Photosynthesis in Water

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Photosynthesis is not only responsible for the production of food on land, but also for manufacturing microscopic single-celled plants called phytoplankton in the oceans. Phytoplankton is responsible for the nourishment of the entire marine food web. The lives of all animals that live in the sea -- with the exception of hydrothermal vent organisms (See box “Sulfur-Based Life”) -- depend on phytoplankton for energy and minerals. The rate of photosynthesis is highest, not at the surface, but at a depth of about 10-20 meters where light intensity is not too high. As we go deeper, the rate of photosynthesis slows and eventually stops (a).



(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Additional Comments

(a) The study of algae growth in the euphotic zone shows that maximum photosynthetic activity occurs at a depth of only 10-20 m beneath the surface of water. The warmer surface temperatures limit the amount of carbon dioxide that can be dissolved. Below this point, the photosynthesis becomes light-limited, and so decreases with depth.

Further Reading

Sims, R., Bioenergy Options for a Cleaner Environment in Developed and Developing Countries, Elsevier, 2003.

Tillman, D., Combustion of Solid Fuels & Wastes, Academic Press, 1991.

Biofuels for Transport: Global Potential and Implications for Energy and Agriculture, The Worldwatch Institute, 2007.

Biomass and Bioenergy, Science Direct Elsevier Science Publishing Company.

External Links

National Renewable Energy Laboratory: Biomass Research (

US Department of Energy (

Biomass Energy Research Association (

American Bioenergy Association (