|MadSci Network: Botany|
I wouldn't recommend that type of experiment because plants make all the sugar they require via photosynthesis. Plant roots are not designed to absorb sugars. Table sugar (sucrose) added in the irrigation water will harm or kill the plants because it reduces water availability because of an osmotic effect. It can also promote tremendous growth of soil microbes which may compete with the plant roots for mineral nutrients and oxygen or excrete potentially phytotoxic waste products. Artificial sweeteners are designed to trick human tastebuds and have little to no nutritional value so could not nourish plants. An artificial sweetener in the irrigation water would probably have no beneficial effect on plants but probably would not harm them either unless used at a very high concentration. If you do try a sugar versus artificial sweetener experiment, grow the plants in potting soil, sand culture or hydroponics. Plant growth will not be satisfactory in a zip lock bag containing a paper towel because plant leaves require access to atmospheric carbon dioxide and plant roots require oxygen and mineral nutrients. Be sure to have replication (three or more plants per treatment) and a control treatment, which would be a fertilizer solution, such as Peter's, Miracle-Gro or other houseplant fertilizer. You might also want a tap water control (zero sugar) and several concentrations of sugar to show that the more sugar, the poorer the plant growth. Students often use bean, corn, tomato, sunflower, or other vegetables in science projects. The plants often get undesirably tall because they prefer full sun and do not usually get optimal light indoors. House plants such as spider plant, wandering jew and piggyback plant are good experimental plants because they are easily rooted from cuttings and do well under low light levels in most homes. Another excellent plant is devil's backbone or mother-of- thousands (Kalanchoe daigremontiana) which produces an abundance of foliar plantlets. Wisconsin fast plants are widely used in teaching but require a fluorescent light bank. They go from seed to seed in 5 weeks. If you have a fluorescent light bank, you might also try various dwarf flowers such as marigold, zinnia and impatiens or small vegetables such as leaf lettuce or radish. If you want a much more interesting experiment using sugar and plants, examine "Can Feeding Albino Plants With Sucrose Substitute for Photosynthesis?" Buy albino corn seeds from a science supply company such as Carolina Biological Supply. The goal would be to keep the albino plants alive by feeding them sugar through the tips of their leaf blades. With a scissors, cut about 3 mm off the leaf tip every other day to keep the veins open to enable the sugar solution to enter the vascular system. Arrange small test tubes of sugar solution so the leaf tips dip into them. Replace the sugar solution every other day or when it becomes cloudy due to microbe growth. Spoehr (1942) kept albino corn alive for 3 to 4 months and produced small ears or corn using sucrose. He found 0.3 molar sugar solution (103 grams/liter) optimal. Spoehr noted that seedlings often died for no apparent reason, so start with ten or more seedlings per treatment to protect against such losses. You might also want to experiment with a floral preservative, such as Floralife, which contains sugar, an acidifier, and "stem unpluggers" to help keep the vascular system free flowing. It is designed to be absorbed by a plant's cut vascular system. It was a technology unavailable when Spoehr did his experiments. However, I doubt flower preservatives contain as much sugar as Spoehr used. The main ingredient in flower preservatives is sugar so you can easily estimate how much sugar a floral preservative provides and add additional sugar to reach 103 g/liter. For example, Floralife is added at the rate of 10 g/liter so estimate that it provides about 10 g of sugar and add 93 g more sugar per liter. The photo shows an albino corn plant being fed sugar solution through its leaf tips. The pictured plant was grown in solution culture or hydroponics, but it would be easier to grow the plants in potting soil. Twisted wire was used to keep the test tubes at the appropriate height so the leaf tips dipped in the solution. For plants grown in pots, the support wires could be stuck in the potting soil instead of being attached to support rods as in the photo. Cotton was used to stopper the tubes but today plastic wrap might be a better option. Irrigate the plants with a houseplant fertilizer, such as Miracle-Gro, to provide adequate mineral nutrients. Use fertilizer at about half the rate the label recommends to avoid overfertilization. As controls, grow some albino plants whose leaves receive plain water rather than sugar solution. There are other albino plant seeds for sale but corn works especially well because its parallel leaf veins travel the length of the leaf, an efficient arrangement for uptake via leaf veins. You might be tempted to do the experiment with a nonalbino corn plant grown in the dark. However, the original researcher found this to be unsatisfactory because even albino plants got very tall and spindly in the dark due to etiolation. The albino corn plant can be grown in the light where it does not become spindly but cannot photosynthesize because it has no chlorophyll. References Re: Why will plants grow in Diet Coke and water and not other sodas? Kalanchoe daigremontiana Wisconsin Fast Plants Floralife Spoehr, H.A. 1942. The culture of albino maize. Plant Physiology 17:397-410. Photo of Albino Corn Being Fed Sucrose
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