Unit 4: Homeostasis and Diffusion
Standards Addressed:
BIO.A.4.1.1.Describe how the structure of the plasma
membrane allows it to function as a regulatory structure
and/or protective 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).
Concepts addressed:
BIO.A.4.1.3.Describe how membrane-bound cellular
organelles (e.g., endoplasmic reticulum, Golgi apparatus)
facilitate the transport of materials within a cell.
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.4.2.1.Explain how organisms maintain homeostasis
(e.g., thermoregulation, water regulation, oxygen
regulation).
2. Compare and contrast active vs. passive transport
mechanisms.
3. Describe how membrane-bound cellular organelles
facilitate intracellular transport of materials.
4. Explain mechanisms organism use to maintain
homeostasis.
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The Cell Membrane
Watch the Bozeman science video of Cellular Structure and Function
(http://www.youtube.com/watch?v=S7CJ7xZOjm0 ), write a reflective summary of the process of diffusion
and transport.
Draw and describe the phospholipid. Label the head and the tail and include the polar and nonpolar ends of the
molecule.
Describe how is the musk ox similar to the phospholipid?
Using the diagram below, answer questions that follow.
Why is the cell membrane model called the Fluid Mosaic Theory
What are the two major parts of the membrane?
What is the function of the proteins?
2
The phospholipid layers allow certain things through the membrane. What are they and why are they permitted
to go through the membrane?
How does glucose and water get through the membrane?
Describe an aquaporin. What type of biomolecule is the aquaporin?
Another type of membrane protein uses an active transport process to move molecules through the membrane.
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Cell Membrane
Interactive Construction
Name: ____________________________
Period: ________
This exercise introduces the dynamic complexes of proteins,
carbohydrates, and lipids that comprise cell membranes. You should
learn that membranes are fluid, with components that move, change,
and perform vital physiological roles as they allow cells to
communicate with each other and their environment.
Objectives:
! Learn the general components of a cell membrane.
! Build a membrane
! Determine the makeup and basis for membrane function
Go to the following link: http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP1101
Overview
The cell membrane is mainly composed of _______________ and _______________.
Its framework consists of a double layer of _______________. There are two major
types of proteins: tightly coiled, rod-shaped, _______________ proteins and the more
compact, globular-shaped _______________ proteins and _______________ proteins.
Name that Structure:
4
Because the membrane is mostly _______________, it only allows
_______________ -soluble substances, such as _______________,
_______________, and _______________, to go through. Water-soluble
substances, such as _______________, _______________
_______________, _______________, and _______________, need the help
of various proteins for transport.
Explain how the phospholipids form a bilayer for the cell membrane.
Label the hydrophilic and hydrophobic portions of the membrane
below.
Explain the function and location (where they are located within the
membrane) of fibrous proteins in the cell membrane.
Explain the function and location of pore proteins in the cell
membrane.
Explain the function and location of channel proteins in the cell
membrane.
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What does it mean to be a peripheral protein?
Name and describe the two types of peripheral proteins listed in the
activity.
What is the function of cholesterol?
True or False: all cell types contain cholesterol in their membrane.
Explain the location of cholesterol in the cell membrane.
Now take the quiz and build your membrane!
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7
iPad app
Name: ____________________
Cell Defense
The Plasma Membrane
Date: _____________________
Period: ___________
Directions: Read the steps here and all the information on the iPad screen. Follow all the
steps carefully filling in all the blanks.
Step 1: Click touch here to begin the app. You want to move to the “Choose Your
Challenge!” menu. From the menu choose “Build a Membrane!” Dr. Vial has a vile weapon
(note the play on words) that destroys plasma membranes. Without _______ ________________
cells of living things will die because they are unable to maintain _________________________.
Step 2: Zoom in on the plasma membrane. From the “Urgent Message” you learn that
phospholipids are a ________________ Head and __ __________ ________ TAILS.
The heads are _______________________________ which means ______________________________.
The tails are ________________________________ which means _______________________________.
The heads face out towards the ________________ and the tails facing ____________ _________.
Draw and label the phospholipid in the box:
Step 3: Repair the phospholipid membrane.
How many phospholipids did it take? _______
Step 4: What do you have to put into
the membrane in order to help stabilize it?
___________________________________ How many did you add? _____
Step 5: What is another word for selectively permeable? _________________________________.
What does that mean? __________________________________________________________________
________________________________________________________________________________________.
Step 6: What 2 molecules easily pass through the membrane? Record why for each.
Molecule 1
Molecule 2
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Step 7: What 3 molecules cannot easily pass through the membrane? Record why for each.
Molecule 1
Molecule 2
Molecule 3
What does polar mean?
Step 8: Insert channel proteins into the membrane. Transport substances across the
membrane. Note: You can only transport substances using channel proteins until there were
_________________________________________________________________________________________.
What is this process called?
Step 9: Moving from ______ to _______ concentration requires the use of energy to _________
substances. This is called ______________________________ transport and uses: (place answer in table)
1.
2.
Which is cell ______________
Step 10: Carbohydrates are like identification badges. Cells that have different membrane
carbohydrates do different ________________. The immune system uses the carbohydrates to
_____________________ that your cells belong to ________ and are not ______________________,
____________________, or other foreign cells.
What does the immune system do to foreign invaders?
What kind of cell does this?
Step 11: Next take the “Membrane Structure Challenge!”
Step 12: Take the “Diffusion Challenge!”
Step 13: Take the “Energy and Transport Challenge!”
How many ATP did you use? ______ What type(s) of protein(s) were used? __________________
_________________________________Explain when each type was used._______________________
__________________________________________________________________________________________
Step 14: Take the “Osmosis Challenge!”
What is Osmosis? _________________________________________________________________________
What is the name of the special proteins that let water pass through? ______________________
Is this passive or active transport? ______________________________________
Step 15: From your Scores Sheet record:
Lab Score (% correct): ____________
Number Correct:
_______
Number Incorrect:
_______
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Cell Membrane Structure and Function
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Chapter 5 - Membrane Structure and Function
The Plasma Membrane
fluid mosaic model, semi-permeable (selectively permeable), double layer of phospholipids with embedded proteins
Jobs of the cell membrane
Isolate the cytoplasm from the external environment
Regulate the exchange of substances
Communicate with other cells
Identification
Phospholipids (fats) contain a hydrophilic head and a nonpolar hydrophobic tail, which creates a barrier.
