what is photosynthesis?
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Answer:
the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a by-product
Answer:
Photosynthesis is the process used by plants, algae and certain bacteria to turn sunlight, carbon dioxide (CO2) and water into food (sugars) and oxygen. Here's a look at the general principles of photosynthesis and related research to help develop clean fuels and sources of renewable energy.
There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis. They both follow very similar principles, but oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria.
During oxygenic photosynthesis, light energy transfers electrons from water (H2O) taken up by plant roots to CO2 to produce carbohydrates. In this transfer, the CO2 is "reduced," or receives electrons, and the water is "oxidized," or loses electrons. Oxygen is produced along with carbohydrates.
Oxygenic photosynthesis functions as a counterbalance to respiration by taking in the CO2 produced by all breathing organisms and reintroducing oxygen to the atmosphere.
Anoxygenic photosynthesis, meanwhile, uses electron donors that are not water and do not produce oxygen, according to "Anoxygenic Photosynthetic Bacteria" by LibreTexts. The process typically occurs in bacteria such as green sulfur bacteria and phototrophic purple bacteria.
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THE PHOTOSYNTHESIS EQUATION
Though both types of photosynthesis are complex, multistep affairs, the overall process can be neatly summarized as a chemical equation.
The oxygenic photosynthesis equation is:
6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O
Here, six molecules of carbon dioxide (CO2) combine with 12 molecules of water (H2O) using light energy. The end result is the formation of a single carbohydrate molecule (C6H12O6, or glucose) along with six molecules each of oxygen and water.
Similarly, the various anoxygenic photosynthesis reactions can be represented as a single generalized formula:
CO2 + 2H2A + Light Energy → [CH2O] + 2A + H2O
The letter A in the equation is a variable, and H2A represents the potential electron donor. For example, "A" may represent sulfur in the electron donor hydrogen sulfide (H2S), according to medical and life sciences news site News Medical Life Sciences.
HOW IS CARBON DIOXIDE AND OXYGEN EXCHANGED?
stomata are the gatekeepers of the leaf, allowing gas exchange between the leaf and surrounding air.
Stomata are the gatekeepers of the leaf, allowing gas exchange between the leaf and surrounding air. (Image credit: Waldo Nell / 500px via Getty Images)
Plants absorb CO2 from the surrounding air and release water and oxygen via microscopic pores on their leaves called stomata. Stomata are the gatekeepers of gas exchange between the inside of plants and the external environment.
When stomata open, they let in CO2; however, while open, the stomata release oxygen and let water vapor escape. In a bid to reduce the amount of water lost, stomata close, but that means the plant can no longer gain CO2 for photosynthesis. This tradeoff between CO2 gain and water loss is a particular problem for plants growing in hot, dry environments.
HOW DO PLANTS ABSORB SUNLIGHT FOR PHOTOSYNTHESIS?
Plants contain special pigments that absorb the light energy needed for photosynthesis.
Chlorophyll is the primary pigment used for photosynthesis and gives plants their green color, according to science education site Nature Education. Chlorophyll absorbs red and blue light to use in photosynthesis and reflects green light. Chlorophyll is a large molecule and takes a lot of resources to make; as such, it breaks down towards the end of the leaf's life, and most of the pigment's nitrogen (one of the building blocks of chlorophyll) is resorbed back into the plant, according to Harvard University's The Harvard Forest. When leaves lose their chlorophyll in the fall, other leaf pigments such as carotenoids and anthocyanins begin to show their true colors. While carotenoids primarily absorb blue light and reflect yellow, anthocyanins absorb blue-green light and reflect red light.