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Objectives

Students Should be able to:

  1. Describe prokaryotic and eukaryotic cells and similarities and differences between them.

  2. View prokaryotic and eukaryotic cells using microscopy.

  3. Identify and describe the function of plant and animal cell organelles.

  4. Describe diffusion of materials into and out of cells.

  5. Determine the rates of diffusion of different materials across semipermeable membranes.

  6. Describe the process of osmosis.

  7. Describe hypotonic, hypertonic and isotonic solutions and how they affect the diffusion of solvents and solutes.

  8. Determine the effect of hypo and hypertonicity on the movement of materials into and out of cells.

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Introduction

The basic unit of life is the cell. In the exercise on the chemical aspects you investigated some of the non-living components of cells. In this laboratory exercise you will investigate the structure of prokaryotic and eukaryotic cells as well as some of the aspects of cellular diffusion, osmosis, and the effect of environmental factors on diffusion and osmosis.

The cell theory set forth by Schleiden and Schwann, the development of the microscope by Hooke and Leeuwenhoek and Virchow's Principle were important contributions to our early understanding of cells. Our modern understanding is of course much more complex, due, in part, to the development of the electron microscope, DNA research and the ability of biologists to microdissect cells.

Cells are either prokaryotic, meaning they have no membrane bound nucleus or they are eukaryotic, which have a membrane bound nucleus. There are however, more differences between prokaryotic and eukaryotic cells.

All cells have a cell membrane, and cytoplasm. Eukaryotic cells have a membrane bound nucleus and prokaryotic cells have a nucleoid region containing the genetic material, but it is not membrane bound. Prokaryotic and eukaryotic cells also have organelles, the types and numbers of which vary depending on the type of cell.

In order to stay alive and functioning, cells must interact with their environment to obtain nutrients, water, ions, etc., and to get rid of wastes and to export materials. This is accomplished by the processes of diffusion, and osmosis, which are passive mechanisms. Other passive mechanisms which allow materials to pass in and out of cells such as facilitated transport. There are also active transport mechanisms, which require the expenditure of ATP energy. They include ion "pumps", endocytosis, and exocytosis.

Osmosis is the movement of water from an area of higher concentration to an area of lower concentration. It is effected by the concentration of dissolved solutes in the external and internal environments of the cell. The solutions surrounding the cell and ones that are internal consist of a solvent, which is water, and solutes, which are substance dissolved in the water. The concentration of dissolved solutes in solution make them hypertonic, hypotonic or isotonic to each other. Solutions that have more solute dissolved than another one are said to by hypertonic to the solution they are being compared to. The solution with the lower solute concentration is therefore hypotonic. if both solutions being compared have equal amount of dissolved solutes then the solutions are isotonic to each other. Water always moves between the two solutions. It moves from hypotonic to hypertonic. So there will be a net gain of water by the hypertonic solution. If the two solutions are isotonic, water still moves but there is no net gain of water by the other solution. There is always some confusion with tonicities, so pay careful attention in your reading and laboratory work involving tonicity.

Diffusion is the movement of substances (other than water) from an area of higher concentration to an area of lower concentration. Osmosis is a special case of diffusion, because it deals only with water. We can even define osmosis as the diffusion of water. When it comes to living systems, the diffusion of materials such as ions, nutrients, gasses, etc. is of extreme importance. In diffusion materials always have a net diffusion from hypertonic to hypotonic. In isotonic solutions the materials move but again there is no net gain of materials. (see osmosis and isotonicity)

This exercise will concentrate on the processes of diffusion, osmosis and the effect of environmental factors on them.

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Pre-lab Activities

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Pre-Lab Activity #1 - Prokaryotic cells vs. Eukaryotic cells

  1. Using any resources at your disposal find a labeled picture of a prokaryotic cell and a eukaryotic cell. Attach them to your Pre-Lab Questions.
     

  2. Using any media resources, find a chart which compares the likenesses and differences between plant and animal cells. If you cannot find on then develop one yourself. Attach them to your Pre-Lab Questions.

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Pre-Lab Activity #2 - Osmosis and the Effect of Tonicity

Note: Uses available media player for your computer. Files are in .mpg format.

Below are several movies of plant and animal cells that have been placed in isotonic and hypertonic solutions. As you watch these movies note what happens, and use these observations to assist you in answer the related Pre-Lab Activity Questions

Plant Cells: Isotonic and Hypertonic Solutions

                Isotonic                                                Hypertonic

                                      

            Click on the picture                                       Click on the picture
              for movie                                                        for movie

Animal Cells: (red blood cells, or RBC's)

                    Isotonic                                                        Hypertonic

                                     

            Click on the picture                                       Click on the picture
               for movie                                                       for movie

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Pre-Lab Activity #3

Download the Data Collection Sheet for Cell Structure and Function

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Pre-Lab Activity #4

  1. Download and Print out the following:

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Image of Dialysis setup

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Spreadsheet for Osmosis and Diffusion of Solutions

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Pre-Lab Questions (html version)               Pre-Lab Questions (Word Version)

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The Laboratory Activities and Data Collection

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Lab Activity #1 - Observation of Prokaryotic and Eukaryotic Cells

Materials:

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Microscope

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Prepared slides of prokaryotic cells

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Prepared slides of eukaryotic cells


Procedures:

  1. Observe (at 4x, 10x and 40x) the prepared slide of prokaryotic cells. Note the size, shape and the presence or absence of a nucleus

  2. Observe (at 4x, 10x and 40x) the prepared slide of eukaryotic cells. Note the size, shape and the presence or absence of a nucleus.