Cholesterol - stiffens the membrane by connecting phospholipids
Glycolipids - signal molecules
Glycoproteins - have an attached chain of sugar (antibodies)
Proteins embedded in membrane serve different functions
1. Channel Proteins - form small openings for molecules to difuse through
2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell, (gated channels)
3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel
proteins)
4. Cell Recognition Proteins - ID tags, to idenitfy cells to the body's immune system
5. Enzymatic Proteins - carry out metabolic reactions
Transport Across Membrane
-The membrane is selectively permeable (also called semipermeable )
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Cell Membrane Structure and Function
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- Small particles, or particles with no charge can pass through the bilayer (carbon dioxide and oxygen)
- Water has a charge, does not easily cross the membrane - a channel protein, Aquaporin helps water across
Passive Transport
Simple Diffusion - water, oxygen and other molecules move from areas of high concentration to areas of low concentration,
down a concentration gradient
Facilitation Diffusion - diffusion that is assisted by proteins (channel or carrier proteins)
Osmosis - diffusion of water
Solutions: Hypertonic | Isotonic | Hypotonic
Contractile vacuoles can help pump out excess water in freshwater organisms
The central vacuole of plants can store excess water, creating a turgor pressure; plants are less likely to burst due to cell
walls
Active Transport
- involves moving molecules "uphill" against the concentration gradient, which requires energy (ATP)
Endocytosis - taking substances into the cell (pinocytosis for water, phagocytosis for solids)
Exocytosis - pushing substances out of the cell, such as the removal of waste
Sodium-Potassium Pump - pumps out 3 sodiums for ever 2 potassium's taken in against gradient
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Bozeman Biology
Transport across Cell Membranes video
http://bit.ly/WIoQ4x
1. Does the movement of molecules to fill the room require energy?
_____________________________________________________________________
_____________________________________________________________________
2. What are the two forms of transport?
a. ______________________________________________
b. ______________________________________________
3. What is Diffusion and describe an example in living systems.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
4. What is specific to Osmosis?
_____________________________________________________________________
_____________________________________________________________________
5. What is a specific type of diffusion that requires proteins called?
_____________________________________________________________________
_____________________________________________________________________
6. What substance is needed for active transport?
_____________________________________________________________________
_____________________________________________________________________
7. What is large scale active transport? Give two examples:
_____________________________________________________________________
_____________________________________________________________________
Honors Biology
Mathew
12
1
8. When the gray and black particles move, what determines in what
direction do they go? is this ordered movement?
_____________________________________________________________________
_____________________________________________________________________
9. Where can diffusion be seen in living systems?
_____________________________________________________________________
_____________________________________________________________________
10.
Define Osmosis.
_____________________________________________________________________
_____________________________________________________________________
11.
Describe the U-tube experiment:
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
12.
Why does the slug shrivel up?
_____________________________________________________________________
_____________________________________________________________________
13.
Describe the significance of Osmosis with respect to red blood cells
in different concentrations of water.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
14.
Define Hypertonic
Honors Biology
Mathew
13
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_____________________________________________________________________
_____________________________________________________________________
15.
Define Isotonic
_____________________________________________________________________
_____________________________________________________________________
16.
Define hypotonic
_____________________________________________________________________
_____________________________________________________________________
17.
Define facilitated diffusion.
_____________________________________________________________________
_____________________________________________________________________
18.
What is the difference between diffusion and facilitated diffusion?
_____________________________________________________________________
_____________________________________________________________________
19.
What is a concentration gradient?
_____________________________________________________________________
_____________________________________________________________________
20.
Describe how glucose enters the cell.
_____________________________________________________________________
_____________________________________________________________________
21.
What is co-transport? describe an example.
_____________________________________________________________________
_____________________________________________________________________
22.
What is active transport?
_____________________________________________________________________
_____________________________________________________________________
Honors Biology
Mathew
14
3
23.
Describe how the sodium potassium pump works.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
24.
What is the ATP : Na : K ratio?
_____________________________________________________________________
_____________________________________________________________________
25.
What is endocytosis? Describe how does it take place.
_____________________________________________________________________
_____________________________________________________________________
26.
What could a phagosome be called as well? (Not in the video)
_____________________________________________________________________
_____________________________________________________________________
27.
What is exocytosis?
_____________________________________________________________________
_____________________________________________________________________
28.
Describe an example of this.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Honors Biology
Mathew
15
4
Topic 3: Cell Transport
Diffusion Introduction
Water and small, non-charged molecules have no difficulty crossing the
lipid portion of the membrane. Ions and charged molecules cannot cross
easily, nor can large molecules. It is important that many types of
substances be able to enter or leave cells. There is a variety of
mechanisms by which this occurs, some requiring energy and some
utilizing carrier proteins.

Lipid ‐ Organic compound that is insoluble in water; notably fats, oils, and steroids. Ions ‐ Atom or group of atoms carrying a positive or negative charge. Energy ‐ Capacity to do work and bring about change; occurs in a variety of forms. Carrier Protein ‐ Protein molecule that combines with a substance and transports it through the plasma membrane. 


Gas Exchange in the Lungs of Humans
Gas exchange in the lungs occurs by diffusion. Carbon dioxide (CO2) will follow its
concentration gradient into the alveolus, oxygen (O2) will follow its concentration
gradient into the capillary.


Alveolus ‐ (pl, alveoli) ‐ Air sac of a lung. Capillary ‐ Microscopic vessel connecting arterioles to venules and through the thin walls of which substances either exit or enter blood. Osmosis
Osmosis is the diffusion of water across a membrane. Like other molecules, water will move from an area of high concentration
to an area of low concentration. The more solute there is in a solution, the lower the concentration of water in that solution.
There is terminology to describe concentration differences between two solutions. A solution with higher solute concentration is
hypertonic relative to one with lower solute concentration. Conversely, a solution with lower solute concentration is hypotonic
relative to one with higher solute concentration. If two solutions have the same concentration they are isotonic. Water will move
from a hypotonic to a hypertonic solution.





Osmosis - Movement of water from an area of higher concentration of water to an area of lower
concentration of water across a differentially permeable membrane.
