Experiment Tracking Sheet
Topic of this Lab: Experiment 1
Summary (What are you going to do?):
Independent Variable:
Dependent Variable (Data):
Hypothesis:
Control Variables (What do you need to make sure stays the same?):
Positive or Negative Control Experiments (If any, what are they?):
Data Taken:
Conclusions (Was your hypothesis correct? What does this demonstrate about the Topic from above?):
Experiment 2
Summary (What are you going to do?):
Independent Variable:
Dependent Variable (Data):
Hypothesis:
Control Variables (What do you need to make sure stays the same?):
Positive or Negative Control Experiments (If any, what are they?):
Data Taken:
Conclusions (Was your hypothesis correct? What does this demonstrate about the Topic from above?):
Experiment 3 (If necessary)
Summary (What are you going to do?):
Independent Variable:
Dependent Variable (Data):
Hypothesis:
Control Variables (What do you need to make sure stays the same?):
Positive or Negative Control Experiments (If any, what are they?):
Data Taken:
Conclusions (Was your hypothesis correct? What does this demonstrate about the Topic from above?):
(Note: You must fill out this sheet for every wet-lab experiment. It will help you track information for discussion groups, lab reports, quizzes and exams. Do not turn this sheet in. It is for your notes.)
Photosynthesis: Experiment Instructions (Lab Report)
LEARNING GOALS
By the end of this unit, you should be able to do the following:
1. List the reactants and products of photosynthesis.
2. Explain how different pigments absorb and reflect different colors of light.
3. Explain how each step of the floating leaf experiment relates to the reactants or products of photosynthesis.
4. Explain how the chromatography experiment uses polar paper and nonpolar solvent to
separate different pigments based on polarity.
5. Identify the Independent, Dependent, and Control Variables in your experiment.
Note: These experiments were adapted from two different web sites. Links are provided to them so that you can look at their wonderful pictures and illustrations that make the process more clear. However, you need to follow the instructions here to do the experiment correctly.
MATERIALS NEEDED (Oxygen Production)
Lamp with bright LED bulb or Compact Fluorescent (the curly bulb), the brighter the better!
Fresh Spinach Leaves
Straw or single hole puncher
Liquid Soap or Liquid Dishwashing Soap (for handwashing dishes, not machine washing
detergent)
Plastic Syringe with NO NEEDLE! (ask a pharmacist for the measuring syringe to give a child
liquid, oral medicine)
Baking Soda
Clear Glass or Cup
Timer
Box or Cover to block light
MATERIALS NEEDED (Chromatography of Plant Pigments)
Tall, Clear Glass
Fresh Spinach Leaves and one other type of leaf (Fall leaves work well, but they must not be
dry)
Pencil
Rubbing Alcohol or Spray hand sanitizer or nail polish remover
White Coffee Filters (#4 conical works best, but any works)
Nickel
Ruler
Don’t forget to fill out the Experiment Tracking Sheet for each section of the exercise. Remember to take one picture of Floating Leaves and one picture of Chromatography for the lab report.
PHOTOSYNTHESIS
You will be cutting out circles of spinach leaf and watching them float to show oxygen production during photosynthesis. After cutting out the circles of leaf, you will place them inside a plastic syringe and pull back on the plunger to create a vacuum and suck out the air from inside the leaves. The leaf circles will now sink. After 10-20 minutes in bright light, the leaf circles will have produced enough oxygen to inflate and float like tiny rafts. You will use different colors of food coloring to see which colors work well for photosynthesis.
You will also be crushing leaf pigments onto a coffee filter (paper is polar) and then drawing rubbing alcohol (mostly non-polar) up the filter to see which pigments move up with the alcohol and which stay still. You will measure the distance each pigment moves and compare it to the total distance the alcohol moved.
Experiment #1 – Oxygen Production
(https://www.youtube.com/watch?v=vw8baZO89oc)
Note: Please watch the video above first. It is hard to visualize this experiment from just words, but the video makes everything clear.
1. (Identify Control Variables) Add 1/2 tablespoon of baking soda to 4 cups of water. (When baking soda dissolves, it releases CO2 into the water.) Add a small drop of liquid soap to the water and stir to mix. If you see a large number of bubbles, start over and use less soap.
2. Using the end of a straw or single hole punch, cut out 15-20 circles of spinach leaf.
3. Pull the plunger completely out of the syringe and put the leaf circles into the syringe. Push the plunger back in. Use the syringe to suck up the baking soda water until the syringe is about 1/4 or 1/3 full of liquid.
4. Place your finger over the end of the syringe and pull back on the plunger as far as you can without pulling the plunger out. This should create a vacuum. (If leaf circles stick to the sides of the syringe up in the air space, swirl the solution so that they fall down into the solution.)
