Photosynthesis

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Photosynthesis

  1. 1. Photosynthesis!<br />
  2. 2. Intro <br />Organisms (autotrophs) obtain energy from the sun and store it in organic compounds (glucose) during photosynthesis<br />Energy is necessary to do work<br />Growth and repair, active transport across membranes, reproduction, synthesis, etc.<br />Carbon dioxide and water are combined to create glucose and oxygen<br /> 6CO2 + 6H2O + energy 6O2 + C6H12O6<br />
  3. 3. Chloroplasts!<br />Absorb sunlight during the light dependent reactions<br />Double membrane organelles with an inner membrane folded into discs called thylakoids<br />Thylakoids contain chlorophyll and are arranged into stacks called granum<br />Granum is surrounded by a gel-like material called stroma<br />Light-capturing pigments in granum are organized into photosystems<br />
  4. 4. Pigments in Chloroplasts!<br />When all colors are absorbed the object appears black<br />When all colors are reflected the objects appears white<br />If a color is reflected the object appears that color<br />Chlorophyll a and chlorophyll bare common types of chlorophyll<br />The light energy absorbed in chlorophyll b is transferred to chlorophyll a in the light reactions<br />
  5. 5. Overview!<br />Light Reactions (H2O O2 + ATP + NADPH2)<br />Water splits, giving off oxygen<br />Dependent on sunlight for activation<br />Light is absorbed by chlorophyll a and “excites” the electrons in the cholorphyll molecule<br />Electrons are passed through a series of carriers and ATP is produced<br />Takes place in thylakoids<br />
  6. 6. Overview (cont.)<br />Dark Reactions (ATP + NADPH2 + CO2 C6H12O6)<br />Carbon dioxide is split, providing carbon to make sugars<br />Glucose is the final product<br />Does not require light energy<br />Includes the Calvin Cycle<br />Takes place in the stroma<br />
  7. 7. The Calvin Cycle!<br />STEP 1<br />CO2 is diffused into the stroma<br />An enzyme combines CO2 with a five-carbon carbohydrate called RuBP<br />The resulting six-carbon molecule splits into a pair of three-carbon molecules called PGA <br />
  8. 8. The Calvin Cycle (cont.)<br />STEP 2<br />Each PGA molecule receives a phosphate group from ATP<br />It also receives a proton from NADPH and releases a phosphate group producing PGAL<br />This produces ADP, NADP+, and phosphate which are used in Light Reactions<br />
  9. 9. The Calvin Cycle (cont.)<br />STEP 3<br />Some PGAL is converted to RuBP to continue the cycle<br />Some PGAL leaves the cycle to create organic compounds<br />Each turn of the cycle fixes one CO2 molecule and it takes six turns to make one glucose molecule<br />
  10. 10. Photosystems and ETC!<br />Only 1/250 chlorophyll molecules (chlorophyll a) actually convert light energy into usable energy – these are called reaction-center chlorophyll<br />Other molecules (chlorophyll b, c, d, and carotenoids absorb light and send it to the reaction-center chlorophyll – aka antenna pigments<br />Photosystem – a unit of hundreds of antenna pigments and a reaction center (Photosystem I and II)<br />Light is absorbed by the antenna pigments of photosystem I and II <br />
  11. 11. Photosystems and ETC (cont.)<br />Photosystem I<br />Energy is moved to the reaction center (P700)<br />Electrons from the water are moved to the cytochrome complex<br />Activates P700 which reduces NADP+ to NADPH<br />Photosystem II<br />Energy is moved to the reaction center (P680)<br />P680 loses an electron and becomes positive<br />It can now split water and release electrons<br />
  12. 12. Chemiosmosis<br />ATP<br />The making of<br />Dependent on the concentration gradient of protons (H+) across the thylakoid membrane<br />Concentration of protons is higher inside the tylakoid<br />ATP synthase creates ATP by adding a phosphate group to ADP <br />
  13. 13. Alternate Pathways<br />C3 plants commonly use the Calvin cycle<br />Stomata are small openings in the leaves for gas exchange<br />Guard cells open and close the stomata<br />C4 plants fix CO2 to four-carbon compounds during the hottest part of the day when the stomata is partially closed<br />
  14. 14. Rate of Photosynthesis<br />Light intensity – as intensity increases the rate increases and eventually levels off into a plateau<br />Temperature – only dark reactions are dependent on temperature because of the enzyme<br />Increasing amount of CO2increases rate of photosynthesis<br />

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