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Photosynthesis

Photosynthesis. Honors Biology. Overview of Photosynthesis. What is Photosynthesis? 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 light energy Photosynthesis is the process of converting light energy into food energy (glucose, chemical energy stored in chemical bonds).

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Photosynthesis

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  1. Photosynthesis Honors Biology

  2. Overview of Photosynthesis • What is Photosynthesis? • 6 CO2 + 6 H2O → C6H12O6 + 6 O2 light energy • Photosynthesis is the process of converting light energy into food energy (glucose, chemical energy stored in chemical bonds). • Photosynthesis carried out by plants and algae.

  3. Structures of Photosynthesis • Cross-section of a Leaf: • 6 CO2 + 6 H2O → C6H12O6 + 6 O2 light energy

  4. Structures of Photosynthesis • Cross-section of a Leaf: • Palisade Mesophyll • Spongy Mesophyll • Guard cell • Stomata • Epidermis • Cuticle • Vein

  5. What is Solar Energy and Visible Light? • Visible Light is made of photons that travel at various wavelengths and frequencies. • Photons (packets of energy) are formed when an electron is energized and moves to a higher energy level, which is unstable. When the electron falls back to its original energy level, then a photon is released that travels at a particular wavelength. • The longer the wavelength, the lower the energy. The shorter the wavelength, the higher the energy.

  6. What is Solar Energy and Visible Light? • Visible light is only one form of energy in the Electromagnetic Spectrum. • Different colors of light have different wavelengths. • Which color of light contains the most energy? Least energy?

  7. How do Plants Capture Solar Energy for use in Photosynthesis? • Each plant cell contains 40-50 chloroplasts. • Chloroplasts contain pigments that either absorb or reflect different wavelengths of visible light. Absorbed wavelengths are used for photosynthesis. • Each thylakoid membrane contains 250-400 chlorophyll pigments

  8. Review Parts of a Chloroplast

  9. Plant Pigments • Reaction Center Pigment = Chlorophyll a • Antennae/Accessory Pigments = Chlorophyll b, carotenoids, phycobilins (red algae) • What is the absorption spectra for each pigment? (spectrophotometer) • Chlorophyll a and b – red, orange, yellow, blue, and violet (reflects green) • Carotenoids – violet, blue, and green (reflects red, orange, and yellow) • Phycobilins – violet, blue, green, yellow, and orange (reflects red)

  10. Photosynthesis is Composed of 2 Reactions: • What are the two main reactions of Photosynthesis? Reactants? Products? Where located? • Light-Dependent reactions = Energy capturing reactions, captures solar energy and traps it as ATP and NADPH. Occurs in Thylakoid membranes. • Light-Independent reactions = Synthesis reactions, uses the ATP and NADPH and captured CO2 to make glucose. Occurs in the Stroma.

  11. What factors affect the rate of photosynthesis? • Amount of Visible light and CO2: • Amount of H2O, Minerals, Temperature:

  12. Light-Dependent Reactions: 1. Photosystem II absorbs light energy and transfers an excited electron to the Primary electron acceptor.

  13. Light-Dependent Reactions: 2. Primary Electron Acceptor molecule transfers high energy electrons to the Electron Transport System, which establishes a H+ ion gradient across the thylakoid membrane.

  14. Light-Dependent Reactions: 3. Energy from the Electron Transport Chain establishing a H+ ion gradient is used for Chemiosmotic Phosphorylation production of ATP. (Photophosphorylation)

  15. Light-Dependent Reactions: 4. The electron from the Electron Transport System is accepted by the reaction center chlorophyll of Photosystem I. 5. The Electron Acceptor molecule of Photosystem I sends its electron to ultimately form NADPH.

  16. Light-Dependent Reactions Reviewed Where does the light reaction take place? • At the thylakoid membrane What are the inputs to the light reactions? • Light energy, water What are the products of the light reaction? • ATP, NADPH, and O2

  17. Light-Independent Reactions (Calvin Cycle) • Synthesis reactions that occur in the stroma • CO2 + ATP + NADPH → Glucose • Carbon dioxide – comes into the leaf via stomata • ATP and NADPH – from the Light reactions • No light required but typically occurs during the day

  18. Three stages of the Calvin Cycle: 1. Carbon Dioxide Fixation 2. Carbon Dioxide Reduction 3. Regeneration of RuBP

  19. Review Photosyntheis • What are the two reactions of photosynthesis? • How are the light reactions connected to the Calvin cycle?

  20. Three Modes of Photosynthesis • C3 Plants • C4 Plants • CAM Plants • The pathways of photosynthesis discussed in this presentation are for C3 plants. • Examples: wheat, rice, oats • Optimum temperature = 15-25°C

  21. C4 Plants • Mesophyll cells fix CO2 into a C4 molecule (oxaloacetate) during the day. • Uses PEPCase enzyme instead of Rubisco to fix CO2 • C4 molecule pumped to Bundle sheath cells where Calvin Cycle occurs. • Examples: sugar cane, corn, bermuda grass, crabgrass • Net photosynthetic rate is greater than C3 plants. • More heat tolerant, optimum temperature = 30-40°C

  22. CAM Plants • Like C3 plants, Mesophyll cells fix CO2 in the Calvin Cycle, but it occurs at night. Stomata only open at night to bring in CO2 and reduce water loss. • Like C4 plants, CO2 is fixed into a C4 molecule and then stored in large vacuoles in mesophyll cells to be used the following day when ATP and NADPH are available from the light reactions. • Uses PEPCase enzyme instead of Rubisco to fix CO2 • Examples: succulents like cacti that live in deserts (CAM = Crassulacean-acid metabolism) • Low photosynthetic rate, variable • Most heat tolerant, optimum temperature = 35°C

  23. Review C3, C4, and CAM plants • What are the differences between C3, C4, and CAM plants?

  24. References • http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html

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