KEYSTONE REVIEW PACKET ANCHOR 4: Homeostasis and Transport
LEARNING OBJECTIVES:


Identify and describe the cell structures involved in transport of materials into, out of, and throughout the cell
o Describe how the structure of the plasma membrane allows it to function as a regulatory structure and/or
protective barrier for a cell
o Compare the mechanisms that transport materials across the plasma membrane (i.e., passive transport – diffusion,
osmosis, facilitated diffusion; and active transport – pumps, endocytosis, exocytosis)
o Describe how membrane-bound cellular organelles (e.g., endoplasmic reticulum, Golgi apparatus) facilitate the
transport of materials within a cell
Explain mechanisms that permit organisms to maintain biological balance between their internal and external environments
o Explain how organisms maintain homeostasis (e.g. thermoregulation, water regulation, oxygen regulation)
VOCABULARY:
active transport
carrier (transport) proteins
cell membrane (plasma
membrane)
concentration gradient
cytolysis
diffusion
endocytosis
endoplasmic reticulum
equilibrium
exocytosis
facilitated diffusion
homeostasis
hypertonic
hypotonic
impermeable
isotonic
negative feedback loop
osmoregulation
osmosis
passive transport
phagocytosis
pinocytosis
plasmolysis
positive feedback loop
pumps (ion or molecular)
semi/selectively permeable
thermoregulation
turgor pressure/turgid
Main Concept 1: Describe how the structure of the plasma membrane allows it to function as a regulatory
structure and/or protective barrier for a cell

Cell Membrane - surrounds the cell. It plays an active role in determining which substances enter and exit
the cell. Some substances can pass freely through the cell membrane and others cannot, the membrane is
said to be selectively permeable, or semipermeable. The cell
membrane is composed primarily of lipids (phospholipids),
proteins, and carbohydrates.

Phospholipids - have a polar, hydrophilic (water loving)
phosphate head and 2 nonpolar hydrophobic (water fearing)
fatty acid tails. They arrange themselves in a double layer
(phospholipid bilayer) so that the heads face the outer and
inner cell surfaces and the tails are sandwiched in between.

Cholesterol – small molecules inserted between the lipids, help to maintain membrane fluidity and prevent
membrane from freezing at low temperatures.

Membrane proteins – different types of proteins are embedded in the membrane to perform different
functions such as transport of materials, and enzymes to regulate reactions.

