Unit 4
Homeostasis and
Transport
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Unit 4: Cell Membrane – Passive and Active
Transport
STANDARD
3.1.10.A5. Relate life processes to sub-cellular and cellular structures to their functions.
3.1.B.A5. Explain how the cell membrane functions as a regulatory structure and protective
barrier for the cell.
3.1.B.A5. Describe transport mechanisms across the plasma membrane.
ANCHOR
BIO.A.4.1 - Identify and describe the cell structures involved in transport of materials
into, out of, and throughout a cell.


BIO.A.4.1.1 - Describe how the structure of the plasma membrane allows it to function
as a regulatory structure and/or protective barrier for a cell.
BIO.A.4.1.2 - Compare the mechanisms that transport materials across the plasma
membrane (i.e., passive transport—diffusion, osmosis, facilitated diffusion; and active
transport—pumps, endocytosis, exocytosis).
VOCABULARY
plasma membrane, impermeable
intracellular, extracellular, concentration, concentration gradient, passive transport, osmosis ,
diffusion, facilitated diffusion, active transport, carrier (transport) protein, pumps (ions or
molecular), endocytosis, exocytosis
OBJECTIVES
Identify the parts of the cell membrane.
Describe the functions of the cell membrane proteins.
Describe selective permeability and how it is essential to maintaining cellular homeostasis.
Relate diffusion and equilibrium.
List the differences between passive and active transport and give examples of each.
Distinguish among diffusion, facilitated diffusion and osmosis.
Explain how protein pumps are used in active transport.
Illustrate the difference between endocytosis and exocytosis.
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Chapter 5: Homeostasis and Transport
Passive Transport
Passive transport is:
Explain the following concepts:
Diffusion:
Concentration gradient:
Equilibrium:
Simple diffusion:
What determines whether or not molecules will pass through the membrane?
Osmosis
Osmosis is:
How is osmosis related to passive transport?
Explain each of the following solutions, and tell what would happen to a cell placed in
each of them:
a) isotonic:
b) hypotonic:
c) hypertonic:
How do cells deal with water problems?
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What is:
a) turgor pressure:
b) plasmolysis:
c) cytolysis:
Facilitated diffusion
Explain facilitated diffusion:
What do carrier proteins do?
Sketch and explain figure 5-5 (page 101): neatly!!!!!
Diffusion through ion channels:
What are ion channels?
What are gated channels, and what 3 things control them?
Active Transport
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What is active transport?
What is the function of cell membrane pumps?
How does a sodium-potassium pump work?
Movement in vesicles
Explain:
Endocytosis:
Pinocytosis:
Phagocytosis:
Exocytosis:
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NAME_________________________
INVESTIGATING CELL MEMBRANE ACTIVITY
Problem: How can a cell maintain homeostasis of water when placed in different types of
solutions?
Hypothesis: ___________________________________________________________________________
______________________________________________________________________________________
Materials:
Electronic balance
distilled water
10 % salt water
tap water
3 potato cores 3 cm. in length
3 paper cups
Procedure:
1. Trim 3 pieces of potatoes (they should resemble thin french fries) so that each is
exactly 2 cm.
2. Weigh each piece in grams and record the weights in the table below.
Do not mix up your potato pieces
3. Place potato piece #1 in a cup of distilled water, piece # 2 in tap water and piece # 3
in salt water. Label these cups!!!!
4. After 24 hrs, remove each piece from its cup, measure its length in cm. and its mass
in grams. DO NOT MIX UP THE PIECES!!!!!!!
5. Record all information in the chart below.
Results:
potato #
weight
before
weight
after
difference
in mass+/-
length
before
length
after
difference
in length +/-
1
2
3
Conclusion: Did you support or reject your hypothesis? Describe what is happening in each cell.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
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Lab extension: Osmosis and Blood pressure
Background knowledge: Blood pressure is a measure of the force of blood as it is
pumped through the circulatory system (veins and arteries). As with any closed hydraulic
system, the more liquid you have in the system, the higher the pressure as it is pumped.
Therefore, as more fluid moves into the circulatory system (into the blood), the higher
your blood pressure.
Paramedics and doctors are able to control blood pressure in an emergency situation
using intravenous (IV) fluids. These are fluids that can be pumped directly into the blood
stream. An isotonic solution is 0.9 percent saline, often referred to as “normal saline”.
By changing the osmotic concentration of the fluid, they can lower or raise the blood
pressure over time.
Question: What types of intravenous (IV) fluid solutions do medical professionals use to
control blood pressure?
