ANATOMY AND PHYSIOLOGY 1 (2125)

NEED HELP WITH ANATOMY AND PHYSIOLOGY LAB ASSIGNMENT DUE 1/28/2021

A

NATOMY & PHYSIOLOGY

Cell Structure and Function

Investigation
Manual

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CELL STRUCTURE AND FUNCTION

Table of Contents

2 Overview
2 Outcomes
2 Time Requirements
3 Background
7 Materials
8 Safety
9 Preparation
9 Activity 1
10 Activity 2
14 Disposal and Cleanup
14

Observations

Overview
In this investigation, the student will explore the structure and
function of the animal cell, particularly the selectively perme

–

able plasma membrane. The student will model the processes of
simple diffusion and osmosis and assess the tonicities of aqueous
solutions.

Outcomes
• Identify the parts of an animal cell and describe their functions.
• Describe the structure of the plasma membrane of the cell and

explain why it is selectively permeable.
• Model the processes of simple diffusion and osmosis.
• Calculate the rate of diffusion and determine how it is affected

by molecular weight.
• Assess the relative tonicities of aqueous solutions.

Time Requirements
Preparation ………………………………………………………….. 30 minutes
Activity 1: Simple Diffusion ……………………………………. 60 minutes
Activity 2: Osmosis ……………………………………………….. 75 minutes

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Background
The cell is the fundamental structural and
functional unit of all living things. Although the
human body is composed of an amazing variety
of different, specialized cell types, all cells
have certain characteristics in common. Most
importantly, all animal cells possess three main
components: a nucleus, a cytoplasm, and a
plasma membrane.

The Nucleus
The nucleus houses most of the genetic mate
rial of the cell. Most of the time, the genetic
material exists in the form of a threadlike
complex of DNA and proteins known as

–

chromatin. When a cell goes through the
process of division, the chromatin coils up tightly
to form compact structures called

chromosomes. Within the nucleus lies at least
one nucleolus. This is where ribosomes, the
machinery of protein synthesis, are assembled.
The contents of the nucleus are separated from
the rest of the cell by the nuclear envelope.
This double membrane is penetrated by nuclear
pores that permit materials to pass in and out of
the nucleus.

The Cytoplasm
The cytoplasm occupies the area between
the nucleus and the plasma membrane. It
consists of the cytosol (which is mostly water
with dissolved ions and proteins), the protein
filaments of the cytoskeleton, and a variety of
organelles, which are specialized structures
devoted to specific cellular tasks (Table 1).

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Table 1.

Structure Function
Ribosomes Protein synthesis

Rough endoplasmic reticulum (rough ER) Processing and transport of proteins
Smooth endoplasmic reticulum (smooth ER) Lipid and carbohydrate metabolism; detoxification
Golgi apparatus Processing and transport of proteins, especially

secreted proteins
Lysosomes Intracellular digestion
Peroxisomes Catabolism of fatty acids
Mitochondria ATP production

Centrioles Organization and movement of chromosomes during
cell division

Cilia Movement
Flagella Movement
Microfilaments Cytokinesis; changes in cell shape; cell motility
Intermediate filaments Strength and support for cells and tissues
Microtubules Motility (internal components of cilia and flagella);

intracellular transport; chromosome movements during
cell division

CELL STRUCTURE AND FUNCTION

Background continued
The Plasma Membrane
The plasma membrane of the cell (also
called the cell membrane or the cytoplasmic
membrane) surrounds and defines each cell
and separates its internal environment from the
external environment. The plasma membrane
is composed primarily of phospholipids. A
phospholipid molecule consists of a glycerol
skeleton with two fatty acids and a phosphate
group attached. The fatty acids are nonpolar
hydrocarbon chains, and thus, they are hydro-
phobic (i.e., repelled by water). The negatively
charged phosphate group forms the polar head
of the molecule and is hydrophilic (i.e., attracted
to water). Recall that the cytosol within the cell
is mostly water, and most cells of the human
body are bathed in extracellular fluid, which is
also mostly water. These conditions cause the
phospholipid molecules to cluster together so
that their hydrophilic heads are oriented toward
the water and their hydrophobic tails exclude
water. The resulting structure is a phospholipid
bilayer: two layers of molecules, with the hydro-
philic heads directed to the inside and outside of
the cell and the hydrophobic tails sandwiched in
between.

