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Formal Lab Report Fall 2010: Cell Membrane Lab Directions

Lab Background: A shipwrecked sailor is stranded on a small desert island with no fresh water to drink. She knows she could last without food for up to a month but if she didn't have water to drink she would be dead within a week. Hoping to postpone the inevitable, her thirst drove her to drink the salty seawater. She was dead in two days. Why do you think drinking seawater killed the sailor faster than not drinking any water at all? Today we explore the cause of the sailor's death. We'll prepare solutions of salt water to represent the sea, and we'll cut up slices of potato to represent the sailor’s cells. Potatoes are made of cells, as is the sailor! To determine the cause of the sailor's death, we will determine the effects of salt water on slices of potato. Our assumption is that potato cells will behave like the sailor's cells in her body. We will compare salt water to fresh water so we can see if there is an effect caused by the salt in the water. The water at ______% acts as a control in this experiment.

Introduction- Provides the background knowledge needed to understand this experiment in 1-1.5 pages (4-5 paragraphs). Read the background informationabove and answer the questions below in the Introduction section of your paper.Questions to address in your intro: (3 differently sourced internal citations are required- 1 must be textbook; NO dictionaries; use .edu, .gov, .org sites)

Plasma membrane- What is it? What is its role? Components?

Selective permeability- what does this term mean with regard to a cell membrane?

Diffusion and osmosis- their relationship, specifics about each

Passive and active transport- explain all types, contrast and compare

Hypertonic, isotonic, and hypotonic solutions- explain in detail what occurs to cells when placed in these solutions

Properties of salt water, potato cells, and human cells (with regards to solutes)

Proper Hypothesis “If…then…because…” format

Last sentence of section provides the objective, or purpose statement, for the lab

Example:The purpose of this lab was to ….

Procedure-

  • Flowchart or numbered; BEFORE starting the lab on Monday. No procedure= no lab.
  • You may want to make flowchart on computer- this document will be handed in electronically.
  • Procedure must be numbered!
  • Procedurecannot be copied word-for-word from procedures below. Paraphrasing is fine.
  • Labeled flowchart if including drawings.
  • Procedure has manipulated, responding, and controlled variables underlined and identified.
  • Procedure has amounts, units, etc.
  • Data tables are set up. You cannot begin the lab unless your data tables are ready. (See data section)

Note: The success of this experiment depends on making sure your potatoes are DRY before massing them at all times! Do NOT oversqueeze the potatoes as you are drying them. Construct your materials list and procedures from the following description of the investigation.

DAY ONE

a)To determine if the salt in the water has an effect on the potato cells, cut sixequal sized slices of potato to represent the sailor. Core 3 strips of potato 3-5 centimeters (cm) long. Cut the potato slice into two equal pieces, 3-4 cm long. The goal is to end up withsix potato slices of exactly the same sizeto be able to compare and draw conclusions about the effects of the water and salton potato cells.

b)Record the length of the potato slices into yourdata table BEFORE you place them in the solutions so you can compare them to the size of the potato slice the following day.

c)Use masking tape to label 6 test tubes with the different concentrations of salt water AND your period and initials. Bottles of 0% (distilled water),0.1%, 0.25%, 0.5%, 1%, and 2% salt solution (NaCl-sodium chloride) are provided.

d)Add the solutions to the properly marked test tubes. Fill the test tubes up halfway (about 30 mL of solution). Do NOT add the potatoes yet!!!!!

e)BEFORE adding your potato slices to the test tubes,dry each piece of potato COMPLETELY with a paper towel and record the following data:

  • initial length to the nearest tenth
  • initial mass to the nearest hundredth (ex. 2.46 g). Remember to Tare the electronic balance for each massing.
  • Turgidity- the appearance of the potato before the experiment- is it crisp or faccid?

f)Add potatoes to their respective solutions.

g)Cover the test tubes with Saran wrap, a stopper, or Parafilm.

DAY TWO

a)On a sheet of paper, rewrite all the concentrations of the sea water solutions.

b)Drain the test tubes and dry each piece of potato COMPLETELY with a paper towel. Do NOT oversqueeze!

c)Place each potato on top of the corresponding concentration on your paper (this is done so that you don’t confuse each piece).

d)Measure and record the resulting length and mass of each potato slice.

