Photosynthesis

Photosynthesis – transfer of light energy into the chemical energy of sugars and other organic food molecules using CO2 and H2O

Light energy

6CO2 + 6H2O ------ C6H12O6 + 6O2

in chloroplasts

in presence

carbon dioxide + water ------ glucose + oxygen

of light

  • fuel for cell respiration ultimately comes from photosynthesis

Chloroplast – site of photosynthesis, contains chloroplasts

2 parts of chloroplast:

grana: stacks of thylakoids (one sac) where light reactions occur

stroma: fluid around grana where dark reactions occur

- Traps energy during photosynthesis

- Chlorophyll a is most efficient pigment

- Other accessory pigments absorb other wavelengths of light and transfer light

to chlorophyll a

Energy storing compounds of photosynthesis:

1)NADP – add hydrogen to reduce it, becomes electron carrier to transfer energy to another compound Ex: NADP+ + H2 - NADPH + H+

2)ATP – cell’s energy source; formed in mitochondria during cell respiration * only a small amount is made during photosynthesis

Photosynthesis Overview: 2 parts – Light reactions and Calvin cycle

  1. Light reactions
  2. Where: In Grana of chloroplasts
  3. When: In presence of light
  4. How:
  5. Light energy trapped and transferred to chlorophyll A
  6. Absorbed light energy excites electrons to move down electron transport chains
  7. This energy splits H2O into 2H and an O atom, O is released combines with other single O to form O2 – released
  8. 2H are trapped by NADP to form NADPH + H + sent to Stroma for use in Calvin cycle (dark reaction)
  9. Energy from electron transport chains powers chemiosmosis across thylakoid membranes to make ATP for use in Calvin cycle
  10. Why:
  11. ATP and NADPH produced to power dark reaction (Calvin cycle)
  12. O2 from split H2O diffuses into the atmosphere

All of this is H2O being oxidized to form O2

  1. Calvin cycle (AKA dark reactions)
  2. Where: Stroma of chloroplasts
  3. When: all the time
  4. How:
  5. CO2 from atmosphere combines with RuBP (5C) to form 6C sugar
  6. 6C sugar breaks into 2 PGA (3 carbons each)
  7. PGA uses ATP to pull 2H from NADPH (From light reactions) to make G3P (3C). H2O released as a byproduct.
  8. 2 G3P’s form Glucose C6H12O6 (or other organic compound). Others go back to make more RuBP – restart cycle
  9. Why:
  10. Glucose produced to power cell respiration
  11. G3P can be used to make ATP in emergencies or to make other organic compounds
  12. Makes more RuBP to restart cycle

All of this is CO2 being reduced to form C6H12O6

««GreetingLine»»