Topic 4 Membrane transport

Cell Membrane

Obj 13,14 Simple Diffusion Particles move from areas of high concentration to areas of low concentration Diffusion across a membrane Occurs as long as the particle can move through that membrane Concentration gradient Differences in concentration with in a solution or across a cell membrane Drives diffusion

The diffusion of solutes across membranes Obj 13,14

Osmosis Obj 15 Movement of water over a semipermeable membrane Driven by a solute concentration gradient *Review* – Solutions Homogenous mixture Solute dissolved in a solvent Universal Biological solvent Water! Solutes – usually a collection of biological molecules Glucose Amino acids Electrolytes

Osmosis *Result* *Important* Low solute concentration High Water Concentration High solute concentration Low Water Concentration *Result* Water moves over the membrane until solute concentration is the same on both sides Homeostasis! *Important* Solute particle is too big to cross the membrane Water is small enough Time

Osmosis in Cells Obj 19 Isotonic – cell and external environment have the same solute concentration No net water movement Hypertonic environment – external environment has a high solute concentration (low water concentration) Water moves out of the cell Hypotonic environment – external environment has a low solute concentrations (high water concentration) Water moves into the cell *Terms used to compare solutions*

Water balance in living cells Plant vs Animal Obj 19 Water balance in living cells Plant vs Animal Start with Plants for G block

Passive Transport Obj 15 Movement of substances without energy Driven by a concentration gradient Two types… Simple Diffusion (objective 13) Substances move through the phospholipid membrane Facilitated Diffusion Requires a transport protein Ion Channel (Tunnel) Protein changes shape (boat lock)

Active Transport Obj 16 Transport Protein Needed Energy required Substances moved against the concentration gradient Glucose into a cell (sometimes) Electrolytes (Sodium-Potassium Pump)

Passive and Active transport Summary

Selective Permeability OBJ 17, 19 Selective Permeability Passes freely through the membrane Needs a special protein transporter Needs to use other methods to pass through Polarity and Size Nonpolar molecules (steroids, N2, O2) Some very small polar molecules (water, ethanol, etc) Small polar molecules (amino acids, sugars, etc) Large polar molecules (proteins) Electric Charge No charge Charged atoms (H+ or Ca+) Endocytosis Exocytosis (Active Transport) Passive or Active Passive Transport Active Transport

The contractile vacuole of Paramecium: an evolutionary adaptation for osmoregulation Start here with G (Active Transport)

Endocytosis “Enter” Obj 17 Active transport of substances from the extracellular fluid Requires energy Forms a vesicle inside the cell 3 types Phagocytosis Solid particles Cellular “eating” Pinocytosis Liquids/dissolved substances Cellular “drinking” Receptor-mediated endocytosis Vesicle forms in the presence of a specific substance Exocytosis with C block

Obj 17 Exocytosis “Exit” Active transport of substances to the extracellular fluid Energy required Excretory vesicles formed by the golgi apparatus