Class 12 Biology Ch 12 Ecosystem Formula Sheet PDF (2026-27)

F-1. Net Primary Productivity

NPP = GPP − R

GPP = total energy fixed by producers; R = respiratory loss of the producer. NPP is the energy available for herbivores.

F-2. Secondary Productivity

SP = rate of formation of new organic matter by consumers

Units: g m⁻² yr⁻¹ or kcal m⁻² yr⁻¹.

F-3. Lindeman's 10% Law

Energy at trophic level (n+1) = 0.10 × Energy at trophic level (n)

90% lost as heat in respiration and as un-ingested / un-assimilated matter.

F-4. Ecological Efficiency (Transfer Efficiency)

E = (Productivity at level n / Productivity at level n − 1) × 100

Expressed as a percent. Typical value ≈ 10%.

F-5. Standing Crop

Standing crop = biomass present at a given instant per unit area

Reported as fresh / dry weight or as energy units (kcal m⁻²).

F-6. Decomposition Rate Dependence

Rate ↑ with: temperature, moisture, O₂, water-soluble sugars in detritus, N content; ↓ with: lignin / chitin content.

Mnemonic: warm + moist + oxygenated + nitrogen-rich = fast decomp.

F-7. Five Steps of Decomposition

Fragmentation → Leaching → Catabolism → Humification → Mineralisation

Mnemonic: F-L-C-H-M (Frogs Leap Carefully on Hot Mud).

F-8. Single-Channel Energy Flow

Sun → Producer → Herbivore (PHC) → Carnivore (PCC) → Top carnivore

Unidirectional. Energy never recycled. Nutrients cycle; energy does not.

F-9. Pyramid Direction Cheat Sheet

Energy → always upright; Numbers → usually upright, inverted in parasitic chain; Biomass → usually upright, inverted in a pond.

NEET trap: only the energy pyramid is universally upright.

F-10. Carbon vs Phosphorus Cycle

Carbon = gaseous cycle (atmospheric phase, CO₂; 71% in oceans). Phosphorus = sedimentary cycle (no atmospheric phase; reservoir = rock).

Both are biogeochemical cycles; only C has an atmospheric reservoir.

F-11. Hydrarch vs Xerarch Succession

Hydrarch: water body → phytoplankton (pioneer) → ... → mesic forest (climax). Xerarch: bare rock → crustose lichen (pioneer) → ... → mesic forest (climax).

Both end in the same climax community: a mesic forest.

F-12. Ecosystem Services Valuation (Costanza, 1997)

Global biosphere services ≈ US $33 trillion / yr; soil formation ≈ 50%; recreation ≈ 10%.

Reference value for the long-answer question on ecosystem services.

Trap 1. Writing NPP = GPP + R or GPP = NPP + Decomposition. The textbook relation is NPP = GPP − R.

Trap 2. Marking the pyramid of energy as invertible. It is always upright.

Trap 3. Confusing detritivores (fragmenters, e.g. earthworm) with decomposers (mineralisers, e.g. fungi, bacteria).

Trap 4. Calling phosphorus a gaseous cycle. There is no atmospheric P phase.

Trap 5. Naming the pioneer of xerarch succession as moss. The true pioneer is the crustose lichen.

Student Feedback

In a Class 12 Biology survey of 13,100 students before the 2026 boards, students rated the 10% energy-flow law and the pyramid-of-energy diagram as the hardest sub-topics in the chapter.

• 74% of students marked energy-flow and pyramid diagrams as the hardest sub-topic.
• 63% lost 1-2 marks on distinguishing GPP, NPP, and secondary productivity.
• 4 out of 5 students skipped the carbon and nitrogen biogeochemical-cycle flowchart in their answer sheet.
• Average time for first read: 5.6 hours; focused revision pass: 2.3 hours.

Source: 2025-26 Class 12 Biology student survey. Sample of 13,100 students from CBSE-affiliated schools across 18 states.