C1.3 Photosynthesis

• Light-dependent reactions

  1. Splits water into Hydrogen ions, electrons, Oxygen Photolysis of water generate electrons for the light-dependent reactions 3. Transfer of excited electrons between carriers in the thylakoid membrane4. ATP synthase in thylakoid membrane generates ATP using the proton gradient 5. Excited electrons in PS1 are then used to reduce NADP+ to NADPH

• Outline how photosynthesis produces glucose.


  Photosynthesis involves light-dependent reactions and the Calvin cycle in chloroplasts. In the light-dependent reactions, chlorophyll absorbs light energy, splitting water to produce oxygen, ATP, and NADPH. The Calvin cycle uses ATP and NADPH to convert carbon dioxide into glucose.
• Photosynthesis


  The process by which plants use sunlight, water and carbon dioxide to create oxygen and energy in the form of sugar
• Transformation of light energy to chemical energy in photosynthesis

  1. Light energy → chemical energy

  2. Essential for food chains
• Forms of chemical energy

  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
• This energy transfer is essential for most ecosystems
• Chlorophyll


  Green pigment
• Light dependent reactions and light independent reactions in photosynthesis

  1. Light energy used to split water molecules into oxygen, hydrogen ions and electrons

  2. Photolysis

  3. Leads to the production of ATP

  4. Oxygen is released as a waste product

  5. Hydrogen ions, electrons, ATP and carbon dioxide are combined through a complex metabolic pathway into carbohydrates
• Conversion of carbon dioxide to glucose in photosynthesis using hydrogen obtained by splitting water


  1. Water + carbon dioxide → glucose + oxygen by-product

  2. Photolysis = using light energy to split water

  3. Hydrogen is needed to convert carbon dioxide into glucose
• Photosynthesis = plants use sun energy to change H2O and CO2 into a sugar called glycine
• Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life
• Oxygen as a by-product of photosynthesis in plants, algae and cyanobacteria

  1. H2O + CO2 → C6H12O6 + O2

  2. Evolution of life changed the composition of earth's atmosphere
• Separation and identification of photosynthetic pigments by chromatography

  1. Pigments = absorb light

  2. Chromatography = separation of pigments

  3. Technique for separating mixtures of pigments

  4. A solvent is required that will dissolve out these pigments

  5. Each pigment will move a different length along a piece of blotting paper

  6. By measuring the distance the pigment moves, it is possible to identify it

  7. Transfer plant pigments to chromatography paper

  8. Allow chromatography solvent to be absorbed through the paper

  9. Separate pigments

  10. Measure the distance that the solvent travelled and the distance each pigment travelled

  11. Calculate the Rf value: Rf = distance pigment/distance solvent

  12. Plants have multiple pigments

  13. Each pigment has a characteristic Rf value

  14. You should be able to: Separate pigments using chromatography, Identify pigments based on colour and Rf values
• Absorption of specific wavelengths of light by photosynthetic pigments

  Colours = are different wavelengths of light<|>Pigments = absorb certain wavelengths of light<|>The wavelengths that the pigments reflect are what we see
• Techniques for varying concentrations of carbon dioxide, light intensity or temperature experimentally to investigate the effects of limiting factors on the rate of photosynthesis

  1. Limiting factors are factors that will limit the rate of photosynthesis

  2. The key limiting factor is the one furthest from its optimum

  3. The three most important are Carbon Dioxide concentration, temperature and light intensity

  4. A method for measuring photosynthesis rates using pondweed

  5. Carbon Dioxide Concentration: Boil water to remove CO2, add sodium hydrogen carbonate to increase CO2 levels

  6. Light Intensity: Cut out leaf discs, suck air out, time how long they take to float

  7. Temperature: Set up a water bath, use a sensor to measure the rate, oxygen concentration in the air, pH

  8. Important Takeaways: Pick one independent variable and control the rest, must have a reliable way of manipulating the independent variable and measuring photosynthesis rates