An Investigation of Photosynthetic Electron Transport of Chloroplasts from Silverbeet Leaves

Essay by sallyy_12College, UndergraduateA, April 2013

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An Investigation of Photosynthetic Electron Transport of Chloroplasts from Silverbeet Leaves

Introduction

Photosynthesis is the process by which plants use the energy from sunlight to produce sugar, which cellular respiration converts into ATP, the "fuel" used by all living things. The conversion of unusable sunlight energy into usable chemical energy is associated with the actions of the green pigment, chlorophyll. Light Dependent Reactions are the initial stage of photosynthesis, in which solar energy is converted into potential energy. This reaction produces oxygen gas and converts ADP and NADP+ into ATP and NADPH.

Among all living organisms on planet earth, only plants are capable of producing their own food and deriving energy from it. By producing energy, the plants supply all the necessary nutrients and energy directly/indirectly to the other living creatures. The production of this energy is possible through photosynthesis.

The aim of this practical is to investigate the effects of different treatments on photosynthetic electron transport by using isolated chloroplasts from silverbeet leaves.

As photosynthesis proceeds, any electrons produced will reduce the dye DCPIP to its colourless form, so a rapid decrease in dye colour will indicate a rapid rate of photosynthetic electron transport. Given this, I predict that placing the reaction in the dark will produce no change in colour as well as the treatment of adding DCMU, as it is an inhibitor of photosynthesis, and the treatment of boiling. I also predict that the treatment using only red wavelengths of light will proceed at a more rapid rate of photosynthetic electron transport than the treatment using only green wavelengths of light, resulting in a rapid decrease of dye colour.

Method

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

0.01 M DCMU

(ml)

-

-

-

-

0.10

-

-

E

DCPIP (ml)

(add this last)

-

0.20

0.20

0.20

0.20

0.20

0.20

Seven spectrophotometer tubes were numbered and solutions A-D were added according to the volumes shown in Table 1. Tube 1 was capped and inverted several times. The absorbance was calibrated using Tube 1, which contained chloroplasts and sucrose only, as the blank, to ensure that any changes in colour for the other treatments could be attributed to the rate of the dye DCPIP. At time zero (mins), absorbance was recorded for all treatments immediately after addition of the dye DCPIP and mixing of contents. Immediately following the time zero reading, tube 2 was wrapped in foil and tubes 6 and 7 were placed into larger tubes covered in red and green cellophane respectively. Tubes 1-5 were also placed into larger tubes. All tubes were then placed horizontally on ice, under lights. At fifteen minute 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.

Results