Carbohydrates – used for cell to cell communication and cell identification
*Fluid Mosaic Model - model that describes the structure of cell membranes. In this model, a flexible layer made of lipid
molecules is interspersed with large protein molecules that act as channels through which other molecules enter and
leave the cell
What are the 3 main macromolecules that make up the plasma membrane?
Phospholipids- have a polar, hydrophilic (water loving) phosphate head and 2 nonpolar hydrophobic (water
fearing) fatty acid tails. They arrange themselves in a double layer (phospholipid bilayer) so that the heads
face the outer and inner cell surfaces and the tails are sandwiched in between.
Membrane proteins – different types of proteins are embedded in the membrane to perform different
functions such as transport of materials, and enzymes to regulate reactions.
Carbohydrates – used for cell to cell communication and cell identification
1. What are the 2 main regions of a phospholipid? Which side is attracted to water?
Phosphate Head: polar, hydrophilic (water loving) and 2 Fatty Acid tails: nonpolar hydrophobic (water fearing)
2. What macromolecule is used for cell communication and identification?
Carbohydrates –
Main Concept 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)
Cellular Transport
The cell membrane is semipermeable, some substances can pass through it
freely, while others cannot. The movement of substances that can pass freely
through the membrane depends on the concentration gradient of the
substance, size of the substance and polarity of the substance.
A. Passive Transport
– Does not use energy
– Moves from a high concentration to a low concentration
Examples:
 Diffusion: The movement of particles from regions of higher concentration to
regions of lower concentration
 Facilitated Diffusion: Transport proteins help ions and polar molecules diffuse
through the membrane
 Osmosis: The diffusion of water across a selectively permeable membrane.
Osmotic conditions:
 Isotonic – concentration of solute is the same on both sides of
the membrane (equilibrium)
 Hypertonic – the solution with a greater concentration of
solute
 Hypotonic – the solution with the lesser concentration of
solute
Active Transport
–
–
Requires energy (usually energy used is from ATP)
Moves from a low concentration to a high concentration
Examples:
 Protein Pumps: an integral protein that transports ions
and small molecules against their concentration
gradients (ex. sodium potassium ion pump)
 Endocytosis: The movement of a large substance into a
cell by means of a vesicle
 Exocytosis: The movement of material out of a cell by
means of a vesicle
3. Circle the diagram letter that shows Endocytosis?
A
A or B
B
4. Circle the diagram letter that shows Exocytosis?
A
or B
Sodium-potassium pump: One of the most important carrier
proteins in animal cells. In nerve cells the pump is used to
generate gradients of both sodium and potassium ions. These
gradients are used to propagate electrical signals that travel along
nerves.
5. What does ‘semi-permeable’ mean when referring to the cell membrane?
Semi-permeable = selectively permeable: some things can pass, while others cannot
6. What 3 things determine whether something can pass freely through the cell membrane?
Size, concentration, polarity/charge
7.
What is passive transport? Give 3 examples. Movement that does NOT require energy, substances move
down/with the concentration gradient from MORE  LESS (examples: diffusion, osmosis, facilitated diffusion)
8. The paramecium is a fresh water protozoan. The salt content of its cytoplasm is greater than that of the
surrounding medium.
a. Does water tend to enter or leave the paramecium? Is this process passive or active transport?
Water will enter the paramecium by osmosis (going from more  less)
b. How does the paramecium expel water? Is this process passive or active transport? Explain.
Paramecium will expel water by using its contractile vacuole (pumps of xx water) active transport
9. Where does the energy for active transport come from and why is energy required for active transport?
Energy comes from ATP (made during cellular respiration) and it is required because substances are
moving AGAINST the concentration gradient (lessmore)
10. Identify a similarity and a difference between diffusion and osmosis?
Both are types of passive transport
Diffusion is the movement of molecules like CO2
Osmosis is the diffusion of water
11. Define the following terms and describe what would happen if you put a red blood cell in each type of solution.
a) Hypertonic- ABOVE: more solutes = less water, water will leave the cell and go into the solution, cell will
shrink, shrivel
b) Hypotonic- BELOW: low solutes = more water, water will enter the cell, animal cell can EXPLODE/CYTOLYSIS
c) Isotonic- EQUAL: equal solutes in the cell and in the solution, water moves in and out at the same rate
12. The cell in this beaker is bathed in a 2% NaCl solution. The membrane is permeable to water but not to NaCl.

