Tonicity: Instructions for Experiment and Individual & Group Reports (Online Version)
To understand the concepts of hypertonic, hypotonic, and isotonic solutions and to understand how and why molecules move by processes of osmosis in these types of solutions you will conduct a combination hands-on and application lab. Make sure you read the material in your textbook on the plasma membrane and membrane transport in Chapter 5 as well as the cell membrane lab topic information.
In the first part of the lab (section A) you will examine water molecule movement when you expose the plant cells that make up a potato to hypertonic or hypotonic solutions. Remember that the potato is made-up of plant cells. One big difference between plant and animal/human cells is that plant cells have rigid cell walls external to the plasma membrane and our cells don’t. The cell walls in plant cells result in regulation of hydrostatic and osmotic pressures that are not present in animal/human cells due to the lack of cell walls in our cells. These differences result in different outcomes when plant or animal/human cells are placed in hypertonic or hypotonic solutions. Information on this can be found in Chapter 5 in your textbook.
In the application portion of the lab you will be observing what happens in animal/human cells when they are exposed to hypertonic, hypotonic, and isotonic solutions. Complete the tasks as described and apply what you have learned to complete your lab report. Remember that the lab report must contain information for each section (A – plant & B- animal) of the lab experiment.
Section A: Hands-on Lab (Potato)
This portion of the lab will allow you to observe the process of osmosis by incubating potato or carrot slices in water or salt-water to create solutions hypotonic or hypertonic relative to the fluid within the cells.
Use the household items and carry out the following experiment:
1. Fill two dishes with water.
2. Slice a potato lengthwise into two small pieces so that each has a flat side and the skin is removed. You may cut the potato to a smaller size to fit into the dish. Don’t allow the slices to be too thick.
3. Add three tablespoons of salt to one of the dishes.
4. Using a ruler, measure and record (in millimeters) the length, width and height of each of the potato pieces. Record visual appearance of color and texture. Then place one potato piece into the dish with the plain water and the other into the dish with the salt water.
5. Let the potato soak for about 30 minutes.
6. After the time has expired remove the potato pieces, measure and record the length, width and height (in millimeters). Compare the potato in the two dishes for color, texture and record. You will describe these differences in your lab report. (See the instructions below for where to include the respective information from the experiment).
Section B: Application Lab (Red Blood Cells)
In Section A you observed the effect of hypertonic and hypotonic solutions on plant cells. In the application section of the lab we will concentrate on the effects of hypertonic, hypotonic, and isotonic solution on animal/human cells.
Click here to watch an animation about the effects of different tonicities on red blood cells. Make sure that you have the volume on your computer speakers turned up so that you can listen to the narration for the animation. Observe the effects that the different solutions have on red blood cells.
Now that you have completed the experiment, move on to the report. Below is an outline for the sections of the lab report to clarify what it should contain and issues you will want to address for the report. Each section – except the cover page – should be at least 1 well-formed paragraph and should have a section heading.
Abstract – Will not be done. You will write a conclusion instead.
Introduction – You will want to include information about why these experiments were done. The section should also include background information on the principle concepts of the experiment. This includes, what is osmosis, and how is it different from diffusion? What is the difference between hypertonic, hypotonic and isotonic solutions? In the preface above there is information about where you can find these topics. The introduction must also contain a hypothesis as to what you expect to your results to be for the experiments in both sections and why (justify your hypothesis with supportive information). Think about what you will be doing before you complete the experiments and formulate a hypothesis on what you think will happen. For example, what do you think will happen to the cells that comprise the potato when exposed to the different solutions? What about animal cells when exposed to different solutions?
Materials & Methods – Briefly state the materials you used and how you did the experiment. This should be in paragraph form; do not list material items by bullet points or by commas.
Results – Briefly present your results (data). For example, simply state your observations of what happened when you conducted the experiments, and also include any measurements you took. You must include your height, width, and length measurements (before and after soaking) in this section, and calculate the volume of the potato slices before and after soaking. You must also calculate the percent change in volume before and after soaking in order to better determine if your slices changed size. All of this can be done in your choice of or a combination of text, data tables, and images. This is not the place to offer an explanation for your results. This will be addressed in the discussion.
