Photosynthesis
Botany · Biochemistry · Cell Biology
Say it: foh-toh-SIN-thuh-sis
Photosynthesis is the process in which plants, algae and cyanobacteria capture light energy and store it in sugar built from carbon dioxide and water.
Also: photosynthesize, photosynthesise, photosynthetic
Definition
What is photosynthesis?
Photosynthesis is how plants, algae and cyanobacteria capture the energy of sunlight and store it in the chemical bonds of sugar. Using carbon dioxide from the air and water, they build glucose and give off oxygen as a byproduct. The overall reaction is often summarized as six molecules of carbon dioxide plus six of water, powered by light, giving one molecule of glucose and six of oxygen. In plants it happens mainly in the leaf mesophyll, inside chloroplasts, with carbon dioxide entering through pores called stomata.
It runs in two linked stages. In the light-dependent reactions, on the thylakoid membranes, chlorophyll absorbs light, water is split to release oxygen, and the energy is stored in the carrier molecules ATP and NADPH. In the Calvin cycle, in the fluid stroma around the thylakoids, those carriers power the fixing of carbon dioxide into a three-carbon sugar that the cell turns into glucose and other compounds.
Nearly every food chain on Earth begins with photosynthesis, and it supplies the oxygen that most organisms need for respiration. It also draws carbon dioxide out of the atmosphere, making it a central part of the carbon cycle.
Word parts
Where does the word “photosynthesis” come from?
- photo-
- lightGreek phos, photos
- syn-
- togetherGreek syn
- -thesis
- placing, puttingGreek thesis
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Terms that go with it
- ChloroplastA chloroplast is the green organelle in plant and algal cells that captures light energy and uses it to make sugars by photosynthesis.
- ChlorophyllChlorophyll is the green pigment in plants, algae and cyanobacteria that absorbs light energy to drive photosynthesis.
- StomataStomata are tiny pores in the epidermis of leaves and stems, each opened and closed by two guard cells to control gas exchange and water loss.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
- Carbon cycleThe carbon cycle is the movement of carbon among the air, oceans, living things, soils and rocks through processes like photosynthesis and respiration.
- Electron transport chainThe electron transport chain is a series of membrane proteins that pass electrons to oxygen and use the energy released to pump protons.
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