Investigation Cell TypesProkaryotic vs. Eukaryotic vs. Plant vs. Animal

MaterialsFor Class Chopped Onion Iodine solution Sprigs of Elodea densa Prepared slide of Gram stained cheek epithelium. Prepared slide of human bloodFor Groups Compound microscope Microscope slide Coverslips Forceps Plastic ruler Paper towels

Figure 1: Epithelial Tissue

Introduction Cells are the basic functional units of all living organ-isms. They may single, colonial or multicellular. When cells join together to take on a specialized function within a multicellular organism, they form a tissue. There are 2 major divisions into which all cells fall...prokaryotic (NO membrane bound nucleus and organelles) and eukaryotic (membrane bound nucleus and organelles present). Domains Archaea and Bacteria alone are prokaryotes while the cells of Domain Eukarya (Kingdoms Protista, Fungi, Plantae & Animalia) are eukaryotes. Plant and animal cells, both eukaryotic, share many char-acteristics, which you will observe in this lab. They also differ in several important ways.

Prelab Preparation Both animal and plant cells are organized within tissues of multicellular organisms. Because they take on a wider variety of functions, animal cells are generally more specialized than plant cells. Epithelial cells and blood cells are examples of tissues. In this lab, you will prepare and observe epithelial cells from both plants and animals. Epithelial cells form the skin of outer body surfaces and linings of inner surfaces. These cells are specialized as a protective barrier and to transport specific sub-stances. The cells of these layers may be shaped like cubes, col-umns, or be flat, depending on their location and function within the tissue (Fig. 1). Blood cells (Fig. 2) appear very different from other cells due to their specialization for transporting oxygen or fighting infection. Blood is a tissue in which the cells are suspended, maintained and transported by an aqueous solution, plasma. Red blood cells (RBCs), erythrocytes, contain hemoglobin, a protein that transports oxygen through the body. As erythrocytes ma-ture, the nucleus and organelles diminish, eventually being forced out of the cell to make room for hemoglobin, so mature human RBCs have no nucleus. White blood cells (WBCs), leukocytes, are a diverse collection of cells specialized for fighting infection as part of the immune system. They must retain their nucleus to perform this function. Platelets are small cell fragments that are important in blood clotting to stop bleeding.

Figure 2: Blood CellsWhite Blood Cell

Plasma

Red Blood CellsPlatelets

Gram Stained Bacteria

Prelab Questions1. What are the basic structural features that distinguish plant and animal cells (Eukaryotes) from bacterial cells (Prokaryotes)? (Hint: 5 words)

2. As multicellular organisms become more complex, cells become more specialized and the diversity of cell types increases / decreases (circle one). Which has greater cell diversity, an earthworm or a human? Why?

3. In what way do blood cells resemble unicellular organisms? (Hint: Look at the picture on the first page and note that unicellular organisms live free of contact with other cells.)

4. Why is blood considered a tissue? (Hint: What is the definition of a tissue? LOOK IT UP!)

5. Can mature erythrocytes (red blood cells) be classified as eukaryotic cells? Explain! (Hint: How are other human cells different than mature erythrocytes?)

ProcedurePart 1: Plant CellsOnion bulbs are organized tissue that, under the appropriate conditions, will give rise to an entire plant. The curved pieces that flake away from a slice of onion are called scales. Separating each scale is a thin membrane made up of epithelial tissue.A. Obtain a piece of onion scale. Use forceps or your fingernail to pull away the epithelium from the inner curved surface. Be careful not to fold or wrinkle the membrane. Prepare a wet mount of the epithelium by placing it flat on a slide and adding a drop of water.

B. Examine the epithelium first with scanning, then low, then high power objectives. Unstained specimens are often seen better with less light. Try reducing illumination by adjusting the dimmer switch and/or diaphragm.

6. How many cell layers is the epithelium? (Layers will come into focus separately as you focus up and down.)

7. What is the general shape and size (length and width), in microns (µ) of a typical cell? (On low power, Cell Size = 1.3mm/Number of cells across, 1mm = 1000µ)

C. To stain your specimen, remove your slide from the microscope stage. Remove the coverslip, place a drop of iodine on your specimen and replace the coverslip. Examine your specimen under scanning, low and high.

8. Within individual cells, where is the nucleus most often located? (Middle? End? Side?) Why do you think this is? (Hint: what is the largest organelle within plant cells? Look it up!) EXPLAIN!

SHOW WORK!

9. Draw several cells as observed under high power. Label the following structures in one cell: nucleus, cell wall, central vacuole (invisible, you must infer its location), and cytoplasm.

10. Onions are green plants... do you see green cells? Where in the onion plant are green cells? Why?

E. Obtain a single leaf of Elodea and prepare a wet mount of it. (It's already wet, so just add a cover slip.)

11. Examine Elodea under scanning, then low power. Draw what you see (not bigger) draw a pointer line and label one cell.

12. Examine Elodea under scanning, low, then high power. Draw a single cell and label the cell wall, central vacuole, nucleus and chloroplasts (larger than it appears.)

13. Look closely... Are the chloroplasts moving? Make an inference to explain this. (Hint: Even if yours aren't moving, infer a possible advantage to moving in performing their function? THINK!)

Part 2: Animal CellsAs you observe these different types of cells, think of how differences in cell structure might be related to specialization of cell function.F. Prepare a slide of cheek epithelial cells by scraping the inside of your cheek with a toothpick and swirling the sample into a drop of iodine. Examine the cells under scanning, low, and high power.

15. Inside the mouth, these cells are joined together in a sheet of epithelial _______________________.

16. Draw a few cells under high power and label one cell (plasma membrane, nucleus, and cytoplasm). Observe the prepared slide of Gram stained cheek epithelium. Draw and label one cheek cell along with some bacterial cells (prokaryotes).

Your Cheek Epithelium Gram Stained Cheek Epithelium + BacteriaG. Obtain a prepared slide of blood and examine it under high power. This specimen has been prepared with Wright Stain, which causes erythrocytes (RBCs) to appear pink. Some are reticulocytes, immature erythrocytes that still have their nuclei. The nuclei stain deep blue or purple and the endoplasmic reticulum will look like a blue mesh. Leukocytes (WBCs) appear blue due to their nuclei, and platelets are small, violet or purple with no nuclei.

17. How many different cell types can you find? List them!

18. In what ways are these cells similar to each other and to the cheek epithelial cells you observed? (What specific structures do animal cells have in common?)

Postlab Analysis 19. Describe the major difference observed between eukaryotic cheek epithelial cells and prokaryotic bacteria.

20. Describe ALL the structural differences you observed between plant and animal cells.

21. Relate one structure (1 pt.) of the cells you have observed to the overall function (1 pt.) of each cell?

Onion Epithelium -

Elodea Leaf -

Cheek Epithelium-

Red Blood Cell -

White Blood Cell -