EP-M.1 Onion Cell Lab

     The M1 class of Mr. Wouter Scott did an experiment about the onion lab. An onion is made up of layers separated by a thin membrane. In this experiment, the thin membrane will be used to observe the onion cells. This can easily be acquired by peeling a tiny layer of the onion using tweezers.

     The layers of an onion contain simple sugars (carbohydrates) some of which are stored as starch.Since iodine tends to bind with starch, it stains the starch granules when the two come in to contact making them visible. Although onions may not have as much starch as potato and other plants, the iodine used as a stain allows for the little starch molecules to be visible under the microscope. While onions are plants, students will not see any chloroplasts in their slides. This is because the chloroplast which is necessary for photosynthesis is largely present in the leafy part of the onion which is exposed to the sun and absent in the bulb which is below ground and away from sunlight.

     This easy and fun activity allows the students to learn about the cell structure. Students had the opportunity to experiment and observe the onion membrane using iodine as the stain. Without the stain, it will be difficult to observe the differences. The students also observed other types of prepared slides after their activity and discover interesting forms and structure of other cells.


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