Diffusion - Movement of molecules from a region of higher concentration to a region of lower
concentration.
Solute - Substance dissolved in a solvent to form a solution.
Hypertonic - Solution that has a higher concentration of solute and a lower concentration of water than
the cell.
Hypotonic - Solution that has a lower concentration of solute and a higher concentration of water than the
cell.
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Facilitated Diffusion
Both simple and facilitated diffusion involve a substance following its concentration gradient, from high to low
concentration. If the substance is lipid soluble, it readily passes through the membrane. If it is not lipid soluble,
it can cross the membrane only with a specific carrier protein.
Active Transport
Introduction
Active transport involves a protein which uses ATP
to pump molecules against their concentration
gradients. The same protein may be used to pump
two different substances in opposite directions. This
is the case for the very important sodium-potassium
pump.



Active Transport ‐ Transfer of a substance into or out of a cell from a region of lower concentration to a region of higher concentration by a process that requires a carrier and an expenditure of energy. ATP ‐ Adenosine Triphosphate (ATP) ‐ Nucleotide with three phosphate groups. The breakdown of ATP into ADP 1 Pj makes energy available for energy‐requiring processes in cells. Sodium‐Potassium Pump ‐ Transport protein in the plasma membrane that moves sodium ions out of and potassium ions into animal cells; important in nerve and muscle cells. 17
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HOMEOSTASIS AND TRANSPORT
All Materials © Cmassengale
I. Cell Membranes
A. Cell membranes help organisms maintain homeostasis by controlling
what substances may enter or leave cells
B. Some substances can cross the cell membrane without any input of
energy by the cell
C. The movement of such substances across the membrane is known as
passive transport
D. To stay alive, a cell must exchange materials such as food, water, &
wastes with its environment
E. These materials must cross the cell or plasma membrane
F. Small molecules like water, oxygen, & carbon dioxide can move in and
out freely
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G. Large molecules like proteins & carbohydrates cannot move easily
across the plasma membrane
H. The Cell Membrane is semipermeable or selectively permeable only
allowing certain molecules to pass through
II. Diffusion
A. Diffusion is the movement of molecules from an area of higher
concentration to an area of lower concentration
B. Small molecules can pass through the cell membrane by a process called
diffusion
C. Diffusion across a membrane is a type of passive transport because it
does not require energy
D. This difference in the concentration of molecules across a membrane is
called a concentration gradient
E. Diffusion is driven by the kinetic energy of the molecules
F. Kinetic energy keeps molecules in constant motion causing the
molecules to move randomly away from each other in a liquid or a gas
G. The rate of diffusion depends on temperature, size of the molecules,
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& type of molecules diffusing
H. Molecules diffuse faster at higher temperatures than at lower
temperatures
I. Smaller molecules diffuse faster than larger molecules
J. Most short-distance transport of materials into & out of cells occurs by
diffusion
K. Solutions have two parts --- the solute which is being dissolved in the
solvent
L. Water serves as the main solvent in living things
M. Diffusion always occurs down a concentration gradient (water moves
from an area where it is more concentrated to an area where it is less
concentrated)
N. Diffusion continues until the concentration of the molecules is the
same on both sides of a membrane
O. When a concentration gradient no longer exists, equilibrium has been
reached but molecules will continue to move equally back & forth
across a membrane
III. Osmosis
A. The diffusion of water across a semipermeable membrane is called
osmosis
B. Diffusion occurs from an area of high water concentration (less solute)
to an area of lower water concentration (more solute)
C. Movement of water is down its concentration gradient & doesn’t
require extra energy
D. Cytoplasm is mostly water containing dissolved solutes
E. Concentrated solutions have many solute molecules & fewer water
molecules
F. Water moves from areas of low solute concentration to areas of high
solute concentration
G. Water molecules will cross membranes until the concentrations of water
& solutes is equal on both sides of the membrane; called equilibrium
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H. At equilibrium, molecules continue to move across membranes
evenly so there is no net movement
I. Hypertonic Solution
1. Solute concentration outside the cell is higher (less water)
2. Water diffuses out of the cell until equilibrium is reached
3. Cells will shrink & die if too much water is lost
4. Plant cells become flaccid (wilt); called plasmolysis
J. Hypotonic Solution
1. Solute concentration greater inside the cell (less water)
2. Water moves into the cell until equilibrium is reached
3. Animal cells swell & burst (lyse) if they take in too much water
4. Cytolysis is the bursting of cells
5. Plant cells become turgid due to water pressing outward against cell
wall
6. Turgor pressure in plant cells helps them keep their shape
7. Plant cells do best in hypotonic solutions
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K. Isotonic Solutions
1. Concentration of solutes same inside & outside the cell
2. Water moves into & out of cell at an equal rate so there is no net
movement of water
3. Animal cells do best in isotonic solutions
IV. How Cells Deal With Osmosis
A. The cells of animals on land are usually in isotonic environment
(equilibrium)
B. Freshwater organisms live in hypotonic environments so water
constantly moves into their cells
C. Unicellular freshwater organisms use energy to pump out excess water
by contractile vacuoles
D. Plant cell walls prevent plant cells from bursting in hypotonic
environments
E. Some marine organisms can pump out excess salt
V. Facilitated Diffusion
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A. Faster than simple diffusion
B. Considered passive transport because extra energy not used
C. Occurs down a concentration gradient
D. Involves carrier proteins embedded in a cell’s membrane to help move
across certain solutes such as glucose
E. Carrier molecules change shape when solute attaches to them
F. Change in carrier protein shape helps move solute across the membrane
G. Channel proteins in the cell membrane form tunnels across the
membrane to move materials
H. Channel proteins may always be open or have gates that open & close to
control the movement of materials; called gated channels
I. Gates open & close in response to concentration inside & outside the cell
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VI. Active Transport
A. Requires the use of ATP or energy
B. Moves materials against their concentration gradient from an area of
lower to higher concentration
C. May also involve membrane proteins
D. Used to move ions such as Na+, Ca+, and K+ across the cell membrane
E. Sodium-Potassium pump moves 3 Na+ out for every 2 K+ into the cell
1. Causes a difference in charge inside and outside the cell
2. Difference in charge is called membrane potential
F. Ion pumps help muscle & nerve cells work
G. Plants use active transport to help roots absorb nutrients from the soil
(plant nutrients are more concentrated inside the root than outside)
VII. Bulk Transport
A. Moves large, complex molecules such as proteins across the cell
membrane
B. Large molecules, food, or fluid droplets are packaged in
membrane-bound sacs called vesicles
C. Endocytosis moves large particles into a cell
D. Phagocytosis is one type of endocytosis
1. Cell membrane extends out forming pseudopods (fingerlike projections)
that surround the particle
2. Membrane pouch encloses the material & pinches off inside the cell
making a vesicle
3. Vesicle can fuse with lysosomes (digestive organelles) or release their
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contents in the cytoplasm
4. Used by ameba to feed & white blood cells to kill bacteria
5. Known as "cell eating"
E. Pinocytosis is another type of endocytosis
1. Cell membrane surrounds fluid droplets
2. Fluids taken into membrane-bound vesicle
3. Known as "cell drinking"
F. Exocytosis is used to remove large products from the cell such as wastes,
mucus, & cell products
G. Proteins made by ribosomes in a cell are packaged into transport
vesicles by the Golgi Apparatus
H. Transport vesicles fuse with the cell membrane and then the proteins are
secreted out of the cell (e.g. insulin)
BACK
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Diffusion & Osmosis Name: ____________________________
