Ib potato osmolarity lab PDF

Preview

Summary

123...

Description

IB Membrane Diffusion Lab – Practical #2 – Osmolality of Potato Cells Name: ________________________________ ____ Partner:________________________________

Block:_____

Introduction In order to survive, all organisms need to move molecules in and out of their cells. Molecules such as gases (e.g., O2, CO2), water, food, and wastes pass across the cell membrane. There are two ways that the molecules move through the membrane: passive transport and active transport. While active transport requires that the cell uses chemical energy to move substances through the cell membrane, passive transport does not require such energy expenditures. Passive transport occurs spontaneously, as a result of the Kinetic Energy that all molecules have (KMT). Diffusion is the movement of molecules by passive transport from a region in which they are highly concentrated to a region in which they are less concentrated. Diffusion continues until the molecules are randomly distributed throughout the system, thus reaching equilibrium. Osmosis, the movement of water across a membrane, is a special case of diffusion. Water molecules are small and can easily pass through the membrane. Other molecules, such as proteins, DNA, RNA, and salts are too large to diffuse through the cell membrane. The membrane is said to be semipermeable, since it allows some molecules to diffuse through but not others. If the concentration of water on one side of the membrane is different than on the other side, water will move through the membrane down its own concentration gradient which is always opposite the solute gradient. When water concentration outside a cell is greater than inside, the water moves into the cell faster than it leaves, and the cell swells. The cell membrane acts somewhat like a balloon. If too much water enters the cell, the cell can burst, killing the cell. Cells usually have some mechanism for preventing too much water from entering, such as pumping excess water out of the cell or making a tough outer coat that will not rupture. When the concentration of water inside of a cell is greater than outside, water moves out of the cell faster than it enters, and the cell shrinks. If a cell becomes too dehydrated, it may not be able to survive. Under ideal conditions, the water concentration outside is nearly identical to that inside. Key Terms:  Diffusion: The spontaneous tendency of a substance to move down its concentration

gradient from a more concentrated to a less concentrated area. Osmosis is the diffusion of water.  Hypotonic Solution: In comparing two solutions, it is the one with the lower solute concentration  Isotonic Solution: Having the same solute concentration as another solution.  Hypertonic Solution: In comparing two solutions, it is the one with the higher solute concentration. Objectives:  Particles move across membranes by simple diffusion, facilitated diffusion osmosis and

active transport  Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic

solutions (Practical 2)

Materials: (for each group)  Six 50 or 100ml beakers (all six need to be of same size) 0.0, 0.2, 0.4, 0.6, 0.8, 1.0.  40 ml each of distilled water, 0.2 Molar, 0.4 Molar, 0.6 Molar, 0.8 Molar and 1.0

Molar Saline solutions  6 potato cubes

Procedure: 1. Label each beaker with it’s appropriate solution concentration 2. Pour 100 ml of distilled water into the beaker marked “0.0.” 3. Repeat this for the remaining saline solutions in the 5 beakers with their respective concentrations. 4. Record the temperature of each of the cups and record in Table 1 under “Initial Temperature.” 5. Cut 6 potato cubes to a length of 2x2x2cm (be as accurate as possible!). Remove any skin from the cubes. 6. Find and record the mass for each potato cube and record in Table 1 under “Initial Mass.” 7. Place 0.0 Molar potato cube in its’ respected beaker. 8. Repeat Steps 5 and 6 for each of the remaining saline solution beakers. 9. Ensure that all potato cubes are completely submerged; add an equal amount of solution to all beakers if one cube is not submerged. 10.After 48 hours, record the temperature of the solutions in each of the beakers in Table 1. 11.Remove the potato cube out of the 0.0 Molar Solution cup and carefully blot dry with a paper-towel. 12.Find and record the 0.0 Molar potato cube mass under Final Mass in Table 1. 13.Repeat Steps 11 and 12 for each of the remaining saline solutions. 14.Calculate the percent change in mass for each of the solutions:( (Final Mass-Initial Mass)/Initial Mass) x 100% 15. Turn in group data for Percent Change in Mass for each solution concentration to the Google Sheet linked on my website THIS IS YOUR SECTIONS TO COMPLETE Research Question/ Purpose: Hypothesis: Data Tables: Table 1: Mass Change in Potato Tissue in Various Salt Solutions (my group only) Solution Molarity

Initial Temp (C)

Final Temp (C)

Initial Mass (g)

Final Mass (g)

% Change in Mass

0.0 0.2 0.4 0.6 0.8 1.0 Table 2. Class Mean % Change in Mass in Potato tissue in various Saline Concentrations

*Each Trial represents the data from a different class group as found on the class data spreadsheet Percent Change of Potato Trials

Molarity of Solutions 0.0

0.2

0.4

0.6

0.8

1.0

1 2 3 4 5 6 7 8 9 10 Mean Standard Deviation

Table 3. Measurement Uncertainties of Temperature and Potato Cube Size Temperature Uncertainty Mass Measurement Uncertainty Table 4. Qualitative Observations of salt Concentration Effect on Potato Cube Mass 0.0 Molar

0.2 Molar

0.4 Molar

0.6 Molar

0.8 Molar

1.0 Molar

Qualitative Observatio ns Data Analysis Please complete the following conclusion & evaluation questions on a separate piece of paper (please type) and staple to your lab packet.

1. Create a graph from the class data in Table 2. Place the percent change in mass on the YAxis and Salt molarity on the X-Axis. Insert a best fit linear regression line, R 2 value, and show the degree of uncertainty for each concentration as measured by 95% Confidence Interval. Upload an image of your graph here 2. Calculate an estimate of the osmolarity in the potato cube (meaning, what solution would create a balanced equilibrium/isotonic solution) based on the X-intercept of your graph from the best fit line of the class average. Conclusion & Evaluation: 3. Restate the question and hypothesis. 4. Describe if the hypothesis was supported or not supported using data and statistical analysis to support your explanation and analysis of the hypothesis. 5. Explain the results obtained in the experiment in terms of diffusion and solution types (hypotonic, hypertonic, isotonic). 6. Justify your calculation of the osmolarity in the potato cube using data and statistical analysis. 7. Explain and justify your confidence in the reliability of your data (class data) based on the statistical tests completed. Justify your explanation using data. 8. Analyze the measurement uncertainties (not error) associated with your experiment. 9. Describe the importance of conducting statistical tests (standard deviation, linear regression, and graph error bars). 10.Evaluate and explain the influence of procedural errors of this experiment.. 11.Discuss in as much detail as possible, ways that the errors and uncertainties discussed in question nine could be minimized or eliminated in future experiments. Also discuss any other ways you can think of that the reliability of the data could be improved. Assessment: Lab Standard: Analysis

Exceeds

Meets

Nearly Meets

Beginning

Lab Standard: Evaluation

Exceeds

Meets

Nearly Meets

Beginning

A full explanation of the lab standard rubric can be found here...