rp8

Question 1

role of enzyme dehydrogenase in photosynthesis

Answer 1

catalyses reaction of NADP in the LDR
nada accepts electrons from photoionisation of chlorophyll

Question 2

how can rate of dehydrogenase activity in extracts of chloroplasts be measured

Answer 2

extract chloroplasts from leaf sample and set up test tubes
CONTROL 1 - set up volume of DCPIP water and chloroplasts in isolation medium covered in foil to block light
CONTROL 2 - set volume of DCPIP water and isolation medium without chloroplasts
STANDARD - set volume of water and chloroplasts in isolation medium without DCPIP
EXPERIMENT - set volume of DCPIP water and chloroplasts in isolation medium
shine light on test tubes and time how long it takes for DCPIP to turn form blue to colourless in tube d

Question 3

examples of variables to control

Answer 3

source of chlorplasts
volume of chloroplast suspension
volume of DCPIP

Question 4

explain purpose of control 1

Answer 4

shows light required for DCPIP to decolourise
shows chloroplasts alone dont cause DCPIP to decolourise

Question 5

why odes DCPIP in control 1 remain blue

Answer 5

no light so no photoionisation of chlorophyll
so no electrons released to reduce DCPIP

Question 6

explain purpose or control 2

Answer 6

shows chloroplasts require for dcpip to decolourise and light alone cant do it

Question 7

why does dcpip change from blue to colourless

Answer 7

dcpip redox indicator so it gets reduced by electrons
from photoionisation of chlorophyll

Question 8

limitation of method and how it could be modified

Answer 8

end point colour change is subjective
use a colorimeter
measure light absorbance of Sample at set time intervals
zero colorimeter using colour standard