Cell Membranes Osmosis and Diffusion

Functions of Membranes 1. Protect cell 2. Control incoming and outgoing substances 3. Maintain concentrations of various substances 4. Selectively permeable - allows some molecules in, others are kept out

Define selectively permeable membrane A membrane that allows only certain materials to cross it Materials pass through pores in the membrane

Phospholipid Bilayer

Fluid Mosaic Model

Methods of Transport Across Membranes 1. Diffusion passive transport 2. Osmosis passive transport 3. Active Transport requires energy to transport molecules against a concentration gradient – energy is in the form of ATP

Solutions Solutions are made of solute and a solvent Solvent - the liquid into which the solute is poured and dissolved. Water is a universal solvent. Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.

Define Diffusion The movement of molecules from an area in which they are highly concentrated to an area in which they are less concentrated. Movement from one side of a membrane to another, un-facilitated = no energy used

Draw a diagram of an example of diffusion

Diffusion

Define osmosis The diffusion of water across a selectively permeable membrane. Passive transport = no energy used

Define osmosis http://www.usd.edu/~bgoodman/Osmos.htm

Why are osmosis & diffusion important? All living things have certain requirements they must satisfy in order to remain alive – maintain homeostasis These include exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes. These tasks happen at the cellular level. Molecules move through the cell membrane by diffusion

Why are osmosis & diffusion important? This membrane is a complex structure that is responsible for separating the contents of the cell from its surroundings, for controlling the movement of materials into and out of the cell, and for interacting with the environment surrounding the cell.