Laboratory. Investigating Biological Membranes

Transcription

1 Laboratory 4 Investigating Biological Membranes

2 Biology 171L SP18 Lab 4: Investigating Biological Membranes Student Learning Outcomes 1. Gain experience using a digital spectrophotometer. 2. Practice formulating and testing hypotheses. 3. Practice summarizing and interpreting data, in particular the results of different treatments of alcohols and detergent on beet tissue, in terms of likely tissue damage. Relevant Readings Campbell Biology, Chapter 7, especially pp A short Guide to Writing about Biology, Chapter 9, especially pp Homework Synopsis (see pages 4-13 & 4-14 for full description) Part I Mastering Biology Part II Science Communication Materials & Methods and Results exercises Part III Data Analysis Short Answer Scientific Literature Assignment INTRODUCTION Today s experiment will examine the stress that various physical factors, such as detergent and alcohol molecules, have on biological membranes. Membranes facilitate organization within cells and also provide protection. Factors that disrupt membrane integrity can be devastating to living cells and organisms. Beets will be used for this lab and the release of the betacyanin pigment will be used as an indicator of membrane damage and cell distress. Plant cells, on average, are some of the largest cells, primarily because most plant cells contain a vacuole, a large chamber filled with water. But, even outside the vacuole, the cell s cytoplasm is mainly composed of water. The cell s cytoplasm is surrounded by the cell membrane, and within the cell, the vacuole, and other organelles, are also encased by membranes. In last week s lab, the terms hydrophilic and hydrophobic were introduced to describe how membranes form. To truly understand why a substance loves or fears water, it is important to understand polarity and the concept that like attracts like / like dissolves in like. Ionic compounds disassociate easily into ions, that is, atoms or molecules with charges. Polar molecules are neutral overall, but an unequal dispersal of electrons creates partially positive and negative poles within the molecule. Water, H 2O, is a very common, polar molecule. Ionic and polar solutes dissolve in polar solvents because of the attraction between positive and negative charges. They re drawn together like magnets. Because of their attraction to water molecules, ions and other polar solutes are hydrophilic. Fig 1: Attraction between water molecules Non-polar molecules are not charged, and are thus unaffected by the charged poles present in water molecules. Oils, or lipids, are a very common type of non-polar molecules. Oil will dissolve in other non-polar solvents, because non-polar molecules are not held together by any attraction. On the other hand, oil will not Fig 2: Oil and water do not dissolve in each other Biology 171L - SP18 Investigating Biological Membranes 4-2

3 dissolve in water, because there is no intermolecular attraction between them. Two separate layers will form. The water molecules are drawn together into one layer, pushing the non-polar oil molecules out of the way into a separate layer. Do you know why the oil layer floats on top of the water layer? The saying that oil and water don t mix holds true under most conditions; however, the addition of amphiphilic (some books use the word amphipathic) molecules changes the interaction. Amphiphilic molecules possess both hydrophobic and hydrophilic regions. The hydrophilic ends of the molecules try to mix with water while the hydrophobic ends try to keep away from the water. In a sufficient amount of water, amphiphilic substances often form structures called micelles, in which the hydrophobic tails all stay together, while the hydrophilic ends are on the outside boundary of the micelle. Soaps and detergents are types of amphiphilic molecules and will form micelles in large amounts of water. We see examples of soaps and detergents at work daily. Our skin contains glands that produce oils that coat the skin and hair, also trapping dirt and cell debris. Water, by itself, is an inefficient cleaning agent, because it is unable to form an attraction to the oil molecules. The layer of oil does not dissolve in water and resists being washed away. Soaps and detergents cause the oils to become soluble in water. The hydrophilic heads of soap and detergent molecules form weak intermolecular bonds with the water, while isolating the oil within the hydrophobic core of the micelles. The oil is rendered soluble in water and the oil layer can be washed away. Fig 3: Amphiphilic agent forms a micelle Another class of amphiphilic molecules is phospholipids, the main components of biological membranes. Phospholipids have a hydrophobic hydrocarbon chain with a hydrophilic phosphorous head. Because of their hydrophilic and hydrophobic properties, they form various structures within the cell cytoplasm. They can form a micelle, a liposome, or bilayer sheet. The hydrophobic core keeps membranes from Figure 4: Phospholipids and possible formations dissolving within the cellular cytoplasm and also plays a huge role in a membrane s permeability. Today you will be studying the interaction between two amphiphilic substances; a) sodium dodecyl sulfate (SDS), an anionic detergent; and b) the phospholipid membranes in beet cells. Alcohols and Membranes Alcohols are a group of chemical molecules where an OH group has bonded with a hydrocarbon. Hydrocarbons are simple organic compounds that consist of a carbon chain bonded to hydrogen atoms. The names of hydrocarbons can give you a lot of information about the structure of the molecule. The names indicate the number of atoms that make up the carbon chain backbone, types of bonds making up the carbon backbone, and whether there are special atoms or groups attached to the hydrocarbon. Biology 171L - SP18 Investigating Biological Membranes 4-3

