TOPIC 5 Practicals

Question 1

What is the compensation point?

Answer 1

when there is no next exchange of gases in or out of a plant

Question 2

How can you measure the rate of photosynthesis of an aquatic plant?

Answer 2

measure volume of oxygen produced

Question 3

How do you release the pigments of a leaf?

Answer 3

place it in a mortar - add acetone and use a pestle to grind up leaf sample to release pigments

Question 4

What piece of apparatus is used to extract pigment and blot it onto chromatography paper?

Answer 4

capillary tube

Question 5

How do you identify pigments in leaves?

Answer 5

compare Rf values of pigments to known Rf database values

Question 6

What is dehydrogenase?

Answer 6

enzyme found in plant chloroplasts - catalyses reaction of NADP accepting electrons, to form NADPH

Question 7

What redox indicator dye can be used to investigate activity of dehydrogenase?

Answer 7

DCPIP

Question 8

What is the colour change of DCPIP when it is reduced?

Answer 8

blue —> colourless

Question 9

What 2 control conditions should be used in measuring rate of dehydrogenase activity in chloroplasts?

Answer 9

1. experiment should be done in a darkened room
2. sample should not be too close to lamp as temperature may affect results

Question 10

How can data/ graph be plotted from measuring DCPIP absorbance?

Answer 10

if DCPIP is blue = absorbance is higher (lower rate of photosynthesis as less electrons are released from chlorophyll, so DCPIP accepts less electrons)
- plot absorbance against time
- steep gradient (higher rate of decrease) = dehydrogenase is highly active

Question 11

How can rate of respiration be measured?

Answer 11

using a redox indicator dye (e.g. methylene blue)
- accepts electrons
- undergoes colour change (blue —> colourless)

Question 12

What data is collected when measuring rate of photosynthesis?

Answer 12

time taken for solution to turn colourless (for methylene blue to be reduced)

Question 13

What is positive control?

Answer 13

a treatment when you expect a known effect (so you know the method has worked)

Question 14

What is negative control?

Answer 14

a treatment when you expect no effect (so you can check that any change is due to the independent variable and not something else)

Question 15

What is a positive control in measuring dehydrogenase activity in chloroplast using DCPIP?

Answer 15

chloroplast and DCPIP under normal light
(we know the dehydrogenase should work and reduce DCPIP)

Question 16

What is a negative control in measuring dehydrogenase activity in chloroplast using DCPIP?

Answer 16

DCPIP and buffer only, no chloroplasts (no colour change is expected)