Homeostasis and Transport
Keystone Eligible Content:
 Describe how the structure of the plasma membrane allows it to function as a regulatory
structure and/or protective barrier for a cell
 Compare the mechanisms that transport materials across the plasma membrane (i.e. passive
transport - diffusion, osmosis, facilitated diffusion; and active transport – pumps, endocytosis,
exocytosis)
 Describe how membrane-bound cellular organelles (e.g. endoplasmic reticulum, Golgi
apparatus) facilitate the transport of materials within a cell
 Explain how organisms maintain homeostasis (e.g. thermoregulation, water regulation, oxygen
regulation)
Describe how the structure of the plasma membrane allows it to function as a regulatory
structure and/or protective barrier for a cell.
1. Draw a small section of the cell membrane (phospholipid bilayer) and label the following
terms: fatty acid, polar, hydrophobic, hydrophilic, nonpolar, and glycerol.
2. Identify the function of the cell membrane.
To regulate entry and exit of ions, molecules, and fluids into and out of the cell.
3. How does facilitated diffusion differ from diffusion?
Facilitated diffusion uses a protein channel to facilitate the movement of molecules in and out of
the cell. Both are passive.
4. Which class of organic compounds makes up the channels and pumps that help move
materials from one side of the cell membrane to the other?
a. Carbohydrates
c. Proteins
b. Lipids
d. Nucleic Acids
Compare the mechanisms that transport materials across the plasma membrane
(i.e. passive transport- diffusion, osmosis, facilitated diffusion; and active transportpumps, endocytosis)
5. Distinguish between active and passive transport and give two examples of each type of
transport.
Active transport requires ATP and examples include exocytosis and use of protein pumps (push
material against gradient)
Passive transport requires no energy and moves materials from high to low concentration.
Examples include simple diffusion and facilitated diffusion
6. Identify a similarity and a difference between diffusion and osmosis?
Diffusion and osmosis do not require energy (passive). Diffusion could be the movement of
anything from high to low, but osmosis only applies to water.
7. Define the following terms and describe what would happen if you put a red blood cell in each
type of solution.
a) Hypertonic- Cell would shrink (water would leave the cell)
b) Hypotonic- Cell would swell (water would enter the cell)
c) Isotonic- the cell is in equilibrium and would not change.
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
8. Label the areas that are hypertonic and hypotonic
Inside cell – hypertonic, outside cell hypotonic
9. In which direction is the net movement of water here?
Water moves into the cell.
2% NaCl
10. How will this affect the cell?
Cell would swell and possibly lyse (break)
Describe how membrane-bound cellular organelles (e.g. endoplasmic reticulum, Golgi
apparatus) facilitate the transport of materials within a cell.
11. Identify the function of the following organelles:
Endoplasmic Reticulum – synthesizes proteins to be used outside the cell, modified
proteins coming from free ribosomes, used to transport proteins around the cell.
Golgi Apparatus – Packages and sort proteins from the ER. Uses vesicles to send the
protein outside the cell membrane.
12. Trace the correct path of a protein in a cell using all of the organelles listed below:
ER
Nucleolus
Ribosome
Golgi Apparatus
____nucleolus_____  ____ribosome____  __ER_____  ____Gogi________
Explain how organisms maintain homeostasis (e.g. thermoregulation, water regulation,
oxygen regulation).
13. What is meant by the term homeostasis?
An organism maintains a stable internal environment.
14. What is a contractile vacuole and how can it be used to maintain homeostasis?
An organelle that stores water and nutrients, but has the ability to push water out of the
cell. This organelle can take water in or pump it out depending on conditions around the
organism. Regulating the water balance maintains homeostasis.
Assessment Anchor – Homeostasis and Transport:
Describe how the structure of the plasma membrane allows it to function as a regulatory
structure and/or protective barrier for a cell.
Use the following diagram to answer questions 1 and 2.
1. A researcher noticed that a similar CH2 molecule structure was also located in the
plasma membrane of an animal cell. This CH2 molecular structure contained a
negatively charged phosphate group. Which statement best describes the primary
function of the CH2 and phosphate molecular structure located in the plasma
membrane?
A. It contains the genetic information needed for protein production.
B. It catalyzes specific chemical reactions in the cytoplasm of a cell.
C. It stores the energy that a cell needs to perform various life processes.
D. It allows a cell to regulate the movement of materials into and out of a cell.
2. Which type of organic molecule was most likely formed by the scientist in the
laboratory?
A. Lipid
C. Nucleic acid
B. Protein
D. Carbohydrate
3. Carbon dioxide and oxygen are molecules that can move freely across a plasma membrane.
What determines the direction that carbon dioxide and oxygen molecules move?
a. orientation of cholesterol in the plasma membrane
b. concentration gradient across the plasma membrane
c. configuration of phospholipids in the plasma membrane
d. location of receptors on the surface of the plasma membrane
Use the diagram below to answer question 4.
4. 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
Compare the mechanisms that transport materials across the plasma membrane (i.e. passive
transport - diffusion, osmosis, facilitated diffusion; and active transport – pumps, endocytosis,
exocytosis).
5. Some animals can produce a potassium ion concentration inside their cells that is
twenty times greater than that of their environment. The ion concentration gradient is
maintained by the plasma membrane.
A. Identify the process in the cell membrane that produces this difference in
concentration.
______________________________________________________________________________
___ Active because as you can see from the diagram ATP is used to power the protein pump.
B. Explain the process that occurs as the cell produces the ion concentration gradient.
____ ATP is the energy currency of the cell. Without ATP the cell can not do work. When ATP
powers the protein a bond between the 2nd and 3rd phosphate group breaks and energy is released.
Therefore, ATP (adenosine triphosphate) becomes ADP (adenosine diphosphate).
ADP can then later be converted back to ATP by the mitochondria through cell respiration.
C. Compare the process of potassium ion transport to another mechanism that moves
material across the plasma membrane.
______________________________________________________________________________
____ This type of transport is specific to NA+ and K+, the protein is built to fit these ions. Also
this transport is active. Facilitated diffusion also uses a protein, but only as a channel and the
movement across the membrane is passive, following the concentration gradient from high to low.
No ATP is needed.
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
Use the diagram below to answer question 7.
7. 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
c. Osmosis Across a Membrane
b. Active Transport in a Cell
d. Facilitated Diffusion Across a Membrane
Describe how membrane-bound cellular organelles (e.g. endoplasmic reticulum, Golgi
apparatus) facilitate the transport of materials within a cell.
8. The rough endoplasmic reticulum and Golgi apparatus work together in eukaryotic cells.
What is one way that the rough endoplasmic reticulum assists the Golgi apparatus?
a. It assembles nucleic acids from monomers.
b. It breaks down old, damaged macromolecules.
c. It packages new protein molecules into vesicles.
d. It determines which protein molecules to synthesize.
Explain how organisms maintain homeostasis (e.g. thermoregulation, water regulation,
oxygen regulation).
9. 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