4 Some examples of common hydrocarbon chains follow: Number of Carbons Name Molecular Formula Structural Formula 1 Methane CH 4 CH 4 2 Ethane C 2H 6 CH 3CH 3 3 Propane C 3H 8 CH 3CH 2CH 3 4 Butane C 4H 10 CH 3CH 2CH 2CH 3 The first part of the chemical name is determined by a prefix indicating how many carbons are present in the carbon chain. Meth indicates a hydrocarbon with just a single carbon atom while eth indicates that you have two carbon atoms. The second part of the name provides information about the bonds that hold the carbon chain together. In this case, the ane ending tells us that these hydrocarbons are members of the alkane family and the carbon atoms are held together by single bonds. By adding a special group of atoms, a hydroxyl group (an oxygen and a hydrogen atom), to these hydrocarbon chains, we form a group of molecules called alcohols. Naming alcohols involves the additions of -ol to the end of the chemical name. So, when an OH group replaces one of the hydrogen atoms in ethane (C2H6), it forms one of the more commonly known alcohols, ethanol (C2H5OH). Ethanol is one of the alcohols we are studying today. Ethanol is found in low concentration in alcoholic beverages, but can cause poisoning and even death at higher concentrations. You will be looking at two other alcohols as well: methanol and propanol. Both pose risks to living cells and tissues. Methanol in particular can cause blindness and death. You will be observing what stress, if any, alcohol places on beet membranes, and comparing the different types of alcohols. If beet membranes are damaged due to chemical or physical stress (cutting, pressure, etc.), the red pigment will leak out into the surrounding environment. The intensity of the color released should be proportional to the amount of cellular damage sustained by the beet. To measure color intensity, you will be using a spectrophotometer. In this device, a light source will emit a beam of light that passes through your test solution and strikes a photocell on the other side. The spectrophotometer monitors the light received by the photocell as either an absorbance or percent transmittance value. You will prepare five solutions of differing alcohol concentrations (0%, 10%, 20%, 30%, and 40%) for each of the three alcohols. A small piece of beet will be placed in each solution. After ten minutes, each alcohol solution will be transferred to a small, rectangular cuvette and placed into the spectrophotometer. The alcohol solutions are clear. If beet cell damage occurs, the beet pigments will alter the solution s color and light absorbance. The absorbance is directly related to the amount of red pigment in the solution. By plotting the percent alcohol vs. the amount of pigment (that is, the absorbance), you can assess the amount of damage that the different alcohols cause to cell membranes. Biology 171L - SP18 Investigating Biological Membranes 4-4

