Photosynthesis

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Photosynthesis

  1. 1. Photosynthesis
  2. 3. Photosynthesis <ul><li>Method of converting sun energy into chemical energy usable by cells </li></ul><ul><li>done by autotrophs </li></ul><ul><li>takes place in specialized structures inside plant cells called chloroplasts </li></ul>
  3. 4. <ul><li>Capturing light energy </li></ul><ul><li>Using captured energy to make ATP and NADP + (energy carrying co-enzyme like NAD. It is reduced by 2 H atoms to NADPH + + H + ) </li></ul><ul><li>Using ATP and energy from NADPH to synthesize molecules like glucose. </li></ul><ul><li>first 2 steps require sunlight (light dependant) and occur in chlorophyll </li></ul><ul><li>last step does not necessarily need sunlight (light independent) and takes place in stroma </li></ul>3 Steps of Photosynthesis
  4. 6. Light-Dependent Phases <ul><li>occurs in thylakoid membrane </li></ul><ul><li>light energy converted to chemical energy of ATP & NADPH (reduced NADP = NADPH) </li></ul><ul><li>photosystems (highly organized light capturing complexes) are found in thylakoid membranes and made of 2 parts: </li></ul><ul><ul><ul><li>antenna complex – system of chlorophyll molecules and pigments that transfers energy to reaction centre </li></ul></ul></ul><ul><ul><ul><li>reaction centre – protein complex containing chlorophyll a that absorbs energy from antenna complex and raises it to high energy level to start photosynthesis </li></ul></ul></ul>
  5. 7. <ul><li>there are 2 kinds of photosytems (I and II) depending on which wavelength of light chlorophyll a absorbs </li></ul>
  6. 8. Steps in Light Dependent Reactions <ul><li>Photoexcitation: </li></ul><ul><li>Sunlight hits leaf and some energy passes into stroma then absorbed by antenna complex of photosystem II and passed along to chlorophyll a . </li></ul><ul><li>Electron Transport: </li></ul><ul><li>An electon gets boosted to a higher level and passed along a ETC (like in cellular respiration) in thylakloid membrane. </li></ul><ul><li>This energy boost also causes H 2 O to split which releases H + ions and O 2 which is vital to other living things. </li></ul>
  7. 9. <ul><li>e- passes through several carriers via redox reactions releasing energy as they pass through the proteins. H + ions are pumped from stroma into intermembrane space which creates electrochemical gradient. </li></ul><ul><li>Chemiosmosis: </li></ul><ul><li>H + ions move through ATPase complex back into stroma converting ADP to ATP a process called photophosphorylation . It takes 4 H + to make 1 ATP. </li></ul><ul><li>At same time light of a different wavelength is also striking photosystem 1. e - from P1 pass through another ETC, then move to enzyme NADP reductase that reduces NADP to NADPH which moves to Light Independent Phase . </li></ul>
  8. 10. <ul><li>Reactants: H 2 O, sunlight </li></ul><ul><li>Products: ½ O 2 , NADPH, ATP </li></ul><ul><li>YouTube - Light (Dependant) Reactions of Photosynthesis Animation </li></ul>
  9. 13. 2. Light Independent Reactions (the Calvin Cycle) <ul><li>ATP and NADPH generated in light reactions used to fuel the reactions which take CO 2 and break it apart, then reassemble the carbons into glucose. </li></ul><ul><li>called carbon fixation : taking carbon from an inorganic molecule (atmospheric CO 2 ) and making an organic molecule out of it (glucose) </li></ul><ul><li>occur in stroma </li></ul><ul><li>don’t require light </li></ul><ul><li>also known as C 3 Cycle </li></ul>
  10. 15. Steps in Light Independent Phase: <ul><li>Carbon Fixation </li></ul><ul><li>CO 2 molecule combines with 5C molecule called RuBisCO (ribulose biphosphate) to produce 2, 3C molecules called 3-PGA (3-phosphoglycerate). </li></ul><ul><li>2. Reduction Reactions </li></ul><ul><li>3-PGA phorphorylated by ATP then reduced by NADPH to produce G3P (glycerate 3-phosphate). </li></ul><ul><li>3. RuBisCO Regeneration </li></ul><ul><li>G3P phosphorylated by ATP to re-create RuBisCO to restart the cycle. For every 2 G3P, 1 molecule glucose is removed from cycle, so need 6 CO 2 to create 1 glucose. </li></ul>
  11. 17. Other Methods of Carbon Fixation Succulents, cacti, orchids, pineapple… Water efficiency night CAM Corn, sugar cane, grasses… Faster photosynthesis day C 4 Most plants Uses fewer ATP day C 3 Examples Advantages Stomata open Type of carbon fixation

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