CLASS SET
Mrs. Torres

OSMOSIS LAB

I. Objective

The purpose of this lab is to observe the effect of salt concentration on tugor pressure of potato cores.

II. Problem: Will changing the concentration on salt in a solution have an effect on the tugor pressure in potato cells? Generate a hypothesis in response to this problem applying what you know about osmosis.

III. California Standards(Cell Biology)

1a. Students know cells are enclosed with semi-permeable membranes that regulate their interaction with their surroundings

IV. Background

Explain the process of diffusion and osmosis. Describe the various types of solutions (isotonic, hypotonic, hypertonic).

IV. Materials

BeakerSalt waterWaterPaper towel

PotatoPotato corerRazor bladePaper

BalanceMetric ruleAluminum foilPen/Pencil

V. Procedure:

DAY 1

  1. You need to cut six equal sized slices of potato to represent the sailor. The best way to do this is to core 3 long strips of potato 8 centimeters (cm) long. If necessary, trim the potato slice with razor blade so that they all have sides. Cut the potato slice into two equal pieces, 4 cm long. The goal is to end up with six potato slices of exactly the same size. It is important to enter the length of the potato slices into the data table so you can compare it to the size of the potato slice tomorrow.
  2. Record the initial length (cm), initial mass (g), and initial diameter (mm) on your data table 1 (quantitative potato data). Have twopeople verify your quantitative observations.
  3. Record your qualitative data on data table 2. Write as much detail as possible to describe the characteristics of the original slice.
  4. Take and label six100 mLbeakers: fresh water, unknown A, unknown B, unknown C,unknown D, and unknown E.
  5. Add 20 mL of each salt solution to the appropriate beaker (solution A to beaker A).
  6. Add one potato slice to each beaker and cover with aluminum foil.
  7. Clean lab station and all equipment.

DAY 2

  1. Remove each potato from its beaker and pat it dry with a paper towel.
  2. Measure its final length, mass, and diameter and record in the data table. Have two people verify your quantitative observations.
  3. Make qualitative observations on each potato slice and record these in data table #2.
  4. Clean lab station and all material.

Table 1: Quantitative Data

Sample / Initial Length (cm) / Final Length (cm) / Initial Mass (g) / Final Mass (g) / Initial Diameter (mm) / Final Diameter (mm) / % Change
L / M / D
Unknown A
Unknown B
Unknown C
Unknown D
Unknown E
Fresh Water

**To calculate the % change for the length: FINAL LENGTH – INITIAL LENGTH (x100)

INITIAL LENGTH

To calculate the % change for the mass: FINAL MASS – INITIAL MASS (x100)

INITIAL MASS

To calculate the % change for the diameter: FINAL DIAMETER– INITIAL DIAMETER (x100)

INITIAL DIAMETER

(-) number means it shrunk(+) number means it expanded

Data Table #2: Qualitative Observations

Sample / Flexibility / Firmness
Unknown A
Unknown B
Unknown C
Unknown D
Unknown E
Fresh Water

GRAPH/CHART

**Create two bar graphs which compare the solution (% salt water) to the length and mass of each potato cylinder. You should have two bars for each potato cylinder (initial and final) on each graph.

Analysis

  1. Which beaker contained the control in the experiment?
  2. What is the purpose of having a control?
  3. What was the independent variable?
  4. What was the dependent variable?
  5. Described what happened to each potato for the 24 hour period it was submerged ineach solution. (In terms of what moved in or out; change in length, mass, diameter)

Unknown A:

Unknown B:

Unknown C:

Unknown D:

Unknown E:

6. Identify each beaker and with the % solution below based on your results:

Unknown solution / % solution / Reasoning / Type of Solution
(hyper-, hypo-, iso-)
A
B
C
D
E
Fresh Water

7. Is diffusion or osmosis responsible for changes in the length and mass of the potato slices? Support your answer.

7. Choose one of your potato slices and its solution to diagram and explain what moved where inthe test tube. Use arrows to show the movement

CONCLUSION (in paragraph form). Remember this section is worth the most points. Be clear with your explanations!

  1. Restate purpose
  2. Restate hypothesis.
  3. Was my hypothesis supported or refuted?
  4. Cite evidence/data collected from your experiment for your answer to #3.
  5. How accurate was my data? What were the sources of error in this experiment?
  6. How would I perform this lab investigation differently if given the opportunity to repeat?
  7. How could the concepts learned in this lab connect to real world experiences or problems?