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• Photosynthesis is the way that plants, algae, some protists and some bacteria produce glucose using sunlight
• Photoautotrophic organisms


  Organisms that produce their own food using sunlight
• Photosynthesis


  • Light energy from the sun is transformed into chemical energy in the form of glucose
  • Most efficient in wavelengths of red and blue
• Stages of photosynthesis


  1. Light dependent stage

  2. Light independent stage (Calvin cycle)
• Light dependent stage


  • Occurs in the grana of the chloroplast
  • Light energy is trapped and converted into chemical energy (ATP and NADPH)
• Light independent stage (Calvin cycle)


  • Occurs in the stroma of the chloroplast
  • Involves carbon fixation, reduction and regeneration of RuBisCO
• RuBisCO


  • Key enzyme involved in the light independent stage
  • Can bind to CO2 or O2, facilitating further reactions
• Calvin cycle


  1. Carbon fixation

  2. Reduction

  3. Regeneration of RuBisCO
• One glucose molecule is produced for every two cycles of the Calvin cycle
• Types of photosynthesis


  • C3
  • C4
  • CAM
• C3 plants


  • No limits on photorespiration
  • No separation of initial CO2 fixation
  • Stomata open during the day
  • Advantages: doesn't consume extra energy
  • Disadvantages: susceptible to photorespiration
  • Best adapted to moderate or cool and wet environments
• C4 plants


  • Limit photorespiration
  • Separation of initial CO2 fixation between cells
  • Stomata open during the day
  • Advantages: minimized photorespiration
  • Disadvantages: more energy consumption
  • Best adapted to hot sunny habitats
• CAM plants


  • Limit photorespiration
  • Separation of initial CO2 fixation between night and day
  • Stomata open at night
  • Advantages: minimizing photorespiration and reducing water loss
  • Disadvantages: consumption of extra energy
  • Best adapted to very hot dry habitats
• Factors affecting rate of photosynthesis

  • Light intensity
  • Temperature
  • pH
  • CO2 concentration
  • Water availability
  • Enzyme inhibition
• Increasing light intensity


  Increases rate of photosynthesis until a plateau is reached
• Increasing temperature (below optimal)

  Increases rate of photosynthesis
• Increasing temperature (above optimal)


  Decreases rate of photosynthesis
• Increasing pH (below optimal)

  Increases rate of photosynthesis
• Increasing pH (above optimal)

  Decreases rate of photosynthesis
• Increasing CO2 concentration


  Increases rate of photosynthesis until a plateau is reached
• Increasing water availability


  Increases rate of photosynthesis
• Increasing enzyme inhibitors


  Decreases rate of photosynthesis
• The major limiting factors that restrict the rate of photosynthesis are light intensity, temperature, and CO2 concentration