Photosynthesis Overview

Role of Photosynthesis
1. Plants use it to make food
2. Animals eat plants
3. Produces O2
4. Responsible for the formation of fossil fuels
Equation
1. 6CO2 + 6H2O + light ------> C6H12O6 + 6O2 Chlorophyll
Stages
1. Light is absorbed
  1. Sunlight is trapped by chlorophyll
2. Water is split
  1. Trapped sunlight is split into H2O
    1. 2H2O --> 4H+ + O2 + 4e- (photolysis)
3. Products of splitting water
  1. e- = passed into chlorophyll
  2. H+ = released into a storage pool of H+ in chloroplast
  3. O2
    1. Pass from chloroplast to cytoplasm to atmosphere
    2. Used within cells of leaf in respiration
4. Light energises electrons
  1. Some of the sunlight energy trapped by chlorophyll is passed onto electrons in chlorophyll to form high energy electrons
5. Glucose is formed
  1. High energy electron from chlorophyll along with protons from pool of stored protons combine with CO2 to form glucose
Sources of light, CO2 + H2O
1. Light
  1. Sun
  2. Artificial in greenhouse
2. CO2
  1. Air (via leaf))
  2. Produced by respiration
  3. Artificial: burning gas in greenhouse
3. H2O
  1. Absorbed by plant from soil via roots, passed through stem + to leaves
Light Stage
1. Grana of chloroplast
2. No enzymes
3. Light is absorbed by a range of pigment clusters found in the chloroplast (green is reflected)
4. Light is transferred to the electron that has been passed to the chlorophyll
5. Chlorophyll is in the pigment cluster + is near an electron acceptor
6. Pigment cluster absorbs as much light energy as possible --> chlorophyll --> electron
7. Energised electron is passed to the electron acceptor which can than send it on 2 pathways
8. Pathway 1
  1. Electrons pass from the 1st electron acceptor to a series of other electron acceptors + back to chlorophyll
  2. Electrons lose energy as they're passed
  3. Lost energy is used to join a phosphate + ADP = ATP (H2O is also formed)
  4. ADP + energy + P --> ATP + H2O
    1. Phosphorylation = addition of P to ADP
  5. Cyclic Phosphorylation
9. Pathway 2
  1. 2 high energy electrons at a time pass from chlorophyll to electron acceptor + then along another series of electron acceptors
  2. Breaks up water
  3. Electrons don't return to original chlorophyll
  4. Energy lost is used to make ATP
  5. 2 e- combine with NADP+ to form NADP-
  6. Chlorophyll molecule is short of e- + gains more H+
  7. NADP- + H+ --> NADPH
  8. Non cyclic phosphorylation
10. End products
  1. ATP provides energy for dark phase
  2. NADPH provides H+ and energised e- for dark phase
  3. O2 made by splitting of H2O
Dark Stage
1. Uses energy from breaking down of ATP --> ADP + P
2. Uses hydrogen ions +e- from breaking down of NADPH --> NADP+ + 2e- + H+
3. CO2 is reduced to C6H12O6
4. Stroma of chloroplast
5. Controlled by enzymes + can be affected by temp
6. CO2 from air/respiration enters the chloroplast where it combines with H+ and e- to form glucose

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