Lesson Overview
7.3 Cell Transport
Lesson Overview
Cell Transport
Cell Membranes
o All cells contain a cell membrane that ______________
what enters and leaves the cell and also
_______________________________________the cell.
Lesson Overview
Cell Transport
Cell Membranes
o The cell membranes is a double-layered sheet called a
______________________, which gives cell membranes
a flexible structure and forms a strong barrier between
the cell and its surroundings.
Lesson Overview
Cell Transport
The Properties of Lipids
o
Many lipids have oily ____________________ attached to
__________________________ that interact strongly with water.
o
The fatty acid portions of such a lipid are ______________,
or “water-hating,” while the phosphate end of the molecule is
____________________________, or “water-loving.”
Lesson Overview
Cell Transport
The Properties of Lipids
o When such lipids are mixed with water, their
________________________cluster together while
their ________________________are attracted to
water. A ________________________is the result.
Lesson Overview
Cell Transport
The Properties of Lipids
o The __________________of lipids in a bilayer are
exposed to water, while the _________________form
an oily layer inside the membrane from which water is
excluded.
Lesson Overview
Cell Transport
The Fluid Mosaic Model
o Most cell membranes contain _____________
molecules that are embedded in the lipid bilayer.
________________________ molecules are
attached to many of these proteins.
Lesson Overview
Cell Transport
The Fluid Mosaic Model
Because the proteins embedded in the lipid bilayer can move
around and “float” among the lipids, and because so many
different kinds of molecules make up the cell membrane,
scientists describe the cell membrane as a “_______________.”
Lesson Overview
Cell Transport
The Fluid Mosaic Model
o Some of the __________ form channels and pumps
that help to move material across the cell membrane.
o Many of the ___________________ molecules act
like chemical identification cards, allowing individual
cells to identify one another.
Lesson Overview
Cell Transport
The Fluid Mosaic Model
o
Although many substances can cross biological membranes,
some are ____________or too ______________________to
cross the lipid bilayer.
o
If a substance is able to cross a membrane, the membrane is
said to be ______________________to it.
o
A membrane is _______________________to substances that
cannot pass across it.
o
Most biological membranes are ________________________,
meaning that some substances can pass across them and
others cannot. Selectively permeable membranes are also called
semipermeable membranes.
Lesson Overview
Cell Transport
Passive Transport
o Every living cell exists in a
_____________________environment.
o One of the most important functions of the
cell membrane is to keep the cell’s internal
conditions relatively ___________. It does
this by regulating the movement of
molecules from one side of the
membrane to the other side.
Lesson Overview
Cell Transport
Diffusion
o The cytoplasm of a cell is a ________________ of
many different substances dissolved in water.
o In any solution, __________ particles tend to move
from an area where they are _____________________
to an area where they are _______________________.
o The process by which particles move from an area of
high concentration to an area of lower concentration is
known as __________________.
o Diffusion is the driving force behind the movement of
many substances across the cell membrane.
Lesson Overview
Cell Transport
Diffusion
o Suppose a substance is present in ________________
concentrations on either side of a cell membrane.
Lesson Overview
Cell Transport
Diffusion
o If the substance can cross the cell membrane, its
particles will tend to move toward the area where it is
______ concentrated until it is evenly distributed.
Lesson Overview
Cell Transport
Diffusion
At that point, the concentration of the substance on both sides of the
cell membrane is the same, and __________________ is reached.
Lesson Overview
Cell Transport
Diffusion
o
Even when equilibrium is reached, particles of a solution
will_______________________________across the membrane in
both directions.
o
Because almost equal numbers of particles move in each
direction, there _______________________in the concentration on
either side.
Lesson Overview
Cell Transport
Diffusion
o Diffusion depends upon
________________________. Substances
diffuse across membranes without
requiring the cell to use additional energy.
o The movement of materials across the
cell membrane without using cellular
energy is called ___________________.
Lesson Overview
Cell Transport
Facilitated Diffusion
o Cell membranes have ____________ that act as
carriers, or channels, making it easy for certain
molecules to cross.
o Molecules that cannot directly diffuse across the
membrane pass through special protein channels in a
process known as ____________________________.
o Hundreds of different proteins have been found that
allow particular substances to cross cell membranes.
o The movement of molecules by facilitated diffusion
does not require any additional use of the cell’s
_____________.
Lesson Overview
Cell Transport
Osmosis: An Example of Facilitated
Diffusion
o
The inside of a cell’s lipid bilayer is
hydrophobic—or “____________.”
Because of this, water molecules have a
tough time passing through the cell
membrane.
o
Many cells contain water channel
proteins, known as ______________,
that allow water to pass right through
them. Without aquaporins, water would
diffuse in and out of cells very slowly.
o
The movement of water through cell
membranes by facilitated diffusion is an
extremely important biological process—
the process of __________________.
Lesson Overview
Cell Transport
Osmosis: An Example of Facilitated
Diffusion
o ____________________ is the diffusion
of water through a selectively permeable
membrane.
o Osmosis involves the movement of
__________ molecules from an area of
___________ concentration to an area of
______________ concentration.
Lesson Overview
Cell Transport
How Osmosis Works
o In the experimental setup below, the barrier is
permeable to water but not to sugar. This means that
water molecules can pass through the barrier, but the
solute, sugar, cannot.
