Observing Starch in Plant Materials

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Observing Starch in Plant Material Starch is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produce by all green plants as an energy store. It is the most common carbohydrate in the human diet and is contained in large amounts in such staple foods, as potatoes, wheat, corn, rice, and cassava. Objective: To test the presence of starch in common foods using iodine tincture Materials used: Microscope Microscope glass slide Cover glass Pipette Substances used: Iodine Onion juice Potato juice Testing for the presence of starch: Experiment 1: We tested the presence of starch in onions. First we made a wet mount slide. We took a small piece of the onion and rubbed it on the microscope slide to obtain onion juice. Then, we added a small drop of iodine on top of the onion juice and covered it with the cover lens. We made sure no air bubbles were present under the cover lens and the glass lens. We placed the lens on the microscope objective and waited a few minutes. Experiment 2: We tested the present of starch in potatoes First, we washed the microscope and cover lens. Then, we followed the same procedure from the first experience, but this time we used a potato. Results and discussion: From the first experiment, iodine with onion juice, the cells barely chanced color indicating that starch is not present in onions. From the second experiment, iodine with potato juice, I observed cells packed together. Their intense blackness revealed the presence of the starch in the potato cells. I also looked at other classmates’ experiments and realized the darker the color the more starch we have.

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