Cell membrane

Separates cell protoplasm from non-living environment

Allows nutrients to enter Allows waste and other materials to exit

Structure Phospholipid bilayer

2 layers of phospholipids Hydrophilic (water loving) heads on the

outside Hydrophobic (water hating) tails on

inside

*small uncharged lipids can pass right through*

Glycoprotein molecules

Proteins embedded within the phospholipid bilayer

Most glycoproteins carry a special sugar molecule

These sugar molecules vary between species, and between individuals within a species

This accounts for different blood types and rejection of donor organs by recipients

Glycoproteins function as entry and exit points for materials (they transport materials actively)

Glycoproteins also act as receptor sites for hormones

Glycolipids

Specialized sugar attached to lipid Function may be known but we don't know it

yet!

Passive transport

Movement of materials across the cell membrane without expending energy

Movement occurs with the concentration gradient

Diffusion

Movement of particles from high to low Can occur across membranes The kinetic molecular theory (KMT) states that

molecules move and collide (in cells this is called Brownian motion)

This causes molecules concentrated in one area to spread out, until they are evenly distributed (equilibrium)

In equilibrium there is no net movement either way but the system is dynamic not static

Diffusion across a membrane

http://www.johnkyrk.com/index.html

Rate of diffusion...

Can be increased by increasing.... the concentration of the solute the temperature the pressure (ex. Blood pressure) Membrane permeability Size of molecule *decreasing size = faster* Molecule solubility

Research on your own…

Use the internet to help you define the following words:

Crenation and plasmolysis

Have your definitions for next class!