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C1.1.3—Anabolic and catabolic reactions

Anabolic reactions build larger molecules, while catabolic reactions break molecules down and release usable materials or energy for cellular processes.

Syllabus
First assessment 2025
Objective
C1.1.3
Level
SL

Exam analysis

Chance of appearing7%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1

Common command terms

  • Identify
  • Distinguish

Recent exam appearances

November 2025Paper1A ["SL"] · TZ14[ 1 ]C1.1.3—Anabolic and catabolic reactions
May 2025Paper1A ["SL"] · TZ24[ 1 ]C1.1.3—Anabolic and catabolic reactions
May 2023Paper1 ["SL"] · TZ26[ 1 ]C1.1.3—Anabolic and catabolic reactions
May 2022Paper1 ["SL"] · TZ21[ 1 ]C1.1.3—Anabolic and catabolic reactions
May 2021Paper1 ["SL"] · TZ26[ 1 ]C1.1.3—Anabolic and catabolic reactions

Coverage 2016–2025 · Updated 15 Jul 2026

Metabolism Builds, Breaks and Transfers Energy

Metabolism is the complete set of enzyme-controlled reactions in a cell or organism. Because each step needs a particular enzyme, cells regulate which routes operate by controlling enzyme amount, activity and location.

Route Change in matter Typical chemistry Energy relationship
anabolism smaller units → larger, more complex molecules condensation and reduction requires an energy input
catabolism complex molecules → smaller products hydrolysis and oxidation releases usable energy

The two routes are coupled: catabolic reactions release energy and provide small molecules; anabolic reactions use both to build cell components. Respiration is mainly catabolic, while protein synthesis is anabolic.

SL Checkpoint: Explain the Curve, Not Just Its Shape

globular fold → active-site chemistry → induced fit → lower activation energy → faster turnover → controlled metabolic pathways

When explaining a rate pattern, identify what changed, then connect it to:

  • molecular motion and successful collisions
  • active-site occupancy
  • active-site shape and charge
  • depletion or changing conditions during measurement

A strong investigation measures initial rate, changes one independent variable, controls alternatives, includes a relevant control and uses repeats to reveal variation.

Anabolic and catabolic reactions

[ 2 ]

Identify the following processes as either anabolism or catabolism by placing a tick ( ✓ ) in the correct box.

ProcessAnabolismCatabolism
Light-independent reactions of photosynthesis□\square□\square
Glycolysis□\square□\square

Concept essentials

  • Anabolism builds larger or more complex molecules from smaller units.
  • Catabolism breaks molecules down into smaller products.
  • Condensation is commonly anabolic, while hydrolysis is commonly catabolic.
  • Metabolism includes both anabolic and catabolic reactions.