biology help

Osmosis Lab Instructions Updated 9/3/14

Materials Obtain the following materials before starting the lab:

• 3 (or 4) eggs • Vinegar (that is at least 3% acetic acid; 5% or more is better) • Water • Syrup (corn syrup, cane syrup, maple syrup, golden syrup, simple syrup,

molasses, or treacle) • Salt or sugar • Piece of string (for measuring circumference) • Marker • Metric ruler • Pen or pencil • 3 clear jars or glasses (large enough to contain an egg) • Aluminum foil (or other covering for glasses or jars)

Note: The eggs get slippery so you might want to start with four in case one breaks.

Lab Procedure: Part 1 1. Soak each egg in vinegar until you are able to wipe away the remnants of the shell. This will likely take between 36 hours and 48 hours (2 days) of soaking. The eggs can soak in a single jar or in separate glasses. Cover each container with aluminum foil or some other airtight lid or covering so that the vinegar does not evaporate.

2. Wait approximately 48 hours, and then remove the eggs from the vinegar.

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3. Record the following results:

a. Observe any physical changes in the eggs and the vinegar. How did the eggs change as a result of being immersed in vinegar for approximately 48 hours? b. Record your observations in “Part 1 Results, Sections a and b” of the Osmosis Lab Report.

4. Wash each egg to remove any residue.

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5. Record the following results:

a. Using the string, measure around the largest section of each egg (see diagram below).

b. Mark the thread with a marker. Then, measure the string length to the nearest millimeter by using a ruler. Record your measurements in centimeters in the table below. Repeat and record this measurement three times for each egg, as the circumference may be a bit difficult to measure accurately. Scientists make multiple measurements in order to gauge the reliability of their measurement process.

Table 1.1 Egg circumference measurements (in centimeters, before treatment)

Measurement Egg A Egg B Egg C

Try #1 Try #2 Try #3

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6. Use your data in Table 1.1 to improve your estimate the circumference of each egg by adding the three measurements of each egg and dividing that number by three. This is the average measurement of the circumference of your egg. Estimate the uncertainty in your measurement by subtracting your lowest value measurement from your average value. Enter these values in Table 1.2.

Table 1.2 Egg circumference average value and uncertainty (in cm)

Egg A Egg B Egg C

Average Value Uncertainty

7. Record the results from Steps 5 and 6, above, in “Part 1 Results, Section c” of the Osmosis Lab Report. Then proceed to “Lab Procedure: Part 2” on the following page.

Note: The acetic acid in the vinegar dissolved the calcium carbonate in the eggshells, essentially removing each egg’s shell. The outer covering that remains is a membrane with properties similar to the plasma membrane of a cell.

8. In order to investigate which direction water moves across the eggs’ membranes in different solutions, you will place eggs in three different solutions. Label three Cups #1 to #3. Put drinking water in Cup #1, syrup in Cup #2, and either a saturated saltwater solution or a saturated sugar water solution in Cup #3. Use one of the following instructions to prepare your solution for Cup #3:

• Saturated saltwater solution: To prepare a saturated saltwater solution, pour

one cup of water in the cup and add salt while stirring. When the salt no longer dissolves in the solution, it is saturated.

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• Saturated sugar water solution: To prepare a saturated sugar water solution, pour one cup of water in the cup and add sugar while stirring. When the sugar no longer dissolves in the solution, it is saturated.

9. Before placing the eggs in the cups, measure the height of your prepared solution in each cup and record it in Table 1.3 Also record which type of solution you prepared for Cup #3 in the appropriate table cell.

Table 1.3 Solution height measurement in cm (before treatment, without egg)

Cup #1 Cup #2 Cup #3

Solution: water only syrup Height (cm)

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Lab Procedure: Part 2

Now place your eggs in solution. Be sure that you track which egg goes in which solution and label each cup.

• Cup #1: Place Egg A in Cup #1 with water. • Cup #2: Place Egg B in Cup #2 with syrup. • Cup #3: Place Egg C in Cup #3 with your prepared solution. You will need to

identify this solution in Tables 1.3 onwards.

3. What do you predict will happen to each egg based on what you have learned about osmosis? Create a set of expected observations and record them in the “Expected Observations” section of the Osmosis Lab Report before proceeding to the “Part 2 Results” of that report. 4. Once you have placed Egg A in Cup #1 (with water), Egg B in Cup #2 (with syrup), and egg C in Cup #3 (with a saturated, salt or sugar water solution), cover the jar or glass with aluminum foil or some other airtight lid or covering so that the liquid does not evaporate.

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5. Wait 24 hours, and then remove the eggs from the jars. 6. Record the following results:

a. Observe any physical changes in the eggs and solutions and record your observations in “Part 2 Results Section a” of the Osmosis Lab Report. b. Observe and measure the height of each solution after removing the eggs. Record your findings in Table 2.3.

Table 2.3 Solution height measurement in cm (after treatment, without egg)

Cup #1

Cup #2

Cup #3

Solution: water only syrup saturated ___water

Height (cm)

c. Using the string, measure around the largest section of each egg (see diagram below).

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d. Mark the thread with a marker. Then, measure the string length to the nearest millimeter by using a ruler. Record your measurements in the Table 2.1.

Table 2.1 Egg circumference measurements (after treatment)

Egg A

Egg B

Egg C

Solution: water only syrup saturated ___water

Measurement #1 Measurement #2 Measurement #3

7. Use your data in Table 2.3 (above) to improve your estimate of the circumference of your egg by adding the three measurements of each egg and dividing that number by three. This is the average measurement of the circumference of your egg. Estimate the uncertainty in your measurement by subtracting your lowest value measurement from your average value. Enter these values in Table 2.4.

Table 2.2 Egg circumference average value and uncertainty (after treatment)

Egg A Egg B Egg C

Solution: water only syrup saturated

___water Average Value

Uncertainty

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8. Record the results from the tables, above, in the Osmosis Lab Report in “Part 2 Results” section.

9. Dissect (cut open) each egg and record your observations of the physical characteristics of each egg. Record these observations in “Part 2 Results, Section e” of the Osmosis Lab Report.

10. Complete the “Analysis and Conclusion” sections of the Osmosis Lab Report. Complete the Osmosis Lab Report via the instruction contained therein.

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