Structure of the Plasma Membrane Lipid bilayer – two sheets of lipids (phospholipids). – Found around the cell, the nucleus, vacuoles, mitochondria, and chloroplasts. – Embedded with proteins and strengthened with cholesterol molecules.

Membrane Proteins 1. Determine what particles can pass through the membrane. 2. Serve as enzymes (may speed reactions). 3. Act as markers that are recognized by chemicals and molecules from the inside and the outside of the cell (the immune system).

Passive

Three Forms of Transport Across the Membrane

Passive Transport Simple Diffusion  Doesn’t require energy  Moves high to low concentration Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out  Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.

Cell Concentrations Hypertonic solutions – more dissolved solute. Hypotonic solutions – less dissolved solute. Isotonic solutions – the same dissolved solute. Solvent=does the dissolving Solute=solid(usually) which is dissolved

There are three types of solutions: (1) Hypotonic - a solution which is more dilute (i.e., less solutes) than the cytosol. The cell gains water and swells. (2) Hypertonic - a solution which is more concentrated (i.e., more solutes) than the cytosol. The cells loses water and shrinks. (3) Isotonic - a solution which has the same concentration of solutes as the cytosol. The cell neither gains nor loses water and remains unchanged.

TONICITY = the relative amount of solute

HYPERTONIC: Concentration outside cell is ____________________ inside cell More water leaves cell than enters so cell ____________

HYPOTONIC: Concentration outside cell is ________________ inside the cell More water enters than leaves cell so cell will ___________________

ISOTONIC: Concentration outside cell __________ concentration inside cell Water entering = water leaving so cell _____________________

Osmosis Diffusion of water across a selectively permeable membrane. Occurs until water is balanced on both sides of the membrane.

Passive Transport Facilitated diffusion  Doesn’t require energy  Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell.

Active Transport  Requires energy or ATP  Moves materials from LOW to HIGH concentration  AGAINST concentration gradient

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating”

Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell Cell environment

Pinocytosis Most common form of endocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle Takes in dissolved molecules as a vesicle.