Activity: Based on the background knowledge, decide what you would do in each
situation below. Defend each position using your knowledge of osmosis and the
background knowledge.
Use these common saline solutions to in the situations below:
A.
B.
C.
D.
E.
1000ml 0.45% saline solution
250ml 0.45% saline solution
1000 mL 1.8% saline solution
250 mL 1.8% saline solution.
1000mL 0.9% saline solution
Situation one:
A patient arrives with dangerously high blood pressure, which can possibly lead to a
stroke. The doctors decide to administer IV fluids. Which of the following solutions
should they use?
Situation two:
Paramedics arrive on seen to find a patient who is experiencing an allergic reaction,
causing her blood pressure to drop drastically. They decided to administer IV fluids.
Which solution do they use? Defend your position using your knowledge of osmosis and
the background knowledge.
Situation three:
A patient is having a heart attack and needs fluid, however their blood pressure is normal.
Which solution should the triage nurses administer?
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Cell Transport Lab
Introduction
In the series of experiments, , you will discover how and why a cell transports
molecules through the cell membrane. Transportation is the job of the cell membrane,
because it is the structure that controls what goes in and out of the cell. But as you will
see, there are other factors that affect the movement of materials into or out of the cell.
The factors that have the greatest affect on whether a molecule moves into or out
of the cell are the molecules’ size and charge. In addition, the turgor pressure will help
control molecule movement, as will the concentration gradient of the molecule. Simply
put, greater water pressure causes more molecules to move, and likewise a greater
difference in amount from one side of the membrane to the other will cause more
movement.
You will also see the effects that solute level has on cell shape, size and function.
You will see how changing the amount of solute in plant and in animal cells will greatly
affect how those cells look and function. Maintaining the correct level of solute is vital if
the cell is to survive. Hopefully you will discover first-hand exactly why that is.
Directions
Experiment # 1
1. Get a beaker, some water, and some NaCl (table salt).
2. Make a salt solution of your choice. The formula for making a salt solution of a given
percentage (X) is:
(percent desired)(0.01 grams of salt) + 10 ml of water = X % salt solution
For instance, to make a 10% salt solution, I would take .1 g salt (10% desired x
.01 grams) plus 10 ml of water.
3. After making your salt solution, label the beaker with a piece of tape indicating the %
salt.
4. Take a piece of celery or elodea, place it on a CLEAN slide, and place a drop of tap
water on it (and a cover slip).
5. Make a proper lab drawing of what the cells look like. Be particularly observant
about the overall shape and size of the cells, and label the drawing. Repeat steps 4
and 5 with your salt solution and then with DISTILLED water.
6. Write a paragraph describing WHAT happened to the cells and WHY it happened.
7. CLEAN and dry slides and beakers when finished. CLEAN lab tables and sinks with
sponge and Simple Green.
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Experiment # 2
1. Get 6 plastic cups, rinse them out, and place about a ½ cup of one of the following
solutions in each. Label the cup A, B, C, D, E, or WATER (depending on which
solution you put in it).
2. Cut a potato into 6 slices, each about 1 cm thick.
3. Determine the mass of each potato slice. Record the mass of each, and put it into
one of the beakers (be sure to record which slices went into which beaker).
4. Cover the cups with parafilm, and let them sit overnight.
5. The next day, remove the potato slices from the beakers and quickly blot the
slices with a paper towel.
6. Determine the mass of each slice again, being careful to not mix up slices from
different beakers.
7. Record the change in mass, if any, for each slice. Also note any changes in
appearance of the potatoes, and record them.
8. Calculate the percent change by using the formula:
% change = amount of increase or decrease X100
starting mass
9. Using this information, place the solution letters in order from HIGHEST to
LOWEST amount of water in the original solution.
Experiment # 3
1. Get a drop or two of starch solution, place it on some scrap paper, and add a drop of
iodine solution (IKI). Note the color change, and write this information down.
2. With that information in mind, get a piece of dialysis tubing, and a 500 ml CLEAN
beaker.
3. Add 250 ml of water to the beaker, and 5 ml of the IKI solution.
4. The dialysis tubing is serving as a cell membrane. Place 15 ml of glucose/starch
solution into the bag, and tie off the end of the bag. Rinse the bag under water for a
few seconds and place the bag into the beaker. Make a drawing showing the colors of
the beaker and bag.
5. Test the g/s solution and the water in the beaker with glucose test tape, and record the
results in table 3.
6. After setting up the experiment, let it sit for about 30 minutes.
7. After 30 minutes, again test the water in the beaker (and bag) with glucose test tape.
Make a second drawing showing the colors of the beaker and bag.
