1.4 Membrane transport

Understandings Applications Particles move across membranes by simple diffusion, facilitated diffusion, osmosis, & active transport The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis Vesicles move materials within cells Applications Structure & function of Na-K pumps for active transport and K channels for facilitated diffusion in axons Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis Nature of Science Experimental Design: accurate quantitative measurements in osmosis experiments are essential Skills Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions

4 ways particles move across membranes Simple diffusion Facilitated diffusion Osmosis Active transport

SIMPLE DIFFUSION Diffusion = spreading out of particles (from area of high concentration to area of low concentration) Molecules are in constant motion Molecules randomly collide with each other If more molecules are in one area, there’s more chances for random collisions, so more spreading out takes place Passive = No energy input is required Net movement = movement in one direction – movement in the other direction (can be zero even when molecules are still moving) Molecules are always moving (even in solids, molecules vibrate); movement is driven by heat Concentration gradient = a difference in the concentration of particles in one area compared to another

Concentration gradient No gradient Concentration gradient

What is the only part of the human body that has no blood supply?

So how does the cornea get oxygen? From the Air!!

Let’s look at osmosis on U Tube

Osmosis * movement of water across a semi-permeable membrane from area of lower solutes to higher solutes * water movement has to do with the amount of solutes dissolved in it * water moves from HYPO to HYPERtonic

Active transport Against concentration gradient Requires ATP Requires globular proteins called “protein pumps” Proteins take in particle, change configuration (shape) using ATP, then particle moves to other side

Passive vs active transport

Application: Structure & function of sodium-potassium pumps for active transport in axons http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Application: potassium channels for facilitated diffusion in axons http://highered.mheducation.com/sites/0072943696/student_view0/chapter8/animation__voltage-gated_channels_and_the_action_potential__quiz_1_.html

Application: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis Osmolarity = solute concentration Hypertonic = higher osmolarity Hypotonic = lower osmolarity

Normal saline 0.9% NaCl = 300 mOsm (milliosmoles) Sterile IV for replenishing fluids or electrolytes Rinse wounds & abrasions Moisten skin before skin grafts Ingredient in eye drops Frozen for packing organs for transplant

SKILL: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. DBQ p41-42 OsmOSIS IS DUE TO SOLUTES THAT FORM BONDS WITH WATER SOLUTES ARE SAID TO BE “OSMOTICALLY ACTIVE” E.G. Glucose, Na+, K+, Cl+ Cells contain many osmotically active solutes Osmolarity = total concentration of osmotically active solutes Unit = osmoles or milliosmoles (mOsm) Normal = 300 mosm Isotonic solution = same osmolarity as human tissue