pho·​to·​syn·​the·​sis ˌfō-tō-ˈsin(t)-thə-səs How to pronounce photosynthesis (audio)
: synthesis of chemical compounds with the aid of radiant energy and especially light
especially : formation of carbohydrates from carbon dioxide and a source of hydrogen (such as water) in the chlorophyll-containing cells (as of green plants) exposed to light
photosynthesize intransitive verb
photosynthetic adjective
photosynthetically adverb

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Photosynthesis Has Greek Roots

The Greek roots of photosynthesis combine to produce the basic meaning "to put together with the help of light". Photosynthesis is what first produced oxygen in the atmosphere billions of years ago, and it's still what keeps it there. Sunlight splits the water molecules (made of hydrogen and oxygen) held in a plant's leaves and releases the oxygen in them into the air. The leftover hydrogen combines with carbon dioxide to produce carbohydrates, which the plant uses as food—as do any animals or humans who might eat the plant.

Examples of photosynthesis in a Sentence

Recent Examples on the Web And Foley said the process of photosynthesis contributes to temperature rise by accumulating heat energy. Edmund H. Mahony, Hartford Courant, 8 July 2024 Plants lose more water through their leaves, stop forming flowers and fruit, and eventually are unable to perform photosynthesis. Rachel Siegel, Washington Post, 23 June 2024 Likely prevalent on Earth well before the advent of plant-type photosynthesis, such bacteria could be primed to thrive on planets that circle cooler red dwarf stars – the most common type in our galaxy. Eric Lagatta, USA TODAY, 22 Apr. 2024 But for the Spanish thistles, evaporative cooling could be the goal rather than just a side effect of photosynthesis. Elizabeth Anne Brown, Scientific American, 27 Feb. 2024 See all Example Sentences for photosynthesis 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'photosynthesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


New Latin

First Known Use

1898, in the meaning defined above

Time Traveler
The first known use of photosynthesis was in 1898

Dictionary Entries Near photosynthesis

Cite this Entry

“Photosynthesis.” Dictionary, Merriam-Webster, Accessed 24 Jul. 2024.

Kids Definition


pho·​to·​syn·​the·​sis ˌfōt-ə-ˈsin(t)-thə-səs How to pronounce photosynthesis (audio)
: the process by which plants and some bacteria and protists that contain chlorophyll make carbohydrates from water and from carbon dioxide in the air in the presence of light
photosynthetic adjective

Medical Definition


pho·​to·​syn·​the·​sis ˌfōt-ō-ˈsin(t)-thə-səs How to pronounce photosynthesis (audio)
plural photosyntheses
: synthesis of chemical compounds with the aid of light sometimes including the near infrared or near ultraviolet
especially : the formation of carbohydrates from carbon dioxide and a source of hydrogen (as water) in chlorophyll-containing cells (as of green plants) exposed to light involving a photochemical release of oxygen through the decomposition of water followed by various enzymatic synthetic reactions that usually do not require the presence of light
photosynthesize intransitive verb
also British photosynthesise
photosynthesized also British photosynthesised; photosynthesizing also British photosynthesising
photosynthetic adjective
photosynthetically adverb

More from Merriam-Webster on photosynthesis

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