Photosynthesis

• What is dehydrogenase?

  An enzyme found in plant chloroplasts
• What is the role of dehydrogenase in photosynthesis?

  It is crucial to the light dependent stage
• What do electrons get accepted by in the light dependent stage?

  NADP
• Who discovered the reaction involving NADP?

  Robin Hill in 1938
• What is the Hill reaction?

  The reaction where NADP accepts electrons
• What does dehydrogenase catalyze?

  The reaction where electrons are accepted by NADP
• What happens to DCPIP when it is reduced?

  It turns from blue to colourless
• What equipment is needed for the experiment?

  • Leaf sample
  • Scissors
  • Mortar and pestle (cold)
  • Nylon mesh
  • Filter funnel
  • Centrifuge
  • Centrifuge tubes
  • Ice-water-salt bath
  • Glass rod
  • Measuring cylinder
  • Beaker
  • Pipettes
  • Bench lamp
  • Buffer
  • Isolation medium
  • DCPIP solution
• What are the steps in the method for the experiment?

  1. Remove stalks from leaf samples and grind.
  2. Filter sample using muslin cloth.
  3. Chill the sample in an ice water bath.
  4. Centrifuge at high speed for 10 minutes.
  5. Remove supernatant and add pellet to fresh medium.
  6. Store isolation solution on ice.
  7. Set colorimeter to red filter and zero it.
  8. Add DCPIP to test tube and measure absorbance.
  9. Measure absorbance every 2 minutes for 10 minutes.
  10. Repeat for different distances from lamp.
• Why should the experiment be done in a darkened room?

  To make results more reliable
• What is the risk associated with DCPIP?

  It is an irritant to skin and eyes
• What safety precaution should be taken when using DCPIP?

  Wear eye protection
• What should you do if DCPIP contacts skin or eyes?

  Wash with cold water immediately
• What is a potential risk when using lamps in the experiment?

  Temporary damage to eyes
• What should you avoid doing with wet hands near electrical appliances?

  Touching lamp or wires
• What is the relationship between light intensity and the rate of photosynthesis?

  • As light intensity decreases, the rate of photosynthesis decreases.
  • Lower light intensity slows photoionisation of chlorophyll.
  • This results in fewer electrons released by chlorophyll.
• What does a higher rate of absorbance decrease indicate?

  Dehydrogenase is highly active
• What does DCPIP being blue indicate?

  The absorbance is higher
• What does a steep gradient on the graph indicate?

  A higher rate of decrease in absorbance
• What is the purpose of plotting a graph of absorbance against time?

  To analyze the rate of photosynthesis
• What is the effect of temperature on the experiment results?

  It may affect the results