Cellular respiration is the kind of topic that feels simple right up until the exam question asks you to explain it.
You remember the gist: glucose goes in, ATP comes out, life continues. But in IB Biology, marks are often hiding in the details you assume are “obvious”--like balancing atoms, naming products correctly, and linking the equation to mitochondria, redox, and gas exchange. If you can write the correct general equation for cellular respiration quickly and talk about what it means, you usually feel calmer everywhere else in metabolism.
The correct general equation for aerobic cellular respiration (IB Biology)
The balanced general equation you should use in IB Biology is:
C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP (energy)
Think of it as a “whole-process summary.” It doesn’t show the intermediate steps (glycolysis, link reaction, Krebs cycle, oxidative phosphorylation), but it correctly tracks where atoms end up and signals the overall energy conversion.
Quick interpretation checklist
Use this mini-checklist when the equation appears in a question:
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Glucose is the fuel (organic substrate)
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Oxygen is required for aerobic respiration and functions as the final electron acceptor
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Carbon dioxide is produced when carbon compounds are broken down (decarboxylation in later stages)
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Water forms at the end of the electron transport chain
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ATP is the usable energy currency (the point of the whole process)
For targeted syllabus-aligned practice, the fastest way to lock this in is to drill it inside a respiration topic hub like IB Biology Topic C1.2: Cell Respiration and then immediately apply it using the Cell Respiration Questionbank.
Why the equation earns marks (not just memory points)
In IB Biology, you rarely get rewarded for writing an equation alone. You get rewarded for using it.
The general equation helps you answer the questions that examiners love because it connects multiple units of the course:
It’s a redox story
Glucose is oxidized (loses electrons/hydrogen), and oxygen is reduced (gains electrons/hydrogen) to form water. If you can say “oxidation and reduction” confidently, you’ll sound like you understand respiration instead of reciting it.
It links directly to mitochondria and membranes
Yes, glycolysis happens in the cytoplasm. But a lot of the “high ATP yield” logic depends on the mitochondrion and its membranes. If you need a structured refresher, build it from Notes for 2.8 Cell respiration, then reinforce with Flashcards for C1.2 Cell respiration.
Aerobic vs anaerobic: what changes from the general equation?
The general equation above is for aerobic respiration. But IB Biology expects you to compare it with anaerobic pathways when oxygen is limited.
Anaerobic respiration in humans (muscle cells)
A simplified summary is:
glucose → lactate + ATP
Key idea: far less ATP is produced because the electron transport chain cannot run without oxygen as the final electron acceptor.
Anaerobic respiration in yeast (fermentation)
A simplified summary is:
glucose → ethanol + CO₂ + ATP
This matters for data questions involving CO₂ production, and for practical contexts where students measure gas output.
If you’re practicing comparison-style questions, it’s worth combining content review with technique using How to Understand IB Biology Command Terms for Exam Success so you don’t underwrite an “explain” or overwrite an “outline.”
How this shows up in IB exam questions
In IB Biology, the cellular respiration equation appears in predictable disguises:
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Multiple choice: identify products, location, or role of oxygen
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Short answer: explain why more ATP is made aerobically than anaerobically
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Data-based: interpret oxygen uptake or carbon dioxide output trends
A smart way to train for that is to practice under pressure, then review like an examiner. RevisionDojo makes this loop simple: learn the content in notes, test yourself in Questionbank, and use AI Chat to clarify the exact misconception you had in the moment.
For full-timing rehearsal, you can also build stamina with IB Predicted Papers and then patch weak points using targeted drills and Grading tools.
Common mistakes IB Biology students make with this equation
These are small errors that cost marks because they signal shaky understanding:
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Forgetting the 6 in front of O₂, CO₂, or H₂O (unbalanced atoms)
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Writing “energy” but never mentioning ATP
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Confusing respiration with photosynthesis (direction of gases)
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Treating oxygen as “used to make ATP” rather than as the final electron acceptor
If your goal is to stop repeating these errors, combine active recall with feedback: do short daily sets in the Cell Respiration Questionbank, then turn the misses into a mini deck using RevisionDojo Flashcards.
Closing: the equation is a compass
The correct general equation for cellular respiration is short, but in IB Biology it acts like a compass: it points you toward redox, mitochondria, ATP yield, and the kind of language examiners reward.
If you want to turn that one line into consistent marks, build a loop that actually trains performance: learn with RevisionDojo Study Notes, drill with the Questionbank, lock it in with Flashcards, get unstuck fast with AI Chat, and rehearse under pressure with Predicted Papers and Mock Exams. When your revision has structure, the equation stops being something you “hope you remember” and becomes something you can use.