Formula for calculating percent change =
Discussion – 1. In this section you will offer an explanation for your results. For example, explain the differences that you saw before and after you soaked the potato in the solutions and before and after red blood cells were exposed to the different solutions. You also need to address the following: – Why did these changes occur? – Why were different effects observed on plant cells (potato) versus animal cells (human red blood cell)? – What would happen to a patient if they were given a solution that was hypertonic or hypotonic relative to their cells? – Why is a clear understanding of these concepts important in a clinical setting? 2. Lastly, you will want to address whether your data supported you initial hypothesis. Explain why it did or didn’t support you hypothesis.
Conclusion – Keep this to a single paragraph that restates the basis for the experiments, what you found and why these findings are important. This is basically a summary of your entire report. Look as the instructions for the abstract and conclusion as a guide.
Literature Cited – You all know my policy on plagiarism (see course syllabus). Don’t do it or there will be consequences. This applies not only to plagiarism of another student’s work but also of a reference material. You must appropriately cite, in APA format, all material used. Be sure to use your own words in your paper. This will ensure that you understand the material to the best degree possible. Remember to refer to the Purdue OWL website to see examples of how to create proper in-text and reference list citations in APA format. The “Library Databases” link in the “TSTC Helpful Resources” box on the side or bottom of the Moodle course will be of help in finding scholarly sources for your paper. Sources should always be listed alphabetically by author’s last name, and there must always be a source listed at the end of the paper that matches up with an in-text citation in the body of the paper. There should never be an in-text citation that does not match up to a source listed at the end, or a source at the end that does not match up with an in-text citation. Also, the information (usually the author’s last name) that appears in the in-text citation should be the first information in the citation for that source at the end of the paper. The in-text citation and the citation at the end should be easy to associate with each other. Acceptable scholarly sources include: hardcopy books, eBooks (including your eText), scientific articles, scientific magazines (National Geographic, Scientific American, Popular Science, Discover Magazine, etc.).
Use the library’s online database to help you search for proper material. The Academic Search Premier is a large database full of research articles. There is also an eBook database for electronic textbooks
Unacceptable sources – Wikipedia, Ask.com, other non-science websites, really websites in general. I will deduct points for not using proper sources.
You must use in-text citations. It is not enough to list your literature cited at the end of the paper, you must also make notations in the body of your paper to show where each of your facts came from. Failure to properly cite within the body is a form of plagiarism.
Format: APA format (see link above for proper formatting of cover page, section headings, and citations), double spaced, 12 pt. font, 1” margins, Times New Roman, no direct quotations (practice paraphrasing). No set page length – as long as it takes to cover all details for each report section. At least 3 scholarly citations.
Submit your report in the individual lab report submission link as a Word document by the due date found in the link and in the course calendar.
Group Report Instructions
Once every group member has completed the experiments above and the individual report, you will be grouped (you will be able to see a list of your group members in the lab report files Moodle link once the individual reports are submitted) so that you can write a group
report by combining and revising the best parts of each of your individual reports. The group report should have the same sections and information in it as your individual reports, but it should be a revised and improved version. Give yourselves ample time to write the report and then revise it until everyone in the group approves of the finished product. You will all receive the same grade on the paper, so make sure it is acceptable to everyone before it is submitted. Each member of the group should contribute equally to the report, and the group should work on making each section as good as it can possibly be, making sure that the report flows well when it is read and all sources are correctly cited. Each group member should review the report before final submission. All group-member names should be included on the submitted paper after every member has approved the paper. Only one member should submit the file. Any group member who does not participate in creating the group paper should not be included in the list of names. It is up to the group to decide whether a member has contributed significantly or not. If a name is not included, please send me an email explaining why they were not included. Submit your group report in the Group Lab Report Submission link. And at some point, before the due date, every member of the group must complete the Peer Evaluation in Moodle once for each group member, excluding themselves. You must complete this evaluation in order to receive credit for the paper.
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