MYP Biology: Cellular Respiration FAQ

Cellular respiration is how cells break down glucose to release energy stored as ATP, the molecule that powers muscle contraction, active transport and protein synthesis. In MYP Biology you study it as part of the energy strand of the sciences framework, usually alongside photosynthesis so you can compare inputs, outputs and where each reaction happens.

Photosynthesis captures light energy in chloroplasts to build glucose from carbon dioxide and water, releasing oxygen. Cellular respiration does the reverse — it breaks glucose down using oxygen to release energy as ATP, producing carbon dioxide and water. They're near mirror-image reactions, which is exactly why IB questions often ask you to compare them directly.

It can be either. Aerobic respiration needs oxygen and releases far more ATP per glucose molecule. Anaerobic respiration kicks in when oxygen is scarce — in human muscle cells it produces lactic acid, in yeast it produces ethanol and carbon dioxide through fermentation. MYP assessments usually expect you to compare both pathways side by side.

The word equation is: glucose + oxygen → carbon dioxide + water (energy released). The balanced chemical equation is C6H12O6 + 6O2 → 6CO2 + 6H2O. Examiners mark you down for omitting water as a product, or for writing "energy is made" instead of "energy is released" — glucose already contains the stored energy.

ATP is the cell's immediate energy currency — it releases energy the instant its terminal phosphate bond breaks, unlike glucose, which first needs to be broken down over several steps. Cells use that quick-release energy for active transport, muscle contraction, nerve impulses and building new molecules, which is why respiration runs continuously, even when you're resting.

Cellular respiration is assessed through the standard four MYP Sciences criteria: Criterion A (Knowing and understanding) covers equations and definitions, Criterion B (Inquiring and designing) and Criterion C (Processing and evaluating) usually come via a practical investigation, and Criterion D (Reflecting on the impacts of science) might ask about respiration's role in exercise or food science.

Common command terms include "state" (the equation), "describe" (the process, step by step), "explain" (why anaerobic respiration yields less ATP), "compare and contrast" (aerobic vs anaerobic) and "outline" (the mitochondria's role). Each term signals how much depth is needed — "state" wants a fact, "explain" wants reasoning with cause and effect.

The classic investigation measures carbon dioxide output from germinating seeds or respiring yeast, often using limewater turning cloudy or a CO2 data logger, while varying temperature or sugar concentration as the independent variable. It's a strong vehicle for Criteria B and C because you design the method yourself, then evaluate its reliability and sources of error.

Most lost marks come from mixing up aerobic and anaerobic products, or forgetting that respiration happens in every cell continuously, not just muscles during exercise. I tell my students to build a simple table of inputs, outputs, ATP yield and location for both pathways, then test themselves from memory until they can reproduce it cold.

The biggest one is calling lactic acid fermentation "anaerobic respiration in humans" as a blanket process, without specifying it happens only in muscle cells during intense exercise. Others include writing "energy is made" instead of "released", forgetting mitochondria as the site of aerobic stages, and confusing respiration (a cellular process) with breathing or ventilation (gas exchange).

Structure your answer around three points every time: oxygen requirement, ATP yield, and end products. Don't just list facts — link them with cause and effect, since that's what separates a describe-level answer from an explain-level one that actually earns the top marks in Criterion A.

MYP cellular respiration is the foundation for DP Biology's more detailed treatment of glycolysis, the Krebs cycle and oxidative phosphorylation, covered under cell biology and metabolism topics. According to the IB, the current DP Biology guide (first exams 2025) builds directly on MYP concepts like ATP, mitochondria and gas exchange — gaps left here tend to resurface as harder problems two years later.

Not conceptually — but it's easy to lose marks through imprecise wording rather than genuinely misunderstanding the biology. Students who struggle usually haven't practised writing full equations or comparing pathways side by side. A comparison table, drilled until it's automatic, tends to fix this within a week or two of focused practice.

Look for MYP-specific revision notes that break the topic into equations, locations and ATP yields, plus topical worksheets built around command-term practice, so your child gets comfortable with "explain" versus "describe" questions before the real assessment. Practising past-style questions under time pressure matters more here than re-reading textbook explanations.