bio 150 #5 osmosis and diffusion lab august 2018averenna/bio150/lab5-osmosis...microsoft word - bio...

Bio 150- Laboratory Manual Human Anatomy & Physiology I DCCC Membrane Transport

Last Modified: 8/23/2018

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Lab #5 – Osmosis and Diffusion

Objectives:

Learn to apply the scientific method to solve a problem

Demonstrate and understand osmosis

Identify solutions as hypertonic, hypotonic, or isotonic

Observe the effect of molecular weight on the rate of diffusion

Complete a scientific lab report

Demonstrate lab skill proficiency in making common lab measurements

Equipment: Remember to bring gloves, goggles, and proper shoes.

Pre-laboratory Activity:

1. Read section II (Osmosis Experiment). Fill in Table 1 on page 3.

2. Write a hypothesis for bag #1 below Table 1 on page 3.

I. Introduction to Cell Membrane Structure and Transport

The cell is the smallest unit of life. Cells come in a variety of shapes and sizes with many being highly specialized to perform their function. In general, cells contain the same basic components (with some notable exceptions). The cell (plasma) membrane, is the outer boundary of the cell that allows it to remain separate from the external environment and maintain a specific internal structure and homeostasis. The plasma membrane of a cell is composed of a phospholipid bilayer, a double layer of phospholipids (Fig. 1). There are other lipids associated with the membrane such as cholesterol. Many proteins are present as well, with some embedded within the membrane (integral membrane proteins) and others more loosely associated (peripheral membrane proteins). Proteins have many functions within the membrane including, but not limited to: enzymes, ion channels, receptors, and cell surface markers. Carbohydrates can also associate with proteins (glycoproteins) and lipids (glycolipids) in the cell membrane.

Figure 1. The plasma membrane components.



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Collectively, the carbohydrates on the surface of a cell are called the glycocalyx. The molecules within the plasma membrane are not static and can move around, changing their relative positions to one another. This is called the fluid mosaic model of the plasma membrane.

The plasma membrane is selectively permeable. This means that substances have different abilities to move across the membrane from the exterior (extracellular) to the interior (intracellular) region and vice versa. Substances that are lipid soluble (other lipids and gases) can freely move across the membrane. Other substances must utilize special channel and transporter proteins in order to pass across the membrane. Water can freely pass across the plasma membrane between the phospholipids and can also pass through special water channels called aquaporins. Diffusion is the random mixing of particles from high concentration to low concentration until equilibrium is reached. The diffusion of water molecules across a selectively permeable membrane is called osmosis.

II. Osmosis Experiment (For the formal lab report)

A. Introduction In this experiment you will apply the scientific method to demonstrate osmosis. You will then use your data to complete a scientific lab report. Dialysis tubing is a selectively permeable membrane, allowing water to pass across, but not certain larger substances such as sucrose (a disaccharide). In this experiment you will place “bags” made of dialysis tubing containing various concentrations of sucrose inside beakers filled with liquid. You will then keep track of the change in weight of the bag indicating how much water is moving through the dialysis tubing and in what direction.

B. Equipment - Electronic Scale A piece of paper towel should be placed on the surface to keep the scale clean. The scale must be zeroed before each use by pressing the zero button. When the readout says 0.00 then you may weigh the tubing as directed. Be certain that you are weighing in grams and not ounces.

C. Hypothesis Figure 2 below illustrates the experimental set-up you will use.

Figure 2. Osmosis Experiment Setup.



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Figure 3. Filling the dialysis tube.

Fill in Table 1 below by determining whether each bag shown in Figure 2 is hypertonic, hypotonic, or isotonic to the solution in the beaker. Hypertonic – more solutes than another solution; Hypotonic – fewer solutes than another solution; Isotonic – equal solutes between two solutions. Table 1. – Predictions

for the Osmosis experiment.

Is the bag hyper, hypo, or isotonic to the

solution? (choose one)

Hypothesis – predict direction (check one).

Should the weight of the bag get heavier, lighter,

or stay the same? (choose one)

into bag out of bag

Bag 1

Bag 2

Bag 3

Bag 4

Bag 5

Hypothesis for bag #1: __________________________________________________________________

D. Procedure for Setting Up Osmosis Experiment

1. Obtain 10 twist ties and 5 dialysis tubes that have been pre-soaked.

2. Tightly twist, fold over and tie the end of each dialysis tube using a twist tie.

3. Use bare hands to open the tubing by rubbing your fingers across the end.

4. Fill each dialysis tube with 15ml of the appropriate solution shown in Fig. 2, tying off the ends securely with twist ties. Use a clean small disposable pipette (Fig. 3) to help fill the bag.

5. As each bag is filled, dry it and place on a dry piece of paper towel labeled with the contents.

6. Check for leaks on the paper towel (tie with another twist tie if necessary).

7. Weigh each bag in grams (make sure they are dry). Record the initial weight (Time 0) of each bag. You can use Microsoft Word to create a table for your data. 8. Prepare 5 large beakers with the liquids shown in Figure 2, labeling them correctly. They all contain water except for beaker 5. Use enough solution to completely cover each dialysis bag.



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9. When you have all 5 bags ready and all 5 beakers ready, then place the correct dialysis bag inside each corresponding beaker. Note the starting time.

10. Weigh the bags again every 15 minutes for 45 minutes. Gently dry the bags before each weighing. Record the weights of the bags in the table you created above.

11. Calculate the change in weight for each bag. Always subtract the Time 0 weight from the new weight. Use Microsoft Word to create a table for your weight change data. A positive number means a gain in weight, and negative number means a weight loss.

12. Use graph paper to construct a graph by hand using your WEIGHT CHANGE data. Be sure to number the graph and provide an appropriate title. In addition, you must label the X and Y axes and include units of measurement.