5 SPECTROPHOTOMETER You will be using the amount of betacyanin pigment released by damaged beet cells as an indication of the amount of damage inflicted by a test sample. In order to quantify the amount of pigment released, you will be studying the concentration of pigment in solution using an instrument called a spectrophotometer. A spectrophotometer works by passing a beam of light through a plastic or glass cuvette (or square vial) containing a sample of solute (Fig. 5). The beam of light passes through the sample and hits a detector on the other side. Figure 5. Cartoon showing light passing through prism and sample to reach the detector. Source: mindexperts.com Light particles, or photons, pass through the sample and some light may be absorbed by the sample. The remaining light particles continue to travel through the sample unaffected and hit the spectrophotometer detector. Your spectrophotometer can give you two kinds of information: Transmittance (T): the fraction of light in the original beam that passes through the sample and reaches the detector Absorbance (A): the fraction of light that was absorbed by the sample If no light is absorbed, then the absorbance is zero and transmittance is 100%. Figure 6. Electromagnetic spectrum showing the portion that constitutes visible light, nm. Biology 171L - SP18 Investigating Biological Membranes 4-5

6 The amount of light absorbed is directly proportional to the concentration of absorbing materials in the sample. The absorbance of a sample depends upon the wavelength of light. You will measure the absorbance at a specific wavelength (540nm) for today s lab. The visible region of light ranges from approximately nm (Fig 6.). The colors of individual pigments are a consequence of the fact that substances absorb some wavelengths and reflect others. For example, chlorophyll absorbs all wavelengths except for green wavelengths, which it reflects. That light is reflected back to our eyes, which we see as green. White is the reflection of all visible wavelengths. It is important to note that there may be molecules other than your target substance in your solution. These substances could affect the absorbance or transmittance of wavelengths and cause your values to be higher or lower than just your substance of interest. To compensate for these unwanted effects, we use controls or reference solutions. The reference or control should contain everything found in the sample solution, except for the substance you are trying to analyze or measure. In this lab, the control is distilled water. EXPERIMENT PROCEDURE Overview: In order to determine which alcohols cause the most disruption to the cell membranes, you will be soaking samples of beet tissue in different concentrations of three different alcohols and measuring the amount of pigment that leaks out the beet cells. The amount of pigment released will be representative of the amount of damage done to the cell membranes. You will determine the relative amount of pigment in each alcohol solution using a spectrophotometer to measure the absorbance of betacyanin. There are two models of spectrophotometers. Identify which one you are using before you begin and turn to the correct protocol for the next step. A. SPECTRONIC 20D+ Your spectrophotometer needs to warm up. It should have been turned on at least 15 minutes prior to starting your lab. If it is not on, turn it on now. Blanking/ Calibrating your spectrophotometer Absorbance measurements are relative measurements; that is, the values we record represent the difference between the amount of light absorbed by our solvent and the amount of light absorbed by our solute. Consequently, we need to calibrate the instrument so that it is subtracting the light absorbed by the solvent. We call this blanking. Set the wavelength to 540nm. Blank the spectrophotometer using the instructions listed on page 4-11, entitled Blanking the Spectrophotometer. Biology 171L - SP18 Investigating Biological Membranes 4-6

7 B. Vernier SPECTROVIS PLUS Your spectrophotometer needs to warm up for at least 5 minutes. If it is not on, turn it on now. Calibrating/ Blanking your spectrophotometer Absorbance measurements are relative measurements; that is, the values we record represent the difference between the amount of light absorbed by our solvent and the amount of light absorbed by our solute. Consequently, we need to calibrate the instrument so that it is subtracting the light absorbed by the solvent. We call this blanking. Calibrate the spectrophotometer using the instructions listed on page 4-12, entitled Vernier SpectroVis Plus Spectrophotometer. When you place your sample in the Spectrovis Plus, the instrument will give you the entire absorbance spectrum. Record the absorbance value at 540nm. Testing Alcohols On your lab bench, you should have the following materials (per pair of students): 1. Spectrophotometer 2. Black cuvette holder 3. Plastic cuvette well microtiter plate 5. Rack with seventeen (17) falcon tubes of De-I water, alcohol and SDS solutions. 6. Watch glass or similar for rinsing beets ml graduated cylinder 8. Forceps 9. Transfer pipets (17 labeled to correspond to solutions) Set-up: 1. Work in teams of two. 2. Rinse out cuvette with distilled water and dry well with tissue (Kim Wipe). 3. Place empty, clean, dry microtiter plate on a white sheet of paper. 4. Recommended: label paper so that you know what alcohol and SDS concentrations are in each well. 5. Rinse pipets with De-I water and shake out excess water. 6. Find a portion of the beet slice that is uniform in thickness and pigment density. 7. Cut 20 uniform beet discs using the smaller end of the conical cutter, so that: All discs/cubes are uniform in shape and size Edges are smooth Pieces do not have any of the outer beet skin Pieces are not dried out Pieces appear consistent in coloring and pigmentation Biology 171L - SP18 Investigating Biological Membranes 4-7

