Chapter 8: Cells & Their Environment
I.
Section 1 – Cell Membrane: pages 175 - 177
A. Introduction
1. EVERY cell is surrounded by a cell membrane/plasma
membrane.
2. What does the cell membrane do for the cell?
Protects the cell and allows substances such as water,
oxygen, food, carbon dioxide & wastes into & out of the cell.
Allow messages to enter & leave the cell.
B. Homeostasis
1. Give 2 examples of how our bodies maintain
homeostasis.
a. constant body temperature of 98.6oF
b. we perspire/sweat to cool our body & keep from
overheating; gets rid of the excess heat
2. Define homeostasis. Maintaining stable conditions inside the
cell even though the environment changes.
3. Identify the 2 organic molecules that form the cell
membrane & all of the other membranes in the cell
(nuclear membrane, Golgi, ER, vacuole, vesicle,
lysosome, mitochondria, chloroplast).
a. phospholipids
b. proteins
4. What are some of the roles of the cell membrane?
See question A#2
C. Lipid Bilayer
1. Identify the type of lipid that forms the cell
membrane.
Phospholipids
2. What is a phospholipid? A type of organic molecule that
forms the cell membrane & all membranes inside the cell.
3. Label the hydrophilic & hydrophobic parts of the
phospholipid.
Hydrophillic 
head
Hydrophobic tails 
4. Structure of Membranes (all membranes of a cell)
(tissue fluid)
(cytoplasm)
a. Why is the cell membrane made of a double
layer of phospholipids; a lipid bilayer? Because there’s
liquid (cytoplasm & tissue fluid) on both sides of the cell
membrane.
b. What parts of the lipid bilayer face the
cytoplasm & the extra-cellular fluid?
The polar heads of the phospholipids
5. Identify the molecules that are able to pass
through the phospholipid bilayer.
Nonpolar molecules can pass through the phospholipid part
of the cell membrane (fats, oils, & steroid molecules) and so
can oxygen, carbon dioxide.
D. Membrane Proteins
Identify the 4 types of proteins found in the cell membrane,
then give their function.
a. Cell Surface Markers – proteins with carbohydrates attached
to them; differ from cell to cell; Ex: liver cells have different
marker proteins than heart cells. These proteins must be
matched when doing organ transplants.
b. Receptor Proteins – receive outside information from the
environment or other cells.
c. Enzymes – are on the inner surface of the cell membrane;
cause chemical reactions to occur inside the cell.
d. Transport Proteins – have pores which enable substances to
enter & leave the cell. Ex: water, ions, food,& wastes can
pass thru these pores.
E. Critical Thinking – use your knowledge of the cell membrane
structure to answer the following questions.
1. What would happen to the cell if the cell
membrane were fully permeable to all substances
in the cell’s environment? If any substance could enter &
leave the cell homeostasis would be disrupted & the cell
would malfunction or die.
2. What would happen if the cell were exposed to a
drug that disabled the transport proteins in the
cell membrane? The cell would not be able to transport
substances like food, water, gases, or wastes in & out of the
cell; cell malfunctions & may die.
II.
Section 2 - Cell Transport : pages 178 – 183
A. Key Terms - Define the following terms:

Equilibrium – When the concentration of the
substance is evenly spread out within the space.

Concentration – The amount of a certain substance
in a given volume.

Concentration Gradient – Difference in the
concentration of a substance from one area to
another.

Passive Transport – NO use of energy involved;
molecules move from the area of higher
concentration to the area of lower concentration
(with the concentration gradient).
Ex: Like fish swimming with the current or taking a
raft trip & going with the flow of the river.

Active Transport – USE of energy to move
molecules from the area of lower concentration to
the area of higher concentration (AGAINST the
concentration gradient); cell uses energy to do
this. Ex: Like fish swimming against the current
(salmon swimming back to the stream where they
were born to mate & lay their eggs)or paddling the
raft upstream against the current.
B. PASSIVE TRANSPORT – the cell does NOT use energy. Molecules
move down/with the concentration gradient; from the area of higher
concentration to the area of lower concentration.
Explain each of the following types of passive transport.
1. DIFFUSION – Movement of solids & gases from
areas of higher concentration to areas of lower
concentration. WITH the concentration gradient;
cell DOES NOT use energy.
2. FACILITATED DIFFUSION – NOTE: to “facilitate”
means “to help”.
Transport proteins in the cell membrane help
molecules move from areas of higher concentration
to areas of lower concentration. Occurs faster than
regular diffusion. Ex: glucose sugar enters our
brain cells via facilitated diffusion.
a. Channel Proteins – transport ions such as
Na+(sodium) & amino acids (to build proteins)
through their pores.
b. Carrier Proteins – have specific areas called
binding sites to which the substance being
transported must attach (sugars such as
glucose). When the substance attaches to the
binding site on the carrier protein, the protein
changes its shape & transports the substance
into the cell.
3. OSMOSIS – the movement of liquids (such as
water) with the concentration gradient; moves
from higher to lower water concentration.
C. Water & Cells
1. What are water channels? Special channel proteins
have pores that allow water to enter/leave cells by
the process of OSMOSIS. AKA: aquaporins
2. How do water channels help cells; what types of
molecules can pass through water channels?
They allow water in & out of our cells; so this is an
example of facilitated diffusion.
3. Predicting Water Movement – predicting water
movement depends on THE CONCENTRATION OF
THE SOLUTION OUTSIDE THE CELL (EXTRACELLULAR
FLUID).
a. Define the following terms:
 hyper – higher than/more of

hypertonic solution – a solution that has
more dissolved substance/solute than the
solution you’re comparing it to.
Ex: A sugar water solution is hypertonic
when compared to plain tap water.

hypo – lower than/less of

hypotonic solution – a solution that has a
lower concentration/less dissolved
substance/solute than the solution you’re
comparing it to.
Ex: Plain tap water is hypotonic when
compared to a sugar water solution.

iso – the same

isotonic solution – has the same
concentration of substances as the
solution you’re comparing it to.
Ex: Two cups of plain tap water or 2 cans
of regular Coke.
b. If a cell is placed into a hypertonic solution,
what will happen to it? The cell will lose water
& dehydrate as the water moves from the area
of higher concentration (inside the cytoplasm
of the cell) to the area of lower concentration,
which is outside the cell.
Cytoplasm of the cell shrinks due to loss of
water; this process is called PLASMOLYSIS.
c. If a cell is placed into a hypotonic solution,
what will happen to it? The cell will gain/take
in water as water moves from the area of
higher concentration (outside the cell) to the
area of lower concentration, in the cytoplasm
of the cell.
Cytoplasm of the cell expands/swells due to
incoming water; this process is called
CYTOLYSIS.
d. If a cell is placed into an isotonic solution, what
will happen to it? NOTHING; its cytoplasm will
stay the same; for every water molecule that
enters the cytoplasm of the cell another water
molecule must leave the cell & go into the
tissue fluid. The cell is in EQUILIBRIUM!
http://www.youtube.com/watch?v=Sw87Q53NZLI – red onion in isotonic, hypertonic & hypotonic solutions
4. Effects of Osmosis
a. Define these terms:
 Plasmolysis – Shrinking of cytoplasm due to
water loss; hypertonic solution (ex: salt or
sugar water solution).

Cytolysis – Swelling of the cytoplasm due to
gaining of water by cytoplasm; hypotonic
solution (ex: distilled water).
b. What keeps plant cells from bursting (going
through cytolysis) when placed in a hypotonic
solution? Cell wall keeps the cell membrane
from expanding to the point of bursting
(cytolysis).
c. How do some unicellular protists get rid of
excess water when they’re in a hypotonic
solution? They have contractile vacuoles which
pump out the excess water.
d. How do our cells (animal cells) keep from
swelling & bursting (cytolysis) when exposed
to hypotonic solutions? Our cells actively PUMP
solute molecules out of the cytoplasm; this
causes the excess water to leave our cells by
osmosis.
D. ACTIVE TRANSPORT - the cell USES energy/ATP.
Molecules move AGAINST the concentration gradient;
from the area of lower concentration to the area of higher
concentration; requires energy in the form of ATP.
Explain each of the following types of active transport.
1. Pumps – carrier proteins in the cell membrane use energy to
pump/push substances against the concentration gradient. NOTE:
Like a fish trying to swim upstream OR you trying to paddle a canoe
AGAINST the current.
 Sodium-Potassium Pump – one of the most
important carrier proteins in our nerve and muscle
cells.
Describe how our cells regulate the amount of
sodium (Na+) and potassium (K+) in our
cytoplasm.
Our nerve cells want a low concentration of sodium
(Na+) & a higher concentration of potassium (K+),
but our tissue fluid has lots of sodium & little
potassium; sodium enters & potassium leaves the
cytoplasm. Our nerve cells have special carrier
proteins in their cell membrane that pick up three
sodium ions & pump them out of the cell, then the
same carrier protein picks up 2 potassium ions from
the extracellular tissue fluid & pumps them back into
the cytoplasm of the nerve cell. The nerve cell uses
energy/ATP (produced by the mitochondria) to do
this, so it’s active transport.
http://www.youtube.com/watch?v=P-imDC1txWw - animation describing the sodium-potassium pump
2. Vesicles – membrane bound sacs which carry
substances. Membrane is made of phospholipid &
protein.

