The Cell Membrane and Passive Transport The Cell

The Cell Membrane and Passive Transport

The Cell Membrane made of two phospholipid layers • The cell membrane has two major functions. • 1. forms a boundary between inside and outside of the cell 2. controls passage of materials cell membrane inside cell outside cell

AKA: Fluid mosaic model • There are other molecules imbedded • All provide a specific function cell membrane carbohydrate chain cholesterol protein channel protein

The membrane is “selectively permeable” • Only some molecules can pass

3. 4 Diffusion and Osmosis KEY CONCEPT Materials move across membranes because of concentration differences.

3. 4 Diffusion and Osmosis Passive transport does not require energy input from a cell. • Molecules can move across the cell membrane through passive transport. • There are two types of passive transport. • diffusion • osmosis

Diffusion: Movement of molecules from an area of high to low concentration Movement continues until equilibrium is reached Equilibrium: same amount of molecules on the outside of a cell as the inside

Diffusion (contd) Passive transport: No energy required to move molecules If more molecules outside the cell… they move inside If more molecules inside the cell…they move outside Will O 2 move into this cell or out of this cell?

Diffusion (contd) Where is the high Oxygen concentration? Where is the high CARBON DIOXIDE concentration? Passive transport: No energy (ATP) required to move molecules If more molecules outside the cell… they move inside (and vise versa)

Where is the HIGH oxygen concentration? Where is the LOW oxygen concentration?

Where is the HIGH oxygen concentration? Where is the LOW oxygen concentration? Cell X gets oxygen through the process of diffusion!

The reverse process is true w/ carbon dioxide.

Where is the HIGH carbon dioxide concentration?

Where is the HIGH carbon dioxide concentration?

Osmosis Defined: Diffusion of water from an area of high to low concentration High H 20 concentration if: less particles dissolved in the water Low H 20 concentration if: more particles dissolved in the water

3. 4 Diffusion and Osmosis • There are three types of solutions in osmosis. • isotonic • hypertonic • hypotonic

Group Explanation A cell has been placed into a mystery solution and appears to have shrunken. 1) 2) 3) 4) Which type of solution is the cell placed in? What can you conclude about the water concentration inside the cells compared to outside? What can you conclude about the solute concentration inside the cells compared to outside? Using your explanation of osmosis, explain why the cell appears to have shrunken.

A cell has been placed into a mystery solution and appears to have shrunken. Which type of solution is the cell placed in? hypertonic 2) What can you conclude about the water concentration inside the cells compared to outside? If the cell shrunk it lost water. This means the cell had a greater water concentration. 3) What can you conclude about the solute concentration inside the cells compared to outside? The solute concentration inside the cell is low. I know this because the cell has a high water concentration. The fewer solutes, the higher the water concentration. 4) Using your explanation of osmosis, explain why the cell appears to have shrunken. The cell shrunk because it lost water. There was a greater water concentration inside the cell so therefore water diffused out of the cell. 1)

3. 4 Diffusion and Osmosis Some molecules can only diffuse through transport proteins. • Some molecules cannot easily diffuse across the cell membrane. • Facilitated diffusion is diffusion through transport proteins.