required practical 8: investigate the effect of a named factor on the rate of dehydrogenase activity of chloroplasts

Question 1

what is the role of dehydrogenase in photosynthesis

Answer 1

catalyses the reduction of NADP in the light dependent reaction

Question 2

how is rate of dehydrogenase of chloroplasts measured

Answer 2

extract chloroplast from leaf sample.
set up 2 controls, 1 standard and an experiment test tube.
control A: set volume of DCPIP water and chloroplasts in isolation medium covered in foil
control B: set volume of DCPIP water in isolation medium with no chloroplast.
standard: set volume of water and chloroplast in isolation medium with no DCPIP.
experiment: set volume of DCPIP water and chloroplast in isolation medium.
shine light and time how long it takes for colour change - blue to colourless
work out rate: 1/time

Question 3

what are control variables of this experiment

Answer 3

plant leaf
volume of chloroplast
volume/concentration of DCPIP

Question 4

what is the purpose of control A

Answer 4

to show that light is required for DCPIP to decolourise, shows that it is not the chloroplast

Question 5

why does the DCPIP in control A not change colour

Answer 5

as there is no light, there is no photoionisation, so no electrons are released to reduce NADP

Question 6

what is the purpose of control B

Answer 6

shows chloroplasts are required for DCPIP to decolourise, shows that light alone does not cause DCPIP to decolourise

Question 7

why does DCPIP change colour from blue to colourless

Answer 7

DCPIP is a redox indicator, is reduced by electrons during photoionisation of chlorophyll

Question 8

what is a limitation with this method and how is it improved

Answer 8

the end point is subjective but you can use a colorimeter to measure light absorbance of sample