Chapt. 7-3 Cell Membrane and Osmosis
I.
Cell Membrane- a selectively permeable coating which surrounds the cell protecting and
separating it from its surroundings
A. Lipid Bilayer- a collection of phospholipids which form a double layered pattern
B.
II.
III.
IV.
Cell Membranes have proteins and carbohydrates embedded in the lipid bilayers
1. Proteins- make up channels and pumps to move materials across the cell membrane
2. Carbohydrates – act as chemical identification cards
Cell Walls- located outside the cell membrane to provide structural support for plant, algae
and some bacteria
A. Composed of carbohydrates like cellulose
B. Cell walls are porous and allow substances like gas and water to pass through
Movement across or through a cell membrane
A. Concentration- mass (solute)/volume(solvent) 12 g./3 L. = 4 g/L
1. Relative concentrations :
a. Isotonic – Concentrations of two solutions are equal
b. Hypertonic – The stronger of two solutions “above strength”
c. Hypotonic- The weaker of two solutions “below strength”
B. Diffusion – random particle movement (air or water) from high concentration to low
concentration (hypertonic to hypotonic). No energy required!
C. Equilibrium- state when particles are evenly distributed (isotonic solution)
D. Osmosis- diffusion through a selectively permeable membrane (cell membrane). No
energy required!
E. Osmotic Pressure- the force exerted on a cell membrane by an unequal, concentration
gradients
F. Facilitated Diffusion-movement of substances from one side of a membrane to the
other through protein channels (no energy required)
G. Active Transport- Using a protein channel to “pump” a substance against a
concentration gradient (requires energy)
H. Molecular Transport – a form of active transport using specialized molecule pumps
Particle Transport
A. Endocytosis- folding in the cell membrane to create a pocket
B. Phagocytosis- creating a pocket to bring a food particle in for the cell to eat
C. Pinocytosis – creating a pocket to bring in liquid for the cell to drink
D. Exocytosis – folding out the cell membrane to create a pocket of cellular water or
waste