No Bellringer This Week

Agenda

NOTES: Membrane TransportMembrane Structure

Fluid-Mosaic ModelPhospholipid Structure

DiffusionSolutionsDiffusion Gradient

OsmosisIsotonic, Hypertonic, and Hypotonic SolutionsCell Shrinking or Bursting

Function of the Cell Membrane

All cells are surrounded by a thin, flexible barrier known as the cell membrane.

In order for a cell to live, molecules must be able to get in and out of the cell.

Small molecules (like water) are able to pass directly through the membrane, while large molecules require some help.

Structure of the Cell Membrane

The structure of the membrane is sometimes described by the “fluid-mosaic” model.

This is because the membrane is composed of many different types of molecules.LipidsProteinCarbohydrates

The Lipid Bilayer

Membranes are made of a double-layered sheet of phospholipids called the lipid bilayer.

This bilayer is “selectively permeable”, meaning it lets some molecules through, but not others.

Phospholipid molecules have 2 parts:Hydrophilic Head (Polar, Attracted to Water)Hydrophobic Tails (Nonpolar, Repelled by Water)

Solutions

A solution is a mixture of a liquid and solid.The liquid is called the solventThe solid is called the solute

For example, in a solution of saltwater:Water = SolventSalt = Solute

Diffusion

When substances are dissolved in a solution they will spread out evenly.

This process of spreading is called diffusion.Diffusion requires no energy because it is based on the

random movement of molecules.Examples:

If you add a single drop of food coloring to a glass of water, the color will spread through the whole glass.

If someone farts on one side of the room, the smell spreads out to everyone around him.

Diffusion Gradient

When a substance is clumped in one area we say that it has a high concentration, while the area with less substance has a low concentration.

Diffusion always moves a substance from areas of High Concentration to Low Concentration.

This tendency to move from high to low is called “following the concentration gradient”.

High Concentration Low Concentration

Passive Transport

Diffusion moves molecules in and out of the cellThis takes no energy so it’s called “Passive Transport”Diffusion Example

As the cell uses oxygen the concentration inside the cell drops. More oxygen flows in from the high concentration outside of the cell.

As carbon dioxide builds up inside the cell, this high concentration causes molecules to flow towards the lower concentration outside the cell.

BrainPOP: Passive Transport

Osmosis

Osmosis is the diffusion of waterThe Rule for Osmosis is “SALT SUCKS”

Inside of the cell is salty = sucks water inOutside of the cell is salty = pulls water out

Osmosis Terminology

Isotonic – the concentration of solutes is the same inside and outside of the cell

Hypertonic – the higher concentration of soluteHypotonic – the lower concentration of solute

If there is less solute inside the cell then you would say that the cell is Hypotonic and the outside of the cell is Hypertonic.

Effects of Osmosis on Cells

If a cell is placed into a Hypertonic solution, the solutes outside the cell will suck out water and cause the cell to shrivel.

If a cell is placed into a Hypotonic solution, the solutes inside the cell will attract water and cause the cell to burst.

Note that plant cells will not burst because the membrane pushes up against the cell wall.

Assignment

19 Review QuestionsDue Tomorrow