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Cell Biology

Respiration

Follow glucose through glycolysis, the Krebs cycle and the electron transport chain.

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Step-by-Step Respiration

Respiration is a catabolic process: enzymes break glucose down in small steps and the energy released is stored as ATP.

Mode:

Glucose + oxygen → carbon dioxide + water + energy (ATP). About 60% efficient because glucose is fully broken down.

CytosolStep 1 of 5

Stage 1: Glycolysis

In the cytosol, one 6-carbon glucose molecule is broken into two 3-carbon pyruvic acid molecules. No oxygen is needed, so glycolysis is anaerobic. It gives a net gain of 2 ATP and forms 2 NADH.

glucose (6C) 2 ATP invested 2 NAD⁺2 pyruvic acid (3C)net 2 ATP2 NADH
Cytoplasm (no oxygen needed)Glucose6-carbon2 × triosephosphorylated2 pyruvic acid3-carbon2 ATP invested4 ATP made (net 2)2 NADH
Glycolysis in the cytoplasm: glucose splits into two pyruvic acid molecules

ATP total so far

2

Aerobic respiration releases far more energy per glucose because glucose is completely broken down

Build the respiration pathway

Drag each item into the correct stage or location, or tap an item then tap a box.

Glycolysis (cytosol)

stage 1, no oxygen needed

Mitochondrial matrix

stage 2, needs oxygen

Inner mitochondrial membrane

where most ATP is made

Fermentation products

no oxygen available