Practice
Period: ________
Fill in the blanks
1. A __________________________ membrane only allows some materials to enter.
2.
Molecules move in a ________________ fashion.
3. A cell membrane has two __________________ layers embedded with ___________.
4. Molecules naturally move from __________ concentration to __________ concentration.
5.
__________________ is the movement of molecules to a condition of equilibrium.
6. To move molecules, cells use energy in the form of ________________.
7. Using energy to move molecules across a membrane is ______________ _______________.
8. The speed of diffusion can be raised by increasing the ______________________.
9. The movement of water across a cell membrane is ___________________.
10. Complete the following sentence: _________________ is the movement of particles from
_________________ concentration to a _________________ concentration until they are
_________________ spread out.
11. Complete the following sentence: Osmosis is the passage of _________________ molecules from a
_________________ concentrated solution to a _________________ concentrated solution through
a _________________ permeable membrane.
Diffusion Questions
1. These are pictures of molecules frozen at two different times. Draw arrows to show the
direction each particle might travel due to diffusion in diagrams A and B.
A.
B.
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2. Describe the way the particles of a gas move. _______________________________________
_________________________________________________________
3. Diagram A shows the same number of particles as in Diagram B except most particles start out
on one side of the box. Explain why after a while, Diagram A resembles Diagram B. ________
_________________________________________________________
_________________________________________________________
4. Give an everyday example of diffusion in air and in water.
• AIR: _________________________________________________________________
•
WATER: _______________________________________________________________
Osmosis Questions
5. The roots of a plant have root hair cells
that absorb water from the soil. The
diagram shows two different kinds of
roots. The concentration of the solution
inside the cell is higher than the
concentration of the solution in the soil.
• Explain why water moves from
the soil into the root hair cell.
•
Suggest why root hair cells are long and thin and not short and stubby?
6. Strawberry jelly is a very strong solution of sugar. By contrast the cytoplasm in a bacteria is a
much weaker solution.
• The cell wall of a microbe is made up of a semi-permeable membrane. Would water flow
from the microbe to the jam, or from the jam to the microbe by osmosis?
•
Explain why bacteria find it difficult to survive in jam.
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7. Below are animal cells placed in beakers of various concentrations.
1. Draw an arrow to show which way the water would move by osmosis
2. Fill in any missing percentages (water or solute)
3. Write the type of solution OUTSIDE of each cell ABOVE each beaker (isotonic, hypertonic,
or hypotonic)
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8. For each of the following, do these things.
• Determine the solute and solvent for the solution outside the cell (environment) and for the
inside of the cell. Then…
A. Tell whether the solution outside the cell is hypotonic, hypertonic, or isotonic.
B. Tell what will happen to the cell (shrink or swell).
C. Give the direction of the net movement of water (into cell, out of cell, or into & out of
cell at equal rates).
20 % solute
___ % solvent
80 % solute
___ % solvent
A.
B.
C.
___ % solute
10 % solvent
___ % solute
90 % solvent
A.
B.
C.
40 % solute
___ % solvent
30 % solute
___ % solvent
A.
B.
C.
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Passive Transport Practice!!!!
(Diffusion and Osmosis)
1. The drawing to the right represents an overhead view of a
closed box. At one end of this box are placed a few drops of
ammonia. Ammonia is a gas, and at room temperature its
molecules are in constant motion. Will all of the ammonia
remain at one end of the box? ________
Ammonia
Molecules
2. Is it likely that all of the ammonia molecules will move to the opposite side of the
box, leaving the original end of the box empty? _______
3. Draw dots to show how the molecules of ammonia might be
distributed in the box after several minutes of motion.
4. Initially the overall movement of molecules was from (high to
low / low to high . Circle your answer
5. Define diffusion.
_____________________________________________________
_____________________________________________________
6. This time, when the ammonia is placed at one end of the box,
a thin membrane is stretched across the middle of the box.
This membrane is SEMI-PERMEABLE and has pores in it
that allow the passage of ammonia molecules. Will some of
the ammonia molecules eventually reach the opposite side of
the box? ________
Semi-permeable
membrane
Ammonia
Molecules
7. Is it likely that the ammonia will eventually reach equilibrium? _______
8. How will the ammonia molecules will move through the membrane:
- from top to bottom
- from bottom to top
O2
O2
O2
CO2
O2
O2
O2
O2
O2
O2
CO2
CO2
O2
CO2
9. To the left is an animal cell. It is bounded by a cell membrane
which contains pores through which small molecules, (like CO2,
H2O and O2), may pass. Inside, this cell contains many
molecules of CO2 but the water outside the cell is rich in oxygen.
Are these molecules likely to be in motion? _____
CO2
10. As the molecules of oxygen and carbon dioxide begin to move,
is it likely that some of them will pass through the pores in the
cell membrane? _______
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11. Will ALL of the oxygen pass through the membrane to the inside of the cell? _____
12. After several minutes of molecular motion, equilibrium will be reached.
molecules to show how they would appear at this time.
