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|  | General Overview
Equipment and Supply Modifications
Pre-Lab Preparations
Procedure Modifications
Alternative Lab Ideas
Equipment and Supply Modifications
Tip: "Last fall the Vernier catalog had a recommendation for some clamps to go over the tubing around the plants for transpiration. I ordered them and it made all the difference! No Vaseline goop and no leaks!! I cannot find that catalog or I would give you the address of the company that sells them. They are cheap -- 100 for about $13, I think, but the postage came close to doubling the cost, which irked me. Go to the Vernier Fall 1998 catalog or perhaps their Internet site for information. That little package of clamps is a package of little lifesavers when it comes to making the transpiration work with any size stems that fit into the tubing. I found I can reuse the clamps so I plan to use these for years!!"
-- Charlotte Freeman, Girls Preparatory School, Chattanooga, Tennessee. 4/20/99
Tip: "The plastic hose clamps for the transpiration lab can be ordered from Cole Parmer -- Part # 6832-01. Call (800) 323-4340. One hundred little plastic clamps cost about $19. They are reusable and I use them to get tight seals across some of the other connections I make with Tygon tubing, for example, when connecting tubing to inverted pipettes. For the transpiration lab one need no longer use petroleum jelly. The seal is great. What I do is grow beans that I buy from a local nursery (Kentucky Wonder Bean-NK Lawn and Garden) about three weeks in advance. I clip the bean stem at an angle just below the cotyledons. It just barely fits into the tubing and with the clamp you get a beautiful seal. Now, use the syringe that comes with the Vernier biogas probe to fill the tube with water. Place the clamp around the tubing, but don't tighten it yet. Hold the end with the connector up just a little higher than the other end so that water rises to the tip of the tubing. Insert the plant about 1 cm into the tubing, raise the clamp around the end of the tubing where the plant is, and tighten it. Now, there may still be an air bubble inside the stem and you need to have a continuum of water. So, here's the best part (you can't do this with petroleum jelly), invert the plant and tubing upside down and flick the end where the plant is. If there are any bubbles, they will rise to the other end of the tubing. What you now have is an airtight seal and a continuum of water -- the perfect transpirometer! The catalase works super with the same probe, as does respiration. The colorimeter is great for photosynthesis."
-- Bob Goodman, Hunter College High School, New York City. 2/25/99
Tip: "We have the most luck picking weeds with fairly big leaves. This spring I just grabbed whatever was growing in our backyard. In the summer I've used butterfly weed. I'll never forget trying to germinate those horrible bean seeds that are recommended. We never had more than 10 percent germination."
-- Louise Mowbray, Career Center, Lewisville, North Carolina. 6/17/01
Tip: "I used stems from a chrysanthemum plant that the local hardware store had on sale because I didn't look far enough ahead to have two-week-old bean plants. They worked well. The two light groups did have a slightly lower cumulative transpiration rate than the control (classroom conditions), though in the graphing, transpiration was faster in the light in the first few readings. So I think it's valid to think that the stem was losing water too fast, resulting in stomates closing."
-- Margaret Kaminsky, Penfield, New York. 4/4/00
Tip: "For those of you who are as frustrated with photometers as I am -- I purchased a demonstration photometer from Wards 14W8318 $87.95 in their 1999 catalog and tried it out -- results are great! No fumbling with trying to get the tygon tube to fit snugly around the plant stems and pipettes and no air bubbles to contend with! I had the gentlemen in Tech Ed (shop) cut some clear plastic plumbing tube (Ace Hardware) @21mm ID into 15cm lengths/you could also use soda bottle PET preforms (Flinn AP5395, $9.90 for a package of 30) with the bottom cut off. A two hole rubber stopper goes in the bottom with two 90 degree glass bends -- a short length of tube connects one to the graduated pipette or capillary tube, the other connects to a small syringe like the one used in the enzyme lab. A slit one-hole stopper fits in the upper opening of large tube -- choose hole size to match stem diameter. The top-to-bottom slit allows students to easily put stem in stopper; pack with Vaseline to prevent leakage. The syringe allows you to adjust the water level in the pipette easily. Put plant stopper in top opening, invert, and fill with distilled water. Put the two-hole stopper with syringe and pipette part of apparatus in the bottom and return to upright position. Adjust water level and off you go. This made an often painful lab a snap, even the worst lab technique was forgiven by this set up. Got great results with all variables and beans last week."
-- Donna M. Gilbertson, Beloit Memorial High School, Beloit, Wisconsin. 5/16/00
Pre-Lab Preparations
Tip: "The bush beans take about two weeks to become seedlings that you can use in the lab. I have two sizes of plastic tubing on hand -- about 1/8 inch and 1/4 inch so that I can handle all sizes of stems. The bush beans are best if you want to use the lab exactly as written -- the units of surface area calculated from mass is specific to bush lima beans. If you use any other plant, you will need to determine the surface area using centimeter graph paper. Just lay the leaves down on it and count the number of squares within the tracings. There are lots of plants that will work -- a number of them mentioned in the last few weeks. The nice thing about the bush beans you grow from scratch is that the students will only have to deal with two to four good-sized leaves."
