Overview of Photosynthesis

Tianna

pho·to·syn·the·sis

/ˌfōdōˈsinTHəsəs/

noun

the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a byproduct.

How it works

Plants take water up from their roots, take in sunlight and carbon dioxide through their leaves and turn it into sugars and oxygen. The two main processes used to do this are Light Reactions and The Calvin Cycle. The chemical equation for photosynthesis is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Light Reactions

Light reactions take place inside the thylakoids of the chloroplasts. Water and light enter the thylakoid membrane and produce NADH and ATP. Oxygen is a waste product of light reactions.

An electron moves through the electron transport chain (a cluster of proteins) in the thylakoid membrane and is powered by light. It goes through Photosystems 2 and 1 and other proteins and creates NADH. Water splits and oxygen diffuses through the membrane, and the positively charged hydrogen atoms stay on the inside. Every time the electron goes through a protein it pumps protons to the inside, building up a positive charge. The protons move out through a protein called ATP -Synthase and ATP is created.

The Calvin Cycle

The Calvin Cycle takes place in the stroma of chloroplasts. The energy made from Light Reactions (NADH, ATP) transfers to the Calvin Cycle. Carbon Dioxide enters the chloroplast, and together with the NADH and ATP creates glucose.

ATP and NADH provide energy at various points in the Calvin Cycle. Carbon dioxide, a 1 carbon molecule, and RUBP, a 5 Carbon molecule, are attached by an enzyme called Rubisco. This creates a 6 carbon molecule that breaks into two 3 carbon molecules. They get energy from ATP and produce G3P. G3P is turned into glucose, some are released, and some are recycled back into the Calvin Cycle to make more RUBP.

Photorespiration

Photorespiration occurs when its really hot and the plant get enough CO2 because their stomata (where CO2 enters) is closed so they don't lose water. Oxygen then enters the Calvin Cycle and makes a useless chemical and not G3P. Some plants only open their stomata at night or turn CO2 into a chemical they can access later to avoid this problem.

Here is a video explaining photosynthesis in more detail.

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