  3. Record your observations on the Data Collection Sheet.

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Lab Activity #2 - Elodea or Anacharis Leaf

Materials:

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Microscope

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Slide

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Cover slip

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Elodea or Anacharis leaf tip


Procedures:

  1. Make a wet mount slide of the Elodea leaf tip (or Anacharis leaf tip) and observe it under the microscope a low power (10x). Note and identify any cell structures such as chloroplasts, cell wall, nucleus, vacuoles, etc.

  2. Locate some cells along the edge of the leaf, center them, and switch to high power (40x).

  3. Observe the chloroplasts. Note the color and any motion. If you see motion how would you describe it?

  4. Record your observations on the Data Collection Sheet.

  5. With the aid of your instructor, add a hypertonic salt solution to your Elodea leaf (or Anacharis leaf). Observe the leaf for a while. Note what happens to the cell and the cytoplasmic streaming. Record your information on the Data Collection Sheet.

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Lab Activity #3 -  Diffusion (note the instructor will have part of this activity as a demonstration)

Materials:

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Petri dish w/ agar

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2 Petri dishes w/ water

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Perfume or other fragrance

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Potassium permanganate crystals

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Methylene blue crystals

Procedures:

  1. Observe a Petri dish containing agar to which a crystal of potassium permanganate and a crystal of methylene blue have been added. On your Data Collection Sheet record the time and diameter (in mm) of the color movement from the crystals. A ruler has been placed under the dish as a reference. Return an hour later and measure the crystal's color movement diameters. Place this information on your Data Collection Sheet.

  2. Observe a Petri dish containing water and a crystal of potassium permanganate. Note the time when the instructor starts this and measure the diameter (in mm) of the color movement from the crystal. Record this information on your Data Collection Sheet.

  3. Observe a Petri dish containing water and a crystal of methylene blue. Note the time when the instructor starts this and measure the diameter (in mm) of the color movement from the crystal. Record this information on your Data Collection Sheet.

Do this as a lab group

  1. Open the provided fragrance and hold it 15 cm from the nose. (measure this with the small plastic ruler). Record how long it take before the the odor is detected. Record this information on your Data Collection Sheet.

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Lab Activity #4 - Osmosis and Diffusion of Solutions

Materials:

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Plastic cup

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Stirring rod

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Dialysis tubing (15 cm length)

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Dental floss

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Iodine stain

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Sugar / Starch Solution

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Benedict's Solution

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Water bath

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Test tube (10 mm x 75 mm)

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Balance

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Spreadsheet for data

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Image of dialysis setup


Procedures:

  1. Using dental floss, tie off one end of your dialysis tubing using a surgeon's knot.

  2. Fill the dialysis tubing with the sugar / starch solution as directed by your instructor. Note its color!

  3. Tie off the open end of the dialysis tubing (use a surgeon's knot)

  4. Bring both ends of the dialysis tubing together and tie them so it forms a loop.

  5. Rinse and blot dry the dialysis tubing. Make sure you rinse the tied ends to remove any sugar / starch solution that may have spilled.

  6. Mass the dialysis tubing and contents on the electronic balance. Record the mass on your Data Collection Sheet.

  7. Fill the plastic cup 2/3 full with distilled water. Add several drops of iodine stain and stir with the stirring rod.

  8. Slip the stirring rod through the loop formed by the dialysis tubing and suspend it in the plastic cup, with the stirring rod resting across the rim of the cup.

  9. Add more distilled water to the cup if the dialysis tubing and contents are not 95% immersed in the distilled water / iodine solution.

  10. Click here to for visual image of the setup for 8 and 9.

  11. Allow the dialysis bag to set for 15 minutes and measure its mass. Do this every 15 minutes, over the course of one hour (60 minutes). Make sure you rinse the dialysis bag and blot it dry before massing it. Record the mass in your Data Collection Sheet. You will have five readings.

  12. At the end of 60 minutes, remove the dialysis tubing from the cup and observe the contents. DO NOT POUR OUT the contents of the plastic cup. Answer the questions on your Data Collection Sheet which refer to this procedure.

  13. Take a sample of the contents of the plastic cup (note its color), add Benedict's solution and place it in a water bath for several minutes. Note any changes to the color of the sample. Answer the questions on your Data Collection Sheet which refer to this procedure.

  14. Graph the data collected, and attach the graph with spreadsheet to your Data Collection Sheet.

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Post-lab Activity and Data Analysis

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Results and Analysis:

Please examine the following pictures and view the following movie. You will use them to answer post-lab questions 12 and 13.

Pictures:                                                           

 

            Picture #1                                            Picture #2

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Movie:

Note: Uses available media player for your computer. Files are in .mpg format.

Click on the above picture to play the movie

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Results and Analysis: (Continued)

  1. Clean up your lab area and return all materials to their proper location.

  2. Fill in all of the data requested in the Data Collection Sheet.

  3. Answer the Post-Lab Questions

  4. Turn in all requested materials (Data Collection Sheet with Graph, Post-Lab Questions)

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Post-Lab Questions (html version)          Post-Lab Questions (Word version)

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