Required Practical 8 - Dehydrogenase Activity in Chloroplasts Flashcards

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1
Q

Suggest why an isolation medium is used

A
  • separate out chloroplasts

- isotonic to prevent lysis of chloroplasts

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2
Q

Suggest why the midrib and leaf stalks are discarded

A
  • do not contain many chloroplasts
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3
Q

Suggest why solution must be kept cold

A
  • slow enzyme action

- prevent damage to chloroplasts

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4
Q

Suggest why leaves are blended for no longer than 15 seconds

A
  • free chloroplasts without damaging

- avoid heating

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5
Q

Suggest why a muslin cloth is used over filter paper

A
  • finer separations

- only allows chloroplasts to be filtered into solution

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6
Q

Suggest why leaf suspension is centrifuged

A
  • separate chloroplasts from other organelles
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7
Q

Suggest why slightly damaged chloroplasts provides an advantage

A
  • DCPIP can access thylakoid membrane easier
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8
Q

Suggest why DCPIP changes colour

A
  • blue (oxidised) to colourless (reduced)
  • takes place of NADP
  • accepts electrons from electron transfer chain and photolysis of water
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9
Q

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

A
  • no colour change

- proves reaction is light dependent

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10
Q

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

A
  • 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
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