Lab Report – Photosynthesis Lab
Do not copy from the lab manual–use your own words – do not use I, you, we, etc. This should be no more than 4 pages long ( no plagiarism) I would like an A +
The lab report of the experiment will include the section titles below (15 points):
Title – separate page
Introduction
Material
Procedures
Results
Discussion/Conclusion
Literature Citation
TITLE (separate page)
• A unique, brief or descriptive title. I want my reader to understand the subject of investigation
INTRODUCTION
Intro give a background about accessory pigments in chlorophyll a and what an absorption spectrum is this should be no more than half a page
• Purpose of the experiment (objective) – what is the experiment designed to test, why was this study performed.
• Hypothesis – an educated guess of what you expect to happen.
MATERIAL
• List the materials and supplies needed for the experiment and in exact quantities.Material and methods should be no more than half a page
Abstract
Talk about the leaf abstract of spinach
PROCEDURE (
• List (numerical order) the exact steps of the experiment
RESULTS (DATA)
• Use visuals – For the graph use excel (include legend,) Visual Must be titled, axes labeled, variables correctly identified, and data recorded in visual) Add a figure legend and text to refer to the reader of the figures. Determine the absorption spectrum for a spinach leaf extract figure 1 . • Briefly summarize results from visual – explanation of what you learned from the table, graph or chart. (1 pt) My data table would be in the file
DISCUSSION/ Conclusion (most important section of the lab report (4 pts)
• Summarize: The Purpose of the experiment
Talk about major findings , implications of photosynthesis, what color lights are effective for photosynthesis, limitations of the experiment,
Possible errors that may have occurred in your experiment. Ex. Some errors that may have occurred with this lab include _____________. In the future I would ______________ to enhance the lab.
LITERATURE CITATION – APA format
This is the information for the paper ( If this information is not enough you can use a Journal article as a secondary source on photosynthesis) : Introduction: In this laboratory we will separate photosynthetic pigments by a process called paper chromatography and determine the absorption spectrum of a leaf extract by spectrophotometry, a technique about which you have already learned. Paper chromatography is a useful technique for separating and identifying pigments and other molecules from cell extracts that contain a complex mixture of molecules. The solvent moves up the paper by capillary action, which occurs as a result of the attraction of solvent molecules to the paper and the attraction of the solvent molecules to one another. As the solvent moves up the paper, it carries along any substances dissolved in it. The various chemicals are carried along at different rates because they are not equally soluble in the solvent and because they are attracted to different degrees to the fibers of the paper through the formation of intermolecular bonds, such as hydrogen bonds. Although leaves appear green to the naked eye because of chlorophyll molecules, there are actually several other colored pigments ( colored molecules) in leaves that are masked by the dark green chlorophylls. Although chlorophyll a is the photosynthetic pigment that is found in the reaction centers of the thylakoid membrane, there are other accessory pigments in the thylakoid, such as chlorophyll bxanthophylls and carotene that function in absorbing other CH chlorophyll a CHO In chlorophyll b wavelengths of light and transferring the absorbed energy to chlorophyll a Porphyrin ring molecules. The xanthophylls and carotenes together are called the carotenoids. Because these various pigments differ in their respective polarities, they can be readily separated by paper chromatography . For example, compare the respective structures of the atoms not shown ) olive green pigment chlorophyll b and the dark green pigment chlorophyll a : They differ only in a single functional group . Which is more non- polar ? Reprinted from Campbell Biology 9th Edition (2011) by permission of Pearson Education Hydrocarbon tail Another pigment , xanthophyll differs from carotene in that it contains oxygen . Which of these two pigments is more non – polar ?A.) Preparation of a Leaf Extract Safety First We will be using a leaf extract in both parts of today’s laboratory exercise, that is, for determining the absorption Wear Gloves spectrum of the leaf extracts and for the separation of pigments by paper chromatography 1. Prepare a pigment extract by rubbing 2-3 spinach leaves onto a piece of chromatography paper. Make sure the paper is dark green on both sides . Take the green soaked paper and place it into a small beaker containing 20 ml of acetoneSwirl the paper until the solution turns green. Cover the beaker with a piece of parafilm. 2. Filter the extract through a funnel lined with filter paper B.) Determining the Absorption Spectrum of a Leaf Extract by Spectrophotometry 1. Turn on your spectrophotometer. Set the wavelength at 400 nm Transfer 8 ml of the filtered leaf extract to a clean cuvette. 3. Fill another clean cuvette with acetone. This will be your blank 4. Set the limits so that the %T scale reads from 0% T to 100% T as follows: To set the scale to 0% T make sure that the cuvette What is the function holder is empty and using the left hand knob adjust the of the blank in scale to read 0% T. spectrophotometry? To set the scale to 100% T fill a clean cuvette with acetone and place it in the cuvette holder. Adjust the scale to 100% using the right hand knob to read 100% T. 5. Take readings of the leaf extract at 25 nm intervals between 400 nm and 700 nm. REMEMBER to re-calibrate your spectrophotometer for 0% and 100% T each and every time you change the wavelength. 6. Record your data in the table provided. Convert the date to absorbance values and plot the wavelength vs. absorbance for each pigment. Which variable is independent? Which is dependent? C.) Separation of Pigments by Paper Chromatography 1. Add the solvent Petroleum Ether: Acetone (9:1) to the chromatography tube (your instructor will tell you how much)Cap the chromatography tube and put in the test tube rack in the hood. Petroleum ether is extremely flammablell Do not shake it or swirl it. Let it sit 2. Obtain a piece of chromatography paper and cut it as directed by your instructor . 3. Using only a PENCIL draw a faint line on the chromatography paper approximately 1.5 cm from the bottom. Using a pipette tip apply a thin line of leaf extract on top of the pencil mark Why must Let it dry (this should happen quickly since acetone you use evaporates quickly at room temperature ). Be careful not to pencil and get any pigments on the paper other than on the line! Once not pen this thin line is dry, repeat this process (i.e., apply another here? coat of leaf extract to the thin line). Repeat this process TEN TIMES ! 4. Place the paper into your chromatography tube in the hood without disturbing the contents of the tube. Cover the tube and leave it in the hood. 5. The pigments will separate based on their ability to migrate in a non- polar solvent (Petroleum Ether : Acetone ). Since there is more Petroleum ether than acetone , and since petroleum ether is highly non- polar, the more non-polar pigment will be more soluble and will migrate faster up the chromatography paper . 6. Identify the pigments based on their respective colors. Chlorophyll a : blue – green band Chlorophyll b: olive- green band Beta- carotenes : bright orange bands Xanthophylls : multiple yellow bands