-- Tricia Glidewell, Marist School, Atlanta, Georgia. 4/18/99
Tip: "I use transpiration lab in the fall with my plants unit. We will start growing Wisconsin Fast Plants and learn about plants while we gather data for an alternative Mendelian genetics lab. Use a different kind of transpiration lab, asking students to 'bag' leaves of C4 and C3 plants for comparison. Living in the Sonoran desert allows one a bit of flexibility. (Note: I have the students bag any of the legumes -- mesquite or acacia trees and bring their own C3 from a nursery.) I will be moving labs 11 and 12 to the beginning of the academic year (August for us)."
-- Steve Uyeda, Catalina Foothills High School, Tucson, Arizona. 4/19/99
Question: "Can pine branches be picked in advance and freshly trimmed before use?" Answer: "To prevent cavitation when you cut your pine branches immediately put the cut ends in water. When you trim your branches do it in water to keep the water column intact. We use Burford holly branches with very good results using this technique. The source was from a previous issue of American Biology Teacher."
-- Nancy Hein, Hawley High School, Hawley, Texas. 3/11/00
Procedure Modifications
Tip: "My first lab is the transpiration lab, and I tried a different method for setting up the experiment. (My students always had difficulty with the pipette/plastic tubing/ring stand set up -- air got into the tubing, the apparatus leaked, the pipette was difficult to read, and results were not as expected. We had lots of fun with experimental error, but it is nice if things actually work.) The new method worked!
Equipment: - electronic balance for each group (may be borrowed from chemistry, or a local college, or lab -- make phone calls; you only need them for one day)
- small vial that is flat on the bottom (the type that litmus paper comes in)
- plastic wrap or parafilm
- Vaseline (wouldn't be the transpiration lab without it!)
- modeling clay
- plants of the same variety -- I used impatiens because they were growing on my porch; if you plan ahead, 3-6 weeks, you can have the students grow bean plants -- they love to nurture
Procedure: - Fill a vial 3/4 full of distilled (or tap) water.
- Wrap top with plastic or parafilm and 'seal' with rubber band.
- Punch a hole in the center of the plastic.
- Cut off the section of stem you are going to use with a new razor blade or scalpel and insert the plant cutting in the vial. This is where the height of the plant cutting is critical -- if it is too large or tall, it will topple over, but (and here's where the clay comes in) the students can place the vial on the pan of the balance and use the clay to anchor it upright -- three small balls of clay at the base worked just fine, even in the windy/fan-induced experiment.
- Seal top of plastic, where stem is inserted with Vaseline, to remove the evaporation factor.
- Begin timing; the mass will go down. I used a large dry cleaner bag propped over two ring stands; for the 'humid' condition: mist the leaves and cover." Pam Tidswell, Rancocas Valley Regional High School, Mt. Holly, New Jersey. 11/12/99
Tip: "We used Barnes dropping bottles instead of vials. Then we didn't need the clay, and the plant stood up much better! I also use holly twigs, which are still green this time of year, have woody stems, and cooperate very well by transpiring away!"
-- Eloise Farmer, Torrington High School, Torrington, Connecticut. 11/17/99
Tip: "We found a 'trick' for the transpiration lab this week at our workshop that we thought was worth passing on. One of the problems for students has always been getting the potometer and pipette to stay full of water while putting in the plant and placing the apparatus into a stand. Many times students struggle just to get the whole thing set up, while in the process damaging the bean plants. There has been a lot of frustration with this lab because of these problems. Here's the trick: Attach a small syringe to the end of the pipette with a piece of rubber tubing. Use the syringe to pull water up into the potometer, then leave the syringe attached to keep the water under negative tension. Add the plant to the potometer (under water to keep air bubbles from forming at the base of the cut stem). Use petroleum jelly to seal the plant into the tubing. Now move the plant/potometer (with syringe) to the ring stand. We found that the syringe kept the whole system under negative pressure and the water from leaking until the potometer was in place. Once the potometer was positioned, the syringe is removed from the pipette. If the petroleum jelly seal held, the entire tubing/pipette was full of water. If not, all we needed to do was add more petroleum jelly. Using this method we found we could set up a potometer with a plant in about one minute. If the water runs down out of the pipette, add a drop of food coloring or dye to the tip of the pipette. As the plant transpires, the colored drop will move down the pipette allowing easy visibility for taking your readings. I usually have had trouble getting bean plants to survive the trauma of setting up the potometer. Many would collapse from damage and stop transpiring. Using the syringe helped us avoid this problem. Many of the plants were still 'healthy' and transpiring several hours after being placed in the potometer."
-- Jeff Smith, Indiana Academy, Muncie, Indiana. 6/15/01
Tip: "...I have used both bean seedlings and vinca minor leaves.... I use clamps around the tubing with the stems inside and it makes for a good system without the mess of Vaseline. Sometimes I have to stick padding in the clamps if the stems are too small."