8 8. Use wash bottle with distilled water to gently rinse beet pieces to remove pigment released by the physical damage of cutting. Place beet pieces on a kimwipe until you are ready to use them. DO NOT dry the beets. Rubbing them will cause more damage to cells. Absorbance: 9. Fill test wells with 2.5mL of each test solution Methanol (0, 10, 20, 30, 40%) Ethanol (0, 10, 20, 30, 40%) Propanol (0, 10, 20, 30, 40%) 0% alcohol simply stands for de-ionized water and will be the same for all alcohol controls. 10. Change pipets with each alcohol and each concentration sample. Note which pipets are associated with each solution. You will be using the pipets to mix each individual well during the timed period. 11. Start with methanol, and place a piece of beet in each of the five (5) test wells. Begin timing ten minutes. 12. At every minute mark, gently stir the contents of the well using the pipet to mix the layers and disperse the pigment. Use the correct pipet to prevent cross-contamination. 13. At the end of the ten minutes, use forceps to gently extract the beet samples from the wells in the same order they were first placed in the well. 14. Discard the used beet pieces in the trash. 15. You may leave the solutions in your test wells until the end and obtain absorbance readings for ALL your test solutions at once. Or, you may choose to test these solutions in the spectrophotometer as you go along in. 16. Repeat the steps above (11-15) with ethanol. 17. Repeat the steps above (11-15) with propanol. 18. You should now have fifteen alcohol test samples to test for absorbance. 19. Use the spectrophotometer to obtain and record absorbance readings. Record the absorbance value at 540nm. Rinse out transfer pipets with distilled water between each sample and wipe cuvettes well with tissue before each reading. Biology 171L - SP18 Investigating Biological Membranes 4-8

9 Absorbance Readings Concentration (%) Methanol Ethanol 1-Propanol Class Average Absorbance Readings Concentration (%) Methanol Ethanol 1-Propanol Testing SDS and membrane integrity 20. Fill test wells with 2.5 ml of each concentration of SDS. 21. Change pipets with each concentration. Note which pipet corresponds with each particular well. You will be using the pipets to mix each individual well during the timed period. 22. Place a piece of beet in each of the five (5) test wells. Begin timing ten minutes. 23. At every minute mark, gently stir the contents of the well using the pipet to mix the layers and disperse the pigment. Use the correct pipet to prevent cross-contamination. 24. At the end of the ten minutes, use forceps to gently extract the beet samples from the wells in the same order they were first placed in the well. 25. Discard the used beet pieces in the trash. 26. Use the spectrophotometer to obtain and record absorbance readings. Record the absorbance value at 540nm. Rinse out transfer pipets with distilled water between each sample and wipe cuvettes well with tissue before each reading. 27. Compare your results with class averages. Biology 171L - SP18 Investigating Biological Membranes 4-9

10 SDS Concentration (%) Absorbance Readings Class Average Absorbance Record the results in your notes. 29. SDS solutions can be disposed of in the sink with tap water. Alcohol solutions should be disposed of in the bottles marked WASTE. 30. Clean up your space, refill bottles and paper towels, and make sure cuvettes have been removed from spectrophotometer. If you are the last class of the day, turn off and unplug the spectrophotometer. Biology 171L - SP18 Investigating Biological Membranes 4-10