By themselves, the phospholipid molecules
would form a relatively loose, fluid association,
with a consistency similar to that of vegetable
oil. However, phospholipid molecules are not the
only type of molecule in the plasma membrane.
In the membranes of animal cells, the phospho-
lipids are stabilized by sterol molecules, such as
cholesterol. Glycolipids, which have a carbohy-
drate group instead of a phosphate group, are
also present in the outer portion of the bilayer.

Proteins constitute a major component of the
plasma membrane and play important roles

in cell signaling, adhesion, metabolism, and
transport. Peripheral membrane proteins are
weakly associated with the membrane, whereas
integral membrane proteins are more firmly
embedded. In fact, most integral membrane
proteins are transmembrane proteins, meaning
that they completely span the phospholipid
bilayer and have exposed regions on both sides
of the membrane. Many proteins are able to drift
laterally within the phospholipid bilayer, which is
why the plasma membrane is often described in
terms of a fluid-mosaic model.

Cell Transport and Cell Size
All living things take in nutrients and eliminate
waste. These vital functions are facilitated at
the cellular level by the selectively permeable
(i.e., semipermeable) plasma membrane. The
cell membrane permits the passage of mole-
cules and ions of a certain size while restricting
the passage of larger or differently charged
molecules or ions. Some molecules, such as
water, oxygen, and carbon dioxide, can move
freely across the cell membrane’s lipid bilayer.
These molecules move into and out of the cell
by diffusion, which can be defined as the net
movement of molecules or ions down a concen-
tration gradient. Concentration is defined as
the amount of a substance per unit volume,
such as the mass of sucrose (table suguar) in
a milliliter (mL) of water. So when a substance
moves down a concentration gradient, it moves
from a region of higher concentration to a region
of lower concentration. Larger molecules, on
the other hand, are excluded by the membrane
and may enter or leave the cell only through
processes mediated by dedicated transporter
proteins located in the membrane.

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In Activity 1, you will observe how diffusion
occurs in the absence of a membrane. However,
diffusion across a selectively permeable
membrane, such as the plasma membrane, is
subject to certain conditions. Four main factors
determine the rate of diffusion of molecules or
ions across a membrane:

1. The steepness of the concentration gradient:
The greater the difference between the
concentrations on opposite sides of the
membrane, the higher the rate of diffusion.

2. Temperature: Molecules and ions have more
kinetic energy at higher temperatures. When
molecules and ions move more rapidly, diffu-
sion proceeds more rapidly.

3. The surface area of the membrane: The
greater the surface area, the higher the rate of
diffusion. A greater surface area allows more
molecules or ions to cross the membrane at
any point in time.

4. The type of molecule or ion diffusing: Large
molecules (those of higher molecular weight)
tend to diffuse more slowly than smaller mole-
cules (of lower molecular weight). If the large
molecules are contained within a selectively
permeable membrane, they may not be able
to diffuse at all. Ions may move more readily
along a charge gradient; for example, a cation
(positively charged ion) may diffuse more
quickly toward a region rich in anions (nega-
tively charged ions) than toward a region with
an overall positive charge.

Osmosis is the diffusion of water molecules
across a selectively permeable membrane. The

four factors listed above also apply to osmosis.
The net movement of water molecules in
osmosis is to the side of the selectively perme-
able membrane having the higher concentration
of solute, and, therefore, the lower concentration
of water. The cytoplasm is an aqueous solution,
consisting of water with dissolved molecules
and ions. If the cell is surrounded by solute-
free, pure water, the concentration of water is
actually lower inside the cell compared with the
outside, and the net movement of water will be
into the cell. If the cell is in a solution with a high
solute concentration, the concentration of water
may be higher inside the cell compared with the
outside, causing the net flow of water to be out
of the cell.

