Cells and Their Environment

Objectives:1. Relate concentration gradients, diffusion,

and equilibrium.2. Describe the importance of ion channels

in passive transport3. Identify the role of carrier proteins in

facilitated diffusion

Passive Transport

Passive Transport: is movement across the cell membrane that does not require energy form the cell. Particles move along their concentration gradient. Does not require energy.

Concentration Gradient and Equilibrium

Concentration Gradient: A difference in the concentration of a substance across a space.

Equilibrium: is a condition in which the concentration of a substance is equal throughout a space.

Diffusion

Diffusion: The movement of a substance from an area of high concentration to an area of low concentration.

If diffusion is allowed to continue, equilibrium will result.

OsmosisOsmosis: is the diffusion of water

through a selectively permeable membrane along its concentration gradient.

The direction of water movement across the cell membrane depends on the relative concentrations of free water molecules in the cytoplasm and in the fluid outside the cell

Hypertonic

Hypertonic: is when the fluid outside the cell has a higher concentration of dissolved particles.

Water moves out of the cell and into the surrounding solution.

Hypotonic

Hypotonic: The fluid outside the cell has a lower concentration of dissolved solutes than inside the cell.

Water moves into the cell.

Isotonic

Isotonic: When there is no net water movement because there is the same concentration of water on both sides of the membrane.

Facilitated Diffusion

Uses carrier proteins embedded in the membrane to transports specific substances, such as amino acids and sugars, down their concentration gradients.

Active Transport: Transportation of a substance against its concentration gradient, requiring the cell to use ATP!

Example of Active TransportThe Sodium-Potassium Pump

Endocytosis

Endocytosis: The cell membrane forms a pouch around a substance, that closes up and pinches off to form a vesicle.

Exocytosis

Exocytosis: The movement of a substance by a vesicle to the outside of cell

Membrane Receptor Proteins

Receptor Protein: is a protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule