Biology Notes (Part 13) Photosynthesis, Photosystems, and the Calvin Cycle

Photosynthesis

• ==Photosynthesis== is the conversion of light to chemical energy.

• It takes place in the chloroplasts.

• Light is part of the electromagnetic spectrum.

• ==Radiations== travel in waves and particles.

• ==Pigments== are light-absorbing molecules. Pigments found in land plants are Chlorophyll A and Chlorophyll B.

• Each pigment has a specific absorption spectrum. ==ATP== is an energy source.

• ==Pigments== are light absorbers.

• ==NADPH== are electron carriers.

• Wavelengths that are not absorbed are reflected/transmitted.

• The formula for photosynthesis is ==CO2 +12H20 light→ C6H12O6 + 6O2 + 6H20==

• ==Autotrophs== make their own food and ==heterotrophs== take food from outside sources.

• Photosynthesis consists of two reactions: light reactions and carbon-fixation reactions.

• ==Light reactions== describe light energy being used to form ATP and NADPH. Light reactions are composed of photosystems (groupings of proteins and pigment molecules).

  Photosystems I and II

• Photosystem I happens last, and Photosystems II occurs first.

• In ==Photosystem I==, NADPH is produced.

• In ==Photosystem II==, water molecules are split to produce oxygen (O2). The Electron Transport Chain powers the synthesis of ATP.

• ==Carbon-fixation reactions (Calvin Cycle)== describe how ATP and NADPH used to synthesize carbohydrates.

Calvin Cycle

• The Calvin Cycle uses ATP and NADPH to synthesize carbohydrates.
• The Calvin Cycle is a cyclical pathway.
• ==RUBP (ribulose - 1, 5 - biphosphate)== is the starting and ending compound of the cycle.
• Co2 enters plants through an opening in the leaves called “stomata.”
• The Calvin Cycle occurs in three stages: carbon fixation, reduction, and regeneration.
• In the ==Carbon Fixation stage==, CO2 (a gas) is converted to a solid form (a carbohydrate). This is the main purpose of the Calvin Cycle.
• The Carbon Fixation stage is catalyzed by carboxylase (rubisco).
• Carbon is attached to RUBP.
• The result is two ==3-carbon molecules (3PC)==.
• In the ==Reduction Phase==, 3PG is reduced by NADPH with energy from the breakdown of ATP.
• This results in the formation of ==2 3PG (glyceraldehyde - 3 - phosphate) molecules==.
• G3P is the starting molecule for many plant cell metabolic pathways.
• In the ==Regeneration Cycle==, there are three turns of the Calvin Cycle which generate six molecules of G3P.
• RUBP is regenerated using 5 molecules of G3P.
• The remaining G3P molecules used to synthesize carbohydrates and other necessary molecules.

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