-- Charlotte Freeman, Girls Preparatory School, Chattanooga, Tennessee. 4/4/00
Question: "Are their some tricks to seeing plant stomata well?"
Answer 1: "(1) Counting stomates -- Coat the surface of the leaf with clear nail polish. Some brands work better than others. Before it dries, place a little scotch tape over a small part of the wet polish so that you have a tab to pull on. Using the tab of tape, pull off some of the polish and then observe the dry polish with stomate imprints, first under low power (100X) and then high power (400X). If you determine the surface area of the field of view and the surface area of the leaf, then you can determine the number of stomates on the leaf. Or, if you just determine the surface area of the field of view, you can then determine the number of stomates per cm2. Count several fields to get a good sample.
(2) Action of stomates -- Peel off the epidermis of lettuce and place in 0.9 NaCl. To close the stomates, use bibulous paper and replace with 5 percent NaCl. To open them again, replace with distilled water."
-- Bob Goodman, Hunter College High School, New York City. 9/26/00
Answer 2: "I think I am the originator of the 'super glue' idea. You apply a small drop of super glue to the underside of the leaf and then apply to the glass slide and press for about 10-15 seconds with your finger on the topside of the leaf. If the leaf is very waxy, press for about 20-25 seconds. Warning: if your leaf is very thin, place a piece of paper between your finger and the leaf! Remove the leaf and you will have a beautiful look at the impression made by the leaf. I have placed leaves in the dark, and in the light, given them lots of water, and no water, etc. You can very easily see and measure the size of the guard cells and stomata. My students love to do it, and so do I."
-- Patti Carothers, Monte Vista High School, Danville, California. 9/27/00
Answer 3: "You can observe stomata on the lower epidermis of purple cane plants. Bending the crisp leaves tears the epidermis, which you can then peel off in a thin layer. Since the epidermal cells are purple and the stomata have chloroplasts that make them green, they are relatively easy to see."
-- Tricia Glidewell, Marist School, Atlanta, Georgia. 9/27/00
Answer 4: "Re: viewing stomates. The easiest way to observe stomates is to use a whole Zebrina leaf. Viewing the underside of this easily propagated plant inevitably causes the 'aha!' effect with teachers who are observing it for the first time: stomates and guard cells are bright green while the epidermal cells are purple. Once you've tried it, you will never use another method."
-- Phil Vavala, Salesianum School, Wilmington, Delaware. 6/29/01
Answer 5: "I know that some people use clear nail polish but I like to just tear the leaf at an angle. Choose your plants well, though. Some are much more obliging than others. Magnolia, for instance, separates easily, whereas oak does not. Geraniums are usually most accessible and are easy to work with. I advise the students to clean their slides, put a droplet of water in the center, and have a razor blade handy. Once a tear is made (and it should be done so as to yield a transparent lower epidermis), they can place the transparent portion on the water droplet. Next, the razor blade can be used to cut away the rest of the leaf. Add a cover slip and voilà."
-- Donna Light-Donovan, Croton-Harmon High School, Croton-on-Hudson, New York. 9/27/00
Alternative Lab Ideas
Tip: "I've been using a 'trick' given to me by Bobby Hinson (she got it from another teacher): Get a flat of plants (I use vinca-the flower not the vine) and really wet them down. Place the root ball of the plant in a sandwich bag and secure the top. Take the mass daily for a week. It's amazing how good the results are! I just started with a group of AP teachers today."
-- Phil Vavala, Salesianum School, Wilmington, Delaware. 6/18/01
Tip: "I've had good results measuring transpiration by mass rather than volume. Control flasks are necessary, as is a discussion of other possible mass changes due to photosynthesis. This results in a less cookbook approach. Bean seedlings will live a number of days (several have flowered and produced beans) in a flask, especially if the lab is done with roots intact. It is possible to test the effect of the tonicity of the water on transpiration as well."
-- Dwight Petteplace, Bow High School, Bow, New Hampshire. 6/17/01
Tip: "Another transpiration lab trick that Liz Cowles and I demonstrate in our AP Biology Institute at Eastern Connecticut State University, and which I got from Ted Graham of Lawrenceville (New Jersey) Academy and the St. Johnsbury (Vermont) AP Biology Institute: Using a 250 mL flask with a two-hole stopper, put a 1.0 mL pipette in one of the holes and seal with silicone (a la the CR Lab). Cut a small branch of a white pine, or similar woody species, and put through the second hole. Seal this with melted paraffin (you don't want this to be permanent). Then fill the flask to the very top with water. We usually put a few drops of food coloring into the water to make it more visible. Then push the stopper apparatus into the flask, letting water escape from the pipette opening. After the stopper is pushed in securely, just observe the water decrease in the pipette. We have been able to use the same pine stem for many days, although it is necessary to replenish the water. And woody stems are not subject to crushing like the herbaceous stems. I have been told by institute participants of the successful use of conifers other than pine and holly."
-- Fred Brown, retired, West Hartford, Connecticut. 6/20/01
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