Biology
Ch. 8 Sec. 2: Cell Transport
Objectives
• What determines the direction in which passive transport occurs?
• Why is osmosis important?
• How do substances move against their concentration gradients?
Passive Transport
• In a solution, ________________________ moving molecules tend to fill up a space.
• When the space is filled evenly, a state called _______________________ is reached.
• The amount of a particular substance in a given volume is called the
_________________________________________ of the substance. When one area has a higher concentration than another area does, a _________________________________
__________________________________ exists.
• The movement of substances down a concentration gradient is called
_______________________.
• Movement from an area of __________________ concentration to an area of _______________ concentration.

Biology
Ch. 8 Sec. 2: Cell Transport
• The cell membrane separates the ________________________________ from the fluid outside the cell.
• Some substances enter and leave the cell by _________________________________ across the
___________ _______________________________.
• The ______________________________ of movement depends on the
____________________________ gradient and does _____________________ require energy.
• In _____________________ transport, substances cross the cell membrane _________________________ their concentration gradient.
• Some substances diffuse through the ______________
____________________________________.
• Other substances diffuse through _________________
___________________________________.
Simple Diffusion
• Small, ______________________________ molecules can pass directly through the lipid bilayer.
This type of movement is called __________________ _________________________________.
• ______________________________ moves down its concentration gradient into the cell.
________________________ _____________________________ diffuses out of the cell.
• Natural ___________________________ hormones, which are _______________________ and fat soluble, can also ________________________ across the lipid bilayer.

Biology
Ch. 8 Sec. 2: Cell Transport
Facilitated Diffusion
• Many ____________ and __________________ molecules (like water) that are important for cell function __________________________ diffuse easily through the
_______________________ lipid bilayer.
• During __________________________ diffusion, ___________________________
____________________________________________________________ help these substances diffuse through the cell membrane.
• ______________________ types of transport proteins are _______________________ proteins and ______________________________ proteins.
• Ions, sugars, and amino acids can _________________________________________ through the cell membrane through __________________________proteins.
• These proteins, sometimes called _____________________, serve as
______________________________ through the lipid bilayer.
• Each channel allows the ______________________________ of __________________________ substances that have the right size and charge.
• Carrier proteins transport substances that _________ within their ____________________ site.
• A ________________________________ protein binds to a _____________________________ substance on one side of the cell membrane. This binding causes the protein to
_______________________ shape.
• As the protein’s shape _____________________________, the substance is ________________ across the membrane and is _________________________ on the other side.
Osmosis
• Water can _________________________ across a selectively permeable membrane in a process called ________________________________.
• Osmosis in cells is a form of _______________________________________________ diffusion.
• Polar water molecules __________ ___________ diffuse directly through the bilayer.
But the cell membrane contains __________________________ proteins that only water molecules can pass through.
• _____________________________ allows cells to maintain water balance as their environment
_________________________________.

Biology
Ch. 8 Sec. 2: Cell Transport
• When ions and polar substances ________________________ in water, they
_________________________ and ____________________________ some water molecules.
The remaining water molecules are ______________________ to move around.
• If a _______________________________ gradient exists across a membrane for
___________________________, a concentration gradient ___________________ exists across the membrane for _________________ water molecules.
• ______________________ occurs as free water molecules move _____________________ their concentration gradient into the _________________________ that has the _________________ concentration of free water molecules.
• The ____________________________ of water movement in a cell depends on the
__________________________________________ of the cell’s environment.
• If the solution is _______________________________, or has a _____________________ solute concentration than the cytoplasm does, water moves ____________________ of the cell.
• The cell ______________ water and ________________.
• If the solution is _______________________________, or has the ___________________ solute concentration that the cytoplasm does, water diffuses into and out of the cell at _____________ rates. The cell stays the ________________ ____________________.
• If the solution is ___________________________________, or has a _________________ solute concentration than the cytoplasm does, water moves _______________________ the cell.
• The cell _______________________ water and ______________________ in size.
• If left unchecked, the ___________________________ caused by a _______________________ solution could cause a cell to _________________________.
• The ______________________ cell walls of plants and fungi prevent the cells of these organisms from expanding _____________ much.
• In fact, many plants are ____________________________ in a
___________________________ environment.

Biology
Ch. 8 Sec. 2: Cell Transport
• Some _______________________________ eukaryotes have
________________________________ vacuoles, which collect ______________________ water inside the cell and _______________________ the water out of the cell.
• Animal cells have ________________________________ cell walls nor contractile vacuoles.
• Many animal cells can _____________________________________ swelling caused by osmosis by _______________________ _____________________________ solutes from the cytoplasm.
Active Transport
• In order to move substances _________________________ their _________________________ gradients, cells must ______________ energy.
• __________________________ ____________________________________ requires energy to move substances __________________________ their concentration gradients.
• Most often, the energy needed for active transport is ____________________________ directly or indirectly by _______.
Pumps
• Many active transport processes use ____________________ _________________________ to move substances.
• In _________________________________ diffusion, the carrier proteins _______ ___________ require energy.
• In active transport, the carrier proteins ________________ require energy to “_____________” substances ____________________________ their concentration gradient.

Biology
Ch. 8 Sec. 2: Cell Transport
• The _________________________________________________ _________________________ is a carrier protein that actively transports ______________________ sodium ions out of the cell and ___________________ potassium ions into the cell.
• This pump is one of the most _____________________________ carrier proteins in animal cells.
It _____________________________ sodium ions from building up in the cell, resulting in
_____________________________ into the cell.
• The ___________________________________________________ gradients of sodium ions and potassium ions also help _____________________________________ other substances, such as
____________________________, across the cell membrane.
• Many substances, such as _______________________________________ and polysaccharides, are __________ ___________________________ to be transported by carrier proteins.
• Instead, they cross the cell membrane in ____________________________________, which are membrane-bound sacs.

Biology
Ch. 8 Sec. 2: Cell Transport
• The vesicle membrane is a ___________________ ____________________________, like the cell membrane. Therefore, vesicles can bud ___________ from the membrane,
_______________ with it, or fuse with other __________________________.
• The movement of a large substance _________________ a cell by means of a vesicle is called
______________________________________________.
• During ___________________________________________ the cell membrane forms a pouch around the substance.
• The pouch then closes up and ____________________________off from the membrane to form a _____________________________ ______________________________ the cell.
• Vesicles that form by endocytosis may fuse with ________________________________ or other
____________________________________.
• The movement of material _____________ of a cell by means of a vesicle is called
_____________________________________________.
• During __________________________________________, vesicles inside the cell ___________ with the __________ ______________________________. From the cell membrane, the
____________________________ of the vesicle are ______________________________ to the outside of the cell.
• Cells use exocytosis to _________________________ proteins modified by the Golgi apparatus.
Some protists _________________________ their waste products through this process. Some cells also use exocytosis to remove ______________________________ or other microbes.
Summary
• What determines the direction in which passive transport occurs?
• Why is osmosis important?
• How do substances move against their concentration gradients?

Biology
Ch. 8 Sec. 2: Cell Transport