7-3 Movement through the Membrane

•Identify the main functions of the cell membrane.

•Describe what happens during diffusion

•Explain the processes of osmosis, facilitated diffusion, and active transport.

Cell Membrane

• Regulates what enters and leaves the cell

• Provides protection and support

• The core is a double-layered sheet called a lipid bilayer

Diffusion

• Movement of substances from an area of higher concentration to an area of lower concentration

• Equilibrium – all areas of concentration are equal

Diffusion (cont.)

• Diffusion is passive – it does NOT require cellular energy to take place

• Molecules move along the “concentration gradient”

High

Concentration

Low

Concentration

Osmosis

• Most biological membranes are “selectively permeable”

• Only allow certain substances through

How Osmosis Works

• In a sugar-water solution: – Cell membranes are permeable to

water but impermeable to sugar– To reach equilibrium, which all cells

“want” to do…water moves toward the side of the membrane with the higher concentration of solute (sugar) molecules

– See fig. 7-17, pg. 186

Osmotic Pressure

Osmotic Pressure (cont.)

Osmotic Pressure (cont.)

Facilitated Diffusion

• Moves molecules across the membrane that can’t pass by diffusion through special protein channels

• Ions, sugars, salts

Active Transport

• Requires energy to move particles against the concentration gradient

Takes

Energy!

Active Transport (cont.)

• Sodium-Potassium Pump and Coupled Channels

Endocytosis

• Moves LARGE particles into the cell

• Phagocytosis - amoeba

Exocytosis

• Moves large particles to the outside of the cell

• “exit” – “exocytosis”

Section Review

1. What processes are made possible by the cell membrane?

2. How does diffusion affect cells?3. Describe how water moves

during osmosis.4. What is the basic structure of a

cell membrane?5. How does active transport differ

from diffusion?