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What structures are common to cells? Introduction The cell theory states that most living things are composed of units called cells. The microscope reveals that cells are composed to tiny structures called organelles. Although plant and animal cells have many of the same organelles, plant cells have certain organelles that distinguish them fro the cells of animals and animal like protests. All plant cells have a cell wall and all green plant cells have chloroplasts. Animal cells have neither a cell wall nor chloroplasts; in other respects, however, the organelles of animal cells are similar to those of plant cells. Materials Lugol’s iodine solution Toothpicks Compound microscope glass slides and cover slips medicine dropper onion skin Procedure: 1. Using the thin membrane from the inside surface of the onion. 2. Prepare a wet mount slide using iodine as the stain. 3. Focus the specimen in low power, draw what you see. 4. Change to high power, focus, draw what you see. 5. Locate the nucleus and cell wall – label in your drawing. 6. Clean your slide. 7. Prepare animal cell slide 8. Place a small drop of iodine solution in the middle of a clean slide. With the flat end of a toothpick GENTLY scrape the inside of one of you cheeks. This will remove some of the cells that line the inside or the cheek. 9. Dip the end of the toothpick in the drop of iodine solution on the slide. Twist and stir the toothpick in the solution in order to detach the scraped tissue from the toothpick. 10. Apply a cover slip and examine the specimen under the low power objective of the microscope. 11. Draw what you see (using a good area of the specimen) 12. Switch to high power – draw what you see. Questions: 1. Which organelles can you identify? 2. What is the advantage to staining cells? 2. In what ways do animal cells resemble plant cells? 3. In what ways do animal cells differ from plant cells? 4. What is the function of human cheek lining cells? 5. How are cheek lining cells adapted to their function? 6. Which cell appeared larger, the plant cell or the animal cells? 7. What cell part did you observe around onion cells that you did not see around cheek cells? 8. Cheek cells often appear folded over, while onion cells don’t. Give one reason why this is true. 9. Why is it difficult to see the cell membrane in onion cells? 10. The onion cells appear to have two dimensions – length and width. With the help of your microscope, how can you determine whether it also has thickness? 11. Which organelle usually present in plant cells is absent from the cells of the onion skin