1. 8.1 Cell Membrane I. Homeostasis
A. The maintenance of stable internal conditions in a changing environment
1. ex. – _________________
B. Cells stay stable by controlling what comes ________ ________ _________ of the cell
II. Lipid bilayer
A. ________________________
1. specialized lipid made of phosphate “head” & acid “________________”

2. 2. “heads” = polar, attracted to water
3. “tails” = ______________, repel water
B. Tails point inward on both sides of the bilayer and heads make up the outside
C. Only allows certain substances in the cell
III. Membrane ___________________
A. Cell-surface markers- identifies each cell, like a name tag
B. __________________ proteins- allows cell to sense its surroundings by binding to substances
C. Enzymes- help with reactions in the cell

3. D. Transport Proteins- aide in the. movement of substances across the

4. 8.2 Cell Transport I. ________________________ Transport
A. Cell does not use energy in this process
B. Equilibrium is reached when space in a cell is filled __________________
C. Concentration gradient- areas of high & low ____________________of substances
D. _____________________
1. Movement down the concentration _______________________

5. 2. Simple ________________-small, nonpolar molecules pass directly through bilayer
a. ex.- oxygen, CO2, natural steroids
3. Facilitated diffusion- transport proteins help substances diffuse through bilayer

6. E. ___________________
1. Allows cells to keep their water balance in a changing environment
2. Moves from high to low concentration

7. II. Active __________________
A. Uses _____________
B. Pulls substances against concentration gradient
C. ______________-_____________pump

8. 8.3 Cell Communication D. Vesicles 1. _____________________bound sacs
2. ___________________-movement of largr substances into a cell
3. Excytosis- movement of materials out of a cell
8.3 Cell Communication
I. Sending ___________________
A. Cells produce signals, often a molecule, that are detected by the target cell

9. B.Targets
1. Neighboring cells communicate through direct ________________________
2. Long-distance signals are carried by __________________and nerves
C. Environmental Signals
1. ex- the length of _________________
II. ____________________Signals
A. Target cells are hit by many signals but only recognize and respond to a few of them

10. 1. Receptor proteins are responsible for
1. Receptor proteins are responsible for _____________which signals to accept
a. Signals only bind if they are the correct shape of the binding site, works like a lock & key
III. _____________________to Signals
A. The cell may respond to a signal by changing its membrane permeability, by activating enzymes, or by forming a second messenger