3.7% NaCl


Label the areas that are hypertonic and hypotonic.
Cell is hypertonic, solution is hypotonic
In which direction is the net movement of water here?
Water will move INTO the cell
How will this affect the cell?
Cell may BURST/Cytolysis
2% NaCl
Main Concept 3: Describe how membrane-bound cellular organelles (e.g., endoplasmic reticulum, Golgi
apparatus) facilitate the transport of materials within a cell
Ribosomes - are small, dense granules (look like tiny circles on the diagrams) found free in the cytoplasm and on the
rough endoplasmic reticulum. Ribosomes are composed mainly of RNA (rRNA). They are the centers of protein
synthesis in the cell and consists of large and small subunits that join with mRNA and tRNA to make proteins from
directions provided by DNA (a molecule contained in the nucleus).
Endoplasmic reticulum - is a membrane-bound system of channels or tubes
through which materials are transported within the cell. The membranes of
the ER may also serve as sites of biochemical reactions. There are two types
smooth and rough. The rough appearance is due to the presence of
ribosomes on the membrane. Rough ER is found mainly in cells involved in
protein synthesis. Smooth ER which has no ribosomes, is found mainly in cells
involved in synthesis of nonprotein substances. The ER forms vesicles for
transport of proteins to other areas within the cell or to the golgi apparatus.
Golgi Apparatus - is made up of a series of membrane-enclosed sacs, and it is
usually found near the nucleus. This organelle is associated with the
production of lysosomes and with the sorting and packaging of various cellular
products. Produces transport vesicles (packages that move material inside or
export material outside the cell)
13. EXAMINE THE DIAGRAM BELOW, EXPLAIN THE PATH A NEWLY FORMED POLYPEPTIDE LEAVING A RIBOSOME
MAY TAKE AS IT IS MODIFIED OR PACKAGED BEFORE USE WITHIN THE CELL OR OUTSIDE THE CELL:
________________________________________
The polypeptide could proceed to the Rough ER for further modification,
then be transported via a vesicle to the Golgi for final packaging.
From the Golgi it could be sent outside the cell using a vesicle
RIBOSOME ER Vesicle  GOLGI  Vesicle  Destination
Main Concept 4: Explain how organisms maintain homeostasis
HOMEOSTASIS
Every cell or complex organism is a system – a set of components that interact to produce something greater than the
sum of its parts. Living systems work to maintain consistent internal states because changes in temperature or pH can
affect their ability to function. All living things perform a balancing act in which internal conditions (temperature, water,
salt, glucose, and oxygen are regulated and maintained within specific ranges. This process is called homeostasis.
Feedback Loops
 Homeostasis controls internal conditions with feedback loops
A. NEGATIVE feedback loop – the product inhibits the process that creates them (control of body temperature)
A thermostat controls the
heating and cooling systems,
returning the home’s
temperature to a set point
–
POSITIVE feedback loop – the product amplifies the process that creates them (global warming, labor)
• Ex. Labor, global warnming
Thermoregulation – the ability of an organism to keep its body temperature within certain boundaries, even when the
surrounding temperature is very different
Normal human body temperature is maintained by thermoregulation.
The hypothalamus of the brain senses the temperature of the blood
passing through it. If the temperature is too high or low, the
hypothalamus sends signals to various parts of the body that cause it
to release or retain heat. The mechanisms by which the body
regulates temperature include: shivering, perspiration, and the dilation
(widening) or constricting (tightening) of the tiny blood vessels in the
skin.

