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Cell Membranes. The Cell Membrane. Cell Membrane : . At Very High Magnification & in color. Phospholipid Molecule Model. phosphate (hydrophilic/polar). glycerol fatty acids (hydrophobic/nonpolar). Membrane Structure. Hydro Philic/philia Phobic/phobia Polar=soluble in water.

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cell membrane
Cell Membrane:

At Very High Magnification

& in color

phospholipid molecule model

Phospholipid Molecule Model

phosphate (hydrophilic/polar)


fatty acids (hydrophobic/nonpolar)

membrane structure
Membrane Structure

HydroPhilic/philiaPhobic/phobiaPolar=soluble in water

cell membrane6
Cell Membrane

Every cell is encircled by a membrane and most cells contain an extensive intracellular membrane system. Membranes fence off the cell's interior from its surroundings. Membranes let in water, certain ions and substrates and they excrete waste substances. They act to protect the cell.

Without a membrane the cell contents would diffuse into the surroundings, information containing molecules would be lost and many metabolic pathways would cease to work:

The cell would die!

cell membranes7
Cell Membranes:
  • Surround all cells
  • Fluid-like composition…like soap bubbles
  • Composed of:
    • Lipids in a bilayer
    • Proteins embedded in lipid layer (called transmembrane proteins)
    • And, Proteins floating within the lipid sea (called integral proteins)
    • And Proteins associated outside the lipid bilayer (called peripheral proteins).
membrane lipids
Membrane Lipids
  • Composed largely of phospholipids
  • Phospholipids composed of….glycerol and two fatty acids + PO4 (phosphate) group
  • Phospholipids are polar molecules…

P-Lipids are represented like this

membrane lipids form a bi layer
Membrane Lipidsform a Bilayer

Outside layer

Inside Layer

membrane proteins
Membrane Proteins
  • Integral: embedded within bilayer
  • Peripheral: reside outside hydrophobic region of lipids
membrane models

Membrane Models

Fluid Mosaic Model - lipids arranged in bilayer with proteins embedded or associated with the lipids.

What color are the lipids?

What color are the integral proteins?

What color are the peripheral proteins?

membrane functions

Membrane Functions

allows for different conditions between inside and outside of cell

subdivides cell into compartments with different internal conditions

allows release of substances from cell via vesicle fusion with outer membrane:

membrane permeability
Membrane Permeability
  • Biological membranes are physical barriers..but which allow small uncharged molecules to pass…
  • And, lipid soluble molecules pass through
  • Big molecules and charged ones do NOT pass through
  • Semi-permeable / selectively permeable

Solution = solute + solventSolute-- the thing being dissolvedSolvent--does the dissolvingkool-aid chocolate milkTerms that refer to solute:HyperHypoIso

how to get other molecules across membranes
How to get other molecules across membranes??
  • There are two ways to move through the membrane:
  • passive transport and active transport
  • Active transport requires energy (that the cell has obtained from food to move the molecules through the cell membrane)
  • Passive transport does not require energy
membrane transport mechanisms i passive transport
Membrane Transport MechanismsI. Passive Transport
  • Diffusion- simple movement from regions of high concentration to low concentration
  • Osmosis- diffusion of water across a semi-permeable membrane
  • Facilitated diffusion- protein transporters which assist in diffusion
membrane transport mechanisms ii active transport
Membrane Transport MechanismsII. Active Transport
  • Active transport- proteins which transport against concentration gradient.
  • Requires energy input (uses ATP)

- Endocytosis

  • Exocytosis
  • Receptor mediated endocytosis
1.What is the solute?

2. What diffuses?


4.Is this diffusion or osmosis?

5.Which side is hypertonic?

6.Which side is hypotonic?

7.Why doesn’t the sugar diffuse?


Movement of water across a semi-permeable barrier.

Example: Salt in water, cell membrane is barrier. Salt will NOT move across membrane, water will.

osmosis in hypertonic medium


Osmosis in Hypertonic medium

Hypertonic solutions- shrink cells

Plasmolysis in Plant Cells

Crenation in Animal Cells

What happens when you eat salty chips?

osmosis in hypotonic medium
Osmosis in Hypotonic medium

Hypotonic solutions- swell cells

“Hypos make hippos”

Cytolysis in Animal Cells

Turgor Pressure in Plant Cells



For more animations view: http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

for osmosis in action
For Osmosis in Action

View frozen frogs at:


How did the frog use the principles of osmosis and diffusion to survive the winter? Make sure you use the following terms appropriately in your description: hypertonic, hypotonic, solute, solvent, diffusion, osmosis, cytolysis, crenation, isotonic and semi-permeable membrane.

osmosis food preservation
Osmosis & Food Preservation
  • Food can be preserved by causing any microorganism that comes in contact with it to become plasmolysed and, therefore, shrivel and die. To do this food is placed in a high salt or sugar medium. The salt or sugar concentration is higher than the cytoplasm of bacteria or fungi. Bacteria or fungi, that contaminate the food, will lose water by osmosis and their metabolism will decline. Many will die but some bacteria may survive by forming dormant resistant endospores. Meat and fish are often preserved in salt. Fruit is commonly preserved in sugar as in jam or syrup.
  • Transports macromolecules and large particles into the cell.
  • Part of the membrane engulfs the particle and folds inward to “bud off.”
  • Pseudopods
  • Phagocytes
  • Macrophages (phage)_
putting out the garbage
Putting Out the Garbage
  • Vesicles (lysosomes, other secretory vesicles) can fuse with the membrane and open up the the outside…
types of protein transporters
Types of Protein Transporters

A. Facilitated Diffusion

Assist in diffusion process.

Solutes go from High conc to Low conc.

Examples: Glucose transporters

Carrier Proteins

Protein Channels

types of protein transporters active transport
Types of Protein Transporters: Active Transport
  • carrier proteins
  • go against the concentration gradients Low to High
  • require Energy to function (ATP, PEP, light energy, electron transport)
membrane transport active transport

Membrane Transport:Active transport

Movement from region of low free energy(low concentration) to regions of high free energy (high conc.)

Requires energy input

  • http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellMembranes.html
  • www.biologie.uni-hamburg.de/b-online/e22/22.htm
  • More Animations: http://www.kscience.co.uk/animations/anim_1.htm
  • http://fig.cox.miami.edu/~cmallery/150/memb/membranes.htm
  • Pictures: http://biologycorner.com/resources/
  • 1st Semester Final Review