Photosynthesis

• Diffusion is essential to photosynthesis for the movement of molecules of:

  
  

  -CO2 from outside the leaf inside the green leaf cells

  
  

  -O2 from inside the green leaf cells to outside the leaf
• What do plant cells need glucose for?

  
  

  -Respiration which provides chemical energy for cellular processes including:

  
  

  -Cell division

  
  

  Protein Synthesis

  
  

  Excess can be converted into:

  
  

  -STARCH which is a storage carbohydrate (can be broken down to

  glucose again when the cell needs a source of energy).

  
  

  -CELLULOSE which is a structural carbohydrate (used to build

  plant cell walls).
• 2 stages – take place in chloroplast

  
  

  Light reactions

  
  

  -splitting of water

  
  

  Carbon fixation

  
  

  -CO2 combined with H to make glucose
• Light Reactions

  
  

  -Solar (light) energy is trapped by chlorophyll and converted to chemical

  energy.

  
  

  -This energy is used to split molecules of water into hydrogen and oxygen.

  
  

  -Chlorophyll also provides enough energy for the regeneration of ATP

  from ADP and Pi which is used in Stage 2 (Carbon Fixation).
• Light Reactions (cont'd.)

  
  

  -The oxygen is released as a by-product and leaves the cell by diffusion.

  
  

  -The hydrogen combines with a hydrogen acceptor. When loaded with

  hydrogen, the acceptor is said to be reduced. The Hydrogen is also

  needed in Stage 2 (Carbon Fixation).
• Carbon Fixation

  
  

  -Also occurs in chloroplasts.

  
  

  -A series of enzyme controlled reactions which form a cycle.

  
  

  -Allows the carbon in CO2 to become ‘fixed’ into carbohydrate by

  combining with the hydrogen produced during the light reactions.

  
  

  -Carbon fixation results in the formation of glucose (sugar).

  
  

  -Energy is supplied by the ATP from stage 1.
• Limiting Factors of Photosynthesis

  
  

  • Temperature
  • Light intensity
  • CO2 Concentration