Chapter 7 Cell Structure & Function Section 7-3 Movement Through The Membranes

Objectives What are the main functions of the cell membrane and the cell wall? What happens during diffusion? What is osmosis?

The Cell Membrane Key Concept: The cell membrane regulates what enters and leaves the cell and also provides protection and support

The Cell Membrane The cell takes in nutrients and expels wastes plus cell products through the cell membrane The Basic Structure Of Nearly All Cell Membranes Is The LIPID BILAYER

LIPID BILAYERS Form Automatically When Certain Lipids Are Dissolved In Water Tough Flexible Structure Strong Barrier Between Cell Contents And Its Surroundings

LIPID BILAYERS

LIPID BILAYERS

In Addition To The Bilayer, The Cell Membrane Contains: Fluid Mosaic Model In Addition To The Bilayer, The Cell Membrane Contains: Proteins That Form Channels & Pumps Proteins with Carbohydrates That Form Antigenic Sites Communication Sites

Diffusion All Living Cells Contain And Are Surrounded By Liquid. THE CELL MEMBRANE REGULATES THE MOVEMENT OF MOLECULES FROM ONE SIDE OF THE MEMBRANE TO THE OTHER

Is A Solution Of Many Different Substances In Water Cytoplasm Is A Solution Of Many Different Substances In Water

A liquid mixture of 2 or more substances evenly mixed. Solution A liquid mixture of 2 or more substances evenly mixed. Solvent The liquid in which the substances are mixed Solute Substances dissolved in the Solvent

Concentration Of Solution Mass of the solute in a given volume of solvent. Mass/Volume e.g. 12 g. of NaCl dissolved in 3L H2O = 12g./3 l. or 4.0 g/L

In A Solution Molecules Are Moving Constantly They Collide and Bounce off each other This causes them to spread out randomly Resulting In: Movement from an area of higher concentration to and area of lower concentration

DIFFUSION Molecules move away from an area of Higher Concentration to area’s of Lower Concentration Equilibrium Concentration of a solute is the same throughout the solution

Diffusion

Diffusion Causes Many Substances To Move Across A Cell Membrane But: Key Concept: Diffusion Causes Many Substances To Move Across A Cell Membrane But: Does NOT Require The Cell To Use Energy

Diffusion across a membrane

Diffusion & Cells Substances that can diffuse across cell membranes will do so until equilibrium is reached Diffusion continues after equilibrium but the rates in and out are equal

OSMOSIS

Osmosis Permeable Membrane Impermeable Membrane Substance Can Easily Cross Impermeable Membrane Substance Can NOT Cross Selectively Permeable Membrane Some Substances Can Cross, Others Can Not

The Diffusion Of Water Through A Selectively Permeable Membrane OSMOSIS Key Concept: The Diffusion Of Water Through A Selectively Permeable Membrane

The Tonics Hypotonic Isotonic Hypertonic Less concentrated solution Equally concentrated solution Hypertonic More Highly concentrated solution

The Tonics

The Tonics

Osmotic Pressure Pressure exerted on the hypertonic side of a selectively permeable membrane May cause cells to shrink or burst

Osmotic Pressure Cell Walls Contractile Vacuoles

Facilitated Diffusion Molecules that can easily diffuse across the cell membrane: Alcohol Water Small Lipids

Facilitated Diffusion Other molecules can not pass through the cell membrane but still get into the cell. HOW?

Facilitated Diffusion Thru Protein Channels in the Cell Membrane that allow a substance to cross. Allows Diffusion In Both Directions Each Channel Substance Specific DOES NOT REQUIRE ENERGY

Facilitated Diffusion Protein Channel Is Substrate Specific Substrate Can Move Either Direction Depending On Concentration. Always from area of Higher Concentration to area of Lower Concentration!

Active Transport Moves Material Across A Cell Membrane Against A Concentration Gradient (from area of Lower concentration into an area of Higher concentration)

Active Transport Requires Energy

Energy Molecule

Active Transport

Active Transport Endocytosis Exocytosis Used to bring in large molecules, food, and whole cells Exocytosis Membrane surrounded material from inside the cell fuses with the cell membrane, releasing the contents.