Endocytosis – process by which the cell
membrane surrounds a food particle &
encloses it in a vesicle. The vesicle then
enters the cytoplasm of the cell.
NOTE: “endo” means ENTER or INSIDE.
 Two types of endocytosis:
a. Phagocytosis – cell takes in large
particles or bacteria by forming a
vesicle; aka – cellular eating
b. Pinocytosis – cell take in molecules
dissolved in liquid into the vesicle;
aka – cellular drinking
Exocytosis – a waste vacuole or other vesicle
in the cytoplasm moves to the cell membrane
& fuses with it, releasing what’s inside the
vesicle out of the cell into the extracellular
fluid. NOTE: “exo” means EXIT or OUTSIDE.
http://www.youtube.com/watch?v=DuDmvlbpjHQ or http://www.youtube.com/watch?v=qpw2p1x9Cic
– use this site to view endocytosis and exocytosis
E. Critical Thinking – use your knowledge of the cell
transport to answer the following questions.
1. Based on having learned about homeostasis and
osmosis, why should humans avoid drinking sea
water? What about sugary soft drinks?
Drinking salt water causes the tissue fluid to
become hypertonic. This causes the cells’
cytoplasm to lose water/dehydrate & undergo
plasmolysis (shrinking of cytoplasm). Same
situation applies to drinking sugary soft drinks.
2. If a cell wasn’t able to make ATP, how would the
cell membrane’s transport processes be affected?
Name the processes. Without ATP cells couldn’t go
through ACTIVE TRANSPORT; the sodium-
potassium pump wouldn’t function & cells would
die. Endocytosis & exocytosis would not occur;
cells couldn’t take in food properly or get rid of
wastes.
http://programs.northlandcollege.edu/biology/biology1111/animations/transport1.html - animation of all types of
passive and active transport
III.
Section 3 - Cell Communication: pages 184 – 187
A. Sending Signals
1. How do cells communicate & coordinate activities with
each other? Send out chemical signals such as
hormones, or electrical signals like nerve & brain cells.
Ex: testosterone & estrogen are chemical signals.
2. What is a signaling cell? Produces the chemical signal
that will be released & sent to the target cell. Ex: cells in
our testes & ovaries produce the testosterone or
estrogen.
3. What is a target cell? Have specific proteins in their cell
membranes that detect a specific signal molecule.
Ex: Enlargement of breasts (aka: mammary glands),
penis, muscle development; hair under arms &
development of pubic hair; deeper voice (larynx/voice
box)
4. Targets
a. Short-Distance Signals
How do neighboring cells communicate? Direct
contact between their cell membranes.
b. Long-Distance Signals

Hormones – chemicals made in one part of the
body & carried by our bloodstream to target cells
far away.

Nerve Cells – transmit information long
distances through the body; not as widespread
as hormones.
5. Receiving Signals
a. Which proteins in the cell membrane receive the
signals from other cells?
Receptor proteins in the cell membrane.
b. Use the information & Fig. 12 to explain how a
receptor protein works. Each group of receptor
proteins has a specific binding site for a specific
chemical signal; if the chemical signal molecule has
a different shape it CANNOT fit into the binding site
on that receptor protein.
c. When the signal protein binds to the receptor
protein, how does information get into the target
cell? The receptor protein now changes its shape &
this change in shape passes the information into
the cytoplasm of the target cell.
B. Responding to Signals
List 3 ways a cell can respond to a signal.
a. Permeability Change -causes the transport/receptor protein
to either open or close in response to the signal protein.
b. Enzyme Activation-certain enzymes will be “turned on” &
cause specific chemical reactions to occur inside the cell.
c. Second Messenger-binding of chemical signal to the receptor
protein causes a second messenger protein inside the
cytoplasm to form or be activated causing a response in the
cytoplasm or nucleus of the target cell.