The terms hypertonic, hypotonic, and isotonic
are used to compare aqueous solutions of
varying solute concentration in which the solute
cannot cross the membrane. If the solutions
have the same concentration of solute, they are
called isotonic (iso-, “same”). When two solu-
tions have different concentrations of a solute,
the one with the higher solute concentration is
called hypertonic (hyper-, “above”), and the
one with the lower solute concentration is called
hypotonic (hypo-, “below”). The hypertonic
solution, which contains a higher solute concen-
tration than the comparison solution, can also
be thought of as having a lower concentration
of water. In contrast, the hypotonic solution has
a lower concentration of solute, but a higher
concentration of water. Because the solute
cannot cross the membrane, osmosis occurs
between solutions of different tonicities. The
water will move from the solution in which it is

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CELL STRUCTURE AND FUNCTION

Background continued
more concentrated to the solution in which it
is less concentrated. In other words, water will
move from the hypotonic solution to the hyper-
tonic solution. In Figures 1 and 2, the larger
black circles represent the solute molecules,
and the smaller open circles represent the water
molecules. The vertical center line represents a
selectively permeable membrane. In Figure 1,
the concentration of solute molecules is higher
on the left side of the membrane, so the left side
is hypertonic relative to the right side. The right
side is hypotonic relative to the left side.
Figure 2 shows that the left and right sides are
at equilibrium and are isotonic relative to each
other. The concentration of molecules on both
sides of the membrane is equal.

Osmotic pressure is the measure of a solu-
tion’s tendency to gain water when separated
from pure water by a selectively permeable
membrane. A solution’s osmotic pressure is
proportional to its solute concentration; the
greater the solute concentration, the greater
the osmotic pressure and, therefore, the greater
the tendency for the solution to gain water. In
isotonic solutions, water diffuses across the
membrane from one solution to another at an

equal rate in both directions. There is no net
osmotic movement of water and no net osmotic
pressure.

Water enters our cells passively through
osmosis. For instance, most water absorption
in the digestive tract occurs in the large intes-
tine, and there are no channels in the plasma
membranes of intestinal cells that actively
transport water. While water transport relies on
osmosis, there are membrane channels that
actively transport sodium and other ions into
the cytoplasm, using ATP for energy. In order to
manipulate the characteristics of osmosis, the
concentration of solutes can be increased in the
cells of the intestinal lining such that the cyto-
plasm becomes hypertonic relative to the lumen
of the large intestine. Then, water flows into the
cells by osmosis.

The kidneys regulate the water balance in our
bodies. Like the large intestine, the movement
of water by osmosis is regulated by the active
transport of salts. In addition, some cells of the
kidneys have selective channels called aqua-
porins, which allow water to move across the
membrane very quickly in response to osmotic
pressure.

In Activity 2, you will use dialysis tubing to
simulate the plasma membrane of a cell. The
flat, transparent dialysis tubing has microscopic
pores that permit the passage of water, but not
larger solutes such as sugars.

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Figure 1. Figure 2.

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Materials
Included in the materials kit:

Ruler

4 Plastic
cups, 10 oz

Sucrose,
100 g packet

5 Pipets

Petri dish Potassium
permanganate,
1 g

Methylene
blue, 1 g

Teaspoon

2 Micro
spoons

3 Weigh boats

3 Pieces of
dialysis tubing,
8″

Agarose,
30 mL

3 Beakers,
250 mL

Grease pencil

Graduated
cylinder,
100 mL

Graduated
cylinder,
10 mL

Reorder Information: Replacement supplies
for the Cell Structure and Function investigation
(item number 580506) can be ordered from
Carolina Biological Supply Company.

Call: 800.334.5551 to order.

Needed but not supplied:
• Tap water
• Timing device
• Paper towels
• Digital camera or mobile device

capable of taking digital photos
• Pot holder or mitt

(recommended but not
required)

CELL STRUCTURE AND FUNCTION

8 Carolina Distance Learning

Safety
Do not eat, drink, or chew gum while performing
these activities. Wash your hands with soap and
water before and after performing the activities.
Clean up the work space with soap and water
after completing the investigation. Keep pets
and children away from lab materials and
equipment.