11 REFERENCE FOR BLANKING YOUR SPECTROPHOTOMETER Follow the guidelines below. Ask your TA or TI for help, if necessary. Vernier SpectroVis Plus Spectrophotometer Getting Started 1. Ensure Logger Pro software (version or newer) is installed on your computer before using the SpectroVis Plus Spectrophotometer. 2. Connect the Spectrophotometer to a powered USB port on the computer or a powered USB hub. Note: The first time you connect a Spectrophotometer, your computer may ask you a few questions. Do not go online for device drivers. The device drivers were installed when you installed Logger Pro. 3. Start Logger Pro software on your computer. Select the Type of Data (or Units) You Want to Measure The default data type is absorbance. If you want to measure the absorbance of a solution, proceed directly to the Calibrate section below. Calibrate ü To calibrate the SpectroVis Plus, choose Calibrate Spectrophotometer from the Experiment menu. Note: For best results, allow the Spectrophotometer to warm up for a minimum of five minutes. ü Fill a cuvette about ¾ full with distilled water (or the solvent being used in the experiment) to serve as the blank. After the Spectrophotometer has warmed up, place the blank cuvette in the Spectrophotometer. Align the cuvette so the clear side of the cuvette is facing the light source. ü Follow the instructions in the dialog box to complete the calibration, and then click. Collect Data with a Computer There are three general types of data collection that measure absorbance or transmittance, but you will only collect one kind in this class absorbance (or %T) vs. wavelength, which produces a spectrum. Measurement vs. Wavelength (Generate a Spectrum) 1. Fill a cuvette about ¾ full of a sample of the solution to be tested. Place the sample in the Spectrophotometer and click. Click to end data collection. 2. To store the spectrum data, choose Store Latest Run from the Experiment menu. Figure 1 Configure Spectrometer data-collection dialog box Change the Settings in Logger Pro 3 Spectrophotometer Dialog Box The Spectrophotometer dialog box lists all the settings for the device. To display this box choose Set Up Sensors Spectrophotometer from the Experiment menu. Figure 2 Spectrometer Dialog Box For most experiments, the default settings work well. There are four parameters listed in the dialog box. Sample Time: this is similar to the shutter speed of a camera. Logger Pro automatically selects the proper sample time during calibration. Note: For emission studies, you may need to change the sample time manually. Wavelength Smoothing: the number of adjacent readings on either side of a given value that is used to calculate an average value. Note: Be careful adjusting this parameter as it may shift your wavelength values slightly. Samples to Average: the number of readings taken at a given wavelength to calculate an average reading. Wavelength Range: the range is determined by the type of Spectrophotometer in use. By clicking on the picture of the Spectrophotometer in this dialog box, you will gain access to four options: calibrate, configure data collection, go to the support web page, and units of measure. Click on an item to select it. Biology 171L - SP18 Investigating Biological Membranes 4-11

12 Spectronic 20D+ a. Turn on the spectrophotometer by turning Knob 1 clockwise and allow machine to warm up for at least 15 minutes. Your TA may have already turned it on. b. Make sure lever in front of machine at the bottom is set to the appropriate position for your experiment (left side for ). c. Open the hinged lid compartment (CH) and remove black cuvette holder. Close lid well. d. Press the MODE button (upper circle) to select TRANSMITTANCE mode (seen on display screen). e. Make sure that the sample compartment is completely empty and the lid is closed well. Light seeping in will affect the calibration. f. Zero the instrument. Using small increments, adjust Knob 1 until the display reads 0.0 (0% T). g. Use Knob 3 to set the desired wavelength. h. Obtain a cuvette, handling it only by the top edge of the ribbed/textured sides. i. Wipe it clean and dry with a tissue. j. Blank the instrument. Prepare a blank by filling the cuvette ¾ full with distilled water. Always dry outside of cuvette with tissue before placing in spectrophotometer. k. Check that solution is free of bubbles and insert into black plastic cuvette holder without spilling. There is a triangle at the top on one side of the cuvette. This triangle should face outward. l. Wipe the outside of the cuvette again, especially where you might have touched it. m. Open the hinged door of spectrophotometer and insert cuvette holder, so that the triangle faces Knob 3. Line up the white painted arrows on the cuvette holder and the machine. n. Close hinged door carefully and make sure it s closed all the way. o. Turn Knob 2 until transmittance reads 100%. Then hit MODE to switch to ABSORBANCE mode. Absorbance should read at 0%. Your machine is now blanked. Biology 171L - SP18 Investigating Biological Membranes 4-12

