Cell Transport
Homeostasis
-Homeostasis means maintaining a ____________ internally despite what is going on externally.
-Organisms must adjust to changes in the environment in order to survive or they could _____!
 For example, if it is below freezing outside, you must put on a heavy coat, gloves, double
socks, a warm hat, ear muffs, and lots and lots of layers to maintain a healthy INTERNAL
body temperature despite the EXTERNAL temperature
-What structure maintains homeostasis in our cells?
-How does it maintain homeostasis?
By controlling the passage of molecules, such as water, salts, food particles, etc in and out of the
cell.(it regulates what _______________ and _______________)
-How?
Through passive transport, active transport and cell to cell communication!
The Cell Membrane
The Cell Membrane is:
-A phospholipid bilayer
 ___________ layers made of proteins and lipids
-Phospholipid Structure:
 Polar Head (hydrophilic—”water loving”)
 Nonpolar Tails—(hydrophobic—”water fearing”)
-Bilayer arrangement
Draw:
Draw:
Proteins in the Cell Membrane
The proteins embedded in the cell membrane help it to ___________________ properly
 3 Types of Membrane Proteins
o Transport—helps molecules enter or leave the cell
o Marker—identify the cell
o Receptor—allow cells to communicate
1. Transport Proteins
 Function as “gates/passageway”
 Allow sugars, salts, etc to cross the membrane.
 Special channel proteins:
› Gated ion channels—gates that _____________/close
› Carrier proteins—change ___________ to allow specific molecule to pass
2. Marker Proteins
 Cell’s “_____________ _____________”
 Protein sticks out of phospholipid layer
 Often has carbohydrates attached to outside end
 Functions in cell identification to identify the cell to other cells and molecules
 Important in
› immunity—so various white blood cells in your body do not mistake your cells for
foreign cells
› blood typing – so you can’t receive just any ol’ type of blood
3. Receptor Proteins
 Function as “___________________/receiver”
 Receive information from the environment (extracellular fluid, blood, interstitial fluid) and
transmit that info to the inside of the cell
 Protein has specific shape/charge to only allow certain molecules (like hormones) to bond
 Triggers a response in cell
-Proteins are embedded/floating in the lipid bilayer.
The Cell Membrane is:
-Selectively permeable/semipermeable
o permeable means to let objects travel through
o so if it is selectively or semi permeable it only allows ___________
things through and not others
It allows (selects) certain things to pass through it.
Is the membrane permeable to
? ________
Is the membrane permeable to
? ________
Molecules pass through the cell membrane through:
o Passive Transport
o Diffusion
o Facilitated Diffusion
o Osmosis
o Active Transport
o Vesicles
o Pumps
Cell Transport Vocabulary
-Molecule- the _________________ unit of a compound/substance
o Cannot be seen with the naked eye
o 1 drop of water has 16,700,000,000,000,000,000,000 molecules of H20
o 1 grain of salt has 120,000,000,000,000,000 molecules of salt
-Concentration Gradient- an area of ________ concentration next to an area of ______ concentration
High
Concentration
of Molecules
Low
Concentration
of Molecules
-Equilibrium is when there is an _____________ amount of molecules on each side of the membrane
-There is no net movement meaning, there is continuous movement of molecules back and forth
through the membrane.
Passive Transport
-Passive Transport is when molecules move from an area of _______________ concentration to an
area of _______________ concentration until equilibrium is reached.
-Requires ______ ENERGY!
-Examples:
o Diffusion
o Facilitated Diffusion
o Osmosis
o Passive Transport
Diffusion
-Diffusion- the process by which molecules (“stuff”) spread from areas of __________
concentration, to areas of _________ concentration
-Molecules are said to go “___________” or “with” the concentration gradient.
-Requires no energy
Facilitated Diffusion
-What does facilitate mean?
-When substances move from high to low concentration (down the concentration gradient) using
channel/carrier ___________ located in membrane
-Does not require energy
Osmosis
-A special type of diffusion is called _____________
-Osmosis- the process by which ____________ molecules move from an area with a _________
concentration of water to an area of _________ concentration of water.
o OR the “diffusion of water”
-Requires no energy
-In Osmosis water will move in where there is a low
concentration of SOLVENT, and a high concentration of
SOLUTE
o A solute = “stuff” (salt, glucose, food particles)
o A solvent = “water”
There are three ways water can move in a solution:
Hypotonic- water moves __________ a cell and the cell swells (gets bigger)
Hypertonic – water moves _________ of a cell and the cell shrinks (gets smaller)
Isotonic- water moves into AND out of a cell at an __________ rate (remember- molecules are
constantly moving)
Hypotonic-Water moves ____________ the cell (and could burst)
-There is more solvent/less solute on the outside of the cell than the
inside
-So the solvent (water) moves to an area of low solvent (water)
concentration
Hypertonic-Water moves _______ _______ the cell (and will shrink)
-There is less solvent/more solute on the outside of the cell than the
outside
-So the solvent (water) moves to an area of low solvent (water)
concentration
Isotonic-Water moves into and out of the cell at ________ rates and
stays the same size
-So the concentration of solvent and solute on the inside of the
cell is equal to the concentration of solvent and solute on the
outside of the cell
Passive Transport Recap:
o requires ______ __________
o moves from _______ concentrations to _______ concentrations
o Moves _________ the concentration gradient
o Includes diffusion, facilitated diffusion and osmosis
Active Transport
-Active transport is when molecules must move from a ___________ concentration to a
__________ concentration they must use active transport
-Cells must transport certain salts, sugars, etc. into their cytoplasm from the surrounding fluid.
-Some of these substances, however, are already in higher concentrations inside versus outside.
-This requires ______________!
-Opposite of Passive Transport
-Molecules go ______________ the concentration gradient
-Energy is provided by the ATP made in the …. __________________
-Active transport can involve pumps or vesicles
Pumps
-Pumps allow molecules to travel against their concentration gradient
-For example, the sodium/potassium pump actively transports sodium molecules and potassium
molecules through the cell membrane
-Requires ______________
o Na+ pumped out of a cell
o K+ pumped into a cell
-Important because it prevents cells from bursting by lowering the sodium inside causing less water
to enter through osmosis.
Vesicles
-Vesicles can transport molecules across the cell membrane through:
o Endocytosis- moving _____________ the cell
o Exocytosis- moving ______________ of the cell
-Requires energy
-Exocytosis can help get rid of wastes or secrete products like hormones or insulin