Read all of the
instructions for
these laboratory activities before beginning.
Follow the instructions closely and observe
established laboratory safety practices,
including the use of appropriate personal
protective equipment (PPE).

Wear safety goggles, gloves, and a lab apron
while performing this laboratory investigation.
Work in close proximity to a sink or other source
of running water. A kitchen sink sprayer or a
shower may serve as an emergency eyewash
station if needed.

Potassium permanganate is
an oxidizing agent.

Methylene blue is an irritant of the
skin, eyes, and respiratory passages;
exposure may result in drowsiness

or dizziness and may impair fertility or, if preg-
nant, cause harm to an unborn child. If either
substance is inhaled, seek fresh air immediately
and seek medical attention. In case of contact
with the eyes, rinse immediately with plenty of
water and seek medical attention. In case of
contact with skin, wash immediately with soap
and rinse with plenty of water. If skin irritation
results, seek medical advice or attention. If swal-
lowed, call a poison center and/or seek medical
attention immediately.

ACTIVITY 1

Simple Diffusion
Preparation
1. Read the procedure description thoroughly

and become familiar with the kit materials and
procedure steps prior to beginning.

2. Put on PPE (safety goggles, gloves, and lab
apron) and wear throughout the rest of the
preparation and procedure.

3. To prepare the Petri dish containing agarose:
a. Loosen, but do not remove, the cap of the

agarose bottle.
b. Using a microwave, heat the agarose
at 30-second intervals until the
agarose is completely melted. The agarose

must have no lumps and should pour easily.
The container will be hot, so you may wish
to use a potholder or oven mitt.

c. Place the Petri dish on a level surface.
Remove the lid and set it aside.

d. Pour all of the melted agarose slowly into
the Petri dish, making sure the bottom of
the dish is evenly covered and there are no
bubbles in the agarose.

e. Allow the Petri dish to sit undisturbed
and uncovered for 25–30 minutes,

or until the agarose is completely solidified.
4. Turn the Petri dish upside down and use the

grease pencil to draw a line down the center
of the bottom of the dish, as shown in Figure
3. Then turn the Petri dish right side up (agar
facing up).

5. Fill a micro spoon about half full of potassium
permanganate. Use a pipet to suction up
the permanganate crystals and deposit
the contents gently onto the surface of the
agarose in the center of one side of the

dish. Take care not to scatter any crystals of
potassium permanganate across the surface
of the agarose.

6. Use a pipet to suction an equivalent amount
of methylene blue and deposit the contents
onto the surface of the agarose in the center
of the opposite side of the dish.

If scattering does occur, you may wish to
try again using a clear area of the agarose
surface. Just make a note of the new dye
location and make sure it is as far from the
other dye as possible.

7. Put the ruler underneath the
Petri dish, and record the initial
diameter of each dye ring (in mm) in Data
Table 1. Start the timer. Take a photo of the
Petri dish.

Figure 3.

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ACTIVITY

A

ACTIVITY

ACTIVITY 1 continued
8. Record the diameter of each dye
ring in Data Table 1 at 15-minute
intervals for 1 hour. At the end of the hour,

take a final photo of the Petri dish.
9. Determine the rate of diffusion for each dye

using the following formula:

where time is the time in minutes when the
dye front reaches the edge of the Petri dish or
the hour had elapsed.

10. Based on the information recorded in Data
Table 1, determine whether the two dyes
diffused at the same rate or at different
rates.

ACTIVITY 2
Osmosis
Preparation
1. Read the procedure description thoroughly

and become familiar with the kit materials
and procedure steps prior to beginning.

2. Put on PPE (safety goggles, gloves, and lab
apron) and wear throughout the rest of the
preparation and procedure.

3. Prepare one solution of 40% sucrose and two
solutions of 20% sucrose:

a. Label two 250-mL beakers “20% sucrose”
and one 250-mL beaker “40% sucrose.”

b. Add five level teaspoons (20 g) of sucrose
to a “20% sucrose” beaker. Add warm tap
water to approximately the 90-mL mark
on the beaker and stir with the teaspoon
until the sugar is completely dissolved.
Pour into the 100-mL graduated cylinder,
and carefully add more water to reach a
total volume of 100 mL. Pour back into the
beaker and rinse the graduated cylinder
and teaspoon with tap water.

c. Repeat Step 3b to produce another beaker
of 20% sucrose solution.

d. Add 10 level teaspoons (40 g) of sucrose
to the “40% sucrose” beaker. Add warm
tap water to approximately the 90-mL mark
on the beaker and stir with the teaspoon
until the sugar is completely dissolved.
Pour into the 100-mL graduated cylinder,
and carefully add more water to reach a
total volume of 100 mL. Pour back into the
beaker and rinse the graduated cylinder
and teaspoon with tap water.

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Rate of diffusion (mm/min) =
final diameter – initial diameter

time (min)

A

e. Allow all three sucrose solutions to cool
to room temperature before starting the
procedure.

4. Label three weigh boats “A,” “B,” and “C” for
each treatment.

5. Label three plastic cups “A,” “B,” and “C” for
each treatment.

Procedure
1. Use the 100-mL graduated cylinder to
measure 90 mL of 20% sucrose solution.
Pour into Cup “A.”
2. Use the 100-mL graduated cylinder to
measure 90 mL of 20% sucrose solution.
Pour into Cup “B.”
3. Use the 100-mL graduated cylinder to
measure 90 mL of 40% sucrose solution.
Pour into Cup “C.”
4. Fill another clean plastic cup with

tap water. Place the flat, transparent
dialysis tubing in the water. Allow the dialysis
tubing to remain in the water for at least 30
seconds.

5. Remove the dialysis tubing from the water,
and gently roll the end of the tubing between
your index finger and thumb. This should
cause the dialysis tubing to open. Slightly
wetting your fingers will make opening the
dialysis tubing easier.
Opening Dialysis Tubing
https://players.brightcove.

net/17907428001/HJ2y9UNi_default/
index.html?videoId=4573412134001

6. Continue rolling the tubing down its length
until the tubing is completely open. Tie

a simple knot on one end of the dialysis
tubing, as shown in Figure 4. This knot
should be as close to the end as possible.
Repeat this process for all three pieces of
dialysis tubing.

Figure 4.

7. Use the 10-mL graduated cylinder to
measure out 6 mL of 20% sucrose solution.
Use a pipet to transfer all 6 mL into a piece of
dialysis tubing. You may need to pour the last
milliliter or so into the open end of the tubing.

8. Carefully remove almost all of the air from the
space above the sucrose solution, leaving
only a small bubble, so the tube will float
when placed in its designated cup. To expel
the air, gently squeeze upward with the
thumb and index finger of one hand while
supporting the filled tubing with the other
hand.

continued on next page

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https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=4573412134001

https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=4573412134001

https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=4573412134001

https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=4573412134001

ACTIVITY

ACTIVITY 2 continued
9. Twist the top inch of the tubing and tie a

simple knot at the top end, as shown in

Figure 5.

10. Rinse the outside of the dialysis tubing with
water, and gently blot it dry with a paper
towel.

11. Place the dialysis tubing in the weigh boat
labeled “A.”

12. Repeat steps 7–10 with the next piece of
dialysis tubing. Place the tubing in the weigh
boat labeled “C.”

13. Rinse the 10-mL graduated cylinder with tap
water. Use it to measure out 6 mL of 40%
sucrose solution. Use a new pipet to transfer
all 6 mL into the last piece of dialysis tubing.
Pour the last bit into the open end of the
dialysis tubing if necessary. Repeat Steps
8–10, and place the tubing in the weigh boat
labeled “B.”

14. Take a photo of all three pieces of filled
dialysis tubing sitting in their weigh boats.

15. Measure the volume of each solution in each
tube by displacement:

a. Add 80 mL of tap water to the 100-mL
graduated cylinder.

b. Drop tubing “A” into the graduated
cylinder and make sure the solution inside
the tubing is completely submerged.

c. Observe the new water level and record
the value as “initial volume” in Data
Table 2.

d. Remove the tubing from the graduated
cylinder and discard the water. Dab each
end of the tubing with a paper towel to
remove any excess water, and place the
tubing in its designated weigh boat. continued on next page

12 Carolina Distance Learning

Figure 5.

c. Observe the new water level and record
the value as “final volume” in Data
Table 2.

d. Remove the tubing from the graduated
cylinder, squeeze any excess water out
from the ends of the tubing, and place
the tubing in its designated weigh boat.
Discard the water.

e. Perform Steps 21a–d for tubing pieces
“B” and “C.”

22. Determine the change in the volume of
solution within each piece of dialysis tubing
and record in

Data Table 2.

23. Determine the percentage change in the
volume of solution within each piece of
dialysis tubing and record in Data Table 2.

24. Based on the results, determine whether
the solution in each piece of tubing was
isotonic, hypotonic, or hypertonic relative
to the solution in the cup. Record your
conclusions in Data Table 2.

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e. Perform Steps 15a–d for tubing pieces
“B” and “C.”

16. Transfer the tubing pieces into the labeled
cups containing the appropriate sucrose
solutions as follows:

a. Cup “A”: 20% sucrose solution in the cup
and 20% sucrose solution in the dialysis
tubing.

b. Cup “B”: 20% sucrose solution in the cup
and 40% sucrose solution in the dialysis
tubing.

c. Cup “C”: 40% sucrose solution in the cup
and 20% sucrose solution in the dialysis
tubing.

17. Make sure the dialysis tubing is
completely submerged, and start the
timer.

18. Allow the tubing to sit in the cups for
1 hour.
19. Remove each piece of tubing from its cup,

dab each end of the tubing with a paper
towel to remove any excess water, and place
the tubing back into its corresponding weigh
boat.

20. Take a photo of all three pieces of filled
dialysis tubing sitting in their weigh boats.
21. Measure the new volume of the solution in

each piece of tubing.
a. Add 80 mL of tap water to the 100-mL

graduated cylinder.
b. Drop tubing piece “A” into the graduated

cylinder and make sure it is completely
submerged.

ACTIVITY

14 Carolina Distance Learning

Disposal and Cleanup
1. Keep your PPE (safety goggles, gloves, and

lab apron) on throughout the disposal and
cleanup process.

2. Carefully pour all liquids down the drain,
flushing with excess tap water for at
least 1 full minute.

3. The weigh boats, plastic cups, pipets, and
dialysis tubing should be disposed of in the
household trash.

4. Secure the lid on the Petri dish of agarose,
wrap in a plastic bag, and dispose of in the
household trash.

5. Wash and dry the teaspoon, micro spoons,
beakers, and graduated cylinders.

6. Store remaining materials in the materials kit
bag or equipment set.

7. Sanitize the work space and wash your
hands.

Data Table 2.

Treatment A Treatment B Treatment C

Solution in dialysis tubing 20% sucrose 40% sucrose 20% sucrose

Solution in cup 20% sucrose 20% sucrose 40% sucrose

Initial volume (Vi) (mL)

Final volume (Vf) (mL)

Change in volume
(Vf−Vi) (mL)

Percent change in volume
(change in volume/Vi) x 100

Hypotonic, isotonic, or
hypertonic

Observations

Time
(min)

Diameter,
Potassium

Permanganate
(mm)

Diameter,
Methylene Blue (mm)

0
15
30
45
60

Data Table 1.

NOTES

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ANATOMY & PHYSIOLOGY
Cell Structure and Function

Investigation Manual

www.carolina.com/distancelearning
866.332.4478

Carolina Biological Supply Company
www.carolina.com • 800.334.5551
©2019 Carolina Biological Supply Company

CB781901901 V2.1

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Cell Structure and Function
Table of Contents
Overview
Outcomes
Time Requirements
Key
Background
The Nucleus
The Cytoplasm
The Plasma Membrane
Cell Transport and Cell Size
Materials
Safety
ACTIVITY 1
A Simple Diffusion Preparation
ACTIVITY 2
A Osmosis
Preparation
Procedure

Disposal and Cleanup
Observations