E. Demonstration of a Lab Skill During lab, your instructor will ask each student individually to demonstrate accurate measurement skills involving volume. Your instructor will provide specific directions for this task. This will be graded accordingly and included as part of your lab report grade.



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III. Diffusion Demonstration-Set up by Instructor - Observe near end of lab (Not part of the formal lab report) The rate of diffusion is dependent on many factors including the size and mass of the diffusing particle, the distance of diffusion, temperature, and the surface area available for diffusion. In this demonstration you will observe the diffusion of two different substances, potassium permanganate (molecular mass = 158.03 g/mol) and methylene blue (molecular mass = 319.85 g/mol). Their different molecular masses and different particle sizes will affect their rates of diffusion. A crystal of similar size of each substance will be placed on an agar plate by the instructor for you to observe the diffusion of the molecules. Answer the questions regarding the results you observe in the laboratory report.

1. For each plate, label the chemical used and its molecular weight below. 2. Use a ruler to measure the diameter of the diffused chemicals in mm and record your results. 3. Use colored pencils to draw in the diffusion results in the circles provided. Name of Chemical ______________________ _________________________ Molecular weight ______________________ _________________________ Diameter of Chemical _____________________ _________________________ (millimeters)

1. Which substance would you predict to diffuse faster based on its molecular weight?________

2. Which substance would you predict to diffuse faster based on the crystal sizes? __________

3. Which substance actually diffused faster (made a larger dye “print” in the agar)? __________

4. Based on your results, what can you conclude about the relationship between molecular weight and the rate of diffusion?



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Lab Report # 5 Scientific Lab Report for Osmosis

I. General Manuscript Guidelines for Writing Lab Report # 5 Lab report #5 should be written up for the osmosis experiment only - do not include the diffusion experiment. Please follow the manuscript guidelines below:

A. Formatting 1. Typewritten on standard size paper (81/2 X 11 inches) 2. Double-spaced 3. Font -use either Times New Roman, Arial, or Calibri 4. Font Size 12 5. You may use Microsoft Word to create tables. 6. Graphs must be done by hand. You may use the attached graph paper. 7. Stapled (no other types of attachments are acceptable)

B. Writing Style

1. Each student should individually write his/her own lab report. Students will be penalized for plagiarizing work from another student or another source.

2. Report should be written in scientific style – clear and concise. Do not use wordy, repetitious, or run-on sentences. 3. Must be written in complete sentences in your own words. It is not acceptable to

copy sentences or paragraphs directly from the lab exercise. 4. Avoid using the first person (ex. I placed the dialysis bag in the beaker).

Instead use a passive voice (ex. The dialysis bag was placed in the beaker). 5. Report should demonstrate evidence of thoughtful scientific inquiry. 6. Points will be deducted for incorrect grammar or spelling. 7. Do NOT include pages directly from the lab report.

II. Scientific Lab Report Format Lab report #5 must be organized to follow the format below. You should separate each section as you see below and use the section headings (Introduction, Materials and Methods, Results, Discussion, Conclusion) in your report.

Create a descriptive title for the lab report which appropriately reflects the nature of the lab experiment. The title should not be too long and wordy, but straightforward and clear. DO NOT just copy the name of the lab.

Introduction (6 – 10 sentences)

Provide some background information by explaining the concept of osmosis and associated terms such as isotonic, hypotonic, and hypertonic. Describe the exact purpose for completing the lab – what are you trying to accomplish by doing the experiment? Clearly state your hypothesis (hypotheses) and logically explain the line of reasoning that



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led you to develop your particular hypothesis. DO NOT just include table 1 from the laboratory for this part. You must explain what you expect to happen and why.

Materials and Methods

Use a vertical listing of all materials used in your experiment and be as specific as possible. Include any chemicals, equipment, glassware used along with sizes and amounts, and concentrations when appropriate. Just list materials – do not write sentences.

Example: 5 ml of 10 % NaCl Graduated cylinder (10 ml) Dialysis tubing (5 strips) 60 % sucrose (500 ml)

Then use a paragraph format to describe in detail the exact steps you followed from beginning to end when you performed the experiment. You must include sufficient detail so that it would be possible for someone else to repeat the experiment exactly as you performed it, using the same equipment, same chemicals, and same measurements. Do not use a numbered list to describe your methods–you must use complete sentences in paragraph form.

Results Your first sentence should make a general statement about your overall

results. (expected / unexpected). Then present your actual data using tables and/or graphs when appropriate. Be sure your results are reported using the correct number of significant figures. Tables may be constructed using Microsoft Word, but graphs must be done by hand.

Be sure the tables and graphs have titles. For graphs, the X and Y axis must be appropriately labeled (including units of measurement) so that it would be easy for anyone unfamiliar with the experiment to understand the data. Make sure Tables and Figures (graphs) are numbered according to the order they are described in your report. You will be evaluated on proper table and graph presentation.

You must describe the results in sentences as well, referring to tables and figures by number in order. You describe the data trends here (what when up and down) being specific, but save the why and how for the discussion.

Discussion (5-10 sentences) Your first sentence should make a clear statement regarding whether the data supports

or does not support your hypothesis. Discuss your results by referring to specific results in your tables or graphs that back up your first discussion statement. If you think there may have been possible sources of error in your results, now is the

time to mention these issues. If you do not think there were sources of error, then you do not need to address this issue.



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Conclusion (2-3 sentences)

Summarize the major concepts you demonstrated in this experiment. It is important that when you state your conclusion, you should relate the

conclusion directly back to the information in your introduction.



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bio 150 #5 osmosis and diffusion lab august 2018averenna/bio150/lab5-osmosis...microsoft word - bio...

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