Photosynthesis

Photosynthesis

1. Leaf structure

   • Large surface area
   • Leaves minimise overlapping.
   • Thin = short diffusion pathway.
   • Transparent cuticle
   • Long narrow mesothelioma cells.
   • Air spaces
   • Large number of stomata
   • Xylem and phloem

2. Chloroplast structure

   • Small and flattened
   • Double membrane = chloroplast envelope
   • Thylakoids are stacked up grana
   • Lamellae link thylakoid membranes
   • Photosynthetic pigments
   • Two photosystems
   • Stroma

3. Light dependent reaction

   • Non-cyclic photophosphorylation
     • PSII absorbs light
       • Pair of electrons excited
         • Move to higher energy level
           • Free electrons taken up by electron carrier.
             • Redox reactions
               • Photolysis of water
                 • Replenishes lost electrons
                   • Protons move into thylakoid
                     • Protons move down concentration grdaient
                       • Energy causes ADP +Pi = ATP
                         • PSI electrons excited, moving them to higher energy level
                           • NADP reduced using H ions and electrons
   • Cyclic photophosphorylation
     • Electrons are recycled and continuously flow through PSI.
   • Occurs in thylakoid membrane

4. Light independent reaction

   • Carbon dioxide combines with RuBP
     • 6C unstable
       • Breaks down to glycerate-3-phosphate (GP)
         • ATP (light dependent stage) provides energy
           • GP turns into triose phosphate (TP)
             • Reduced NADP recycled to NADP
               • TP converted to useful organic compounds
                 • RuBP regenerated
                   • ATP produced
   • Occurs in stroma

5. Factors affecting photosynthesis

   • Temperature
   • Carbon dioxide
   • Light intensity