Cell Membrane 111610 Cell Membrane Function Controls what

Cell Membrane 11/16/10

Cell Membrane • Function – Controls what enters and exits the cell. • Importance – By regulating this movement it helps the cell to maintain homeostasis.

Homeostasis • Maintaining a constant internal state in a changing environment. – All living things respond to their environment • Cells maintain homeostasis by limiting the movement of substances across the cell membrane – Acts as a gatekeeper

Cell Membrane • Structure – Phospholipid bilayer • Hydrophilic heads • Hydrophobic tails – Carrier Proteins • Help transport through membrane

Solutions • In solutions, moving molecules fill up a space. • Equilibrium is when the concentration of a substance is the same throughout a space. • When there is a difference in the concentration of a substance, a concentration gradient exists. – This concept will be important when talking about some of the vocabulary.

Movement Across Membranes • Two types of transport – Passive Transport • Requires no energy to occur – Active Transport • Requires energy to occur – Boat Analogy

Types of Passive Transport • Diffusion – Movement of a substance from high concentration to low concentration – Diffusion of water is referred to as osmosis. • Facilitated Diffusion – Uses carrier proteins to help the substances diffuse through the cell membrane. http: //www. zerobio. com/flashmx/transport. swf

Diffusion

Osmosis • Predicting the movement of water depends on the concentration of the cell’s environment • Solutions can have three different concentrations: – Hypertonic: Higher concentration outside the cell. – Isotonic: Concentration is the same inside and outside the cell. – Hypotonic: Lower concentration outside the cell. http: //www. zerobio. com/flashmx/tonicity. swf

Osmosis Practice 90% Saltwater • Saltwater solution – What is the solute? – What is the solvent? • Water is the substance moving through the membrane. • Which way will the water move? 98% Saltwater

Osmosis Practice 4% Saltwater • Saltwater solution – What is the solute? – What is the solvent? • Water is the substance moving through the membrane. • Which way will the water move? 2% Saltwater

Osmosis Practice 15% Sugarwater • Sugarwater solution – What is the solute? – What is the solvent? • Water is the substance moving through the membrane. • Which way will the water move? 15% Sugarwater

Active Transport • In active transport, substances are being transported against their concentration gradient. – Requires energy – Molecules move from an area of lower concentration to an area of higher concentration

Active Transport • Cell Membrane Pumps – Proteins that move molecules through the cell membrane

Active Transport • Endocytosis – Movement of molecules into the cell through a vesicle • Exocytosis – Movement of molecules out of the cell through a vesicle