An Investigate of Light-Dependent Electron Transport Using Dcpip

Title:

An investigate of light-dependent electron transport using DCPIP

Introduction:

Photosynthesis is defined as a process which the conversion of light energy from the sun to chemical energy that is stored in other organic molecules and sugar (Reece et al., 2011). It produces oxygen and makes carbohydrates for organisms. The chemical equation in photosynthesis is: 6CO2 + 6H2O + light energy C6H12O6 + 6O2.

There are two processes of photosynthesis that occur in the chloroplast which are light dependent reaction and light independent reaction. In this practical, electron transport chain in light reaction is focused. Electron transport chain showed a sequence of membrane protein that pass electrons to another through redox reactions to release energy for the synthesis of ATP (Reece et al., 2011).

The aim of this experiment is to investigate the relationship between the electron transport in different treatments of chloroplast and the rate of photosynthesis by using DCPIP. The hypothesis of this experiment is, the faster the rate of hypothesis, the faster the DCPIP being reduced and turn to colourless.

Methods:

“Seven spectrophotometer tube were measured and solutions A-D were added accordingly to the volumes shown in Table 1. Tube 1 was capped and inverted several times. The spectrophotometer was calibrated using Tube 1, which contained chloroplasts and sucrose only, as the blank, to ensure that any changes in chloroplast for the other treatments could be attributed to the reduction of the dye DCPIP. At the time zero (mins), absorbance was recorded for all the treatments immediately after addition of DCPIP and mixing the contents. Immediately following the time zero reading, Tube 2 was wrapped in foil and Tube 6 and 7 were place into larger tubes covered in red and green cellophane respectively. Tube 1-5 were also placed into larger tubes. All the tubes were then placed horizontally on ice, under lights. After 15 minutes intervals, readings of absorbance were taken for all treatments, except for the dark tube which was kept wrapped in foil for 60 minutes, after which its absorbance was measured.”

Table 1. Experimental design for the electron transport experiment.

TREATMENT

BLANK

1 DARK

2 LIGHT

3 BOILED

4 DCMU

5 RED

6 GREEN

7

A chloroplast

suspension (ml)

1.5

1.5

1.5

-

1.5

1.5

1.5

B buffered sucrose

(ml)

5.5

5.3

5.3

5.3

5.2

5.3

5.3

C boiled chloroplast suspension (ml)

-

-

-

1.5

-

-

-

D 0.01M DCMU

(ml)

-

-

-

-

0.10

-

-

E DCPIP (ml)

(add this last)

-

0.20

0.20

0.20

0.20

0.20

0.20

Results:

Table 2. Absorbance readings taken at 30 minute intervals for each treatment.

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