Vertebrates can regulate their body temperature in 2 different
ways:
o
Ectotherms – “cold blooded” - reptiles, fish, amphibians, warm bodies by absorbing heat from its
surrounding. Aquatic animals have body temps close to water temp, terrestrial animals change to get
more sun/shade as needed. Can’t live in very cold climates.
o
Endotherms –“warm blooded” - mammals and birds, have rapid metabolism which generates heat
needed to warm body. Also have insulation, such as hair, feathers, and fat.
14. The human body maintains a constant internal temperature of 98.6o F. Which changes occur when the
hypothalamus detects a temperature of 100.1oF?
A. Muscle tissue shivers and skin capillaries dilate
B. Perspiration increases and skin capillaries dilate
C. Muscle tissue shivers and skin capillaries constrict
D. Perspiration increases and skin capillaries constrict
Osmoregulation – the control of water concentration sin the bloodstream which controls the amount of water
available for cells to absorb
Water is a critical component of life. Organisms must carefully regulate the balance of water and solutes in the bodies, a
process called osmoregulation. The challenges of osmoregulation vary, depending on the organism’s environment.
The fresh water of lakes and rivers is HYPOTONIC to the cells of living things. Organisms that live in freshwater
environments are faced with excess water entering the body and the loss of solutes. Freshwater fish, for example,
excrete very dilute urine to eliminate excess water.
Organisms that inhabit saltwater oceans and seas are ISOTONIC to their environment. However, they must find ways to
retain the solutes they need and eliminate the excess sodium and chloride ions in seawater. Marine fish have
specialized gill cells that excrete excess chloride ions.
The challenge for land animals is to conserve water. To achieve
this, their urine is much more concentrated than their blood,
containing a high ratio of solutes to water. This allows them to
excrete excess solutes while conserving water. In the kidneys, the
blood is first filtered into an intermediate fluid. Then, the kidneys
reabsorb water and useful solutes from this fluid. By controlling
reabsorption, the body can control how much water is los in urine.
Another mechanism for maintaining water balance is the sensation
of thirst. The brain sends signals to the mouth and throat that
produce a feeling of dryness. This creates a motivation to drink
fresh water, replacing the water that the body has lost.
Land animals constantly lose water through evaporation,
perspiration, and urination. Water balance must be maintained to
prevent dehydration. In mammals the hypothalamus of the brain
senses the concentration of solutes in cells. Nerve signals from
special blood vessels sense the amount of fluid in the blood. These signals tell the hypothalamus whether the body
needs to take in and conserve water, or whether excess water should be excreted. The brain produces hormonal signals
that affect the amount of water the kidneys reabsorb.
Plants (regulated by stomata)
•
Leaves take in CO2, release O2 and H2O through stomata
•
Guard cells surround the stomata
•
–
Water abundant  water pressure in guard cells
is HIGH, stomata OPEN, release water, CO2 enters
–
Water scarce  water pressure in guard cells is
LOW, stomata CLOSED, loss of water limited
Generally 
–
Stomata open during the day (photosynthesis)
•
–
Stomata closed during the night
(decreased photosynthesis,
prevent water loss)
Exceptions  HOT & DRY conditions may result in
closed stomata during the day
Oxygen Regulation/Gas Exchange – O2 levels must be regulated according to activity level. The more active the
body/cells the more oxygen needed. During periods of slower activity less oxygen is needed. Rate is controlled by the
brain/brain stem to make sure carbon dioxide levels and oxygen levels are suitable for life (lungs in mammals, gill in
fish, book lungs in spiders, cell membranes etc.)
The body’s cells require oxygen to carry out respiration, which produces carbon dioxide. The levels of dissolved oxygen
and carbon dioxide in the blood must be regulated to allow respiration to take place.
Fish perform gas exchange through gills. Water flows over the capillaries in the gills, which contain a higher
concentration of carbon dioxide and a lower concentration of oxygen than the surrounding water. These differences
cause carbon dioxide to move into the water and oxygen to move into the bloodstream, through passive transport.
Mammals perform gas exchange through passive transport within the lungs. Capillaries, tiny blood vessels, surround
each of the microscopic air sacs in the lungs called
alveoli. The blood flowing to the alveoli contains too
much carbon dioxide and too little oxygen. Carbon
dioxide in the capillaries crosses the surface of the
alveoli and enters the air inside. Oxygen in the alveoli
crosses in the other direction, into the capillary blood.
When cells use up oxygen more quickly, such as during
strenuous exercise, the body compensates by moving
air into and out of the lungs faster. This increases the
rate of gas exchange and helps to maintain the levels of
oxygen and carbon dioxide in the bloodstream.
Blood Glucose (regulated by pancreas)
If blood glucose levels fall too low or rise too
high, homeostatic control mechanisms bring it
back into range. The control of glucose is an
example of a negative feedback loop
•
Blood sugar too high:
–
•
Pancreas releases insulin; body
cells take in glucose and moves
it to long term storage in liver
(glycogen)
Blood sugar too low:
–
Pancreas releases glucagon;
