What is the function of dehydrogenase in chloroplasts?
It catalyses the acceptance of electrons by NADP in the light dependant 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 any chloroplasts
What was the purpose of using a blender?
to break open cells and release chloroplasts
Explain why it was important that the isolation medium was isotonic with the spinach tissue
- Prevents osmosis
- So organelles don’t burst or shrivel
There are large pieces of tissue and other organelles in your chloroplast suspension. Describe hoe you could isolate the chloroplasts from the other components in the suspension
- Filter
- At low speed, then high speed
- Collect pellet
DCPIP is decolourised more slowly when ammonium hydroxide is added. Use your knowledge of the light-dependant reaction to suggest a reason why
Ammonium hydroxide stops transfer of electrons along ETC
Some weed killers are substances that accept electrons during photosynthesis. Suggest how these substances kills weeds.
- Slows light dependant reaction
- Less ATP/ NADPH made
- Light independent reaction slowed
Suggest one disadvantage of using these weed killers on weeds growing in a crop
- Reduced grow
- Slows respiration