Draw the
13. When the carbon dioxide molecules first began to move, more molecules passed
through the membrane
- from inside to outside
- from outside to inside
14. When the oxygen molecules first began to move, more molecules move:
- from inside to outside
- from outside to inside
15. The movement of molecules from where they are in ______ concentration to an
area where they are in _____ concentration is called DIFFUSION. Can diffusion
occur through a cell membrane? _______
16. OSMOSIS is a special kind of diffusion in which water diffuses through a semipermeable membrane. Water molecules move from an area of ___ water
concentration to an area of ___ water concentration.
17. To the right is a cell; the concentration of water inside and outside the
membrane are shown. Water will tend to move ___ the cell.
97%
H2 0
95%
H2 0
18. Under these conditions the cell will increase in size. What may happen
if the membrane cannot stretch to accommodate this?
________________________________
19. The cell to the right would
- lose water and shrink - gain water and expand
90%
H2 0
95%
H2 0
20. In living organisms, concentrations of salt (NaCl), or other dissolved
substances often causes differences in water concentration. A cell with
5% salt would have _____% water.
21. Dissolved substances like salt, due to positive or negative charges, and sugar, due
to large molecular size, will not pass through the pores of a membrane. In most
cells, dissolved substances occupy 3% of cell fluid, so the concentration of water is
about ____.
a. What substances do not diffuse through the cell membrane and why?
_____________________________________________________
_____________________________________________________
b. If a cell is placed into 100% water, what would happen to it? _________
31
c. Would this solution be considered hypertonic or hypotonic? __________
d. If a cell is placed into 6% sugar water, what would happen to it? ________
e. Would this solution be considered hypertonic or hypotonic? __________
22. The body fluids outside human cells are often rich in water, salt, sugar, and
oxygen. Which of these can enter the cell by diffusion? _____________________
23. Would water move into or out of the cell in the following:
a. A cucumber in salt water ________
b. A snail that had salt poured on it _______
c. Vegetables that are sprinked with water _______
24. Look at the diagrams below and draw an arrow showing which way the water
moves. Note: The dots are representing salt, which as mentioned above, cannot
move through the cell membrane.
25. Draw a cell that’s in an isotonic solution.
26. If the cell expends energy to move molecules across its membrane, this is called
ACTIVE TRANSPORT. Which of the following might require active transport (circle
your answer)?
A. movement from low to high concentration
C. ions or charged particles
B. molecules too large to pass through pores
D. all of these
27. The proteins of the cell membrane are very important to active transport. They can
cause molecular movement through the membrane that ______ cannot take care of.
28. Cells expend energy by using ATP molecules. The carrier proteins of the
membrane utilize _____ as a source of energy for active transport.
32
29. To the right are shown three stages in the operation of a carrier protein. What
happens to the shape of the carrier molecule during
Protein
this process?
I
I
I
30. What is the source of the energy needed to
change this shape?
II
I
inside
31. Cells of the human thyroid gland have much higher concentrations of iodine than in
the rest of the body. How did they manage to concentrate iodine to such a degree?
32. If yeast cells are placed in a dye called phenol red, they do not become colored by
this dye. If the yeast is killed by boiling, and then the dye is added, the yeast cells turn
red. What would explain this (circle your answer)?
A. live yeast cells expel phenol red by active transport as it enters by diffusion
B. dead yeast cell membranes cannot use ATP to conduct active transport
33. Complete the table by choosing whether water would be lost, water would be gained
or the amount of water in the cell would remain the same. Assume that the cell is made
only of water and the dissolved particles, (like salt and sugar), called SOLUTE. Also
assume that the solute CANNOT diffuse through the membrane.
water lost, water gained, or unchanged
Cell
97% water
Surroundings
90% water
97% water
100% water
3% solute
1% solute
3% solute
90% water
97% water
5% solute
3% solute
10% solute
3% solute
100% water
34. IMPORTANT: In each case, is the overall movement of water to where the solute
concentration is low or to where the solute concentration is high? EXPLAIN!
35. Test question: What happens to a cell that is put into a highly concentrated solution?
33
Analyzing Experiments Name: _________________________________
Applying Osmosis and Diffusion
Period: __________
EXPERIMENT A
A selectively permeable membrane separates the solutions in the arms of the
U-tube shown at right. The membrane is permeable to water and to substance
A but not to substance B. Forty grams of substance A and 20 g of substance B
have been added to the water on side 1 of the U-tube. Twenty grams of
substance A and 40 g of substance B have been added to the water on side 2
of the U-tube.
Read each question, and write your answer in the space provided.
1. Draw the set-up of the U-tube, indicating the solutes on each side.
2. When the system reaches equilibrium, how many grams of substance A will be in solution on
side 1 of the U-tube? How many grams of substance A will be in solution on side 2? Explain.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
3. When the system reaches equilibrium, how many grams of substance B will be in solution on
side 1 of the U-tube? How many grams of substance B will be in solution on side 2? Explain.
_____________________________________________________________
_____________________________________________________________
4. What will happen to the water level in the U-tube? Explain.
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
5. Draw the U-tube after equilibrium has been established.
34
EXPERIMENT B
The cell membrane of red blood cells is permeable to water but not to sodium chloride (NaCl).
Suppose that you have three flasks:
! Flask X contains a solution that is 0.5 percent NaCl.
! Flask Y contains a solution that is 0.9 percent NaCl.
! Flask Z contains a solution that is 1.5 percent NaCl.
To each flask, you add red blood cells, which contain a solution that is 0.9 percent NaCl.
Read each question, and write your answer in the space provided.
6. What will happen to the red blood cells in flask X? Draw what they will look like and name
the type of solution that they were placed in.
________________________________________
________________________________________
________________________________________
7. What will happen to the red blood cells in flask Y? Draw what they will look like and name
the type of solution that they were placed in.
________________________________________
________________________________________
________________________________________
8. What will happen to the red blood cells in flask Z? Draw what they will look like and name
the type of solution that they were placed in.
________________________________________
________________________________________
________________________________________
35
NAME _________________________________ HR ______ DATE __________
DIFFUSION and OSMOSIS VIRTUAL LAB
http://www.phschool.com/science/biology_place/labbench/lab1/intro.html
INTRODUCTION:
The processes of diffusion and osmosis account for much of the passive
movement of molecules at the cellular level.
