Accelerated Biology
Section 4.1 – Passive Transport
Read each question, and write your answer in the space provided.
1. What is passive transport? Why is diffusion an example of passive transport?
Passive Transport – the movement of molecules from an area of high concentration
to low concentration that does not require energy
Diffusion does not require a cell to use energy
2. How does the cell membrane help cells maintain homeostasis?
The cell membrane is selectively permeable; it only allows certain things to enter or
exit the cell.
3. What determines the direction in which a substance diffuses across a membrane?
Substances will follow the concentration gradient
They will move from an area of high concentration  low concentration
4. Describe the state of equilibrium.
The concentration of a substance is equal throughout space.
In the space provided, explain how the terms in each pair differ in meaning.
5. osmosis, diffusion
Osmosis is the diffusion of water
6. hypertonic solution, hypotonic solution
Hypertonic solution has a GREATER concentration of solutes compared to the cell
Hypotonic solution has a LOWER concentration of solutes compared to the cell
7. isotonic solution, equilibrium
An isotonic solution has reached equilibrium.
In the space provided, write the letter of the description that best matches the term or phrase.
8. ___f___ hypertonic solution
a. difference in the concentration of a substance across space
9. ___e___ selective permeability
b. the inside of a typical cell
10. ___c___ osmosis
c. diffusion of water through a cell membrane
11. ___b___ negatively charged
d. allows charged molecules to pass through cell membrane
12. ___g___ facilitated diffusion
e. enables a cell to control what enters and leaves
13. ___a___ concentration gradient
f. will cause a cell to shrivel up
14. ___d___ ion channel
g. involves carrier proteins
Active Reading
Read the passage below. Notice that the sentences are numbered. Then answer the questions that
follow.
1 The diffusion of water through a selectively permeable membrane is called osmosis. 2Like
other forms of diffusion, osmosis involves the movement of a substance—water—down its
concentration gradient. 3 Osmosis is a type of passive transport. 4If the solutions on either side
of the cell membrane have different concentrations of dissolved particles, they will also have
different concentrations of “free” water molecules. 5Osmosis will occur as water molecules
diffuse into the solution with the lower concentration of free water molecules.
Read each question, and write your answer in the space provided.
1. What key term is defined in this passage? What does this term mean?
Osmosis – Diffusion of water
2. How are diffusion and osmosis related?
Both are forms of passive transport, they move substances down the concentration
gradient.
3. What does the word water in Sentence 2 tell you about osmosis?
Osmosis involves the movement of water; any other substance is diffusion.
Section 4.2 – Active Transport
Complete each statement by writing the correct term or phrase in the space provided.
1. The transport of a substance across the cell membrane against its concentration gradient is called
active transport.
2. Active transport requires the cell to use energy.
3. The energy needed for active transport is usually supplied by ATP.
4. The sodium–potassium pump is a(n) carrier protein.
5. The concentration of sodium ions inside the cell is usually less than the concentration of sodium
ions outside the cell.
6. The concentration of potassium ions inside the cell is usually higher than the concentration of
potassium ions outside the cell.
7. The sodium–potassium pump picks up (Na) sodium ions outside the cell.
8. The sodium–potassium pump releases (K+) potassium ions inside the cell.
Read each question, and write your answer in the space provided.
9. Explain why proteins and polysaccharides cannot diffuse through the membrane like water does.
They are macromolecules (very large!)
10. What is the difference between endocytosis and exocytosis?
Endocytosis – The movement of a substance INTO a cell by a vesicle
Exocytosis – The movement of a substance OUT OF a cell by a vesicle
11. How do sodium–potassium pumps support the efficient functioning of cells?
It helps to maintain the concentration gradient. If sodium were to build up in the
cell, water would enter the cell by osmosis, causing the cell to swell and possible
burst
Vocabulary Review
Match the words on the left with the statements on the right.
1. ___b___ passive transport
a. difference in the concentration of a
substance across a space
2. ___a___ concentration gradient
b. does not require energy from a cell
c. molecules move from an area of high
3. ___d___ equilibrium
concentration to a lower concentration
d. concentration of a substance
4. ___c___ diffusion
is equal throughout a space
Match the words on the left with the statements on the right.
5. ___c___ osmosis
a. causes a cell to shrink because of osmosis
6. ___a___ hypertonic solution
b. produces no change in cell volume because of osmosis
7. ___d___ hypotonic solution
c. diffusion of water through a semi permeable membrane
8. ___b___ isotonic solution
d. causes a cell to swell because of osmosis
Match the words on the left with the statements on the right.
9. ___d___ ion channel
a. movement of a substance against substance’s
10. ___c___ carrier protein
11. ___b___ facilitated diffusion
12. ___a___ active transport
concentration gradient
b. passive transport using carrier proteins
c. protein used to transport specific substances
d. transport protein through which ions can pass
In the space provided, write the letter of the term or phrase that best completes each statement or
best answers each question.
1. ___b___ When a cell uses energy to transport a particle through the cell membrane to an area of
higher concentration, the cell is using
a. diffusion.
c. osmosis.
b. active transport.
d. facilitated diffusion.
2. ___a___ The excretion of materials to the outside of a cell by discharging them from vesicles is
called
a. exocytosis.
c. osmosis.
b. endocytosis.
d. diffusion.
3. ___a___ The mechanism that prevents sodium ions from building up inside the cell is called
a. the sodium–potassium pump.
c. diffusion.
b. endocytosis.
d. exocytosis
Questions 4–6 refer to the figures below.
4. Figure A illustrates a cell in a(n) hypertonic solution. (flaccid)
5. Figure B illustrates a cell in a(n) hypotonic solution. (turgid)
6. Figure C illustrates a cell in a(n) isotonic solution.
Read each question, and write your answer in the space provided.
7. Suppose you want to explain a concentration gradient to someone. Create a scenario that illustrates
passive transport down the concentration gradient.
8. Using your understanding of osmosis, describe why putting salt on a pork chop before cooking it
on a grill is likely to result in a dry, tough piece of meat.
Water will move out of the pork chop through the process of osmosis to try and
dilute the salt
9. How is facilitated diffusion different from the other passive transport processes?
Facilitated diffusion – Larger molecules, or ions, use a carrier protein to cross the
membrane
Diffusion – molecules simple pass through the phosolipid bilayer that makes up the
cell membrane
10. How does a cell consume a food particle that is too large to pass through a protein channel?
Phagocytosis “cell–eating” or endocytosis