Data

a.Construct data tables for your recorded data. GIVE YOUR DATA TABLES A PROPER TITLE! Your data table(s) should be clear as to your manipulated and responding variables.

b.Add a second table (below) to your data section that shows the increase or increase in length and mass.

c.For length change use a plus (+) to indicate a slice has grown and a minus (–) to indicate a slice shrunk overnight. (Example +2.6 mm means grew 2.6 mm / –3.8 mm means shrunk 3.8 mm).

Table 1 (YOU must provide a real title for this table!)

Sample / Initial Length
(in cm) / Final Length
(in cm) / Initial Mass
(in g) / Final Mass
(in g) / Turgidity (before)
Crisp / Flaccid
0 % Salt
0.1% Salt
0.25% Salt
0.5% Salt
1% Salt
2% Salt

Table 2 (YOU must provide a real title for this table!)

Sample / Length Change
(+ or -)(cm) / Mass Change
(+ or -) (grams) / Appearance / Turgidity (final) / Tonicity of solution
Crisp / Flaccid / Hypo- / Iso- / Hyper-
0 % Salt
0.1% Salt
0.25% Salt
0.5% Salt
1% Salt
2% Salt

d.Make a graph(s) displaying your results. Make sure you answer these questions as you complete your graph. You may make this graph on Excel or another program and paste it into your FLR.

  • Is the graph a bar or line graph?
  • What are the variables we are testing in this investigation? (Remember DRY MIX)
  • What data did we collect?

Optional: You can take Before and After pictures as a way to enhance your observations/results.

Analysis and Conclusions

You MUSTshow an understanding of results of the lab as it pertains to the hypothesis. Draw a connection between your predicted hypothesis and what actually occurred. YOU MUST REFER TO YOUR DATA and cite actual numbers form the data tables to support your conclusion. Address the following questions in complete sentences and in paragraph form.

  1. The purpose of this experiment was to…
  2. To achieve this purpose we… What did you do in the lab? Be very brief.
  3. The hypothesis tested was…
  4. The data does/does not support my hypothesis because... What happened overnight to the potato cores?)
  5. An explanation for the results might be…Use concepts covered in class- come to a correct interpretation of conclusion-why did it happen? Answer all questions below…

a)How is diffusion or osmosis related to any changes you noted in length of the cores? Define both these terms as you answer this question.

b)Which of the six solutions is isotonic (or closest to) to potato cells? Define the term isotonic. How do you know which one is isotonic?

c)Which of these six solutions is hypertonic? Define the term hypertonic. How do you know?

d)Which of these six solutions is hypotonic? Define the term hypotonic. How do you know?

e)Why did the sailor die more quickly drinking salt water than not drinking at all?

f)What do you think killed the sailor?

Error Analysis- Paragraph form. Evaluate the validity of the results. What have you done to ensure that the results could be repeated or give you a valid result?

*Include at least 3

*Address the issue of number of trials and how it affects the validity of your experiment. *If you don’t think your lab data was valid – give reasons why. Consider what might have not worked well in the lab. Explain how potential errors would influence your final result – be specific. What could have been done to improve the experiment?

To ensure valid results in the lab we …(discuss your validity measures)

Our lab results were/were not valid because… (Discuss factors that affected your results. What affect did the error have on your data? Be specific.

Application Question- Choose one question and thoroughly answer it with 2/3 page of single-spaced writing. You must have a minimum of 3 internal citations that are different from the ones on your introduction on this section. Use the rubric as a guide. Remember to cite your sources.

  1. How do dialysis machines work? How are they used in the medical field?
  2. How do salmon (fish that live parts of their life in freshwater and saltwater) survive?
  3. What is reverse osmosis? How does it work? What are applications of reverse osmosis in industry?
  4. How is osmosis used in food preparation/preservation?
  5. Roads are sometimes salted to melt ice. What does this do to plants around the roadside and why?

Remember to have an adult proofread your paper, and thank them for their time- they are doing you a BIG favor .