* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download cells - Reocities
Document related concepts
LAB 3 – CELLS Cells are the basic functional units of all living organisms. They may exist singly, as in unicellular organisms, or in aggregates, as in multicellular organisms. Living things are grouped into three domains. Bacteria and Archaea contain all prokaryotic cells (organized nucleus absent). The domain Eukarya contains all eukaryotic cells (organized nucleus present) that are found in plants, animals, fungi and protists. Both animal and plant cells occur within multicellular organisms. In a multicellular organism each different cell type has a specialized function. Similar cells that work together form tissues. Epithelium, mesophyll, and blood are examples of different tissues. In this lab you will look at epithelial cells in both plants and animals. Epithelial cells form the covering of the outer body surfaces or the linings of the inner surfaces. These cells are specialized for secretion of various substances and for protection. Mesophyll cells are found only in plants. It is the tissue that is responsible for photosynthesis and storage in leaves. Blood cells are found only in animals. Blood is a tissue in which separate cells are maintained and transported by a liquid called plasma. In humans erythrocytes (red blood corpuscles) contain hemoglobin for oxygen transport. As an erythrocyte matures, the nucleus and organelles of the cell are expelled, and the cell becomes entirely filled with hemoglobin. Leukocytes are a diverse collection of white blood cells that work together to fight infection and maintain immunity. Platelets are small cell fragments that are important in blood clotting. Objectives In this investigation you will examine and identify similarities and differences in animal and plant cells. By observing the microscopic characteristics of eukaryotic cells you will be able to infer the functional significance of specific cell structures and cell types. Prelab 1. 2. 3. 4. What is the basic structural feature that distinguishes plant and animal cells from bacteria? Why do multicellular organisms need to have many different cell types? In what way do blood cells resemble unicellular organisms? Why are they considered a tissue? Explain why mature erythrocytes can’t be classified as cells. Hypothesis What are the microscopic structural features that will allow you to determine if a cell is from plant tissue or animal tissue? List at least two observable structures. Materials Red onion Iodine solution Sprigs of Elodea Microscope slides and coverslips Straight-edged razor blade or scalpel Flat-edged toothpick Compound microscope Prepared slides of human blood Prepared slides of three unknown tissues Procedure A. Epithelium 1. Onion cells Onion bulbs are condensed, underground stems that will give rise to an entire plant under the appropriate conditions. The curved pieces that flake away from a section of onion are called scales. On the inside of each scale is a thin, transparent layer called the epidermis. Place a dime-sized piece of this tissue into a drop of iodine solution on a glass slide. Try to smooth out any wrinkles, then gently drop a coverslip onto the tissue. Examine the epidermis first with the low power objective of your microscope. In the space to the right describe how the tissue looks. If the circular field of view is 1500 μ across its diameter, how long is one cell? How many cell layers are there? Switch to high power and observe the ultrastructure of an individual cell. On the data sheet make a labeled diagram of one onion cell as observed under high power. 2. Cheek cells The cells lining the mouth in humans are called squamous epithelium. They form a flat sheet. Place a small drop of iodine solution on a glass microscope slide. Use a toothpick to gently scrape the inside of your mouth to dislodge a few cells from the sheet of tissue. Gently swirl the toothpick into the drop of iodine solution on the slide and add a coverslip. Discard the toothpick. Examine the cells first with the low power objective of your microscope. In the space to the right describe how the tissue looks. Estimate the size of the cells. Switch to high power and observe the ultrastructure of an individual cell. On the data sheet make a labeled diagram of one cheek cell as observed under high power. B. Mesophyll. Obtain a single leaf of Elodea from the young leaves at the tip of the stem. Place it into a drop of water on a microscope slide and add a coverslip. No iodine will be used since we want the cells to remain alive. In the space to the right describe how the tissue looks.. Estimate the number of layers of cells and the size of the cells. Switch to high power and observe the individual cells for several minutes. Describe the relative size, shape and movement of the chloroplasts. On the data sheet make a labeled diagram of one mesophyll cell as observed under high power. C. Blood Observe a prepared slide of human blood under low power. The specimen has been treated with Wright’s stain which causes erythrocytes to appear pink. Leukocytes appear purple, and platelets appear as dark blue/purple cell fragments. Switch to high power. Move the slide around to observe the many different kinds of blood cells. On the data sheet make a labeled diagram of several different blood cells as observed under high power. Notes D. Unknowns Examine each of the three prepared slides of unknown plant or animal tissue. Focus first on low power, then switch to high power and move the slide around to observe different cell types within each tissue sample. On the data table below indicate whether each specimen is from plant or animal tissue and the reason for your decision. Data A. Classification of unknowns Unknown Classification Reason for Classification A B C B. Plant and animal tissues 1. Onion cells Label – nucleus, cell wall, central vacuole cytoplasm Size of cell _____________________________ Number of cell layers _____________________ 2. Cheek cells Label – nucleus, cell membrane, cytoplasm Size of cell _____________________________ 3. Mesophyll Label – nucleus, cell wall, central vacuole cytoplasm Size of cell _____________________________ Number of cell layers _____________________ 4. Blood Label – erythrocytes, various leukocytes, platelets Sketches Analysis A. Epidermis 1. Describe the appearance of the onion tissue (not individual cells) as seen under low power. 2. In an onion cell, describe the location of the nucleus and cytoplasm. How can we infer the presence of a central vacuole from their location? 3. What could account for the granular appearance of the cytoplasm? 4. Describe the appearance of the cheek tissue as seen under low power. Why aren’t the cells connected on the slide as they are in your mouth? 5. In a cheek cell, describe the location of the nucleus and cytoplasm. 6. In what observable ways are cheek cells and onion cells similar? 7. Explain why the cheek cells have an irregular shape compared to the boxy shape of the onion cells. B. Mesophyll 1. Describe the appearance of the mesophyll tissue as seen under low power. 2. What does a single chloroplast look like? Where are they located in the Elodea cells? 3. Describe the movement of the chloroplasts. What causes this movement? 4. In what ways are onion epidermis and Elodea mesophyll tissues similar? 5. Describe at least two ways that the tissues differ. C. Blood 1. Describe the relative number of each cell type in blood tissue. 2. How many different types of leukocytes did you observe? How did you distinguish the different types of white blood cells? 3. In what ways are blood cells similar to the cheek cells you observed? 4. How does blood tissue differ from cheek epithelium tissue? Sources of Error Inexperience is the main source of error in this lab. Describe ways in which this problem may have caused errors in your observations and data gathering. Conclusion 1. All cells have a plasma membrane. Why is this structure difficult to observe in the plant cells we studied? 2. What two cell components could you observe (especially if you stained the cells) under high power in all plant and animal cells except red blood corpuscles? 3. Describe three differences you observed under the microscope between plant and animal cells. 4. All plants, including onions, are photosynthetic. Which parts of the onion plant have cells with chloroplasts? 5. How is the shape and arrangement of the cells in the onion tissue related to its function as an epithelial tissue? 6. How are the Elodea cells related to their function in a mesophyll tissue? 7. Why is blood considered to be a tissue?