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

Did you know?

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 This leaf likely fell off a tree in the fall once the trees paused photosynthesis for the winter and sank to the bottom of the lake, where it was buried. Robert Patalano, Discover Magazine, 9 Feb. 2024 These microalgae use photosynthesis to absorb carbon dioxide and sunlight, generating oxygen and carbohydrates that nourish all types of marine life. Ashley Strickland, CNN, 8 Feb. 2024 While plants are naturally rich with glucose because of photosynthesis, unprocessed meat has virtually no impact on glucose levels. Jack Knudson, Discover Magazine, 24 Jan. 2024 Still, regularly cleaning leaves is an important aspect of houseplant care because dust prevents the leaves from absorbing sunlight and hinders photosynthesis. Lauren David, Washington Post, 17 Jan. 2024 The palest pebbles reflect light, accelerating the photosynthesis process of the vines, while the darker pebbles harvest the daytime sun, releasing heat throughout the night. Cait Bazemore, Robb Report, 10 Dec. 2023 When plants perform photosynthesis, the carbon becomes part of their leaves, stems and trunks. Smithsonian Magazine, Smithsonian Magazine, 27 Nov. 2023 These microscopic marine algae soak up carbon dioxide from the atmosphere to perform photosynthesis and produce at least half of the world’s oxygen. Chirag Dhara, Scientific American, 8 Nov. 2023 The find marks the earliest fossil evidence of photosynthesis. Will Sullivan, Smithsonian Magazine, 4 Jan. 2024 See More

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 25 Feb. 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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