Excerpts from Photosynthesis Methods and Materials Sections

Good Excerpts

Note that while none of these quotes would stand alone as a good Methods and Materials section, a number of these ideas combined together might do quite nicely.

♦ The chromatography paper was laid on a piece of clean paper and subsequently, a spinach leaf was placed on top of the chromatography paper. The edge of a dime was rolled over the leaf to transfer the leaf pigment and create a stripe across the chromatography paper, about 1.5 cm from one end. The leaf was repositioned and this process was repeated several times on the same place on the paper until a dark color was obtained.

♦ The edge of a penny was used to roll a stripe of the spinach across the paper about 2 cm above the end of the chromatography paper. Then the spinach leaf was moved so a new portion of the leaf was over the first stripe and re-rolled to darken the stripe.

♦ With a T-pin, the “top” end (the end without the pigment stripe) of the paper was attached to the bottom of the rubber stopper.

♦ As the chromatography solution was absorbed by the paper, the plant pigments traveled up the paper at differing rates, thus were separated into bands of individual pigments. When the farthest band was about 1 cm away from the stopper, the paper was removed from the flask.

♦ As the solution was absorbed by the chromatography paper, it carried the pigments from the stripe up the paper.

♦ Using scissors, the pigment bands were cut from the chromatography paper. Each band was placed into a separate 13 × 100 test tube containing 5 mL of 100% ethanol. Multiple bands of identical pigments were placed into the same test tubes as each other to make the solutions as concentrated as possible.

♦ The identical bands were cut apart and redissolved in 100% ethanol in separate 13 × 100 test tubes.

♦ A dilute solution of each of the colors of food coloring (red, yellow, green, blue) was made by placing one drop of the concentrate in a small beaker containing 30 mL of 100% ethanol. (— or whatever the ratio actually was)

♦ Absorbance readings for each leaf pigment and color of food coloring were acquired for wavelengths from 350 to 800 nm at 25 nm intervals. Graphs were constructed for each pigment to show maximum and minimum absorption points.

♦ Using a spectrophotometer, absorbance reading were obtained for all the pigments and food colorings at 25 nm intervals from 350 to 800 nm.

♦ A one-holed rubber stopper with a bent 1-mL pipet placed in the hole was used to cap each of the test tubes. Prior to capping, each tube was filled with sufficient solution such that the liquid subsequently filled about ¼ of the pipet.

♦ Eight test tubes containing Elodea were exposed to different lighting conditions to determine in which setting the most photosynthesis occurred as evidenced by the amount of oxygen produced. (— plus a brief description of the contents of each tube)
[Remember that Elodea is a genus name, thus should be italicized.]

♦ The amounts of oxygen evolved by photosynthesis under different colors of light were calculated as a percentage of the rate (in milliliters of oxygen evolved per minute) in white light. (— This is sufficient, and there is no need to go into the minute details of how the calculations were performed.)

Not So Good Excerpts (including some grammatical problems)

♦ In this lab, the following materials were used: (followed by a list).
[Materials should be included in the narrative as you relate what was done, not listed separately.]

♦ There are three parts to this experiment, they will be in sequence into which they were done. In Part A the class used. . .
[The first “sentence” really is two, and should have a period in the middle. This first sentence really is unnecessary — the division into “parts” is purely because of our time constraints and the experiment could just as easily be done all in one (longer) day. Items used should not be listed separately, but should be mentioned (and described) in the narrative when used. There are other grammatical problems here, too.]

♦ The procedure for this experiment began with filling a 250 mL Erlenmeyer flask with. . .
[Do not start your narrative in this manner. Simply state that, “A 250-mL Erlenmeyer flask was filled with. . .”]

♦ Graphs were . . . entered into the class computer and distributed among the class.
[This information/procedure is neither critical to nor specific to this experiment, nor did we enter graphs into the computer.]

♦ It is important to keep the paper as clean as possible and only handle it by the edges. . . The flask was capped so that the air in the flask could become saturated with fumes so that the chromatography would run properly. . . Carefully turn the stopper upside down on the flask so that while the paper is being pinned in place, no fumes escape. . . It is important to keep the flask covered while doing this, to keep all the fumes inside.
[Assume your reader is scientifically literate and knows what paper chromatography is all about. This experiment was not about how to do paper chromatography by itself, but this technique was used to obtain information about plant leaf pigments. Also, remember to report what was done in this experiment, not give orders to someone else. Additionally, the verbs used here do not “match” but switch from “(you) do xxx” to “xxx was done,” and back again.]