Lesson Overview
Cell Transport
How Osmosis Works
o There are more sugar molecules on the right side of the
barrier than on the left side. Therefore, the concentration
of water is __________ on the right, where more of the
solution is made of sugar.
Lesson Overview
Cell Transport
How Osmosis Works
o
There is a net movement of __________ into the compartment
containing the concentrated sugar solution.
o
Water will tend to move across the barrier until _______________
is reached. At that point, the concentrations of water and sugar will
be the same on both sides.
Lesson Overview
Cell Transport
How Osmosis Works
o When the concentration is the same on
both sides of the membrane, the two
solutions will be _______________, which
means “same strength.”
Lesson Overview
Cell Transport
How Osmosis Works
o
The more concentrated sugar solution at the start of the experiment
was __________________, or “above strength,” compared to the
dilute sugar solution.
o
The dilute sugar solution was _____________, or “below strength.”
Lesson Overview
Cell Transport
Osmotic Pressure
o For organisms to survive, they must have
a way to _______________ the intake and
loss of water.
o The net movement of water out of or into
a cell exerts a force known as
_______________________________.
Lesson Overview
Cell Transport
Osmotic Pressure
o
Because the cell is filled with salts, sugars, proteins, and other
molecules, it is almost always ________________ to fresh water.
o
As a result, water tends to move quickly into a cell surrounded by
fresh water, causing it to ________. Eventually, the cell may
_______.
Lesson Overview
Cell Transport
Osmotic Pressure
o
In plants, the movement of water into the cell causes the
_____________________ to swell, pushing cell contents out against
the cell wall.
o
Since most cells in large organisms do not come in contact with
fresh water, they are not in danger of bursting.
Lesson Overview
Cell Transport
Osmotic Pressure
o
Instead, the cells are bathed in fluids, such as blood, that are
________________ and have concentrations of dissolved materials
roughly equal to those in the cells.
o
Cells placed in an ______________ solution neither gain nor lose
water.
Lesson Overview
Cell Transport
Osmotic Pressure
o In a _________________solution, water rushes
out of the cell, causing animal cells to
_________and plant cell vacuoles to_________.
Lesson Overview
Cell Transport
Osmotic Pressure
o Other cells, including those of plants and bacteria, that
come into contact with fresh water are surrounded by
tough _____________that prevent the cells from
expanding, even under tremendous ________________.
Lesson Overview
Cell Transport
Osmotic Pressure
o
Notice how the plant cell holds its shape in __________________
solution, while the animal red blood cell does not.
o
However, the increased osmotic pressure makes such cells
extremely vulnerable to injuries to their cell walls.
Lesson Overview
Cell Transport
Active Transport
o Cells sometimes must move
materials ________________ a
concentration difference.
o The movement of material against a
concentration difference is known as
__________________. Active
transport requires ______________.
Lesson Overview
Cell Transport
Active Transport
o The active transport
of small molecules or
ions across a cell
membrane is
generally carried out
by ______________,
or _______________
that are found in the
membrane itself.
Lesson Overview
Cell Transport
Active Transport
o
Larger molecules and
clumps of material can also
be actively transported
across the cell membrane by
processes known as
______________ and
___________________.
o
The transport of these
larger materials sometimes
involves changes in the
_________ of the cell
membrane.
Lesson Overview
Cell Transport
Molecular Transport
o
Small molecules and ions are
carried across membranes by
__________________ in the
membrane that act like
_____________.
o
Many cells use such proteins
to move
_________________________
_________________________
ions across cell membranes.
o
Changes in protein _________
seem to play an important role
in the pumping process.
Lesson Overview
Cell Transport
Bulk Transport
o ____________ molecules and
even solid clumps of material
may be transported by
movements of the cell
membrane known as
______________________.
o
Bulk transport can take
several forms, depending on
the size and shape of the
material moved into or out of
the cell.
Lesson Overview
Cell Transport
Endocytosis
o ___________________ is
the process of taking material
into the cell by means of
infoldings, or pockets, of the
cell membrane.
o
The pocket that results
breaks loose from the outer
portion of the cell membrane
and forms a
_______________________
_______________________
within the cytoplasm.
Lesson Overview
Cell Transport
Endocytosis
o Large molecules,
clumps of food, and
even whole cells can
be taken up by
_________________.
o Two examples of
endocytosis are
_______________
and _____________.
Lesson Overview
Cell Transport
Endocytosis
o In ___________________, extensions of
cytoplasm surround a particle and package it
within a food vacuole. The cell then engulfs it.
o _________________ use this method for taking
in food.
o Engulfing material in this way requires a
considerable amount of _________ and,
therefore, is a form of _____________________.
Lesson Overview
Cell Transport
Endocytosis
o In ________________, cells take
up ____________ from the
surrounding environment by
forming tiny pockets along the cell
membrane.
o The pockets fill with liquid and
pinch off to form
__________within the cell.
Lesson Overview
Cell Transport
Exocytosis
o
Many cells also
release large amounts
of material from the cell,
a process known as
_________________.
o
During exocytosis,
the membrane of the
vacuole surrounding the
material fuses with the
cell membrane, forcing
the contents
__________________.