RP8 - Dehydrogenase Activity in Chloroplasts

Question 1

What is the function of dehydrogenase in chloroplasts?

Answer 1

It catalyses the acceptance of electrons by NADP in the light dependent reactions.

Question 2

What is the purpose of DCPIP?

Answer 2

It is a redox indicator dye and acts as an alternate electron acceptor instead of
NADP.
It turns from blue to colourless when reduced.

Question 3

Why is the plant extract chilled in an ice-water bath?

Answer 3

To lower the activity of enzymes to prevent them from breaking down the
chloroplasts.

Question 4

How is the control set up?

Answer 4

Fill a cuvette with chloroplast extract and distilled water.

Question 5

How is light intensity controlled?

Answer 5

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.

Question 6

What is the function of the muslin cloth?

Answer 6

To filter out any debris in the ground leaf mixture but allowing chloroplasts to pass through.

Question 7

Why are the stalks of leaves removed before grinding?

Answer 7

The stalks do not contain many chloroplasts.

Question 8

Outline the procedure of investigating the effect of
light intensity, after chloroplast extract has been
obtained.

Answer 8

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.
3. Immediately take a sample and add to cuvette. 4. Measure the absorbance of the sample.
4. Take a sample and measure its absorbance every 2 minutes for 10 mins.
5. Repeat for different distances from lamp up to 100 cm.