required practical 8

Question 1

what is the function of dehydrogenase in chloroplasts?

Answer 1

catalyses the acceptance of electrons by NADP in LDR

Question 2

what is the purpose of DCPIP?

Answer 2

a redox indicator dye that acts as an alternate electron acceptor instead of NADP, it turns from blue to colourless when reduced

Question 3

method

Answer 3

1. remove stalks from leaf samples and grind using a pestle and mortar, place in chilled isolation solution
2. use a muslin cloth to filter solution into beaker, suspend beaker in an ice water bath
3. transfer to centrifuge tubes and centrifuge at high speeds for 10 minutes to separate chloroplasts
4. remove supernatant and add pellet to fresh isolation medium on ice
5. set colorimter on red and zero
6. place test tube in the rack 30cm from light source and add DCPIP, immediately measure absorbance
7. take sample and measure absorbance every 2 minutes for 10 minutes
8. repeat from distances from lamp up to 100cm

Question 4

why is the plant extract chilled in an ice-water bath?

Answer 4

lower activity of enzymes to prevent them breaking down choroplasts

Question 5

how is the control set up?

Answer 5

fill a cuvette with chloroplast extract and distilled water

Question 6

how is light intensity controlled?

Answer 6

adjust the distance of the lamp and perform the practical in a dark room

Question 7

why are the stalks of the leaves removed before grinding?

Answer 7

stalks do not contain many chloroplasts

Question 8

what happens when light intensity is low?

Answer 8

rate of photosynthesis decreases

Question 9

why does rate of photosynthesis decrease when light intensity is low?

Answer 9

slows rate of photoionisation of chlorophyll pigment so less electrons are released hence DCPIP accepts less e-, making it take longer to turn colourless

Question 10

what does a higher rate of absorbance decrease mean?

Answer 10

dehydrogenase is highly active