|MadSci Network: Botany|
Sounds like you had a well-designed experiment. Seed germination was poor with skim milk, apple juice and 7up because they contain high concentrations of sugars. Skim milk also contains high concentrations of sodium salts. High concentrations of sugars and salts reduce the availablity of water to the seed or plant. The reduced availability of water can prevent seed germination or stunt seedling growth. Softened water has had its calcium and magnesium replaced with sodium. Sodium is toxic to most plants, however, you said your tap water seedlings looked healthy so it seems that your softened tap water did not contain enough sodium to completely prevent germination. Were the tap water seedlings smaller than those with distilled water or diet cola? Another possibility is that just six seeds per treatment, maybe you just had lower germination in the tap water treatment by chance. If your tap water comes from a city water company, you should be able to get a water quality analysis from the company. That would indicate whether the water is high in salts or contains other substances harmful to plants. Distilled water had no salts and no sugar so would seem to be the best treatment of the bunch. Diet cola had zero sugar, a tiny amount of artificial sweetener and an unknown amount of salts because the water source used to make it was not known. Perhaps the water for the diet cola had some mineral nutrients that benefited the seed/seedling, such as calcium or potassium. I can't explain the unsweetened Kool Aid treatment. I would expect the Kool Aid mix to have no effect on plants since it has low levels of salts and no sugar, just an artificial sweetener and some food dyes. What water did you use to mix up the Kool Aid? If you used your softened tap water, that may be an explanation. There are lots of answers about similar experiments in the MadSci archives. Botanists have not really done such experiments because human beverages are not usually suitable for plants. It would be very expensive to water plants with diet soda pop or other human beverage. A better "beverage" for plants would be a fertilizer solution. References Hershey, D.R. 1993. Evaluation of irrigation water quality. American Biology Teacher 55:228-232. Re: Why did the liquids kill the plants? Why did the tea do well? Re: What is a good plant to test the effects of sugar or sweetener? Re: Why will plants grow in Diet Coke and water and not other sodas?
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