Download Cell Membrane Lab Day #2

Biology Cell Unit Homework Packet #3
Name
DUE:
HW #5
Egg Demo
HW #6
Elodea
lab
HW #7
Cell
Membrane
and
Transport
HW #8
Hour
Drawings
Analysis
____
____
Drawings
Analysis
____
____
Questions
____
Questions
____
_______ / 5 possible points
Homework #5: Egg Demonstration
An egg can be used to further demonstrate the properties of cell membranes. We will start
this demonstration with an egg that has been soaked in vinegar. We will place the egg in syrup
tonight, and then transfer the egg to water the following night. Be sure to make accurate
drawings of the egg each day.
Egg in vinegar
Egg in syrup
Egg in water
Analysis and Conclusions
Answer the following questions on the lined pages provided using complete sentences. I
will be really impressed if you use what you know about cells and cell parts to answer
them.
A. What did the vinegar do to the egg? Why was it important to put the egg in the vinegar
before placing it in any other solution?
 Vinegar reacted with calcium carbonate in egg shell and dissolved it
leaving only membrane surrounding egg.
B. Use your knowledge of osmosis to explain what happened to the egg in syrup.
 There is a greater concentration of water inside the egg than in the
syrup. When egg is placed in syrup, water leaves the egg (moves from
high to low concentration) making the egg shrivel.
C. Use your knowledge of osmosis to explain what happened to the egg in water.
 When egg is place in water, concentration of water is higher outside
the egg than inside. Water flows into the egg, making the egg
expand.
D. Describe a potential source of error in this lab. How might you design the experiment to
reduce or eliminate this error?
 Answers will vary
Homework #6: Elodea Lab
Background:
Eukaryotic cells are comprised of a cell membrane and many individual cell parts (organelles) that are each
surrounded by their own membrane. These membranes keep the functions of the cell parts separated and more
efficient. Materials must be passed through these membranes and delivered through each of the cell parts.
Today we will observe some organelles and observe water loss (by osmosis) from a plant cell, Elodea. This
process is also known as PLASMOLYSIS.
Procedure:
Part A:
1. Pick one leaf of Elodea, place in a drop of water on a microscope slide. Cover with a
cover slip.
2. Observe cells using medium or high power. I find it easier to use medium for this lab,
but you can use high power if you can distinguish individual cells.
Each of the “bricks” that you cell is a cell and the green dots are
chloroplasts. Draw one typical cell and please label: cell membrane,
cytoplasm, chloroplasts and cell wall.
PAY SPECIAL ATTENTION TOTHE LOCATION OF THE
CHLOROPLASTS!!!! They are either scattered all over the inside of
each cell or clustered in the center of each cell.
Which objective did you use?
Calculate the magnification:
What type of cell?
plant
Part B: Inducing Plasmolysis in Elodea using high concentration salt water.
1. Bring your slide back to the front. Add one drop of 6% salt.
2. Again, draw one typical cell and please label: cell membrane,
cytoplasm, chloroplasts and cell wall.
PAY SPECIAL ATTENTION TO THE LOCATION OF THE
CHLOROPLASTS!!!! They are either all over the inside of the cell or
clustered in the center of the cell.
Elodea in salt water
Post-Lab Questions:
Additional Information: Tap water is typically 1% salt and 99% water. Our 6% salt
water is only 94% water and 6% salt. Cells are usually 98% water and 2% salt.
1. Add arrows to both drawings of Elodea showing the direction water molecules are
moving.
 Arrows should show water molecules moving out of Elodea.
2. Why is water moving in that direction? What is this process called?

