INTERACTIVE EXPLANATION

Where does a plant get the material to grow?

Open a leaf, explore a chloroplast, and supply a tiny carbon-building recipe. Discover what comes from air, what comes from water, and what light contributes.

Enable JavaScript to change the conditions and run the interactive experiment.

Make a discovery

Light supplies energy. Carbon dioxide supplies carbon for new carbohydrate. The oxygen gas released by oxygenic photosynthesis comes from water. These are different roles, even though all three appear in the same overall story.

Make a prediction

Which input provides the carbon in the new three-carbon product?

Sunlight
Carbon dioxide
Oxygen gas

Read the explanation

The three added carbon atoms arrive in three CO₂ molecules. Light supplies energy through chemical carriers; it supplies no carbon atoms.

Understand it

Start in a leaf

Carbon dioxide enters through pores called stomata, and water arrives through the plant’s transport tissues. Photosynthesis occurs in chloroplasts. The leaf view and chloroplast view represent different scales.

Capture energy at membranes

Chlorophyll and other components in thylakoid membranes participate in light-dependent reactions. Water is oxidized and oxygen gas can be released. ATP and NADPH connect light-dependent reactions to carbon-building chemistry.

Build and regenerate

In the stroma, Calvin–Benson reactions fix carbon dioxide. A net three-carbon G3P product can leave while the starting RuBP carbon pool is regenerated. Glucose is not the direct output of one turn of the cycle.

Look closer at the science

A finite recipe, not a growing plant

For one net G3P accounting batch, supply 3 CO₂, 9 ATP and 6 NADPH. The existing three-RuBP pool contains 15 carbons. Adding three carbons gives 18; exporting a three-carbon product leaves 15 to regenerate the pool.

Energy and matter are different

Turning off light in the context view stops its replenishment cue. The recipe bench has separately supplied carrier stocks, which remain available without light. Light is not converted into carbon atoms, and existing products do not disappear in darkness.

Dependencies are not rates

Without CO₂ there is no new carbon export; without sufficient carriers a complete batch cannot finish. The six-second animation is an explanation sequence, not a reaction time or a prediction of plant growth. Plants also respire.

Try it yourself: Account for every carbon

Supplies

18 counters or drawn circles
Paper
Pencil

Make the starting pool
Arrange 15 carbon counters as three groups of five. Label these groups RuBP. Put three incoming CO₂ carbon counters beside them.
Rearrange the carbon
Combine the 18 counters into six groups of three. This tracks carbon only, not every atom or intermediate reaction.
Export and rebuild
Move one three-counter group out as net G3P. Rearrange the other 15 into three groups of five. Explain why energy carriers are also needed.

Can you export something new without losing the starting pool?

An exact carbon-accounting analogy, not an experiment on a living leaf. Paper circles replace loose counters for young children. A plant journal can supplement it but cannot establish carbon origin by itself.

Sources and model limits

Finite stoichiometric recipe and qualitative chloroplast context. No crop-yield, gas-exchange, photosynthesis-rate, drought or climate model.
Molecules are symbols at exaggerated scale. The chloroplast is an original structural teaching model, not microscopy.
The water-to-O₂ arrow identifies oxygen origin. It does not show a complete atom-resolved light-reaction pathway or fixed photons-per-ATP ratio.

Evolved oxygen originates from water oxidation at thylakoid membranes.

How Light-Dependent Reactions Work and figure 8.17 establish the water/O₂ distinction and carrier roles.

OpenStax · Light-dependent reactions

A net G3P batch uses 3 CO₂, 9 ATP and 6 NADPH while regenerating RuBP.

Calvin-cycle stages and figure 8.19 support carbon accounting.

OpenStax · Carbon fixation

Floating leaf disks can indicate net oxygen accumulation under a defined assay.

Further optional activity reference. The simple paper activity below does not measure photosynthesis.

Exploratorium · Leaf investigation

Independent subject review is pending.

Read the sources and model assumptions