Cell Unit NotesCell Unit NotesLecture IILecture II

Cell Biology Standards in Lecture IICell Biology Standards in Lecture II

> 1a ~ students know cells are enclosed > 1a ~ students know cells are enclosed within semi permeable membranes that within semi permeable membranes that regulate their interactions with their regulate their interactions with their surroundingssurroundings

The Cell MembraneThe Cell MembraneThe The cell membrane regulates what regulates what entersenters

and and leavesleaves the cell the cell It also provides support and protectionIt also provides support and protectionThe cell takes in food and water and The cell takes in food and water and

eliminates wastes through the cell eliminates wastes through the cell membranemembrane

The cell membrane is The cell membrane is selectively selectively permeablepermeable

Selective PermeabilitySelective Permeability

The Lipid BilayerThe Lipid Bilayer Most cell membranes are made up of a double-Most cell membranes are made up of a double-

membrane layer called the membrane layer called the lipid bilayerlipid bilayer Along with lipids the membrane also has Along with lipids the membrane also has

proteins proteins that are “stuck” in it that are “stuck” in it (see below)(see below)

The Lipid BilayerThe Lipid Bilayer

Along with the proteins are Along with the proteins are “carbohydrate “carbohydrate chains”chains” that are attached to the protein that are attached to the protein

These “chains” act like an identification card or These “chains” act like an identification card or “face” so the cell can be recognized “face” so the cell can be recognized

Proteinchannel

Carbohydratechains

DiffusionDiffusion All All livingliving cells are surrounded cells are surrounded

by and full of liquidby and full of liquid Even a cactus in the desert Even a cactus in the desert

has moist cells in it’s living has moist cells in it’s living tissuetissue

One of the most important One of the most important functions of the cell functions of the cell membrane is to regulate the membrane is to regulate the movement of molecules movement of molecules from one side of the from one side of the membrane to the othermembrane to the other

DiffusionDiffusion The The concentration

of a solution is the of a solution is the relative “purity” of a relative “purity” of a liquidliquid

There can be a There can be a high concentration to a low concentration

A solution will A solution will movemove in the direction of in the direction of high concentration to low concentration and and this is called this is called Diffusion

DiffusionDiffusionDiffusion allows Diffusion allows

substances to cross substances to cross the cell membrane the cell membrane without requiring the cell to use energy

This is This is veryvery important since important since energy energy mustmust be be conserved – even at conserved – even at the cellular level!the cellular level!

OsmosisOsmosis Selective permeability

means that only means that only select select “things” can pass “things” can pass through the membranethrough the membrane

Osmosis is is “the “the diffusion of water across diffusion of water across a selectively permeable a selectively permeable membrane”membrane”

Osmotic PressureOsmotic Pressure Isotonic – means that on

both sides of the cell membrane it is the same “concentration”

Hypotonic – the cell fills up with water and is in danger of “bursting”

Hypertonic – the cell loses much of its water concentration and can “shrink”

(Animal Cells react differently than plant cells because of the cell wall that plant cells have)

Osmotic Osmotic PressurePressure

Facilitated DiffusionFacilitated Diffusion This is This is diffusion

across the cell membrane with the with the “help” of proteins“help” of proteins

It still flows from a It still flows from a high to high to low concentrationlow concentration

Facilitated Facilitated Active and Passive TransportActive and Passive Transport

Active TransportActive Transport Active transport requires

“action” or “action” or energy energy in order in order to move these particles to move these particles across the cell membraneacross the cell membrane

The input of energy along The input of energy along with special proteins on with special proteins on the surface of the cell can the surface of the cell can move any particles move any particles across any “gradient”

Gradient – relative – relative concentration of a solutionconcentration of a solution

Endocytosis & ExocytosisEndocytosis & Exocytosis

ExocytosisExocytosis The The removal of large of large

amounts of material amounts of material from the cell is known from the cell is known as as exocytosis

The The vesicle fuses with fuses with the cell membrane the cell membrane and forces its and forces its contents out of the contents out of the cellcell