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C4.2.16—Secondary production

Secondary production explains how energy flow, matter cycling, trophic transfer or carbon movement is represented, measured or limited within ecosystems.

Syllabus
First assessment 2025
Objective
C4.2.16
Level
SL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2018
Most common paperPaper3
Typical marks1

Common command terms

  • Calculate

Scoring notes

Common mistake
Reversing food-web arrows instead of showing energy transfer direction.

Recent exam appearances

November 2018Paper3 ["SL"] · TZ012(b)[ 1 ]C4.2.16—Secondary production
November 2018Paper3 ["SL"] · TZ012(a)[ 1 ]C4.2.16—Secondary production
Practice this objective

Coverage 2018–2018 · Updated 16 Jul 2026

Secondary production is consumer biomass formation

Secondary production is the accumulation of carbon compounds in heterotroph biomass through growth and reproduction.

Heterotrophs obtain organic carbon by feeding, but not all intake becomes biomass. Some is not assimilated, and respiration converts absorbed carbon compounds to carbon dioxide and water while releasing energy.

Food carbon → ingestion/digestion → assimilation → respiration losses as CO₂ and water + retained carbon in growth/reproduction. Retained carbon is secondary production.

A growing fish retains part of assimilated food as new tissue, while respiring another part; only the retained new tissue contributes to secondary production.

Secondary production is lower than primary production at ecosystem scale because carbon is lost from biomass at each heterotrophic transfer, especially through respiration.

Secondary production

Assessment in practice

1 marks
How it is assessed

This objective is assessed through structured response, commonly using Calculate.

Command terms

Calculate

What earns marks

Build the answer around this relationship: Secondary production must be linked to the correct source, store, transfer or loss process.

Watch for

Reversing food-web arrows instead of showing energy transfer direction.

Representative question

Question 1

[Maximum number: 1]

Calculate how much food would be required to produce 20 kg of boar meat.

kg

Energy and Matter

  • Ecosystems are open systems: energy flows through them and leaves as heat, while matter is recycled and may enter or leave.
  • Photoautotrophs capture light; chemoautotrophs oxidize inorganic substances. Both build biomass from inorganic carbon. Heterotrophs obtain organic carbon from other organisms.
  • Food-web arrows show energy and biomass transfer. Energy decreases between trophic levels through respiration, heat, egestion, excretion and uneaten material, limiting chain length.
  • Gross primary production minus producer respiration gives net primary production; secondary production is heterotroph biomass gain.
  • Decomposers obtain energy from detritus and return inorganic nutrients to producers.
  • Carbon-cycle diagrams distinguish stores and fluxes. Photosynthesis removes CO2; respiration, decomposition and combustion release it.
  • A sink absorbs more carbon than it releases; a source does the reverse. The Keeling Curve shows a long-term atmospheric CO2 rise with seasonal oscillation.

Concept essentials

  • Secondary production must be linked to the correct source, store, transfer or loss process.
  • The evidence for secondary production depends on distinguishing energy flow from matter cycling.
  • Secondary production is clearer when arrows, units and trophic positions match the biological process.
  • Data or diagrams for secondary production need interpretation as ecosystem transfer evidence.