Required Practical 8 - Dehydrogenase Activity in Chloroplasts

Question 1

Suggest why an isolation medium is used

Answer 1

• separate out chloroplasts

- isotonic to prevent lysis of chloroplasts

Question 2

Suggest why the midrib and leaf stalks are discarded

Answer 2

• do not contain many chloroplasts

Question 3

Suggest why solution must be kept cold

Answer 3

• slow enzyme action

- prevent damage to chloroplasts

Question 4

Suggest why leaves are blended for no longer than 15 seconds

Answer 4

• free chloroplasts without damaging

- avoid heating

Question 5

Suggest why a muslin cloth is used over filter paper

Answer 5

• finer separations

- only allows chloroplasts to be filtered into solution

Question 6

Suggest why leaf suspension is centrifuged

Answer 6

• separate chloroplasts from other organelles

Question 7

Suggest why slightly damaged chloroplasts provides an advantage

Answer 7

• DCPIP can access thylakoid membrane easier

Question 8

Suggest why DCPIP changes colour

Answer 8

• blue (oxidised) to colourless (reduced)
• takes place of NADP
• accepts electrons from electron transfer chain and photolysis of water

Question 9

Suggest why a tube containing DCPIP and leaf extract in the dark is prepared

Answer 9

• no colour change

- proves reaction is light dependent

Question 10

Explain the effect of ammonium hydroxide on rate of decolorisation of DCPIP hence light dependent reaction

Answer 10

• accepts electrons so electrons do not pass long electron transport chain to reduce DCPIP
• slows electron transfer by inhibiting enzyme NADP dehydrogenase
• affects pH so denatures proteins in e- transport chain