Passive Transport

Bell Ringer What is osmosis?

Objectives Relate Concentration Gradients, diffusion, and Equilibrium Predict the direction of water movement into and out of the cells Describe the importance of ion channels in passive transport Identify the role of carrier proteins in facilitated diffusion

Challenge List at least two things that could cause the movement of the dye in the beaker.

Challenge What are you observing? What process is at work?

Movement of particles in Cells Cells maintain Homeostasis by controlling the movement of substances across the cell membrane

Movement in Cells Passive Transport – movement across the cell membrane that does not require energy Concentration Gradient – Difference in the concentration of a substance across a distance.

Equilibrium A condition which the concentration of a substance is equal throughout space.

Challenge For equilibrium to occur, what has to happen to the spheres in this picture?

Diffusion Diffusion – the movement of particles from regions of high density to regions of lower density Diffusion works quickly over short distances, such as the dye moving through the beaker of water.

Diffusion Many substances enter and leave the cell through diffusion. When substances cross the cell membrane they move “down” the concentration gradient. They go from an area of high concentration to an area of low concentration

Osmosis Osmosis – the diffusion of water through a selectively permeable membrane. Movement down the concentration gradient. Osmosis is a type of passive transport

Direction of Water 3 Types Hypertonic Hypotonic Isotonic

Hypertonic Solution The fluid outside the cell has a lower free water concentration than the cytosol, then the outside fluid is hypertonic and water moves out of the cell

Hypotonic The fluid outside the cell has a higher free water concentration than the cytosol, then the outside fluid is hypotonic and water moves into the cell

Isotonic The fluid outside the cell has the same free water concentration than the cytosol, then the outside fluid is isotonic and water moves into and out of the cell at equal rates.

Crossing the Cell Membrane Transport Proteins called Channels provide polar passageways through which ions and polar molecules move across the cell membrane. Each channel only allows specific substances to pass through the membrane Why is this important?

Diffusion through Ion Channels Sodium Calcium Potassium Chloride All are involved in many important cell functions

Ions Essential to the ability of nerve cells to send electrical signals Movement of ions allows your heart to beat Cross the cell membrane by diffusing through ion channels.

Ion Channel Transport Protein with a polar pore through which ions can pass. The pore spans the thickness of the cell membrane Why is this important?

Ion Channel Some pores are always open, others have a gate which can be open or closed. They can open or close in response to different kinds of stimuli. ex. Electrical charge or binding sites.

Facilitated Diffusion Facilitated Diffusion – a type of passive transport that moves substances down their concentration gradient without using the cells energy. Transport proteins transport substances across the cell membrane. These are called carrier proteins.

Facilitated Diffusion

Challenge Why do drawers get sticky when there has been a lot of rain or high humidity. During the winter , salt is sprinkled over icy roads. Plants growing along side the road are often seriously damaged or dead. Why does this happen?