A comprehensive upper-elementary science lesson where fourth and fifth graders explore forest floor chemistry, decomposer networks, and nutrient cycling through simulation and chemical breakdown tracking.
• Delivers nitrogen and phosphorus to baby saplings
• Prevents forest soil from eroding away in storms
Key takeaway: Decomposers digest food on the outside, leaving rich soil for plants Slide 4 of 6
Hands-On Investigation
The Breakdown Network Simulation
Station 1
Shredder
Millipede or Woodlouse
Crushes intact leaf debris into small surface bits.
Takes: 4 Big Debris
Passes: 4 Crumb Tokens
Station 2
Hyphae
White Rot Fungus
Releases enzymes to break complex polymers.
Takes: 4 Crumbs
Passes: 2 Simple Sugars
Station 3
Bacteria
Soil Microbes
Frees locked nitrogen and phosphorus minerals.
Takes: 2 Sugars
Passes: 2 Free Minerals
Station 4
Sapling
New Oak Sprout
Absorbs liberated minerals to grow fresh leaves.
Takes: 2 Minerals
Produces: 1 New Leaf!
Simulation Rule: If any link stops, the entire forest runs out of soil nutrients! Time: 20 Minutes
Get your role cards and token trays ready with your table team Slide 5 of 6
Lesson Debrief
Matter Cycles • Energy Flows
Matter Cycles in Loops
The very same carbon and nitrogen atoms inside an ancient fallen tree will be built into the twigs of a young seedling next spring.
No matter is ever created from nothing, and no matter is ever destroyed.
Energy Flows One Way
Solar energy trapped in leaf sugars is released as heat during decomposition. Energy does NOT cycle back to the sun!
Living organisms require a continuous input of fresh sunlight to survive.
Next Step: Complete your 3-question Nutrient Cycle Cool Down Slide 6 of 6
4 Recycled Forever
Every single atom of carbon in an oak acorn may have passed through a millipede's stomach or a fungus's hyphae ten times over a thousand years. While solar energy flows away as warm metabolic heat, forest matter never disappears—it is locked in an endless dance of rebirth.
Unit 5-LS2 • The Midnight Decomposer Page 1 of 2 • Reading Passage
Reading Comprehension & Pathway Analysis
Demonstrate your understanding of forest floor biochemical breakdown.
Student Task
A Key Concept Check (Circle the Best Scientific Choice)
1. How does the feeding method of a millipede (detritivore) differ from a fungus?
A. Millipedes use photosynthesis; fungi eat dirt.
B. Millipedes chew debris mechanically; fungi digest it externally.
C. Millipedes release enzymes; fungi chew with jaws.
D. Both digest leaves entirely inside a stomach cavity.
2. What role do fungal hyphae play during chemical breakdown on a fallen log?
A. They squirt out enzymes to dissolve wood and absorb nutrients.
B. They catch sunlight to manufacture glucose like tree leaves.
C. They produce seeds that sprout into tiny oak seedlings.
D. They freeze moisture so bacteria cannot survive in the soil.
B The Carbon Trail: Order the Breakdown Steps (Number 1 to 4)
Step [ ]
Fungal hyphae squirt enzymes, dissolving complex wood into nutrient soup.
Chemical Dissolution
Step [ ]
A mature oak tree sheds golden leaves onto the autumn forest floor.
Organic Litter Drop
Step [ ]
Roots of a new baby oak sapling absorb nitrogen and minerals from dark humus.
Plant Uptake
Step [ ]
Millipedes and pill bugs chew big tough leaves into tiny moist crumbs.
Mechanical Shredding
C Scientific Reasoning & Ecosystem Impact
A student claims: "Decomposers are only garbage disposals; a forest would be much healthier and cleaner without bacteria and rotting fungi everywhere." Use evidence from the text to refute this claim. Explain what would happen to living trees if all decomposers were eliminated.
Unit 5-LS2 • The Midnight Decomposer Page 2 of 2 • Student Activity
Synthesize data patterns to explain nutrient cycles and energy dissipation.
Post-Lab Analysis
A Model the Network: Draw Flow Arrows & Heat Dissipation
In the space below, connect the 4 organisms with solid arrows for Nutrient Movement. Add squiggly arrows showing where Metabolic Heat Energy escapes into the surrounding air.
[ Dead Oak Leaf Litter ] [ Millipede Shredder ]
(Draw arrows showing matter flow and thermal energy loss)
[ Fungal Hyphae & Bacteria ] [ Baby Oak Sapling ]
B Biomass Breakdown Math Comparison
Simulation Condition
Starting Tokens
Remaining Debris
Tokens Converted to Humus
Total Leaves Grown
Round 1: Healthy Forest
24
Round 2: Disturbed (No Fungi)
24
C Systems Reflection Prompts
1. In Round 2, the millipedes still shredded the leaves into crumbs. Why were the oak saplings still unable to grow new leaves?
2. Autumn weather brings colder temperatures. How does freezing weather affect the speed of decomposers? What happens to dead leaves under snow?
Unit 5-LS2 • The Midnight Decomposer Page 2 of 2 • Student Activity Sheet