13 You have two assignments Due Week of February 12, 2018!! #1 - Using the Scientific Literature (10% of your total grade) #2 - Lab 4 Homework Format is important. All written homework should be typed, double-spaced, Times New Roman 12-pt font, with 1-inch margins. Remember to include your name, section and the name of your TA. Read about best practices when writing the Materials and Methods (pp ) section of a lab report, and the Results (pp ) section of a lab report in A Short Guide to Writing About Biology, and any other resources you find helpful (e.g., and/or Part 1 Mastering Biology (39 points): 1. Answer the questions in the assignment entitled 5. Respiration in Yeast on the Mastering Biology site. You have until the night before your lab at 11:59pm to complete these questions. Part 2 Science Communication (45 points): A. Writing the Materials & Methods section of a Lab Report (5 pts) a. Describe of the elements of a well-written Materials and Methods section in one or two paragraphs. Include such elements as the purpose, correct amount of detail, proper tense and voice, narrative versus bullet points, why certain steps were taken or omitted, and any other details you believe are important. b. Why is the Materials and Methods section important? How does it contribute to the construction of knowledge in biology? B. Writing the Materials and Methods section of the Biological Membranes Lab (10 pts) a. Write the Materials and Methods section for this lab. Use the guidelines you developed in your answer above, the information you reviewed in the Materials and Methods section in A Short Guide to Writing About Biology, pages , and or to help you. C. Reflection (5 pts) a. Evaluate your Materials and Methods section for the membrane lab (question 2.B.). Describe how well your Materials and Methods section conforms to the guidelines you outlined in question 2.A. Use the rubric provided at the end of this manual to help you. Do you need to make any changes to improve your Materials and Methods section? In your answer, outline the steps you will take. Make these changes now to get maximum points for your answer in part 2.B. D. Writing the Results section of a Lab Report (5 pts)

14 a. Describe of the elements of a well-written Results section in one or two paragraphs. Include such elements as the purpose, correct amount of detail, proper tense and voice, narrative versus bullet points, correct placement of figure and table captions, description of possible trends in the data and any other information you feel is important. b. Why is the Results section important? How does it contribute to the construction of knowledge in biology? E. Writing the Results section of the Biological Membranes Lab (15 pts) a. Write the Results section for this lab. Use the guidelines you developed in your answer above, the information you reviewed in the Results section in A Short Guide to Writing About Biology, pages , the Guide to Writing Lab Reports, and or to help you. F. Reflection (5pts) a. Evaluate your Results section for the membrane lab (question 2.E.). Describe how well your Results section conforms to the guidelines you outlined in question 2.D. Use the rubric provided at the end of this manual to help you. Do you need to make any changes to improve your Results section? In your answer, outline the steps you will take. Make these changes now to get maximum points for your answer in part 2.E. Part 3 Data Analysis (20 points) Summarize your data in graph form to answer the following questions: 1. What are the alcohols doing to the membranes? Why? What interaction of alcohol molecules with membranes leads to the release of betacyanin after exposure of beet tissue to alcohols? (4 pts) 2. How does the size of the alcohol molecules relate to the extent of membrane damage? Suggest an explanation for why this might happen. (3 pts) 3. Did the concentration of the alcohol affect the amount of cellular damage? Is this effect the same for all the alcohols you tested? (3 pts) 4. What effect did the SDS detergent have on cell membranes? Explain your results, including a reference to the different concentration that you tested. (4 pts) 5. Your class uses 70% ethanol solutions to clean their bench areas after labs. Why? And why is it recommended you still wash your hands even after disinfecting your lab area? (3 pts) 6. Do you see any trends in the results? Does the evidence support your initial hypotheses? Describe the evidence in your answer. (3 pts) Biology 171L - SP18 Investigating Biological Membranes 4-14

