Lab

Observing Movement of Molecules Through a Cell Membrane

(EGG LAB)

Purpose | Hypothesis | Prediction | Materials | Procedure | Observations  

My Data | Analysis | Class Averages | Conclusions | Additional Experiments

 

Purpose: 

 To observe the selective passing of materials into and out of a membrane, and observe the types of materials that are and are not passed through.

Hypothesis: 

The passage of solution through the semipermeable membrane of the egg is facilitated diffusion through transport proteins in the egg membrane.

 Prediction:   

By this hypothesis, the acetic acid solution will dissolve the calcium carbonate in the egg's  outer shell, converting it to bubbles of CO2.  The membrane will then allow much passage of vinegar through the membrane to attain equilibrium solute concentration (because the  vinegar will be a more concentrated solution than the inside of the egg).  There will thus be a gain in egg mass.  There will be little net mass change in the glucose solution, but the two  solutes (acetic acid and glucose) will even out on each side of the membrane.  In the water, there will be a net loss of egg mass, as solutes in the egg pass through the membrane to  even the concentration of solutes in the water.

Materials: 

1) One chicken egg

2) One small beaker

3) One graduated cylinder

4) 100 mL 5% acetic acid solution

5) 100 mL 50% glucose solution

6) 100 mL distilled water

7) 5" x 5" square of plastic wrap

8) Rubber band

9) Ruler

10) About 30 cm of string

11) Balance scale

Procedure: 

 1) Measure transverse and longitudinal circumferences of egg using string and ruler.

2) Measure mass of egg using balance scale.

3) Place egg in beaker.

 4) Measure 100 mL of acetic acid solution with graduate.

5) Pour into beaker.

6) Cover beaker with square of plastic wrap and secure with rubber band.

 7) Store egg for one day in an undisturbed, cool, dry place.

8) Repeat steps 1-2.

9) Repeat steps 3-8 for glucose solution and distilled water.

Observations: 

 Upon placing the egg in the acetic acid solution, we observed small bubbles rapidly forming around the outside of the egg.  When we retrieved the egg one day later, the  surface of the solution was foamy, with yellowish film in some places.  The egg was soft and the now-powdery outer shell flaked at the touch.  Where the egg came in contact with the  bottom surface of the beaker, the shell was intact.

 Upon placement in the glucose solution, the egg floated relatively high in the solution.   When the egg was retrieved one day later, it still was covered with small bubbles.  The appearance of the solution had not changed.  The egg still was floating somewhat, but not  nearly as high as it had been.  The outer shell had thinned to an even greater extent, and there was empty space inside the membrane—it could be gently depressed, like a  paper-maché ball with a punctured balloon inside.  The part of the shell which had not been dissolved by the vinegar still was not.

  Upon placement in the water, the egg did not float.  Small bits of dissolved shell began flaking into the water.  When we removed the egg from the water, small flakes of shell  remained suspended in the water, causing it to become slightly murky at the bottom.  The egg no longer had bubbles on its surface, and the powdery surface was cracked in some  places to reveal the translucent membrane.  The egg rested on the bottom of the beaker, and the empty space within it was gone.  The shell could be completely removed by rubbing,  to reveal a translucent yellow, water balloon-like membrane.  Particles of the shell were abrasive and formed a milk-like fluid when rubbed off with water.  The egg sprung back to  the touch.  When popped by a pin, the yolk and white spilled out.

 

My Data:

Date

Mass (grams)

Longitudinal Circumference (centimeters)

Transverse Circumference (centimeters)

Beginning Fluid (mL)

Ending Fluid (mL)

9/21/99

53.8

15.5

13

N/A

N/A

9/22/99

67.4

16.9

16.3

98

79

9/23/99

55.4

17

14.5

99

111

9/24/99

83.9

18.5

16

99

69

 

 

 

 

 

 

 

 Analysis: 

 

The daily changes in egg mass were as follows: 25% in the vinegar, -18% in the glucose,  and 51% in the water.

 

This graph shows the average percent changes over four categories of egg measurement, averaged over several sets of data.

 

The egg absorbed 19 % of the vinegar, increased the volume of glucose 12%, and absorbed 30% of the water.

 

Changes in circumference (average longitudinal and transverse) were 16% in the vinegar,  -5% in the glucose, and 10% in the water.

Class Averages: 

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Chang e in Mass

Change in Longit. Circ.

Change in Trans. Circ.

Change in volume fluid in beaker

Day 1-2

19%

5%

8.5%

-26%

Day 2-3