In this laboratory, you will study some of the basic principles of molecular
movement in solution and perform a series of activities to investigate these
processes.
Click “Next”
KEY CONCEPTS:
1. Define the following terms, if needed click the term to use the glossary
Diffusion
Concentration Gradient
2. What example is used to explain diffusion?
Click “next concept”
3. Define Osmosis
Click “closer look”
Read the information
4. Draw the image then Click “animate”
36
5. Draw the image after animating
6. Explain how/why the water will move
Click “next concept”
7. Explain molecule movement in a solution with several different types of
molecules.
8. Is it possible for molecules to move in both directions?
Click “closer look”
Read the information
Click “animate”
9. Explain the movement of
Starch
Iodine
Water
Click “next concept”
Read the information
Click “annotate”
37
10. Identify which molecules can move through the cell membrane by
completing the table
MOLECULE
Water
Can the molecule move through the cell
membrane?
YES
NO
Sugar
Protein
Waste
Fat
Click “next concept”
11. What are the three terms (hypotonic, hypertonic, and isotonic) used to
compare?
13. Define
Hypotonic
Hypertonic
14. Draw, label, and explain water movement in the first illustration.
15. Define Isotonic
16. Will there be a net movement of water between two isotonic solutions?
Explain
Click “next concept”
38
17. Define Water potential
18. What two factors affect water potential?
Click “animate” for the red blood cell
19. Using this animation, explain water potential
20. Why don't red blood cells pop in the bloodstream?
Click “animate” for the plant cell
21. Explain why the plant cell does not “pop”
Click “next concept”
Skip calculating water potential
Click “next concept”
22. What is the water potential of pure water?
39
40
41
Amoeba Sisters Video Recap of Osmosis
1. The below picture represents diffusion of molecules.
Place the following labels in the diagram: high
concentration, low concentration, and an arrow showing
the direction that the molecules would travel before
equilibrium is reached.
2. Osmosis is a type of diffusion, but it involves the
movement of water. Similar to diffusion, osmosis is the
movement of molecules (water molecules if osmosis) from a
high concentration to a low concentration.
The video clip explains that you can also look at water as
moving to a __________________________________
concentration of solute molecules.
Why can it also be viewed this way?
3. Osmosis Scenario: The video clip mentioned a disaster
scenario of a saltwater fish being placed in fresh water.
4. Osmosis Scenario: Fluid movement into the brain
after traumatic brain injury can result in dangerous brain
swelling.
What would occur if, instead, a freshwater fish was placed
in saltwater?
Your answer needs to have an arrow indicating the
direction of water flow in osmosis, a label for
“hypertonic,” and a label for “hypotonic.”
One treatment that can be used in some of these cases is
adding a ______________________________ saline. You
need to decide whether this blank should be the word
hypertonic or hypotonic. Remember, you are trying to
reduce the excessive fluid in the brain.
Explain your answer:
42
The Gummy Bear Mystery
Do you like gummy bears? We do!
They are one of our favorite snacks,
though we (try) to eat them in
moderation because they are high in
sugar. Consider that your sister is in
a foul mood and decides to dump
your gummy bears in your ice water
about 30 minutes before you get
home.
The gummy bears are greatly
enlarged by the time you get home!
Your sister and some friends have
different viewpoints for what
happened. Draw a diagram below
showing the enlarged gummy bears
in a cup of water. Place the labels
“hypertonic” and “hypotonic” in
your diagram. One label should be
for the gummy bears and one label
should be for the water.
5.
Viewpoints:
6. Whose viewpoint is correct in the
viewpoint column? A good answer
A) Your sister said that the sugar
has a good defense! Defend your
left the gummy bears,
answer, and also give reasons why
because the gummy bears
the other explanations are incorrect.
were hypertonic compared
to the water.
B) Your friend Joe said that
water traveled into the
gummy bears, because the
gummy bears were
hypertonic compared to the
water.
C) Your friend Suzy said the
sugar went into the gummy
bears, because the gummy
bears were hypotonic
compared to the water.
D) Your friend Will said that
water traveled into the
gummy bears by osmosis,
because the gummy bears
were hypotonic compared to
the water.
Hypertonic, Hypotonic, or Isotonic? Oh My!
These red blood cells have all been placed in different solutions! Based on their appearance after being placed in these
solutions for a period of time, place on each line (A) for hypertonic, (B) for hypotonic, or (C) for isotonic.
7. The cells are_________________
compared to the ________________
solution.
8. The cells are_________________
compared to the ________________
solution.
43
9. The cells are_________________
compared to the ________________
solution.
Osmosis Lab
Pre-lab discussion:
Osmosis is the movement of water molecules through a semi-permeable membrane from an area of high
concentration to an area of low concentration.
Iodine is a very small molecule. It can easily move through small holes in a membrane through passive transport from an area of high concentration to an area of low concentration. Corn starch molecules are very large.
Materials:
A. About 1 quarts of water.
B. Iodine (CAUTION! Iodine is a POISON if ingested! Wash thoroughly if you get it on your skin!)
C. Corn starch solution.
D. One length of permeable dialysis membrane and string/thread.
E. 1 beaker and 1 water dropper bottle
Procedure:
1. Place about 100 mL water in beaker.
2. Add 5 drops of iodine to the water in the beaker.
3. Tie off one end of the dialysis tubing with a string. Put 3-5 pipettes of cornstarch mixture into the membrane
and tie off the other end with a second string. Rinse the outside of the membrane off thoroughly. Pat dry with a
towel.
4. Weigh the membrane and record in your data.
5. Carefully place the membrane in beaker making sure the sealed top is in the water.
6. Sit back and wait for about 10 minutes.
7. Remove the filled membrane and observe the results.
8. Pat dry with a towel and weigh the membrane. Record the second weight in the data.
9. Observe beaker. If the iodine moves into the membrane through microscopic openings, the starch solution will
start turning black (or dark blue).
Data:
Analysis:
Q 1: Cells are surrounded by semi-permeable membranes. How could you tell if a plant cell lost water?
Q 2: Why did you rinse off the membrane before placing the membrane into the beaker with water and iodine?
Q 3: How can you tell if the iodine moves from the membrane to the corn starch, or if the corn starch moves from the
beaker/jar into the membrane?
