RP8

• What is the function of dehydrogenase in chloroplasts?

  It catalyses the acceptance of electrons by NADP in the light dependent reactions.
• What is the purpose of DCPIP?

  It is a redox indicator dye and acts as an alternate electron acceptor instead of

  NADP.

  It turns from blue to colourless when reduced.
• Why is the plant extract chilled in an ice-water bath?

  To lower the activity of enzymes to prevent them from breaking down the chloroplasts.
• How is the control set up?

  Fill a cuvette with chloroplast extract and distilled water.
• How is light intensity controlled?

  Adjust the distance of the lamp from the set up.

  Perform the practical in a dark room so that the only light source is the lamp.
• What is the function of the muslin cloth?

  To filter out any debris in the ground leaf mixture but allowing chloroplasts to pass through.
• Why are the stalks of leaves removed before grinding?

  The stalks do not contain many chloroplasts.
• Outline the procedure of investigating the effect of light intensity, after chloroplast extract has been obtained.

  1. Set the colorimeter to the red filter. Zero using a cuvette containing chloroplast extract and distilled water.
  2. Place test tube in the rack 30cm from light source and add DCPIP.Immediately take a sample and add to cuvette. Measure the absorbance of the sample.
  3. Take a sample and measure its absorbance every 2 minutes for 10 minutes.
  4. Repeat for different distances from lamp up to 100 cm.