♦ In photosynthesis experiment, paper chromatography filter paper should be taken and spinach placed on top with rolling a coin across to spinach line across to the filter paper. Then placing the filter paper onto the rubber stopper with a t-pin and submit it into the flask with solution letting the tip of the paper dip into the solution.
[Always check, recheck, and proofread. Make sure your grammar and sentence structure make sense. Read your composition aloud to someone else and/or have someone read your composition aloud to you. Do not use the “implied you” verb form. Do make sure all your verb tenses match. Avoid using the word “take” unless you really obtained something and physically carried it to another location as an important step in some process.]

♦ Add a few millimeters of the 90% petroleum ether to 10% acetone solution to the Erlenmeyer flask and put the stopper on the flask.
[Do not use the “implied you” verb form. You should tell what was done, not give orders. This sentence could be reworded as, “A few millimeters of the 90% petroleum ether to 10% acetone solution were added to an Erlenmeyer flask, and the stopper was placed on the flask.”]

♦ The chromatography paper was then pinned to the bottom of a #8 stopper. This was then put in a solution of 90% EtOH and 10% acetone.
[Was the whole paper plus stopper submerged in the solution? The chromatography solvent system we used did not contain ethanol. In this case, “ethanol” should be written out (if it was correct).]

♦ The T-pin attaches the non-pigment side to the top of the stopper which needs to be folded over so that only the tip is in the solution.
[This person probably meant the end of the paper without the pigment. The paper was pinned to the bottom of the stopper. How was the stopper folded over so only the tip was in the solution? Again, do not use implied you sentence structure.]

♦ When the farthest band is about 1 cm from the stopper, the paper should be removed from the flask.
[Remember, you’re not giving instructions to someone else. This sentence should read, “When the farthest band was about 1 cm from the stopper, the paper was removed from the flask.”]

♦ When finished there will be five different colors on the chromatography paper. These five different colors have a name, at the very top are carotenes, the next down is xanthophyll, then chlorophyll a, chlorophyll b, and then the spinach.
[Do NOT include data in the Methods and Materials section! There are other grammatical problems here, too.]

♦ The spectra of pigment’s lab are done to show the absorbance levels of the different pigments at different wavelengths.
[“Lab” does not belong to “pigment,” so don’t use apostrophe—s here. Does this person mean to say, “The spectra are done,” or “The lab was done?”]

♦ To do this, each pigment and food coloring was placed into its own cuvette. Also, the machine had to be zeroed before each reading with a cuvette of 100% ethanol.
[Assume a scientifically-literate reader knows (or can find out) the procedure for general operation of a spectrophotometer. Again, the spectrophotometer was only used as a tool, and knowing how to adjust it is not the core of this experiment.]

♦ . . . the four different food colorings. . .
[should be reworded as “. . . red, yellow, green, and blue food colorings. . .”]

♦ Grind a piece of spinach leaf with a mortar and pestle. Add 100% EtOH to extract the plant pigments.
[We didn’t do this. Also, here’s that implied you, again. Write out “ethanol.”]

♦ Two groups of students should grind a piece of spinach and the other group grinds some dried parley with a mortar and pestle. . .
[You are not giving instructions to groups of students, but rather, telling what was done. Also, no spinach was ground in this manner. It is not critical to this experiment that the work was done by students and/or in groups. How many “groups”, how many tests/trials, were actually involved? This makes it sound like there were two groups which tested spinach plus a third group which tested parsley, though I suspect the writer may have meant that one group tested spinach while the another tested parsley. This could be reworded as, “Some dried parley was ground with a mortar and pestle. . .”, but it would be even better to specify how much parsley (and how much ethanol) was used.]

♦ The final part of the experiment (or “Part C of the experiment”) was done to determine the oxygen evolution by photosynthesis.
[Spreading of the experiment over three lab periods was an artificial division that was not critical to obtaining good results, thus probably does not need to be mentioned in this manner. This sentence could be reworded something like, “The oxygen evolved by photosynthesis under different colors of light was determined from measurements of fluid levels of bicarbonate solutions containing photosynthesizing plants.”]

♦ All of the solutions were recorded.
[This person probably meant “The fluid level in each of the pipets was recorded.”]

♦ After 20 min, a reading was taken.
[Be more specific about what is being done here. This could be reworded as, “After 20 min, the fluid levels in the pipets were read.”]

♦ After another 20 min, they should be recorded again and they should be moved into the dark. After the tubes are in the dark, the readings should be taken again.
[Who is “they?” How long in the dark? What readings should be taken?]

♦ All glassware should be cleaned and scraps of paper should be disposed of. . . Data should be entered in the computer.
[Yes, but this doesn’t belong in your experiment write-up. While freshman biology students frequently need to be reminded of such things, universal, common-sense procedures like cleaning up after oneself and recording one’s data are “givens” that should not be stated in a scientific paper. Once again, this is incorrectly written as though giving directions, rather than recounting what was done.]