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. “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

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

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 _______________________

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

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

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

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

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

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