Cellular TransportChapter 7-3

Cell MembraneFunctions:

Regulates what enters and leaves the cell.Protects and supports the cellCommunication with other cells and the body.

Composed of: A lipid bilayer - two flexible layers of phospholipids

Membrane proteins, cholesterol, and attached carbohydrates.

Fluid Mosaic ModelFluid mosaic model: the idea that the cell membrane is a “mosaic” of proteins and lipids, which can move “fluidly” throughout the membrane.

Selectively PermeableOnly certain substances can pass through the cell membrane.

DiffusionDiffusion is the movement of molecules

from an area of higher concentration to areas of lower concentration.

DiffusionDiffusion across a cell membrane does not require energy input from the cell (it is a passive process).

DiffusionWhen the concentration of a solute is the same throughout a solution, equilibrium has been reached.

Equilibrium

OsmosisOsmosis is the diffusion of water through a selectively permeable membrane to the highest solute concentration

OsmosisWater will flow towards an area of highersolute concentration (lower water concentration) until equilibrium is reached.

Types of Solutions and Osmosis

Type of Solution

Solute Concentration Water Movement

Isotonic Solute concentration is equal to the inside

of the cell.

No net movement of water into or out of

the cell.

Hypotonic Solute concentration is lower than the inside of the cell.

Water moves into the cell.

HypertonicSolute concentration

is higher than the inside of the cell.

Water moves out of the cell.

Effects of Osmosis on Cells

Effects of Osmosis on RBC’s

Turgor PressurePlants depend on osmosis to bring water into their cells and put pressure on their cell walls. This is called turgor pressure.Without enough turgor pressure, plants will wilt and die.

Contractile VacuolesSome single-celled organisms contain contractile vacuoles to pump water out of the cell so they do not burst.

Facilitated DiffusionFacilitated diffusion is the diffusion of substances in the cell with the help of carrier proteins in the cell membrane.

Active TransportThe movement of substances through a cell membrane from an area of low concentration to an area of high concentration.

Requires the cell to expend energy.

Cell membrane pumps: special carrier proteins that use energy to move substances across the cell membrane.

Endocytosis: the process of taking large amounts of material into the cell by forming a pouch in the cell membrane.

Pinocytosis –“cell drinking”

Phagocytosis –“cell eating”

Exocytosis: The movement of large amounts of cell products and waste out of the cell.

Overview of Cell Transport

Flash Macromedia Membrane Transport