosphere and biosphere. During photosynthesis, trees absorb atmospheric \(\text{CO}_2\) gas through leaf stomata, fixing the carbon atoms into solid glucose and wood fibers (biosphere). When that wood is burned as fuel during combustion, the carbon atoms react with \(\text{O}_2\) and return right back into the atmosphere as \(\text{CO}_2\) gas. Throughout this entire cycle, no atoms are ever created or destroyed; they only change chemical bonds and physical states."
Level 4: Advanced
Level 3: Proficient
Level 2: Developing
Level 1: Novice
Thoroughly explains bidirectional carbon flow between Atmosphere & Biosphere; correctly explains atom conservation and identifies \(\text{CO}_2\) in air and combustion gas.
Identifies that carbon comes from atmospheric \(\text{CO}_2\) and returns via burning; correctly counts atoms in combustion table with zero errors.
Understands trees take carbon from air, but struggles to explain where combustion products go or has minor calculation errors in atom table.
Maintains misconception that tree mass comes from soil or that burning destroys matter; atom table incomplete.
Page 2 of 2 • Teacher Answer Key: Carbon Trackers
How do microscopic sugar molecules build thousands of pounds of rock-hard timber?
Molecular Hierarchy: Gas ⟶ Glucose ⟶ Cellulose Wood 50% Carbon by Dry Weight
1. Glucose Sugar (C₆H₁₂O₆) C₆ Ring Link 2. Cellulose Chain (Polymer) Tens of thousands of linked C-atoms Build 3. Solid Wood Trunk Rigid Biosphere Fiber
Summary: Wood is literally crystallized atmospheric carbon bonded by solar energy. Atmosphere ⟶ Biosphere
The Reversal • Fire & Smoke 05 / 07
Where Does Mass Go When Wood Burns?
You place a 10.0 kg oak log on a campfire. By morning, only 0.1 kg of ash remains.
Combustion Infographic 9.9 kg CO₂ Gas + H₂O Vapor Escapes Back into Atmosphere! 10.0 kg Wood Fuel 0.1 kg Ash
Did the Wood Turn into Pure Energy?
NO! Chemical bonds release thermal energy (heat/light), but physical atoms can never be destroyed!
The Mass Returned to the Sky
The 9.9 kg reacted with atmospheric \(\text{O}_2\) and dissolved right back into the air as invisible \(\text{CO}_2\) gas and steam.
The Great Return: Combustion reverses photosynthesis! Biosphere ⟶ Atmosphere
Law of Conservation: Not a single atom ceased to exist. They simply traded bonds. 100% Mass Conserved
BI-LS2-5 • The Earth Systems Model 07 / 07
The Bidirectional Carbon Cycle
Connecting the Atmosphere and Biosphere across Earth systems.
ATMOSPHERE CO₂ Gas Invisible Reservoir PHOTOSYNTHESIS (Fixes Gas into Wood) BIOSPHERE Wood Cellulose Living Organic Matter COMBUSTION / FIRE (Releases Wood back to Gas)
Day 2 Preview: How living organisms return carbon without fire (Cellular Respiration). Earth System Model Active
