NAME: DATE: PERIOD: The Basic Unit of Life Lab (Adapted from lab of same name) State Standard 12.11.04 In this investigation, you will review the history of the microscope, practice the techniques for making a slide, look at various specimens under the microscope and compare the parts of a cell found in plants and animals. Materials Microscope, compound Metric ruler, clear plastic Cork Anacharis Leaf (Elodea) Slides (2) Cover slips (2) Medicine dropper Iodine Water Toothpick Onion Lens Paper Procedure Part A: History of the Microscope Read the short paragraph below and fill in the blanks in the paragraph using your Cytology notes. The earliest form of the microscope was used about years ago by. Shortly after the creation of the microscope, used the term cell to describe the smallest division of the cork plant. Pairs of convex lenses round pieces of glass that are wider in the middle than on the ends are used in light microscopes. These lenses make very tiny objects such as cells appear larger. When the light rays pass through certain shapes of glass, the rays bend and change direction. As light passes through the first lens, the light rays bend and then cross. As you can see the object is magnified; it appears bigger. If you could see the object after the light passed through the first lens, the object would seem to be upside down. When the light reaches the second lens, it bends again so that you perceive the object as right side up. revised 1
Problem: Are there differences between the organelles found in plant and animal cells? Materials: Microscope Microscope slides Magazine Cover slip Water Iodine stain Toothpicks Cork Dropper Onion Hypothesis: Procedure: You should always be careful when using the microscope. Put one hand on the arm and the other under the base. Before you use the microscope, make sure that the lenses are clean. Use lens paper ONLY! Using any other kind of paper can scratch the lens. Part A The Letter E 1. Look through the eyepiece. Move the diaphragm around until you see the brightest light you can. This light that you are seeing is called the field of view. 2. Turn the nosepiece until the low power objective snaps into place. The low power is the smaller one. 3. Now you must make a wet mount slide. To do this follow these directions: A. Cut the letter e out of a magazine. B. Put the e on a slide and add one drop of water to it. C. Carefully put the cover slip on top of the water and letter e. (See Figure 2) Put your finger here and push. Cover Slip Figure 2 Slide D. Put the cover slip on at angle so that the air gets pushed out the other end. 4. Put your slide with the letter e on the stage of the microscope. Put the stage clips on top of the slide. 5. Find the letter e under low power first. Move the slide around until it is over the hole in the stage. Use the coarse adjustment knob to get the letter in focus (see it clearly). Make sure that the objective does not hit the slide. If you cannot get it into focus, also use the fine adjustment knob. 6. Look through the microscope and move the slide to the left. Which way does the picture you are seeing go? 7. Look through the microscope and move the slide away from you. Which way does the picture you are seeing go? revised 2
8. Draw what you see. After you draw it under low power, turn the nosepiece carefully until the high power objective snaps into place. Only use the fine adjustment knob to focus this. Do not use the coarse adjustment knob! Now draw it under high power. Call the teacher over when you have it on high power. 9. Clean the slide. Throw all solid material in the garbage can and rinse the slide with water. Use Kim wipes to dry the slide and cover slip. Do NOT use paper towels; this will scratch the slide. Low Power High Power Part B The Cell Wall Cork cells are great for looking at cell parts that are common in plant cells. One of these parts is the cell wall. In a cork cell, the cell wall is easy to see. The cork is no longer living and the cell wall is about the only thing that is left. 1. Use a very thin piece of cork, about as thin as a piece of paper. It will actually look like powder. 2. Make a wet mount slide of the cork. 3. Look at the cork under low power and high power. Call the teacher over to see it on high power. 4. Carefully draw what you see on high power. Label the cell wall. Clean the slide and cover slip. CORK CELLS revised 3