8. Explain these results in paragraph form.
9. CLEAN the beaker, rinse and dry.
10. Throw out the bag after dumping the starch solution down the drain.
11. CLEAN lab tables and sinks with sponge and cleaning solution.
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What to hand in
1. The three sketches you made for part 1, along with the paragraph you wrote
explaining it.
2. The answers to the following questions, answered in full sentences and clearly
labeled.
A.
B.
C.
D.
E.
F.
Why did the plant cells shrink more with increasing salt solutions?
What does it mean to describe a solution as being hypertonic?
What is plasmolysis, and how does it tie in with the first experiment?
Why would a smart bar owner put out free popcorn or pretzels?
Why did some of the potatoes actually gain mass?
What does it mean to say that the dialysis tube is representing a selectively
permeable membrane?
G. Why did you rinse the bag before placing it in the beaker solution?
H. Why can some molecules pass through the cell membrane, while others
cannot? Give at least 2 factors that affect this and explain how those
factors affect molecule movement.
3. A chart with your BEFORE and AFTER masses for experiment 2, as well as a
ranking of the solutions from highest to lowest.
Example:
A
B
C
D
E
water
Mass before
Mass after
Highest to Lowest: (This is just an example)
A → B→C → D →E →water
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4. A chart like this one for experiment 3:
Bag
Beaker
Initial
Contents
g/s solution
Water & IKI
Initial
Color
Final
Color
Glucose:
Initial
Glucose: Final
2. The 2 sketches (before and after) of the beaker with the bag in it
3.
Explain the results you obtained. Which substances entered the bag and which
left? Support your answer with evidence from the experiment.
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Osmosis Lab
Biology
Objectives:
1. Prepare a wet mount slide of an Elodea (or celery) leaf
2. Observe an “normal” cell in tap water
3. Observe plasmolysis in the cell as salt solution is added to the wet mount.
4. Observe the reversal of plasmolysis as the salt solution is diluted.
5. Compare and diagram normal cells in tap water with plasmolyzed cells in salt
solution.
Materials:
Microscope
Tap water
Salt solution
coverslip
microscope slide
distilled water
elodea/celery
droppers
paper towel
Procedure:
1. Prepare a wet mount slide of an elodea/celery leaf using tap water.
2. Observe the leaf under both low and high powers. Note the location of the
chloroplasts in relation to the cell wall.
3. Draw a normal cell at 400x in the space provided for you.
4. Label chloroplast, cell wall and cell membrane.
5. Prepare a wet mount slide of an elodea leaf using salt water. Allow the slide to
sit for a couple of minutes.
6. Observe the leaf under both low and high powers. Again, note the location of the
chloroplasts in relation to the cell wall.
7. Draw a plasmolyzed cell at 400x in the space provided for you.
8. Label chloroplast, cell wall and cell membrane.
9. Use a clean dropper to add distilled water along the edge of the coverslip. Place
a piece of paper towel along the opposite edge of the coverslip. The paper towel
will “pull” the distilled water under the cover slip and across the elodea leave
(changing the type of solution the cell is in).
10. Note any changes from the plasmolyzed cell and draw the cell at 400x in the
space provided for you.
11. Label chloroplast, cell wall and cell membrane.
12. Clean up slide, put microscope away and answer the analysis questions.
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Drawings:
Tap Water/ 400X
Salt/ 400X
Distilled Water/400x
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Analysis Questions:
1. Describe the chloroplasts, cell wall and plasma membrane of the elodea in the tap
water.
2. Why does the cell look like this…in terms of osmosis.
3. What type of solution is this?
4. Describe the chloroplasts, cell wall and plasma membrane of the elodea in the salt
water solution.
5. What happened to the water inside the cell after it was put in the salt water?
6. What type of solution is this?
7. What happened to the cell when you placed the elodea in distilled water? (If
nothing happened…what should have happened in more time?)
8. What type of solution is this?
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Cell Transport: Review
Biology
1. Complete the following chart using your notes/book.
2. Then, using some poster board, draw a detailed picture of a cell membrane and show how
each type of transport takes place across that membrane. Please check the example in the
front of the room.
Name of Transport
Energy
Requirem
ent?
Substance(s)
Involved
Description and Concentration levels
Diffusion
Osmosis:
Hypotonic
Hypertonic
Isotonic
Facilitated Diffusion
Ion Channels
Sodium-Potassium Pump
Endocytosis/Exocytosis
(Pinocytosis/Phagocytosis)
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