core prac 11

Question 1

What are the control variables for the hill reaction?

Answer 1

• species of plant used.
• amount of chloroplast/buffer added to each tube.
• amount of DCPIP added to each tube.
• amount of time tubes are left for.
• same pH each time

Question 2

What are the independent variable for the hill reaction?

Answer 2

The light intensity/wavelength reaching chloroplast samples

Question 3

What are the dependent variables for the hill reaction?

Answer 3

The amount of DCPIP reduced.

Question 4

Why is DCPIP used in the hill reaction?

Answer 4

As it’s able to accept electrons released during the light-dependent reaction (acts in a similar way to NADP)

Question 5

What colour is DCPIP when it’s reduced and when it’s oxidised?

Answer 5

• Reduced: colourless

- Oxidised: blue

Question 6

Describe the hill reaction…

Answer 6

Chloroplasts are extracted from the plant leaf and put into a solution with sucrose, a buffer and DCPIP.
The test tubes are left in varying light intensities/wavelengths e.g. one under red light etc.
If the solution is colourless after a certain time then the DCPIP has been reduced.

Question 6

Describe the hill reaction…

Answer 6

Chloroplasts are extracted from the plant leaf and put into a solution with sucrose, a buffer and DCPIP.
The test tubes are left in varying light intensities/wavelengths e.g. one under red light etc.
If the solution is colourless after a certain time then the DCPIP has been reduced.

Question 7

What are the expected results for the hill reaction?

Answer 7

• In the dark: no discolouration since the light-dependent stage requires light to occur.
• in green/yellow wavelengths there’d also be no discolouration since chlorophyll doesn’t absorb these wavelengths.
• greatest discolouration will be seen under bright light.

Question 8

What’s the method of the hill reaction?

Answer 8

1. Grind 5g of leaves with 10cm3 of ice cold sucrose solution using a pestle and mortar.
2. Strain the resulting liquid into a cooled centrifuge tube and centrifuge for 5mins at medium speed.
3. Decant supernatant into another cooled CF tube and spin for another 10mins at high speed.
4. Pipette off the supernatant and discard, using the sediment left add 2cm3 of cold sucrose solution and mix gently.
5. Add 20cm3 of cold pH 7 phosphate buffer solution and mix well.
6. Add 5cm3 of chloroplast solution into each test tube.
7. Add 10cm3 of DCPIP to each of the tubes.
8. leave tubes under different lights for set amount of time.
9. look at tubes and compare colour of DCPIP