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PHOTOSYNTHESIS

Life’s ultimate reaction. PHOTOSYNTHESIS. Photosynthesis. The definition : A process in which light energy, water and carbon dioxide are used to create glucose for energy. Photo = light Synthesis = to make All of life stems from this reaction!.

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PHOTOSYNTHESIS

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  1. Life’s ultimate reaction PHOTOSYNTHESIS

  2. Photosynthesis The definition: A process in which light energy, water and carbon dioxide are used to create glucose for energy. Photo= light Synthesis= to make All of life stems from this reaction!

  3. Name: ______________________________________ Date: _____________________ #______ Photosynthesis The Chemical Equation 6 CO2 6 H2O C6H12O6 6 O2 + + Carbon dioxide + light energy water glucose oxygen

  4. Photosynthesis • Photosynthesis takes place in the chloroplasts. Only the cells of the leaf have chloroplasts. • In eukaryotic cells, the chloroplasts contain specialized light-absorbing pigments. Chloroplast

  5. Pigments • Chlorophyll A (green) is the most important photosynthetic pigment. • Other pigments called antenna or accessory pigments are also present in the leaf. • Chlorophyll B (also green) • Carotenoids (orange / red) • Xanthophylls (yellow / brown) • These pigments are embedded in the membranes of the chloroplast in groups called photosystems.

  6. Photosynthesis: The Chemical Process • Occurs in two main phases. • Light reactions • Dark reactions (aka – the Calvin Cycle) • Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. • Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.

  7. Light Reactions- Overview • Light reactions occur in the thylakoids of the chloroplast. • Light and water are required for this process. • Energy storage molecules are formed. (ATP and NADPH) • Oxygen gas is made as a waste product.

  8. Light Reactions- Specific Steps • Step one: pigments absorb light energy • Step two: pigment electrons gain the energy and jump an energy level (described as “excited electrons”). • Step three: Excited electrons enter an electron transport chain (a series of proteins). • As the electrons are passed from protein to protein, chemical energy is generated and stored in ATP and NADPH (energy storage molecules or energy “carriers”).

  9. Light Reactions- Photolysis Aside from the chain of reactions that occur when pigments absorb light energy, there is another occurrence going on “behind the scenes” during the light reactions. This occurrence is known as photolysis. Photo=light Lysis= to break or split

  10. Light Reactions- Photolysis • During photolysis, water molecules are split apart into hydrogen ions, electrons, and oxygen gas. • Important because the electrons are used to replace excited electrons so that the thylakoids remain stable. • Oxygen gas is released as waste into the atmosphere. • Hydrogen is used to convert NADP+ into NADPH

  11. Dark Reactions- Overview • Dark reactions (light-independent) occur in the stroma. • Carbon dioxide is “fixed” into the sugar glucose in a process known as carbon fixation • ATP and NADPH molecules created during the light reactions power the production of this glucose.

  12. Dark Reactions- The Calvin Cycle • During the Calvin cycle, carbon dioxide from the atmosphere enters a series of reactions and is used to create glucose, as well as other carbon-based compounds. • NADPH and ATP produced in the earlier light reactions are important for this series of reactions. • One glucose molecule is produced per two cycles. • Leftover compounds are recycled. • The process repeats.

  13. Steps of the Calvin Cycle 1. Carbon fixation: One carbon atom from CO2 is added to a 5-carbon sugar called ribulosebiphosphate (RuBP). 2. PGA Formation: The unstable six-carbon sugar formed in step 1 is then split into 2 molecules of phosphoglyceric acid (PGA). 3. Use of ATP and NADPH: A series of reactions involving ATP and NADPH from the light reactions converts a molecule of PGA into PGAL (phosphoglycer-aldehyde), another 3-carbon compound.

  14. 4. Glucose production: After several rounds of the Calvin cycle, two molecules of PGAL leave the cycle to form glucose. 5. ATP and PGAL replenish RuBP: Some PGAL molecules are recycled and reform the 5-carbon RuBP with the help of ATP. Each 5-carbon RuBP is ready to begin the cycle again.

  15. CO2 C-C-C-C-C (RuBP) Unstable ADP + P ATP ATP ADP + P NADPH C-C-C-C-C-C (glucose) NADP +

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