Plasma Membrane Made of 2 groups of organic molecules: phospholipids and proteins Phospholipids: molecules shaped like a head with 2 tails Heads are the phosphorous group which are polar (attract H2O) Tails are long lipid chains that are non-polar (push H2O away) Polarity of the phospholipids causes them to form a 2 layer “sandwich” with the heads outside and wet and the tails inside and dry Prevents most materials from passing in/out of cell

PM Proteins are embedded in the bilayer 3 types: Marker proteins (curley-q) identify the cell as to type Receptor proteins gather info about the cell’s surroundings Channel proteins act as the “gatekeeper” of the cell allowing larger molecules in/out of the cell

Passive & Active Transport: Moving Materials across the Plasma Membrane First a chemistry review: Solute is the substance that dissolves in another substance Solvent is the more plentiful substance that dissolves the solute Mixture of solute and solvent= solution

Passive Transport Does NOT involve the use of E to bring things in/out of cell Molecules seek homeostasis between the inside/outside of cell using the concentration gradient Diffusion: when substances move from an area of higher concentration to an area of lower conc. Example: O2 in your blood stream Osmosis: diffusion of H2O molecules in the direction of higher solute conc. (if solute is high then H2O is low)

P M and 3 solutions Hypertonic solution: solute conc. Out of the cell is higher than in the cell (more H2O molecules in the cell) H2O molecules rush out of the cell to area of lower H2O conc. Causes cell to shrivel

Hypotonic solution: solute conc Hypotonic solution: solute conc. out of the cell is lower than in the cell (more H2O out of cell) H2O molecules rush into the cell Cell swells and can explode!

Isotonic solution: solute conc Isotonic solution: solute conc. is the same inside of the cell as outside of the cell Equal amounts leave/enter the cell to create homeostasis Cell stays the same size This is what they give you in an IV to rehydrate you

One more thing about diffusion………. Facilitated diffusion is when the plasma membrane is selectively permeable—it is choosy about what it lets into the cell Channel protein does the choosing “Regular” diffusion and osmosis do not involve the channel proteins Still does not use E

Active Transport Cell uses E to actively bring substances into the cell against the concentration gradient Doesn’t matter if there is MORE of that substance in the cell—if the cell wants more it uses E to get more!

Plants use proton pumps to pump H atoms that are missing their electrons (hence the name ) through the internal membranes of mitochondria and chloroplasts for E production (Krebs cycle)

Animals use sodium-potassium pumps to pump Na out of the cell and K into the cell Na bonds with a glucose molecule while it is outside and then is pumped back into the cell Glucose is released inside the cell and then Na leaves on another trip through the pumps Nerve cells use the differences in Na and K conc. Caused by these pumps to send signals across the synapses thru-out the body

When food particles are too big to be brought thru the channel proteins, the cell will engulf the particle This is called endocytosis Pinocytosis is when a liquid w/ dissolved molecules are brought in Exocytosis is how wastes are discharged from the cell in vacuoles; can also secrete chemical products (hormones) Phagocytosis is when another cell or part of a cell is brought in; WBC “eat” invading bacteria, or amoebas devour their prey in this manner