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X. PHOTOSYNTHESIS

Learn about the process of photosynthesis, its location in plants, the structure of chloroplasts, the light reaction, and the Calvin cycle. Explore the role of pigments in capturing light energy and producing chemical energy. Discover how plants adapt to different environmental conditions.

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X. PHOTOSYNTHESIS

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  1. X. PHOTOSYNTHESIS • ______________________ – Process of capturing light energy and converting it to chemical energy • Equation: __________________________________ • Plants are ________________ – “self-feeders”; also known as producers. • Ultimate source of all organic compounds comes from autotrophs • _______________________ – use sunlight as energy source • Chemoautotrophs – do not use sunlight as energy source, use other compounds such as ammonia and sulfur

  2. Location of Photosynthesis • Any green part of the plant has chloroplasts (site of photosynthesis) • Leaves contain the most chloroplasts • - Green color comes from • ___________________ • - Chloroplasts are found mainly in the region of the leaf known as _________________ • - CO2 enters leaf through openings known as ________________ • - H2O enters via roots and is transported via veins

  3. Chloroplast Structure • ________________ – site of Light Reaction – 1st step in photosynthesis • __________ – stacks of thylakoids • _____________ – site of Calvin Cycle – 2nd step in photosynthesis

  4. X. PHOTOSYNTHESIS OVERVIEW, cont

  5. XI. LIGHT REACTION OF PHOTOSYNTHESIS • Occurs in _______________membranes • Converts light energy to chemical energy • Light energy • Visible light is a small portion of the electromagnetic spectrum. • Light ____________ by chlorophyll and other photosynthetic pigments to power reactions is _____seen. Light not utilized by plant is reflected & seen by human eye. • Absorption spectrum – graph illustrating how different pigments absorb different wavelengths of light • Action spectrum – graph illustrating rate of photosynthesis vs. wavelength • Light energy measured in _______________.

  6. XI. LIGHT REACTION OF PHOTOSYNTHESIS • 3 Photosynthetic pigments • ***1) Chlorophyll a – absorbs mainly blue-violet and red light • 2) Chlorophyll b – absorbs mainly blue and orange light • 3) Cartenoids – other accessory pigments; expand spectrum of light • energy that can be used for photosynthesis

  7. XI. LIGHT REACTION OF PHOTOSYNTHESIS • A photon of light energy is absorbed by pigment molecule in Photosystem II. • Energy is passes from one molecule to another until it reaches P680 pair of chlorophyll a molecules. • Electron is excited to higher energy state – transferred to primary electron acceptor. • Water is split to replace electron lost by P680. O2 is released and H+ ions remain.

  8. XI. LIGHT REACTION OF PHOTOSYNTHESIS Excited electron moves from primary electron acceptor to Photosystem I via electron transport chain. As electron “falls”, energy is released. Used to synthesize ATP through chemiosmosis. Light energy is transferred via light-harvesting complexes to P700 in Photosystem I. Excited electron is captured by primary electron acceptor. P700’s electron is replaced by electron transport chain on Photosystem II. Electron from P700 moves through a short electron transport chain, reducing NADP+ to NADPH. Noncyclic Phosphorylation

  9. XI. LIGHT REACTION OF PHOTOSYNTHESIS

  10. XI. LIGHT REACTION OF PHOTOSYNTHESIS Cyclic Electron Flow • Alternative pathway seen in some bacteria, plants • May be photoprotective in plants • Only utilizes Photosystem I • No NADPH production • No O2 release • Does generate ATP • So…..what’s the point??? • To generate excess ATP without generating NADPH • Calvin Cycle uses more ATP than it does NADPH

  11. XII. CALVIN CYCLE OF PHOTOSYNTHESIS • Also known as ______________________, Light-Independent Rxn • Occurs in _______________ of chloroplasts • “Synthesis” part of photosynthesis • Utilizes __________, __________ generated in Light Reaction, and ___________ to produce organic molecules • Anabolic; endergonic • Requires enzyme _______________ • Three basic steps • Carbon Fixation • Reduction • Regeneration of RuBP

  12. XII. CALVIN CYCLE OF PHOTOSYNTHESIS Input 3 CO2 , 9 ATP, 6 NADPH Output 1 G3P, 6 NADP+, 6 Pi, 9 ADP

  13. XIII. PLANT ADAPTATIONS • Major problems facing terrestrial plants is ______________. • At times, solutions to this problem conflict with other metabolic processes, especially photosynthesis. • The _____________ are not only the major route for gas exchange (CO2 in and O2 out), but also for the evaporative loss of water. • On hot, dry days plants __________ the stomata to conserve water, but this causes problems for photosynthesis.

  14. XIII. PLANT ADAPTATIONS C 4 CAM

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