photosynthesis

[foh-tuh-sin-thuh-sis]

noun

Biology, Biochemistry.

1. the complex process by which carbon dioxide, water, and certain inorganic salts are converted into carbohydrates by green plants, algae, and certain bacteria, using energy from the sun and chlorophyll.

photosynthesis

/ ˌfəʊtəʊsɪnˈθɛtɪk, ˌfəʊtəʊˈsɪnθɪsɪs /

noun

1. (in plants) the synthesis of organic compounds from carbon dioxide and water (with the release of oxygen) using light energy absorbed by chlorophyll

2. the corresponding process in certain bacteria

photosynthesis

1. The process by which green plants, algae, diatoms, and certain forms of bacteria make carbohydrates from carbon dioxide and water in the presence of chlorophyll, using energy captured from sunlight by chlorophyll, and releasing excess oxygen as a byproduct. In plants and algae, photosynthesis takes place in organelles called chloroplasts. Photosynthesis is usually viewed as a two-step process. First, in the light reactions, the energy-providing molecule ATP is synthesized using light energy absorbed by chlorophyll and accessory pigments such as carotenoids and phycobilins, and water is broken apart into oxygen and a hydrogen ion, with the electron of the hydrogen transferred to another energy molecule, NADPH. The ATP and NADPH molecules power the second part of photosynthesis by the transfer of electrons. In these light-independent or dark reactions, carbon is broken away from carbon dioxide and combined with hydrogen via the Calvin cycle to create carbohydrates. Some of the carbohydrates, the sugars, can then be transported around the organism for immediate use; others, the starches, can be stored for later use.

2. Compare chemosynthesis See Note at transpiration

photosynthesis

1. Use by green plants of the energy in sunlight to carry out chemical reactions, such as the conversion of carbon dioxide into oxygen. Photosynthesis also produces the sugars that feed the plant.

Green plants depend on chlorophyll to carry out photosynthesis.

Other Word Forms

• photosynthetic adjective
• photosynthetically adverb
• nonphotosynthetic adjective

Word History and Origins

Origin of photosynthesis¹

First recorded in 1895–1900; photo- + synthesis

A Closer Look

Almost all life on Earth depends on food made by organisms that can perform photosynthesis, such as green plants, algae, and cyanobacteria. These organisms make carbohydrates from carbon dioxide and water using light energy from the Sun. They capture this energy with various pigments which absorb different wavelengths of light. The most important pigment, chlorophyll a, captures mainly blue and red light frequencies, but reflects green light. In plants, the other pigments are chlorophyll b and carotenoids. The carotenoids are usually masked by the green color of chlorophyll, but in temperate environments they can be seen as the bright reds and yellows of autumn after the chlorophyll in the leaves has broken down. The energy gathered by these pigments is passed to chlorophyll a. During the light reactions, the plant uses this energy to break water molecules into oxygen (O₂), hydrogen ions, and electrons. The light reactions produce more oxygen than is needed for cellular respiration, so it is released as waste. All of the oxygen in the Earth's atmosphere today was produced as waste by photosynthetic organisms, especially cyanobacteria, which have been producing oxygen for some three billion years, since their first appearance in the Precambrian Eon. During the dark reactions, the plant uses hydrogen ions and the electrons to make carbon dioxide into carbohydrates. Within the leaf of a green plant, photosynthesis takes place in chlorophyll-containing chloroplasts in the columnlike cells of the palisade layer and in the cells of the spongy parenchyma. The cells obtain carbon dioxide from air that enters the leaf through holes called stomata, which also allow excess oxygen to escape. Water from the roots is brought to the leaf by the vascular tissues called xylem, while the carbohydrates made by the leaf are distributed to the rest of the plant by the vascular tissue called phloem.

Example Sentences

The AI system distinguished biological from nonbiological materials with over 90 percent accuracy and detected signs of photosynthesis in rocks at least 2.5 billion years old.

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One possibility is that less ice leads to more photosynthesis at the surface, increasing nutrient uptake.

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Under Death Valley-level heat, the plant's mitochondria -- the structures that generate energy -- move closer to the chloroplasts, where photosynthesis occurs.

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However, oxygenic photosynthesis -- produced by cyanobacteria -- had likely evolved hundreds of millions of years before this event.

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This “semi-artificial leaf” replicates photosynthesis, the natural process plants use to turn sunlight into energy, and operates entirely on its own power.

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