5. Repeat step #4 three times. All leaf circles should now sink to the bottom of the liquid. (If some are still floating, repeat step #4 again and make sure the circles are all submerged in liquid.)
6. Place the spinach circles into a clear glass with about 2 inches of baking soda solution. Immediately cover to block out all light.
7. (Positive Control Experiment) Set up the lamp with a compact fluorescent light bulb. When you are ready to begin, place the glass in front of the lamp. Count the number of circles that are floating after each minute for 20 minutes. This is your positive control experiment. Notice the bubbles coming out of the floating circles.
8. (Negative Control Experiment) Are you sure the circles don’t just float on their own after 20 minutes? Create a negative control experiment to confirm that this is a really a reaction between both components.
Use fresh spinach circles to do this experiment. You must have a negative control experiment in your report!
9. (Hypothesis) Repeat the experiment with fresh circles, but use regular water plus soap for all steps instead of baking soda and soap water. Regular water has very little CO2 in it. Make a hypothesis about how lack of CO2 should affect the rate at which circles float.
Conclusions – Did the plant produce oxygen and float as expected? Make a line graph showing the results each minute. The graph should have 3 total lines; 2 for the control experiments and 1 for lack of CO2.
Experiment #2 – Chromatography of Plant Pigments
(https://www.youtube.com/watch?v=_v6_5Zxdb68)
Note: Please watch the video above first. It is hard to visualize this experiment from just words, but the video makes everything clear.
1. Get a few spinach leaves and one or two other leaves of different colors or shades of green from around your house. Medium to large leaves work best. Leaves should not be tough or dry. Red and yellow fall leaves work well, and it is particularly interesting if you can get a two different colored leaves from the same plant.
2. (Identify Control Variables) Cut coffee filters into four strips 1 inch wide. Make strips approximately the same length.
3. Mark each strip 3/4 inch from the bottom with a PENCIL. (Ink separates during chromatography, so only use pencil markings.) Lay one spinach leaf over the coffee filter strip. Roll a nickel across the leaf ONCE at the pencil mark. Press down as you are doing this to crush the leaf but don’t scrub!!!
Set the filter aside for 1 minute to dry. (This is critical. If the filter gets too wet, the leaf pigments will spread out and you won’t get a clear line.) Repeat step #3 at least 15 times to get a dark, colored line at the bottom of the filter.
4. Do this process for each leaf type to be tested, using a different filter paper for each leaf.
5. Tape the top each filter paper to a pencil or pen. (The top is farthest from the leaf line; use one filter per pencil/pen.) Using an empty glass as a guide, roll the filter paper up on
the pencil until the filter is almost touching the bottom of the glass when the pencil is laid across the top. (If you are confused right now, go back and watch the video again.)
6. (Hypothesis) The paper is very polar and the alcohol is mostly non-polar. Using the pictures of each pigment in the prelab, make a hypothesis about which pigments will choose to follow the alcohol higher on the filter and which will stay lower as they cling to the polar fibers of the filter.
7. (Hypothesis) Which pigments will you see more of in your spinach leaf compared to your other leaves? Make a hypothesis about this. (For color reference, chlorophyll is green, xanthophylls tend to be yellow, and carotenes are orange or red.)
8. Pour 1/4 inch of alcohol into a glass. Do this for as many glasses as you have filter papers to run.
9. Set each pencil with a filter strip across the top a different glass with rubbing alcohol. The bottom of the filter should be touching the alcohol, but the leaf pigment line should never be submerged in the alcohol. Tape the pencil in place so it doesn’t roll off the glass. The alcohol should begin moving up the filter, rapidly at first and then more slowly as it climbs.
10. Let the alcohol climb the paper for 30 minutes. Take the filter out of the alcohol and immediately mark the paper with the distance the alcohol moved.
11. Measure the distance each pigment moved from the start line (use cm, not inches) and include these measurements in your lab report. There should be a distance moved for each pigment band, identified by scientific name. For example, a red leaf cabbage leaf might have a red (anthocyanin) and an orange (beta carotene) band. Both bands need a “distance moved” number.
Conclusions – Did you see the pigments you expected to see in each leaf? Was a solid red or green leaf actually just one color? Did you predict correctly which pigments would follow the alcohol vs. stay stuck to the paper?
LAB REPORT
Your fourth full lab report will be written over this lab. The lab report instructions are contained within this module. Consult the Schedule on the Home Page for due dates.
DISCUSSION
Inside this module is a link to the Discussion Group. Contribute to a discussion of at least one of the questions there. It is important that you post by the First Post date, that you post at least three times, and that at least one of your posts be a reply to one of your class mates. Consult the Schedule on the Home Page for due dates.
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