Cellular respiration: follow the atoms
About this app
A mitochondrion as a large 3D section: label C and O atoms and follow them from glucose through glycolysis, oxidative decarboxylation, the citric acid cycle and the respiratory chain. The balance table fills up, and the atom counter shows that oxygen from O₂ ends up in water. Prediction questions, ATP calculation with the range 30–32 and a comparison with lactic acid and alcoholic fermentation.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What it is about
In cellular respiration glucose is oxidised step by step. Glycolysis runs in the cytoplasm, oxidative decarboxylation and the citric acid cycle in the matrix of the mitochondrion, the respiratory chain in the inner membrane. Carbon leaves the cell as CO₂. Electrons reach O₂ via NADH and FADH₂, and water forms. The balance per glucose is C₆H₁₂O₆ + 6 O₂ + 6 H₂O → 6 CO₂ + 12 H₂O. So inhaled oxygen ends up in water. In the balance, the twelve O atoms in CO₂ come half from glucose and half from water.
What the app shows
A mitochondrion stands in the picture as a large 3D section with membranes, cristae, matrix and intermembrane space. On the left is the cytoplasm with glycolysis. All C and O atoms of one glucose and the other substances are spheres that follow their path. Labelled atoms carry a ring and leave a trail. The balance table counts CO₂, NADH, FADH₂, ATP and water per step, and the atom counter sorts O atoms by origin. In the respiratory chain the intermembrane space fills with H⁺ and ATP synthase turns.
What you can try
Tap an atom to label its group, then play the pathway. On the first run the app stops before the respiratory chain and asks where oxygen ends up. Switch to oxygen shortage and compare lactic acid and alcoholic fermentation with respiration. Work out the ATP yield with 2.5 and 1.5 or the older values 3 and 2, and choose the route of NADH from the cytoplasm. Six exam questions, for example on cyanide and FADH₂, give reasoned feedback.
Frequently asked questions
- Where does inhaled oxygen end up in cellular respiration?
- In water. O₂ only reacts at the end of the respiratory chain, at complex IV. There it takes up electrons and H⁺, and six O₂ give twelve H₂O. By then the CO₂ has already formed without O₂.
- Where does the oxygen in respired CO₂ come from?
- In the balance, half from glucose and half from water: six CO₂ contain twelve O atoms. Glucose brings six, the other six come from six H₂O taken up in the citric acid cycle.
- How much ATP does one glucose yield?
- About 30 to 32 ATP, calculated with 2.5 ATP per NADH and 1.5 ATP per FADH₂. Older school books give 36 to 38 ATP because they use 3 and 2. The range depends on the route of NADH from the cytoplasm.
- What does the app show about fermentation?
- You switch to oxygen shortage: after glycolysis pyruvate takes the electrons from NADH in the cytoplasm, forming lactate. In alcoholic fermentation pyruvate first releases CO₂, and ethanal becomes ethanol. The balance shows 2 ATP per glucose. Fermentation itself makes no ATP, it returns NAD⁺.
Subject: Biology (Gymnasium)
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- DNA double helix (3D)
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