15 Revised 01/29/16 Timmerman, USC Biology Universal Lab Rubric 12/28/05 15 Criteria Not addressed Novice Intermediate Expert Methods: Controls and replication Appropriate controls (including appropriate replication) are present and explained. If the instructor designed the experiment: Student explanations Student evidences a of controls and/or reasonable sense of replication are why controls/ vague, inaccurate or replication matter to indicate only a this experiment rudimentary sense of Explanations are the need for controls mostly accurate, but and or replication some Student fails to mention controls and/or replication or mentions them, but the description or explanation is incomprehensible. Explanations of why these controls matter to this experiment are thorough, clear and tied into sections on assumptions and limitations Methods: Experimental design Experimental design is likely to produce salient and fruitful results (tests the hypotheses posed.) Methods are: appropriate clearly explained drawn directly from coursework not modified where appropriate inappropriate poorly explained / indecipherable appropriate clearly explained modified from coursework in appropriate places or drawn directly from a novel source (outside the course) appropriate clearly explained a synthesis of multiple previous approaches or an entirely new approach

16 Revised 01/29/16 Timmerman, USC Biology Universal Lab Rubric 12/28/05 16 Criteria Not addressed Novice Intermediate Expert Results: Data selection Data are comprehensive, accurate and relevant At least one relevant Data are relevant, dataset per accurate and hypothesis is complete with any provided but some gaps being minor. necessary data are Reader can fully missing or inaccurate evaluate whether the Reader can hypotheses were satisfactorily supported or rejected evaluate some but with the data not all of writer s provided. conclusions. Data are too incomplete or haphazard to provide a reasonable basis for testing the hypothesis Data are relevant, accurate and comprehensive. Reader can fully evaluate validity of writer s conclusions and assumptions. Data may be synthesized or manipulated in a novel way to provide additional insight. Results: Data presentation Data are summarized in a logical format. Table or graph types are appropriate. Data are properly labeled including units. Graph axes are appropriately labeled and scaled and captions are informative and complete. Presentation of data: contains some errors contains only minor in or omissions of mistakes that do not labels, scales, units interfere with the etc., but the reader is reader s able to derive some understanding and relevant meaning the figure s meaning from each figure. is clear without the is technically correct reader referring to but inappropriate the text. format prevents the Graph types or table reader from deriving formats are meaning or using it. appropriate for data Captions are missing type. or inadequate includes captions that are at least somewhat useful. Labels or units are missing which prevent the reader from being able to derive any useful information from the graph. Presentation of data is in an inappropriate format or graph type Captions are confusing or indecipherable. contains no mistakes uses a format or graph type which highlights relationships between the data points or other relevant aspects of the data. may be elegant, novel, or otherwise allow unusual insight into data has informative, concise and complete captions.

17 Timmerman, USC Biology Universal Lab Rubric 12/28/05 17 Criteria Not addressed Novice Intermediate Expert Results: Statistical analysis Statistical analysis is appropriate for hypotheses tested and appears correctly performed and interpreted with relevant values reported and explained No statistical analysis is performed. Statistics are provided but are inappropriate, inaccurate or incorrectly performed or interpreted so as to provide no value to the reader. Appropriate, accurate descriptive statistics are provided. Statistical analysis is appropriate, correct and clearly explained Revised 01/29/16