Part C - Cell Membrane and Cytoplasm Human cheek cells can be used for looking at the plasma membrane and cytoplasm. 1. Put a drop of iodine on the slide. If you spill the iodine, wash with water immediately and tell the teacher. Gently scrape the inside of your mouth with a toothpick. You should not be able to see anything on the toothpick when you take it out of your mouth! 2. Put the toothpick into the stain on the slide and mix it around once or twice. Place the toothpick in the garbage immediately NOT back in your mouth! 3. Put on the cover slip and look at the cells under low and high power. 4. Look at the cells that are by themselves, not the ones that are all clumped together. Call the teacher over to see it under HIGH power. 5. Draw several individual cheek cells under high power. Label the cytoplasm and the plasma membrane. Clean the slide and cover slip. CHEEK CELLS Part D Cell Nucleus Onions can show a cell s nucleus. These can be found in most living cells. The nucleus looks like a round shape inside of each cell. 1. Take a small piece of an onion and peel off the thin layer on the inside. 2. Put the thin layer on a microscope slide. 3. Add one drop of iodine to the slide. If you spill the iodine, wash with water immediately and tell the teacher. Cover the slide with a cover slip. 4. Look at the cells under both low and high power. Try to find the cell wall, nucleus, and nuclear membrane. Call the teacher over to see it. 5. Draw what you see and label the three parts that you had to find. 6. Clean the slide and coverslip, and WASH YOUR HANDS! ONION CELLS Magnification revised 4
Part E Cells of a Leaf Although most cells of plants and animals are similar in structure, there are a few major differences. In this investigation, you will observe these differences under the microscope. Procedure and Observations 1. Prepare a wet mount of an Anacharis leaf. The whole leaf should be used. 2. Examine the leaf under the low power of the microscope. Then select a portion of the leaf where the cells are particularly distinct. Center this portion in the microscope field. Bring it into focus under high power. Use the fine adjustment to observe the cells at various depths. 3. Draw some cells of an Anacharis leaf. Label your drawing, indicating the cell wall, cell membrane, chloroplasts, and cytoplasm. ELODEA LEAF (plain water) Magnification 4. Add a drop of salt water solution to the side of the cover slip. 5. Place a piece of paper towel on the side opposite of where you placed the salt water. This should draw the salt water through the entire slide. 6. Look at the cells and notice how they have changed. 7. Draw the cells, now in salt water, under high power. Label your drawing, indicating the cell wall, cell membrane, chloroplasts, and cytoplasm. ELODEA LEAF (salt water) Magnification revised 5
Analysis Part A 1. Fill in the chart below to show the total magnification of your microscope on low power and high power. To find the total magnification, multiply the eyepiece and objective magnifications. EYEPIECE OBJECTIVE TOTAL MAGNIFICATION 5 10 10 45 10 600 2. What is the magnification of the low power objective on your microscope? 3. Describe some of the differences between what the e looks like under low and high power. 4. Is the field of view brighter or darker under the high power? Part B 1. Are the cells of the cork empty or filled? 2. What is the only part of the cell that is still there? 3. Is the cork produced by a plant or an animal? How do you know? Part C 1. Describe the shape of the cheek cell and how this shape is so different from the cork cell that you looked at previously. revised 6
2. Are cheek cells produced by plants or animals? How do you know? 3. Use your notes to describe the job of the plasma membrane. 4. What does the cytoplasm do in the cheek cell? 5. Why did you add stain to the cheek cells? Part D 1. Describe the shape of the onion cell. 2. What does the cell wall do in the onion cell? 3. Compare the shape of the nucleus in the cheek and the onion cell. 4. Use your book to describe the job of the nucleus. Part E 1. Describe the shape of the Elodea cells while they are in plain water. 2. Why do plant cells need chloroplasts? revised 7
3. How did the Elodea change after you added the salt water? Analysis General Complete the following chart. Put an X in the box if the structure is found in the plant or animal cell. Animal Cell Plant Cell NUCLEUS CELL WALL CYTOPLASM NUCLEAR MEMBRANE CELL MEMBRANE Conclusions: 1. Look at the hypothesis that you wrote about the how differences in structures of plant and animal cells are related to the differences in their function. Is your hypothesis supported or rejected by this experiment? Explain your answer. 2. If you were given a cell that was unidentified, how could you determine if it was a plant or animal cell? Be specific in what you would look for in each type of cell. 3. How should you carry a microscope? 4. Why should you only use lens paper to clean a lens? Why can t you just use a paper towel? revised 8