Accumulation of Organic Matter in Plants: Products of Photosynthesis

Plants accumulate organic matter through photosynthesis, the process by which green tissues capture light energy and convert carbon dioxide and water into energy-rich organic compounds. This buildup of organic material is the foundation of plant growth and, ultimately, of nearly all life on Earth. Accumulation of organic matter during photosynthesis

What organic compounds do plants produce during photosynthesis?

Photosynthesis ends with the formation of carbohydrates in many plants, but the final product is not the same in every species. In sugar beet, sugarcane, and onion, photosynthesis concludes with the disaccharide sucrose, whereas in most other plants it concludes with starch. These end products represent the stored chemical energy that the plant can later draw on for growth and metabolism. In sugar beet, sugarcane, and onion, photosynthesis ends with the disaccharide sucrose

Proteins are formed alongside carbohydrates during photosynthesis. Experiments using the labelled nitrogen isotope N¹⁵ demonstrated that plants synthesize more protein in the light than in the dark, confirming that light directly drives protein assembly and not only carbohydrate production.

Protein accumulation reaches its maximum during the flowering phase and does not continue afterward. The composition of photosynthetic products depends on the physiological state of the plant and on environmental conditions — including light intensity, light quality, and the supply of mineral nutrients. The influence of light quality in particular has been measured experimentally, as the table below shows.

How does light quality affect the products of photosynthesis?

Red light promotes the greater formation of carbohydrates, while blue light favours the production of proteins and organic acids. This means the spectral composition of light, not just its brightness, shifts the chemical balance of what a leaf builds. The contrast is clearest when sunflower and maize leaves are illuminated separately with red and blue light.

Content of photosynthetic products (in mg per 315 cm² of leaf area) under red and blue light

The figures show a consistent pattern across both species: red light pushes carbohydrate totals higher, while blue light raises both protein and organic acid totals. In maize, for example, protein content rises from 1.39 mg under red light to 10.90 mg under blue light — almost an eightfold increase — illustrating how strongly light quality can redirect a plant's biochemistry.

How does organic matter accumulation differ between young and mature leaves?

The age of a leaf changes how the absorbed carbon is allocated during photosynthesis. In the leaves of young plants, most of the absorbed carbon is used to build proteins, lipoids, and nucleic acids, with a smaller share going to carbohydrates. This allocation reflects the rapid construction of new cellular machinery in growing tissue.

In mature leaves the allocation reverses, with most of the carbon directed toward soluble carbohydrates, starch, and cellulose. Fully developed leaves therefore act more as producers and stores of structural and energy-rich carbohydrate than as sites of intensive protein construction.

How much organic matter do green plants synthesize each year?

The synthetic activity of green plants can be appreciated through the scale of carbon they assimilate globally. The total amount of carbon assimilated per year is about 175 billion tonnes, divided between land and water plants as follows:

• land plants account for 20 billion tonnes;
• aquatic plants account for 155 billion tonnes.

Plants of the globe

Studies of organic matter accumulation in plants point to two figures that define the planetary importance of photosynthesis:

1. The total production of organic matter synthesized by the world's plants amounts to roughly 450 billion tonnes per year, expressed as glucose — and this is the fundamental material basis of life on Earth.
2. Photosynthesis releases oxygen into the atmosphere at a rate of about 460 billion tonnes per year.

Why is the green plant so important to life on Earth?

The Russian plant physiologist K. A. Timiryazev summarized the role of the green plant on Earth in three functions, which together explain why photosynthesis underpins the biosphere:

1. releasing oxygen into the atmosphere;
2. accumulating organic matter;
3. storing potential energy received from the Sun.

These three roles connect directly to the figures above: the oxygen plants release sustains aerobic life, the organic matter they accumulate feeds every food chain, and the captured solar energy is what powers living systems long after the light itself has gone. For related reading on the natural sciences, see the site's Agronomy and Astronomy sections.