Cell Transport
What can cross the cell membrane easily?
1) Hydrophobic molecules- like lipids, carbon dioxide, and
oxygen can dissolve in membrane and cross it w/ ease
2) Water- although it is polar it’s tiny enough to pass b/w
the fatty acid tails of the membrane (osmosis)
*These molecules use passive transport (diffusion &
osmosis) (no energy used) to cross the membrane
What molecules have trouble crossing the cell
membrane?
1) Sugars and amino acids (large molecules)
2) ions (polar) (ex. Na+ , K+)
*These molecules used facilitated diffusion (w/ help from
transport proteins like channel or carrier proteins) (no
energy used) to cross the membrane or they use active
transport (requires energy)
Equilibrium- concentration of a substance is the same
throughout a space
Solute- substance that dissolves in another
Ex. Sugars, salt, amino acids, & ions
Solvent- substance that dissolves the solute
Ex. In cells, solvent is water
Solution- mixture of solutes and solvent
Passive Transport- movement of a substance through a
cell’s membrane WITHOUT USING ENERGY
*PARTICLES MOVE FROM AN AREA OF HIGHER
CONCENTRATION (LARGE AMOUNT) TO AN AREA OF
LOWER CONCENTRATION (SMALL AMOUNT).
Types of Passive Transport
1. Osmosis- movement of water through a membrane from
an area of high conc. to low conc.
*water always moves across cell membranes to maintain
equilibrium
Types of Osmosis
1A). Isotonic Solution- solute conc. in the solution
outside of the cell is the same as it is inside the cell
-Likewise, conc. of water in the solution outside the cell is
the same as the conc. of water inside the cell
ex. Equal amounts of water will move into and out of the
cell, cell volume/shape is maintained
ex. IV’s at the hospital are isotonic to your cells
1B). Hypotonic Solution- solute conc. in the solution
outside the cell is lower than inside the cell
-Therefore, more water is present outside the cell than
inside
ex. Water moves into the cell and may cause it to burst
ex. Why grocery stores spray fruits and veggies
1C).Hypertonic Solution- solute conc. in the solution
outside the cell is higher than inside the cell
-Therefore, more water is present inside the cell than
outside
ex. Water moves out of the cell and causes it to shrivel
Types of Passive Transport (continued)
2. Diffusion- movement of particles directly through a
membrane from an area of high concentration to low
conc. (ex. Oxygen, carbon dioxide, water, lipids all use
this process)
Ex. Oxygen diffuses into the blood stream b/c there is a
higher conc. of oxygen in the lung’s air sacs than
there is in the blood
2A)Facilitated diffusion- transport of large particles
through a membrane by a channel or carrier protein
Ex. Glucose, amino acids, ions
*particles move from a high conc. to a low conc.
*no energy used
Active Transport- transport of specific particles through a
membrane by a channel or carrier protein
ex. Ions, etc.
*particles move from a LOW CONC TO A HIGH CONC.
*REQUIRES ENERGY
Types of active transport
*Sometimes some food molecules are too large to move into
the cell by transport proteins
1. Endocytosis- process by which large food particles and
extracellular particles are engulfed by a portion of the
cell’s membrane
ex. Phagocytosis (cell eating)- white blood cells engulf
bacteria
ex. Pinocytosis (cell drinking)- uptake of extracellular fluid
(ENTER CELL)
2. Exocytosis- reverse of endocytosis- dumping of waste
materials outside a cell by discharging them from waste
vesicles that fuse w/ the plasma membrane (EXIT CELL)
Overall Idea of Cell Transport
-cell is able to function b/c it is able to control what enters or
leaves
-like a home, a cell membrane has “doors with locks” that
only allow certain particles to pass through
-plasma membrane is selectively permeable b/c it allows the
passage of some solutes but not others