Water moves from high to low concentration across a membrane
through the process of osmosis.
Did the Elodea leaf cell wall change shape in the salt water? Why or why not?
 Cell wall does not change shape. Cell wall is rigid and permeable to
both salt and water.
Homework #7 Membrane Investigation:
Osmosis can be a difficult concept to understand especially because it is hard to see
happening in living cells that are far too small for us to see without using microscopes. However,
we can use an artificial membrane that has many of the same properties of cell membranes. This
artificial membrane, called “dialysis tubing”, allows us to do some important experiments to study
osmosis. Like a cell membrane, dialysis tubing is “selectively permeable” – it has extremely tiny
holes that allow small molecules to pass through the membrane while molecules larger than the
holes are trapped.
In this experiment we are going to make some predictions about the direction of osmosis
using starch and dialysis tubing. Some important factual information first:
-
Osmosis is the diffusion of water from areas of high water concentration to areas of low
water concentration.
-
Starch is a large molecule consisting of many sugar molecules hooked together. It is too
large to pass through the tiny holes in the dialysis tubing.
-
Starch and iodine combine to create a dark purple-black color.
Cell Membrane Lab Day #1
Acts as the “gatekeeper”. Determines
1. What is the role of a cell membrane?
what goes into and out of cell.
2. What would the solution within this model represent?
cytoplasm of the cell.
The solution represents the
__________
3. Record the following information about the experimental setups for Day 1:
A.
90% water
1. 98% water
B.
10% starch
2. 2% iodine
Day 1
A.
B.
1.
2.
Color of
Liquid In
Beaker
Mass of
Tubing
Color of
Liquid in
Tubing
Beaker 1
Day 2
A. 98% water
1. 90% water
B. 2% iodine
2. 10% starch
Day 1
A.
B.
1.
2.
Day 2
Color of
Liquid In
Beaker
Mass of
Tubing
Color of
Liquid in
Tubing
Beaker 2
A. 98% water
1. 98% water
B. 2% iodine
2. 2% iodine
Day 1
A.
B.
1.
2.
Beaker 3
Color of
Liquid In
Beaker
Mass of
Tubing
Color of
Liquid in
Tubing
Day 2
Predictions
4. The beakers and tubing will be stored overnight. Using your knowledge of osmosis, predict
what we will see tomorrow.
Color of liquid in
tubing
Color of liquid in
beaker
Mass of tubing
Beaker #1
Beaker #2
Beaker #3
Cell Membrane Lab Day #2
5. Record your observations for Day 2 next to EACH of the diagrams.
6. For each beaker, use arrows to clearly show which direction each molecule moved.
Results
7. Develop a BAR graph that shows the how the mass of the tubing (Y-axis) changed over time (xaxis) for each beaker. Be sure to include a title, key, and labeled axis (X and Y) on your graph.
Neatness counts.
Cell Membrane Investigation Analysis and Conclusions
Answer the following questions using complete sentences.
E. What cell process was demonstrated by Beaker #1?
 The cell process demonstrated by Beaker #1 was osmosis.
F. What direction did the iodine move? How do you know?
 The iodine moved out of the tubing. We were able to determine this
because the liquid in the beaker turned purple.
G. Place the following items in order from largest to smallest: the size of the holes in the tubing,
iodine, starch.
 The largest was the starch. Then the holes in the tubing. Finally, the
smallest was the iodine.
Homework #8 – Questions:
1. Using pictures, illustrate what is meant by the term “selectively permeable”. Then write a
definition using your own words.
 Answers will vary.
2. Using the terms concentration and equilibrium write one sentence that defines “diffusion”.
 Answers will vary. Should be similar to: “Diffusion is the random
movement of molecules from an area of high concentration to an area of
lower concentration until equilibrium is reached.
3. Below are examples of two typical cells – an animal cell and a plant cell. Remember, starch is
much too big to fit through the cell membrane. Salt is also too big. Draw the appropriate arrows
for water and the final result. The first example is an animal cell and the second is a plant cell.
90% water
80% water
10% salt
20% salt
80% water
60% water
20% starch
40% starch
4. The diagram below describes a few different situations related to osmosis. Predict the end
result of placing a red blood cell or Elodea plant cell into these situations. Draw what each cell
type would look like after it has reached equilibrium.
Cell will shrivel as water leaves cell through
cell membrane. Elodea cell wall will remain the
same.
Cell will enlarge as water enters cell through
cell membrane. Elodea cell wall will remain
the same. Cell membrane may eventually
burst.
Cell will remain same size. It will be at
equilibrium.
5. Would a cell lose or gain water when placed in a solution with a salt concentration greater
than that of the cell cytoplasm?
 Cell will lose water.
6. Would a cell lose of gain water when placed in a solution with a salt concentration less that
that of the cell cytoplasm?
 Cell will gain water.
7. Which way would the water molecules move in the following situations (in or out)? Then
explain why the water molecules move in that direction.
a. Cucumber slice is placed in salt water.

Water will move out of the cucumber cells due to the fact that the
water concentration is greater inside the cells than outside of the
cells.
b. Salt is poured onto a snail.
 Water will move out of the snail cells due to the fact that they contain
more water than the outside environment.
c. Vegetables are sprinkled with water

Water will move into the vegetable cells because the vegetables
contain less water than the surrounding environment.
d. Potato slice is placed in pure water
 Water will move into the potato cells because they contain less water
than the surrounding environment.