Why is a trophic transfer percentage not a universal constant?
Submit: An evidence record, explanation and revision.
Related lesson: Ecology: Population Dynamics
This is a teacher-led extension beyond the short lesson. The task supplies a performance opportunity; completion alone does not certify mastery, full NGSS coverage or state alignment.
Teacher review guideBuild the idea
Only part of the energy available at one trophic level becomes new biomass available to the next. Organisms use energy, release heat and leave material in waste or uneaten remains. Matter is conserved through these pathways, while energy is ultimately dispersed. Transfer percentages depend on the system and what quantities are compared.
Science / engineering practice
Using mathematics and computational thinkingCore idea
Matter and energy transfer among trophic levelsCrosscutting concept
Energy and matterEvidence and model inputs
Invented annual budget in kJ for a defined meadow: producer net biomass energy 10,000; herbivore consumption 2,000; unconsumed producer material 8,000. Of the consumed energy, 500 enters herbivore biomass, 400 leaves as waste and 1,100 transfers through respiration/heat pathways. Separate carbon card: 100 kg C consumed → 25 kg retained + 20 kg waste + 55 kg returned through respiration.
Keep actual observations, published findings and invented model cases labeled separately. If a source or required equipment is unavailable, pause that part with a teacher; do not invent results.
Materials and preparation
Paper, graph paper or spreadsheet, and the linked readings.
Grade-level scope
Use proportional reasoning; avoid universal efficiency rules or confusing energy units with matter mass.
Do the work
- Verify both budgets sum and draw labeled pathways.
- Calculate producer-biomass-to-herbivore-biomass transfer and consumed-energy-to-new-biomass efficiency.
- Explain why the percentages differ: their denominators differ.
- Account for decomposer access to waste and unconsumed material without recycling energy back to the producer input.
- Revise an explanation that assumes exactly 10% transfers at every step.
Learner worksheet
Write on paper or type here and print. Entries stay in this page’s memory and are lost when you leave or reload; they are not saved or submitted.
Check your reasoning
- What fraction of producer biomass energy becomes herbivore biomass?
- What fraction of consumed energy becomes new herbivore biomass?
- Does the carbon account balance?
- Are unconsumed materials simply gone?
Teacher review guide
Review the actual deliverable and discuss the reasoning. For each criterion, use 0 when evidence is absent or fundamentally incorrect, 1 when partly supported with a material error or omission, and 2 when accurate, supported and complete for the stated task. Maximum 8 points is a task score, not a proficiency certification. Give feedback and allow revision.
- Constructs balanced energy and matter accounts.
- Computes ratios with correct denominators and units.
- Explains different fates of matter and energy.
- Rejects a universal transfer percentage using the data.
Answer guidance for the reasoning checks
What fraction of producer biomass energy becomes herbivore biomass?
500/10,000 = 5%.
What fraction of consumed energy becomes new herbivore biomass?
500/2,000 = 25%.
Does the carbon account balance?
Yes: 25+20+55=100 kg C.
Are unconsumed materials simply gone?
No. They remain in the system or enter other pathways that must be tracked.
Access, support and extension
Offer read-aloud support, labeled diagrams, larger print or an oral/recorded explanation while preserving the scientific reasoning. A partner or teacher can handle physical manipulation while the learner plans, records and interprets. Use a teacher-provided measured dataset only when its provenance and limitations are explicit; it does not replace conducting an investigation when that is the assessed practice. For greater independence, remove prompts and ask learners to compare a second explanation or test another justified revision.
Sources and standard reference
- Official NGSS HS-LS2-4 performance expectation — inspect the practice, core idea, crosscutting concept and assessment boundary.
Instructional text and hypothetical cases are original. Linked source readings supply published evidence where specified. Teachers should judge fit with their course and state requirements.