Cell Boundaries 7.3

A.Cell Membrane B. Cell Walls C. Diffusion Through Cell Boundaries 1. Measuring Concentration 1. Measuring Concentration 2. Diffusion 2. Diffusion D. Osmosis 1. How Osmosis Works 1. How Osmosis Works 2. Osmotic Pressure 2. Osmotic Pressure E. Facilitated Diffusion F. Active Transport 1. Molecular Transport 1. Molecular Transport 2. Endocytosis and Exocytosis 2. Endocytosis and Exocytosis How Do Substances Move in Cells?

Cell Membrane Selectively permeable Selectively permeable –Cell controls the ease with which substances pass in and out of the cell Fluid mosaic model Fluid mosaic model –Cell membrane acts like a fluid, allowing membrane molecules to move laterally Fluid mosaic model of cell membrane video

Cell Membranes are Selectively Permeable

Cell Membrane Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Lipid bilayer (phospholipids) Protects the contents of the cell Controls what moves into and out of the cell. Helps maintain homeostasis.

Cell Wall Found in bacteria, plant, fungi, and some protista Found in bacteria, plant, fungi, and some protista Involved in protection and structure Involved in protection and structure Carbohydrates – structural component cellulose Carbohydrates – structural component cellulose Cell wall video

How Do Substances Move in Cells? Substances move within cells and across cell membranes through the processes of PASSIVE TRANSPORT and ACTIVE TRANSPORT Substances move within cells and across cell membranes through the processes of PASSIVE TRANSPORT and ACTIVE TRANSPORT CONCENTRATION GRADIENT - the number of molecules or ions in one region is different than the number in another region CONCENTRATION GRADIENT - the number of molecules or ions in one region is different than the number in another region – In the absence of other forces, a substance will naturally move from a region where it is more concentrated to one where it is less concentrated – A substance naturally moves “down a concentration gradient”

Membrane Crossing Mechanisms  Help supply cells and organelles with raw materials necessary for building and maintenance, and to excrete waste products 1. DIFFUSION 2. OSMOSIS 3. FACILITATED DIFFUSION 4. ACTIVE TRANSPORT using vesicles  Exocytosis  Endocytosis  Pinocytosis and Phagocytosis

Diffusion Movement from an area of high concentration to an area of low concentration. Only the kinetic energy of the molecules is necessary; no additional energy is required. A form of PASSIVE TRANSPORT that does not require energy Diffusion will occur until there is equal amounts of solute spread throughout the system: EQUILIBRIUM

Factors Affecting the Rate of Diffusion Steepness of concentration gradient Steepness of concentration gradient – Steeper gradient = faster diffusion Molecular size Molecular size – Smaller molecules = faster diffusion Temperature Temperature – Higher temperature = faster diffusion Electrical or pressure gradients increase the rate of diffusion Electrical or pressure gradients increase the rate of diffusion

Osmosis The movement of water across a selectively permeable membrane The movement of water across a selectively permeable membrane Membrane prevents solutes from moving across membrane with water. Membrane prevents solutes from moving across membrane with water. Water moves to equalize concentration inside and outside of cell. Water moves to equalize concentration inside and outside of cell. Water solutionGlucose solution

Terms ISOTONIC ISOTONIC –Equal: concentration of solutes is equal inside and outside the cell. –No net movement of water HYPERTONIC HYPERTONIC –Higher solute concentration outside the cell than inside of the cell. –Net movement of water is outside of the cell. HYPOTONIC HYPOTONIC –Higher solute concentration inside the cell than outside the cell. –Net movement of water is into the cell.

2% sucrose solution 1 liter of distilled water 1 liter of 10% sucrose solution 1 liter of 2% sucrose solution Hypotonic Solution Hypertonic Solution Isotonic Solution abc

HYPOTONIC SOLUTION HYPERTONIC SOLUTION membrane permeable to water but not to solutes fluid volume increases In compartment 2 Water tends to move from a hypotonic solution to a hypertonic solution

contractile vacuole fullcontractile vacuole empty Major problem in freshwater environments - hypotonic environment Major problem in saltwater environments - hypertonic environment PARAMECIUM

Facilitated Diffusion A protein channel allows specific molecules to move across the cell membrane A protein channel allows specific molecules to move across the cell membrane A form of PASSIVE TRANSPORT that does not require energy A form of PASSIVE TRANSPORT that does not require energy Glucose molecules Cell membrane outside cell inside cell Protein channel

Active transport Requires energy Requires energy Used to create a concentration gradient Used to create a concentration gradient Moving a substance against the concentration gradient - from area of low concentration to high concentration Moving a substance against the concentration gradient - from area of low concentration to high concentration Pumps: molecules (fig. 7.19) Pumps: molecules (fig. 7.19) Examples: Endocytosis and Exocytosis of larger substances Examples: Endocytosis and Exocytosis of larger substances More concentration Less concentration Concentration gradient

a b EXOCYTOSIS (out from cytoplasm) ENDOCYTOSIS (into cytoplasm)

Types of Endocytosis Phagocytosis: to eat (movement of “food”) Phagocytosis: to eat (movement of “food”) Pinocyctosis: to drink (movement of fluids) Pinocyctosis: to drink (movement of fluids) Hyperlink to endocytosis video

Fig. 4-19, p.70

Membrane Crossing Mechanisms No energy required Facilitated diffusion of water-soluble substances through protein channel;

Exocytosis Endocytosis