Q 4: What was the difference in weight of the membrane? Did the membrane gain or lose mass? How do you account
for the difference in mass?
Q 5: Did the cornstarch move into or out of the membrane? Why or why not? What is your evidence?
Q 6: Did diffusion occur? Which molecules diffused? Did they diffuse into the membrane or out of the membrane?
Q 7: Did water move into or out of the membrane? Why or why not? What is your evidence?
Q 8: Did osmosis occur? Which molecules move in the process of osmosis? What is your evidence?
Q 9: In which concentration direction does diffusion and osmosis occur? Is this passive or active transport? Why?
Q 10: Summarize your observations about diffusion and osmosis by stating from which areas of concentration the
molecules moved. Give evidence for your observations and statements.
44
CELLS & TONICITY
Instructions
For a 3-Tab Foldable
Diagrams:
1. Fold a sheet of paper like a hot dog.
2. With the paper horizontal, and the fold
of the hot dog up, fold the right side
toward the center, trying to cover one
half of the paper.
3. NOTE: If you fold the right edge over
first, the final graphic organizer will
open and close like a book.
4. Fold the left side over the right side to
make a book with three folds.
5. Open the folded book. Place your hands
between the two thicknesses of paper
and cut up the two valleys on one side
only. This will form three tabs.
FRONT SIDE OF TABS (left to right):
1. Use Capital letters and label the top of each tab as follows --Tab 1 – HYPERTONIC, Tab 2 – ISOTONIC, and Tab 3 – HYPOTONIC.
45
2. SKETCH a CELL in the center of each tab and label it CELL. Be sure to draw it large enough to write
the percent salt and percent water it contains.
3. On the BOTTOM OF EACH TAB, print the word environment.
4. TAB 1
 DRAW A CELL that has a 10% NaCl (salt) solution in an ENVIRONMENT with a 15% salt
solution.
 COLOR the cell yellow and the environment light blue.
 In RED INK, write the percent of water inside and outside the cell.
 Use RED INK, and draw arrows showing the direction of movement of water into or out of the
cell.
5. TAB 2
 DRAW A CELL that has a 10% NaCl (salt) solution in an ENVIRONMENT with a 10% salt
solution.
 COLOR the cell yellow and the environment light blue.
 In RED INK, write the percent of water inside and outside the cell.
 Use RED INK, and draw arrows showing the direction of movement of water into or out of the
cell.
6. TAB 3
 DRAW A CELL that has a 6% NaCl (salt) solution in an ENVIRONMENT with a 3% salt solution.
 COLOR the cell yellow and the environment light blue.
 In RED INK, write the percent of water inside and outside the cell.
 Use RED INK, and draw arrows showing the direction of movement of water into or out of the
cell.
INSIDE OF FOLDABLE (NOT THE BACK OF THE TAB)
7. Use a ruler and draw two lines that divide the inside of your foldable into 3 sections.
8. BE SURE TO UNDERLINE THE MISSING TERM(S).
9. In SECTION 1, bullet and answer each of the following questions about HYPERTONIC solutions:
 In HYPERTONIC solutions, water moves _____________ the cell.
 Hypertonicity causes cells to ___________.
 Plants cells _________ water and start to _W_ ___ ___ ___.
 The process of water moving out of a cell is called P__________.
9. In SECTION 2, bullet and answer each of the following questions about ISOTONIC solutions:
 ________ cells need isotonic solutions to be at homeostasis.
 Water DOES or DOES NOT stop moving.
 Cells reach a point called Dynamic _____________ in isotonic solutions.
 Equal amounts of water are ___________ and _________ the cell.
10. In SECTION 3, bullet and answer each of the following questions about HYPOTONIC solutions:
 In HYPOTONIC solutions, water moves __________ a cell.
 Animal cells __________ in size and _________ or lyse in these solutions
 Bursting of cells is called C_________.
 ___________ cells need this tonicity to be at homeostasis.
 ________ _________ results from water inside a plant cell pushing the cell membrane out
against the plant’s cell wall.
46
NAME______________________ DATE_________ PERIOD_________
Cell Membrane Coloring Worksheet
Composition of the Cell Membrane & Functions
The cell membrane is also called the _______________
membrane and is made of a phospholipid _____________. The
phospholipids have a hydrophilic (water attracting) __________ and
two hydrophobic (water repelling) ____________. The head of a
phospholipid is made of an alcohol and __________ group, while the
tails are chains of ____________. Phospholipids can move
_______________ and allow water and other _________ molecules
to pass through into or out of the cell. This is known as simple
____________ because it does not require __________ and the
water or molecules are moving __________ the concentration
gradient. SKETCH AND LABEL a phospholipid coloring the heads red
and the tails blue.
PHOSPHOLIPID
Another type of lipid in the cell membrane is ______________
that makes the membrane more fluid. Embedded in the phospholipid
bilayer are __________ that also aid in diffusion and in cell
recognition. Proteins called _____________ proteins go all the way
through the bilayer, while ____________ proteins are only on one
side. Integral proteins are also called __________ proteins. Large
molecules like ___________ or carbohydrates use proteins to help
move across cell membranes. Some of the membrane proteins have
carbohydrate __________ attached to help cells in recognize each
other and certain molecules.
47
List 4 functions of the cell or plasma membrane:
a.
_________________________________________
b.
_________________________________________
c.
_________________________________________
d.
_________________________________________
Correctly color code and identify the name for each part of the cell
membrane.
Letter
Name/Color
_____ Phospholipid bilayer (no
color)
_____ Integral protein (pink)
_____ Fatty acid tails
(orange)
_____ Phosphate heads
(yellow)
Letter
_____
_____
_____
Name/Color
Peripheral protein
(red)
Cholesterol (blue)
Glycoprotein (green)
_____
Glycolipids (purple)
48
Match the cell membrane structure or its function with the correct
letter from the cell membrane diagram.
Letter
_____
_____
_____
Structure/Function
Attracts water
Helps maintain
flexibility of membrane
Involved in cell-to-cell
recognition
Letter
Structure/Function
_____
_____
Repels water
_____
Help transport certain
materials across the cell
membrane
Make up the bilayer
Osmosis and Tonicity
Define osmosis. _____________________________________
In which direction does water move across membranes, up or down the
concentration gradient? ________________
Define these 3 terms:
a. isotonic_____________________________________
b. hypertonic _____________________________________
c. hypotonic
_____________________________________
Use arrows to show the direction of water movement into or out
of each cell. Color and label the cell in an isotonic environment light
blue, the hypotonic environment yellow, and the hypertonic environment
light green.
