RP8 Flashcards
Controls:
Plant species
Volume of DCPIP
Volume of Chloroplast suspension
Volume of isolation medium
Independent variable
Colour of light
- White
- Red
- Green
[Could do intensity of light]
Dependent variable
Rate of dehydrogenase demonstrated by Absorbance
Or Time taken for DCPIP to decolourise
Why not use the midrib of leaf stalk?
No chloroplasts present in midrib. Midrib is tough material so it will not be cut up by blender.
Why use distilled water?
No other ions that affect colour of DCPIP
Suggest why leaves are blended for no longer than 15 seconds?
free chloroplasts without damaging - avoid heating
Why the isolation medium was ice cold and isotonic?
Cold – prevent enzyme activity so chloroplasts aren’t damaged
Isotonic –Same water potential as plant tissue so no net movement of water by osmosis. This means the chloroplasts won’t burst or shrivel
Why does DCPIP change colour?
blue (oxidised) to colourless (reduced) - takes place of NADP - accepts electrons from electron transfer chain and photolysis of water
How would lower light intensity affect the absorbance?
Lower light levels decreases rate of photoionisation. Less e- released and accepted by DCPIP. DCPIP less oxidised and so stays blue [high absorbance].
Lower light intensity = dehydrogenase activity is lower = higher absorbance [blue].
Higher light intensity = dehydrogenase activity is higher = lower absorbance [clear]
Which colour light would cause DCPIP to decolourise the quickest/ have lowest absorbance?
White then red then green. Green would not decolourise as the green light is not
absorbed
Why do you cover one tube in foil?
Control experiment – allows you to see the effect of no light as a comparison. DCPIP remains blue
What happens if ammonium hydroxide is added?
Ammonium hydroxide accepts the e- and changes pH so that proteins denature. This prevents e- from passing to DCPIP.
DCPIP stays blue = absorbance remains high or time taken to decolourise is very high
