Osmosis through the Cell Membrane of an Egg
Introduction:
The cell or plasma membrane is made up of phospholipids and different types of
proteins that move laterally. These include peripheral proteins, which are attached to
the interior and exterior surface of the cell membrane. Integral proteins are embedded
in the lipid bilayer. Attached to these integral proteins are carbohydrate chains. These
carbohydrates may hold adjoining cells together, or act as sites where viruses or
chemical messengers such as hormones can attach. Cell membranes are selectively
permeable. They allow some substances to pass through, but not others. Small
molecules that are usually nonpolar, such as oxygen, water, and carbon dioxide, easily
move through the lipid bilayer. Larger molecules, such as glucose, the food for all
living things, must seek aid from the carrier proteins in a process called facilitated
diffusion. Facilitated diffusion is a process used for molecules that cannot diffuse
rapidly through cell membranes. Integral proteins are used by calcium, potassium, and
sodium ions to move through the cell membrane. The muscles and nerves use these
ions.
Diffusion is the movement of molecules from an area of higher concentration to an
area of lower concentration. This difference in the concentration of molecules across a
space is called a concentration gradient. Diffusion is a type of passive transport,
meaning it does not require energy input by the cell. This type of transport and
osmosis are the two processes used in this lab. Osmosis is the process by which water
molecules diffuse across a cell membrane from an area of higher concentration to an
area of lower concentration. When the concentration of the solute is higher outside of
the cell, it is known as a hypertonic solution. When the concentration of the solute is
lower outside of the cell, it is known as a hypotonic solution.
Hypothesis:
The substance, syrup, which has a higher solute concentration than the interior of the
eggs, will cause water to leave the eggs’ membrane; the other substance, distilled
water, which has a lower solute concentration than the eggs’ interior, will cause liquid
to enter the eggs’ membrane.
Materials:
The materials necessary for this lab are: two fresh eggs in their shells, a felt tip
marker, 200mL graduated cylinder, five jars, clear Saran wrap, white vinegar, clear
sugar syrup (Karo), distilled water, tap water, pencil, paper, eraser, computer,
electronic scale, and a plastic tray.
Methods:
Day One: On day one, label the five jars, with the felt tip marker: one labeled vinegar,
two labeled syrup, and two labeled distilled water. Also put the group number on each
jar. Find the mass of each egg and record this information in the data table. Place the
two eggs in the jar labeled vinegar. Add vinegar until both eggs are submerged by it.
Cover the jar with the clear Saran wrap. Place the jar on the plastic tray and allow to
set for 24 hours.
Day Two: On day two, observe what has happened to your eggs. Record this in a data
table. Now that the eggs’ shells are dissolved, gently remove the eggs from the
vinegar. Rinse each egg with tap water. Pat the eggs dry with paper towels and mass
them separately on the electronic balance. Record this in the data table. Place the eggs
in the jars labeled syrup. Add syrup to each jar (labeled egg 1 or egg 2) until the eggs
are submerged in syrup. Loosely cover each jar with Saran wrap. Place the jars on the
tray and allow them to soak for 24 hours.
Day Three: On day three, observe what has happened to the eggs and record this
information in the data table. Carefully remove the eggs from the syrup and rinse
them with tap water. Pat dry with paper towels. Using the electronic balance, find the
mass of each egg separately and record these masses in the data table. Place the eggs
in the jars labeled distilled water (labeled egg 1 and egg 2). Add distilled water to
each jar until the eggs are covered. Cover the jars with the Saran wrap and allow them
to sit on the tray for 24 hours.
Day Four: On day four, remove the eggs from the jars and record the eggs’
appearance. Mass each egg on the electronic balance. Record this in the data table.
Dispose of the eggs in the container provided by the teacher.
Results:
Egg 1 Data Table
Substance
egg
submerged
in
Egg’s
mass
before
placed in
substance
Egg’s mass
after
removed
from
substance
Observations of egg
before placed in
solution
Observations of
egg after
removed from
substance
Vinegar
59.2 g
86.0 g
The egg’s shell is
intact and is
The egg’s shell
dissolved and
included in the first
mass.
wasn’t included
in the 2nd mass.
Syrup
86.0 g
53.2 g
The egg is swollen
and soft, yet firm to
touch.
The liquid inside
the egg diffused
into the syrup.
Distilled
Water
53.2 g
86.5 g
The egg has lost
some of its
firmness.
The water
diffused into the
egg, increasing
the egg’s mass.
Egg 2 Data Table
Substance
egg
submerged
in
Egg’s
mass
before
place in
substance
Egg’s mass
after removed
from
substance
Observations of
egg before placed
in solution
Observations of
egg after
removed from
substance
Vinegar
58.8 g
85.6 g
The egg’s shell is
intact and is
included in the
first mass.
The egg’s shell is
mostly dissolved
and so wasn’t
included in
2nd mass.
Syrup
85.6 g
52.2 g
The egg is rough
to touch and feels
rather sturdy.
The liquid inside
the egg diffused
into the syrup.
Distilled
Water
52.2 g
88.9 g
The egg feels more
fragile and lighter
in weight.
The water
diffused into the
egg increasing
the egg’s mass.
Egg in Hypotonic Solution of Vinegar &
Plasmolyzed Egg in Distilled Water
Egg in Hypertonic Solution of Syrup
1. When the egg was place in the water, in which direction did the water molecules
move? The water moved into the eggs from the surrounding environment.
2. On what evidence do you base this? The eggs’ masses had increased from the time
they were placed in the water to when the eggs were removed.
3. How do you explain the volume of liquid remaining when the egg was removed
from the syrup? The volume of the liquid remaining when the egg was removed from
the syrup must have increased because the eggs’ masses had decreased. The liquid
within the eggs left the eggs and diffused into the surrounding syrup.
4. When the egg was place in the water after being removed from the syrup, in which
direction did the water move? The water moved into the eggs.
Error Analysis:
Several errors may have occurred during this lab. When finding the eggs’ masses, on
each occasion, an error may have occurred. Mistakes may have been made when
recording these masses on the data table. Some of the eggs’ shell may have been left
on the eggs’ membranes and changed the outcome of this lab. When the eggs were
rinsed, after being placed in the vinegar and syrup, a small amount of water could
have entered through the membranes of the eggs, effecting their masses. These are
just a few of the errors that may have taken place throughout the lab.
Discussion and Conclusion:
The hypothesis was correct. When the eggs were placed in the syrup, their masses
decreased greatly. This shows that the interior of the eggs must have had a lower
solute concentration than their surrounding environment of syrup. The water within
the eggs left through the membrane and diffused into the syrup, decreasing its solute
concentration. When the eggs were placed in the distilled water, their masses greatly
increased. This shows that the interior of the eggs must have had a higher solute
concentration than their surrounding environment of distilled water. The distilled
water diffused into the eggs’ membrane, decreasing the interior of the eggs’ solute
concentration.