49
Match the description or picture with the osmotic condition:
A. Isotonic
_____ solution with a lower solute concentration
_____ solution in which the solute concentration is the same
B. Hypertonic
_____ condition plant cells require
_____ condition that animal cells require
C. Hypotonic
_____ red blood cell bursts (cytolysis)
_____ plant cell loses turgor pressure (Plasmolysis)
_____ solution with a higher solute concentration
_____ plant cell with good turgor pressure
_____ solution with a high water concentration
Label the tonicity for each solution (isotonic, hypotonic, or
hypertonic):
____________
____________
____________
____________
50
____________
_ ___________
Transport Requiring Energy
What type of transport is represented by the following picture?
_______________________
What energy is being used? ______________
In which direction (concentration gradient), is the movement
occurring? _________________
Color the internal environment of the cell yellow. Color and Label the
transport proteins red and the substance being moved blue.
One type of active transport is called the ________________ pump
which helps muscle cells contract. This pump uses ___________ to
move ions __________ the concentration gradient. The protein that
is used to pump the ions through is called a ____________ protein
and it changes its __________ to move the ions across the cell
membrane. Label and color the carrier proteins red and the ions
green.
51
Name: _____________________________________ TOPIC 3: Cellular Transport Please use the Council Rock Video Podcast to guide you 1. What 4 types of organisms have a cell wall? a. b. c. d. 2. Diffusion moves molecules form a ____________ concentration to a _________ concentration. 3. True or false: after equilibrium is reached, molecules do not move anymore. 4. In a hypotonic solution, there is a low solute / high water concentration outside a cell. Water moves ____ the cell. 5. Circle one: Who does better in a hypotonic solution? PLANTS ANIMALS 6. In a hypertonic solution, there is a high solute / low water concentration outside a cell. Water moves _____ the cell. 7. In an isotonic solution, there is an _________ solute / water concentration outside and inside a cell. 8. Circle one: Who does better in an isotonic solution? PLANTS ANIMALS 9. Facilitated diffusion needs the help of a __________ to move large/charged molecules across a cell membrane. 10. What type of molecule is the “facilitator” in facilitated diffusion? _____________________________ 11. The only type of cellular transport to go AGAINST the concentration gradient is called _____________________. 12. What important energy molecules allows active transport to happen? ____________________ 13. What happens to the shape of the protein when the ATP binds to it? __________________________________ 14. What happens to the shape of the protein when the potassium ions bind to it? ___________________________ 15. In the Na+ K+ pump, _______ ions of sodium go through first. Then, _____ ions of potassium go through. Biology Keystone Review—2012‐2013 52
Cell Transport Review Worksheet
Complete the table by checking the correct column for each statement:
Statement
Isotonic
Hypotonic
Hypertonic
solution
solution
solution
Causes a cell to swell
Doesn’t change the shape of a
cell
Causes osmosis
Causes a cell to shrink
Match the term with its correct description:
a. energy
b. facilitated diffusion
c. endocytosis
d. passive transport
e. active transport
f. exocytosis
g. carrier protein
h. channel protein
________ Transport protein that provides a tube-like opening in the plasma
membrane through which particles can diffuse
________ Is used during active transport but not passive transport
________ Process by which a cell takes in material by forming a vacuole around
it
________ Particle movement from an area of higher concentration to an area of
lower concentration
________ Process by which a cell expels wastes from a vacuole
________ A form of passive transport that uses transport proteins
________ Particle movement from an area of lower concentration to an area of
higher concentration
________ Transport protein that changes shape when a particle binds with it
Match the term with its correct description:
a. transport protein
d. passive transport
b. active transport
e. osmosis
c. diffusion
f. endocytosis
g. exocytosis
h. equilibrium
_____ The diffusion of water through a cell membrane
_____ The movement of substances through the cell membrane without the use
of cellular energy
_____ Used to help substances enter or exit the cell membrane
_____ When energy is required to move materials through a cell membrane
_____ When the molecules of one substance are spread evenly throughout
another substance to become balanced
_____ A vacuole membrane fuses (becomes a part of) the cell membrane and the
contents are released
53
_____ The cell membrane forms around another substance, for example, how the
amoeba gets its food
_____ When molecules move from areas of high concentration to areas of low
concentration
Label the diagrams of cells using the following terms: diffusion, active transport,
osmosis, equilibrium. The arrows show the direction of transport. You may use
the terms more than once!
High
CO2
levels
8 H2O
molecules
25 glucose
molecules
2 H2O molecules
Low CO2 levels
High
protein
levels
2 H2O
molecules
8 H2O molecules
5 glucose molecules
10 H2O
molecules
Low protein levels
10 H2O molecules
Osmosis Practice Activity
Osmosis is the diffusion of water from an area of high concentration to an area of low concentration.
Only water moves in osmosis! The diagrams below show the concentration of water and salt inside
the cell and the concentration of water and salt surrounding the cell. Complete the sentences below
by comparing the concentration of the water inside the cell and the concentration outside the cell.
1.
5% NaCl
95% H2O
95% NaCl
5% H2O
a. Water will flow _____________________ (into
the cell, out of the cell, in both directions).
b. The cell will ______________________ (shrink,
burst, stay the same).
2.
5% NaCl
95% H2O
5% NaCl
95% H2O
a. Water will flow _____________________ (into the cell,
out of the cell, in both directions).
b. The cell will ______________________ (shrink, burst,
stay the same).
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a. Water will flow _____________________ (into the
cell, out of the cell, in both directions).
3.
95% NaCl
5% H2O
5% NaCl
95% H2O
b. The cell will ______________________ (shrink,
burst, stay the same).
4. At which solution of concentration gradient is each cell diagram? (Hypotonic, Hypertonic, Isotonic)
a. _____________
b. ________________
c. ____________
5. This diagram is moving from a high to a low concentration: ___________________
6. Using a transport protein to move particles across the membrane: ___________________
7. Describe the processes occurring in the following pictures:
55