Every carbon atom here is a persistent object, so a labelled carbon can be followed from CO₂ into 3-PGA, around the regeneration shuffle and out as sucrose — including which position it occupies in each molecule. This recreates the experiment Calvin, Benson and Bassham used to deduce the cycle: label briefly, kill the sample at a chosen moment, separate the extract by two-dimensional paper chromatography, and read the radioactive spots off the film.
Node fill shows the fraction of that pool's carbon which is radioactive. Watch the label enter at RuBisCO, appear in 3-PGA first, then spread.
Each line is that compound's share of all label currently in the cycle. 3-PGA spikes first and then falls as the label moves downstream — the observation that identified 3-PGA as the first stable product of carbon fixation.
Simulated 2-D paper chromatogram; darker spots carry more ¹⁴C. Spot positions are schematic — arranged by relative mobility (bisphosphates barely leave the origin, free sucrose runs furthest) rather than measured Rf values.
Carbons 3 and 4 light up first. Both descend from the carboxyl carbon of 3-PGA — the position the incoming CO₂ becomes — which is exactly what aldolase's condensation of two triose phosphates predicts.