Photosynthesis

1
Photosynthesis

• Modern Biology Chapter 6
• Biology Exploring Life Chapter 8

2
Biochemical Pathways

• Series of linked chemical reactions in which the
  product of one reaction is consumed in the next
  reaction
• Ex. Redox Reactions
• Chemical reactions in which electrons are
  transferred between atoms
• Electron(s) given up by one substance is/are then
  accepted by another substance
• Oxidation reactant loses one or more electrons
• Reduction reactant gains one or more electrons

3
Photosynthesis

• Occurs in chloroplasts of eukaryotic cells
• Conversion of light energy to chemical energy
  stored in organic compounds, such as glucose
• 6 CO2 6 H2O ? C6H12O6 6 O2
• Two stages
• Light Reactions
• Calvin Cycle

4
Chloroplast Anatomy

• Thylakoids/granaLight Reactions
• Photosystems I II
• Chlorophyll a
• Accessory pigments
• Chlorophyll b
• Carotenoids
• StromaCalvin Cycle

5
Light Reactions

• Light Absorption
• Excites electrons in two chlorophyll a molecules
  in each of the two photosystems
• Electron Transport Chains (redox rxns.)
• Photosystem I Electrons reduce NADP to NADPH.
• Photosystem II
• Energy released from electron transfer pumps
  protons (H) into thylakoid.
• Electrons replace those lost from photosystem I.
• Splitting of H2O produces O2, more protons for
  the thylakoid, and electrons to replace those
  lost from photosystem II.

6
Light Reactions (continued)

• Chemiosmosis
• Movement of protons from the inside of the
  thylakoid into the stroma provides energy for the
  synthesis of ATP, the main energy currency of
  cells
• Summary
• 6 H2O NADP ADP P ? 6 O2 NADPH ATP

7
Calvin Cycle

• Carbon fixation
• Energy from NADPH and ATP reduces CO2 to C6H12O6.
  
• Summary
• 6 CO2 NADPH ATP ? C6H12O6 NADP ADP P

8
Summary of Photosynthesis

• Light Reactions
• 6 H2O NADP ADP P ? 6 O2 NADPH ATP
• Calvin Cycle
• 6 CO2 NADPH ATP ? C6H12O6 NADP ADP P
• Photosynthesis overall
• 6 CO2 6 H2O ? C6H12O6 6 O2