See the science

Photosynthesis

Photosynthesis uses light energy to build energy-rich organic matter from carbon dioxide and water. In oxygenic photosynthesis, oxygen is released as a by-product.

What goes in, what comes out

The simplest useful summary is: carbon dioxide + water + light energy → glucose + oxygen. Written as a balanced overall equation: 6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂.

This equation is a summary, not a single reaction. Light is absorbed by pigments such as chlorophyll. Part of that energy is used to split water and drive electron transfers; carbon from CO₂ is then incorporated into organic molecules.

Where do the atoms come from?

The carbon atoms in glucose come from carbon dioxide. The oxygen released as O₂ in oxygenic photosynthesis comes from water, not directly from CO₂. That distinction is easy to miss in a simple diagram.

What happens to the glucose?

Glucose is not merely an end product. Plants can use it for respiration, convert it into starch for storage, build cellulose for cell walls, or use its carbon skeletons to make many other organic molecules.

Inputs: CO₂ + H₂O + light. Main outputs: organic matter + O₂. Carbon in biomass comes from CO₂; released O₂ comes from water.

6 CO₂+6 H₂O+☀→C₆H₁₂O₆+6 O₂

What the diagram simplifies

Photosynthesis is not one single reaction. It is a linked set of processes in which light energy is first captured and then used to build organic molecules.

Go one step further

A useful way to understand this phenomenon is to separate the driving force from the visible result. Temperature, pressure, concentration, surface area and the nature of the materials can each change the rate or the final state. In real systems, several of these factors often act at the same time.

That is why the same phenomenon can look different in a laboratory, in the kitchen or outdoors. The underlying chemistry or physics stays the same, but the conditions change the balance.