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Understanding Photosynthesis: The Processes and Importance of Plant Energy Conversion

Photosynthesis is the biological process that converts sunlight into chemical energy, producing glucose and oxygen from carbon dioxide and water. This process includes two main phases: the light-dependent reactions that occur in the thylakoids, using light energy to produce ATP and NADPH, and the Calvin Cycle, which takes place in the stroma to create glucose from ATP, NADPH, and CO2. Additionally, photosynthesis is essential for providing the oxygen we breathe and serves as the foundation for energy transfer in ecosystems.

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Understanding Photosynthesis: The Processes and Importance of Plant Energy Conversion

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  1. PHOTOSYNTHESIS

  2. Photosynthesis • Converts sunlight energy into chemical energy

  3. Chemical Equation • 6CO2+ 6H2O +light energyC6 H 12 O 6 + 6O2 • Carbon dioxide and water are the reactants and glucose and oxygen are the products. • Chlorophyll is the pigment necessary to run the reaction.

  4. Requirements • Light Energy (Sun) • Chlorophyll a,b and accessory pigments (these absorb wavelengths of light) • Raw materials (CO2 and H2O ) • Enzyme: NADP (taxi cab)

  5. Leaf has many layers of specialized cells. Notice the location of the chloroplasts. Cross Section of a Leaf

  6. Stomata • Stomata(leaf mouth) allows gas exchange (O2 and CO2) guard cells create the stomata

  7. Inside the Chloroplast • Saclike membranes called thylakoids contain chlorophyll and accessory pigments. • Stacks of Thylakoids are called Grana. • Stroma is the fluid filled space.

  8. Chloroplast Again Notice the grana are stacks of thylakoids • Chloroplast Below

  9. The Two Phases of Photosynthesis • Phase I - Light Dependent Reaction (occurs in thylakoids) • Light energy is absorbed and converted to chemical energy in the form of ATP and NADPH. • Phase II- Dark Reaction (Calvin Cycle) (occurs in stroma) • NADPH and ATP that were formed during light dependent reactions are used to make glucose.

  10. Light Reactions Overview: 1. Light energy is absorbed in the THYLAKOID. 2. Water is split or pulled apart: 2H and ½ O2 3. CO2 is NOTinvolved yet. 4. ATP is formed. 5. Reactants: chlorophyll, light energy, water, and NADP.

  11. Light Reactions Steps: • Light energy is absorbed by chlorophyll. • Electrons in chlorophyll become “excited” (high energy) and split H2O apart. H2O: 2H + ½ O2 * 6 molecules of water total are split apart: 12 H+ , 6, ½ O2(released into air as a byproduct). 3.An electron is released into the electron transport system.

  12. Light Reactions 4. NADP picks up the H + and electronsand transports them across the thylakoid membrane into the stroma. NADP + H +  NADPH * 6 H2O are split: 12 NADPH are formed by the Light Reaction.

  13. 5. Hydrogen protons (H+) move across the thylakoid into the stroma to create ATPs from ADPs.

  14. Products of Light Reactions • 6, ½ O2 are released into the air via stomata. • NADPH and ATPgo to the stroma for Phase II (The Calvin Cycle).

  15. Calvin Cycle or Dark Reaction • Reactants: • ATP and NADPH from Light Reactions • 6 CO2 • 6 RuBP (ribulosebisphosphates) • Products: Glucose (C6H12O6) and 6 RuBP • Takes place in the stroma.

  16. Steps of the Calvin Cycle (Dark Reaction) • CO2 Fixation: CO2 combines with RuBP6CO2 + 6RuBP 12 PGA PGA is a 3-Carbon molecule and is UNSTABLE! Total: 6 CO2 + 6 RuBP 12 PGA

  17. Calvin Cycle 12 PGA + 12 ATP + 12 NADPH 12 G3P+ 12 ADP + 12 NADP * What happens to NADP? ADP? * PGA and PGAL are 3 Carbon molecules.

  18. Calvin Cycle Con’t. • Formation of glucose: 2G3P 2Glucose C3H6O3 + C3H6O3  C6H12O6 * Recall: G3Pis a 3- Carbon molecule.

  19. Calvin Cycle

  20. Importance of Photosynthesis • Forms glucose which is necessary for cellular respiration. • Forms the source of oxygen we breathe.

  21. Factors that Affect Photosynthesis • 1. Amount of water • 2. Temperatures • 3. Light Intensity • 4. Amount of CO2

  22. Summary of Photosynthesis

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