REPORT 2 PHOTOSYNTHESIS - Assignment Example

Chlorophyll

In the presence of sunlight, plants convert organic compounds into chemical energy (glucose). The chemical energy is converted into adenosine triphosphate (ATP) to release energy during cellular respiration. CO2 provides the carbon and oxygen utilized in the synthesis of carbohydrate. The oxygen produced as a byproduct is released into the atmosphere and is used by all living organisms to sustain life (Mishra, 2004). A cellular component known as chlorophyll is very essential to photosynthesis. Chlorophyll is a green pigment in the chloroplasts which allows the photosynthetic organism to absorb light from the sun. This complex molecule may vary from organism to organism, but the function remains the same. Other accessory pigments can absorb light that cannot be absorbed by chlorophyll a. They include chlorophyll b, c, d and e, carotenoids and xanthophyll (Lichtenthaler & Wellburn, 1983). Chlorophyll pigments c, d and e are found in protistans and algae. The energy absorbed by chlorophyll a comes from the reddish orange-red and violet-blue wavelengths, and some from the green-yellow-orange wavelengths. Photosynthesis takes place in two primary phases:

Phase I: Light Reaction

When light hits the chlorophyll molecules, energized electrons are formed and pass from chlorophyll through a series of electron acceptor molecules. This results in the synthesis of ATP while the electron carrier molecule called NADPH is reduced. The electrons from water replace the electrons that are lost from the chlorophyll.

Phase II: Calvin Cycle

In the Calvin cycle, the hydrogen derived from water reduces CO2 to form a carbohydrate. The energy required in this phase is provided by NADPH and ATP from phase I. In most of the plants, the first product of photosynthesis is phosphoglyceraldehyde (PGAL). The 3-carbon compound is then used to synthesize glucose (Diener, 2010).

Experimental Objectives

The main objectives of this lab experiment were:

• To identify pigments found in leaves, and separate the pigments by using paper chromatography.
• To isolate the leaf pigments and establish the light wavelengths at which these pigments can absorb light.
• To study the relationship between photosynthesis and leaf anatomy.
• To study some of the adaptive modifications of leaves for photosynthesis in different environments.

Methods

Part A: Separation of Plant Pigments by Paper Chromatography

Materials:

• Acetone-petroleum ether 10:90
• Pigment extract
• Chromatograph paper
• Capillary tube
• Leaf material
• Test tubes
• Beakers
• Cuvettes
• Mortar and pestle
• Pasteur pipette
• Water

Procedure:

5 ml of acetone-petroleum ether solvent was poured into a chromatography jar and covered with the lid. About 2g of the leaf material was cut up and then ground using mortar and pestle. The ground leaf material was placed a test tube before adding 4 ml of acetone. The test tube was then corked and shaken vigorously, and then let to stand for about 10 minutes. After this, 3 ml of water was added into the tube and then carefully shaken to form a water soluble pigment. 3 mL of petroleum ether was added in the tube, shaken, and then left for several minutes until different pigment layers were formed. A Pasteur pipette was then used to isolate the upper dark green solvent layer and placed in a separate beaker. Using a capillary tube, a small drop of pigment extract was added to the chromatography paper, about a centimeter from the bottom of the paper. The pigment extract was allowed to dry before another drop was added at the same sport. This was repeated 6 times for different sports. With care, the paper strip was lowered into the chromatography jar until its tip just touched the solvent. The paper strip was secured to ensure that its sides did not touch the jar. The set-up was then left for some time with observations made at frequent intervals. Before the solvent reached the top of the paper, the paper was removed and lest to dry for a few minutes before different colors were examined from top to down (Lab Manual, 2016).