photosynthesis

noun

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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
If photosynthesis has a low conversion rate, feeding crops to animals compounds the problem many times over. Elizabeth Kolbert, New Yorker, 23 June 2025 Leaves may be covered in black, sooty mold that grows on the honeydew, eventually blocking photosynthesis. Brandee Gruener, Southern Living, 12 June 2025 However, there are cons, including that dust can accumulate and cover plants, cutting off their ability to undergo photosynthesis, harming or killing the vegetation. Leah Sarnoff, ABC News, 4 June 2025 On the early Earth, however — before the rise in atmospheric oxygen due to photosynthesis — lightning may have played a crucial role in creating many prebiotic compounds, which are molecules that form the building blocks of proteins. Paul Sutter, Space.com, 20 May 2025 See All Example Sentences for photosynthesis

Word History

Etymology

New Latin

First Known Use

1898, in the meaning defined above

Time Traveler
The first known use of photosynthesis was in 1898

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Cite this Entry

“Photosynthesis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/photosynthesis. Accessed 29 Jun. 2025.

Kids Definition

photosynthesis

noun
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

photosynthesis

noun
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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