section
3.5
Active Transport,
Endocytosis, Exocytosis
Teacher Notes and Answers
SECTION 5
Instant Replay
1.Active transport requires a cell to use energy,
and passive transport does not.
2.They enable a cell to take in or get rid of large
materials or large amounts of materials. They
play important roles in the body’s defense and
in secreting hormones and other molecules.
Vocabulary Check
1.Students should draw the last frame from the
exocytosis figure.
2.Students should draw the first frame from the
exocytosis figure.
The Big Picture
3.energy
4.Answers will vary. Students may list that both
processes require energy and transport
substances in vesicles. Endocytosis takes in
materials. Exocytosis gets rid of materials.
Interactive Reader
1
section
3.5
Active Transport,
Endocytosis, Exocytosis
Key Concept Cells use energy to transport materials that cannot diffuse
across a membrane.
Proteins can transport materials against a
concentration gradient.
You have seen that the cell membrane controls the passive transport
of materials into and out of a cell. However, cells often need large
amounts of materials that cannot diffuse across the membrane.
Cells can use energy to move molecules from an area of lower concentration to an area of higher concentration. This process is called
active transport. As the figure shows, active transport uses energy to
drive molecules through transport proteins. This process plays an
important role in helping cells to maintain homeostasis.
What is the difference between active transport and
passive transport?
outside
energy
During active transport, a cell uses
energy to move substances against
a concentration gradient—that is,
from a lower to a higher concentration.
Endocytosis and exocytosis transport
materials across the membrane in vesicles.
Sometimes a material is too large to cross the membrane. Cells can use
energy to transport these materials in vesicles. A cell uses endocytosis to
take in large materials or liquids. The prefix endo- means “in.” In endocytosis, the cell membrane starts to fold in, forming a pocket around a
substance. The pocket breaks off inside the cell, making a vesicle. The
contents of the vesicle are then broken down or released into the cell.
Phagocytosis (fag-uh-sy-toh-sihs) is a type of endocytosis in
which the cell membrane grows out to surround large particles. The
word literally means “cell eating.” Phagocytosis plays an important role
in the immune system when white blood cells “eat” bacteria and other
invaders.
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The cell membrane folds
inward, enclosing the
substance in a pocket.
The pocket pinches off
inside the cell, forming
a vesicle.
The vesicle fuses with a
lysosome, where enzymes
break it down.
McDougal Littell Biology
inside
Exocytosis is the opposite of endocytosis. The prefix exo- means “out.”
It is the process that moves substances out of the cell. In exocytosis, a
vesicle surrounds materials that need to be removed. The vesicle then
goes to the cell membrane, fuses with it, and lets go of the contents.
Exocytosis is the cell’s way of getting rid of wastes or secreting molecules.
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2
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The cell forms a vesicle
around material that
needs to be removed
or secreted.
The vesicle is transported to the cell
membrane.
The vesicle membrane
fuses with the cell membrane and releases the
contents.
What functions do endocytosis and exocytosis carry out for
the cell?
3.5 Vocabulary Check
active transport
endocytosis
phagocytosis
exocytosis
1. Draw the last step of exocytosis at right.
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1.
2.
2. Draw the first step of endocytosis at right.
3.5 The Big Picture
3. The biggest difference between active transport and passive transport
is the need for the cell to use
.
4. Draw a Venn diagram in the
space to the right to compare
and contrast exocytosis and
endocytosis.
Interactive Reader
3