Cellular Transport Chapter 7.4

Pre-Thinking Power Write Why is cell transport important? What kinds of things do cells need? Does this happen fast or slow? What characteristic(s) of life are we maintaining? “How” are substances able to cross a membrane?

Answers Cells need a variety of substances to stay alive and they do this by transporting them across (thru) the membrane Water, Ions, Glucose, O, Na, K FAST! Homeostasis, Metabolism Substances are in constant motion and in contact with their environment

What is Passive Transport? The movement across the cell membrane that does not require energy.

Diffusion Movement of particles from an area of high concentration to an area of low concentration.

Concentration gradient – the process of particles, (solutes) moving through a solution from an area of higher concentration to an area of lower concentration.

Equilibrium – when the concentration of solute is the same throughout a system.

Examples Quickly get out of your seats and most of you move towards the back of the room 3 of you move towards the front Which part of the room has hi concentration and which part has lo? What will students naturally do to alleviate this problem?

Equilibrium Students should attempt to even out the sides of the room. Some will move and most will stay When the concentration of students are equal on both sides, our room has maintained equilibrium. Now, one from each side switch…still in equilibrium?

Discussion How does this relate to the cell? Particles cross the membrane based on amount of substances inside the cell v. outside! The natural flow (meaning without energy) will always be hi lo Called “down the gradient” This is the process of DIFFUSION!

But wait, doesn’t the membrane stop particles? EXPLAIN: Cell Membrane is selectively permeable WHY: Polar heads and non-polar tails EXPLAIN: What can cross? Interior repels ions and polar molecules So, small and non-polar molecules can diffuse across quickly and quietly!

Osmosis Movement of water across a membrane Does not require energy (passive) Movement is based on concentration of the environment Hypotonic: Watery environment, little particles Hypertonic: Lo water, lots of substances Isotonic: equal to the cell environment                                                     

Which way does the water go? Hypotonic: In the Cell Hypertonic: Out the Cell Isotonic: Movement in and out is equal WHY? To maintain equilibrium!

What is the proper environment? Hypotonic Isotonic Hypertonic

What about the ions and polar molecules? Can enter, they just need a special door! ION CHANNEL: transport protein with a polar pore through which ions can pass Ions responsible for the electrical charge in the brain and heart

Facilitated Diffusion Requires no energy, but it does require a transport protein For big molecules that can’t slide through the membrane Protein changes shape and literally “swallows” the molecule

Review Video http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html\