Topic 5 Core Practicals

Question 1

Theory - Hill Reaction

Answer 1

• light-dependent reaction releases electrons from chlorophyll
• electrons and hydrogen ions are picked up by NADP to from NADPH (Hill reaction)
• rate of Hill reaction can be studied using DCPIP, which accepts the electrons instead of NADP

Question 2

DCPIP colour change

Answer 2

blue (oxidised) -> colourless (reduced)

Question 3

CP11 method

Answer 3

1. Grind up leaves with 20cm^3 isolation solution in pestle and mortar
2. Filter resulting liquid into beaker using funnel and filter paper
3. Transfer filtered liquid into centrifuge tube and centrifuge for 10mins
4. Discard the liquid (supernatant) in the centrifuge and keep the pellet of chloroplasts
5. Place 2cm^3 isolation medium and chloroplast pellet into clean test tube, stirring with a glass rod to re-suspend chloroplasts in the liquid. This is now the chloroplast extract.
6. Transfer chloroplast extract to ice water bath
7. Place a test tube containing 0.5cm^3 chloroplast extract into a test tube rack set up at a set distance from a lamp
8. Add 5cm^3 DCPIP solution to chloroplast extract and mix using glass rod
9. Use a pipette to immediately remove a sample of the mixture and place sample into cuvette
10. Place cuvette into colorimeter and take a reading for absorbance
11. Repeat steps 9-10 every minute for 10 mins