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HONORS BIOLOGY I Cell Structure INTRODUCTION: Although there are great differences in the size, shape, color, and activities of living things, the basic building units of all life have much in common. In this investigation, you will see what some cells look like and compare the structure and organization of cells from different organisms. MATERIALS: onion spider plant leaf cover slip iodine tropical plant leaf toothpick forceps microscope slide PROCEDURE: 1. Hold a piece of an onion "scale" leaf so that the concave surface faces you and snap it backwards. A transparent, paper-thin layer of cells can be seen along the outer curve of the scale. 2. Using forceps or your fingernails peel off a small section of this thin layer and place on a microscope slide with a coverslip on top. 3. Place 1 drop of iodine on the edge of the coverslip and allow the stain to reach most of the thin layer. 4. Examine the slide first with medium power and then with high. 5. Use a pencil for all drawings. Sketch a few cells in high power as they would appear if you could see three dimensions. Label the cell wall, cell membrane, nucleus, and cytoplasm. 6. Mount a spider plant leaf on a slide and observe it on low power and then with medium power. Sketch a few cells as they appear under medium power. Label the cell wall, cell membrane, nucleus, cytoplasm and chloroplasts. 1 7. Mount a tropical plant leaf on a slide and observe it on low power and then with medium power. Sketch a few cells as they appear under medium power. Label the cell wall, cell membrane, nucleus, cytoplasm and chloroplasts. 8. With the broad end of a toothpick, gently scrape the inside of your cheek. It may be in clumps. (Scratching or digging into the cheek tissue is not necessary.) Lay the broad end of the toothpick with the cheek scraping in a drop of iodine on a slide. Roll the toothpick gently to dislodge the cheek cells. Discard the toothpick. Add a cover slip and examine the cheek cells with the medium and then high power of the microscope. Find a field where the cells are separate and distinct and sketch a few under high power. Label the cell membrane, cytoplasm, and nucleus. OBSERVATIONS: ONION CELL-HIGH POWER SPIDER TROPICAL CHEEK 2 DISCUSSION: 1. In the tropical plant and spider plant, what things are not visible? Why? 2. What cell part did you find around plant cells that you did not find around your cheek cells? 3. Why is it difficult to see the cell membrane in plant cells? 4. How did the iodine help? Why do you suppose biologists use different kinds of stains on cells they are studying under the microscope? 3