stimulates liver to break down
stored glycogen (into glucose)
and release into bloodstream
Practice Questions
1. What is a major difference between active and passive transport?
A. Active transport moves ions, while passive transport does not.
B. Active transport requires energy, while passive transport does not.
C. Active transport involves a concentration gradient, while passive transport does not.
D. Active transport uses membrane proteins, while passive transport does not.
2. Cholesterol does not dissolve in blood and other water-based body fluids. To be transported throughout the
body, it must be encased in lipoproteins, macromolecules that are water-soluble. How can a cell take in
lipoproteins from its extracellular fluid?
A. exocytosis
B. endocytosis
C. molecular pump
D. facilitated diffusion
Use the diagram below to answer the next question.
3. Which component of this membrane contains a hydrophobic region and
acts as the primary barrier to most foreign substances?
A. Protein
B. Carbohydrate chain
C. Cholesterol
D. Phospholipid bilayer
Use the list to answer the next question.
Functions of a Cell Structure
o Allows waste to exit the cell
o Allows chemicals required for cellular respiration to enter the cell
o Regulates movement of water into and out of the cell
4. The functions of which cell structure are described in the list above?
A. A lysosome
B. A mitochondrion
C. The plasma membrane
D. The endoplasmic reticulum
Use the diagram below to answer the next question.
5. The relative concentration of solute inside and outside a cell can cause water molecules to move across the
membrane. Which phrase would be an alternate
title to the diagram?
A. Exocytosis in a cell
B. Osmosis across a membrane
C. Active transport in a cell
D. Facilitated diffusion across a membrane
6. A sodium-potassium pump within a cell membrane requires energy to move sodium and potassium ions into or
out of a cell. The movement of glucose into or out of a cell does not require energy. Which statement best
describes the movement of these materials across a cell membrane?
A. Sodium & potassium ions move by active transport, & glucose moves by osmosis
B. Sodium & potassium ions move by active transport, & glucose moves by facilitated diffusion
C. Sodium & potassium ions move by facilitated diffusion, & glucose moves by osmosis
D. Sodium & potassium ions move by facilitated diffusion, & glucose moves by active transport
7. In order for the body to maintain homeostasis, the chemical decomposition of food to produce energy must be
followed by:
A. water intake.
B. muscle contractions.
C. waste removal.
D. nervous impulses.
8. The respiratory system depends on the nervous system for signals to
A. enhance the amount of available oxygen in the lungs.
B. coordinate muscles controlling breathing.
C. release enzymes to increase the exchange of gases.
D. exchange gases with the circulatory system.
9. A jackrabbit has large ears containing blood vessels that help it maintain a constant body temperature by
adjusting heat exchange with the surrounding environment. Which characteristic of life is best described by this
example?
A. Growth
B. Energy use
C. Organization
D. Homeostasis
Use the information below to answer the next 2 questions.
BACTERIA AND ANTIBIOTICS
Bacteria are single-celled microorganisms. The cell walls of these microorganisms serve as barriers to
chemicals that might affect processes that occur within a bacterial cell. Antibiotics are a type of
substance used to stop bacterial growth. Some antibiotics cause the bacterial cell wall to rupture.
10. The function of which human organ is most like the cell walls of bacteria?
A. Skin
B. Liver
C. Heart
D. Pancreas
11. Which statement best describes how antibiotics affect cellular homeostasis?
A. Antibiotics remove chloroplasts from plant cells to cause starvation.
B. Antibiotics interfere with the transport of intracellular and extracellular materials.
C. Antibiotics increase the rate of DNA replication in human cells by forming nucleotides.
D. Antibiotics decrease the rate of cellular respiration in animal cells by producing oxygen.
12. Which example is an activity that a fish most likely uses to maintain homeostasis within its body?
A. using camouflage to avoid predators
B. feeding at night to regulate body temperature
C. moving to deeper water to regulate metabolic wastes
D. exchanging gases through its gills to regulate oxygen levels
13. Some animals excrete nitrogen-containing wastes as urea in urine. Others excrete uric acid in the form of a thick
paste. In which type of environment does the excretion of uric acid provide the greatest advantage?
A. A desert ecosystem
B. A rainforest ecosystem
C. A freshwater pond ecosystem
D. A saltwater marine ecosystem
14. Which is not an example of an organism maintaining homeostasis?
A. A jogger stops to drink at a water fountain.
B. A turtle spends hours sitting on a sunny rock.
C. A deer seeks out salty food to add to its diet.
D. A rabbit hides among grasses to avoid a hawk.
Provide examples of how the following organism would maintain homeostasis under the following conditions and what
organelles or organs systems would be used.
Condition
Animal
Perspiration/panting
Plant
Transpiration (close stomata to prevent too
much water loss)
Shivering
Dormancy
Stop sweating and urination (drink water)
Close stomata to conserve water
Too hot
Too cold
Dehydrated
Low oxygen
Roots grow deeper to search for water
Increase breathing rate to bring in more oxygen
(go to alveoli site of gas exchange in lungs)
Open stomata
Photosynthesis, split water make oxygen