CHAPTER 5 Cell Homeostasis

Section 1: Passive Transport  Cell membranes: controls what enters and leaves the cell  Sometimes it takes energy to do this. Sometimes it does not!

TRANSPORT: movement across the cell membrane  2 types of transport:  Active Energy from the cell is required  Passive No energy is required

Passive Transport  Types of Passive Transport  Diffusion  Osmosis  Facilitated Diffusion

Diffusion  Diffusion is the SIMPLEST type of passive transport.  Diffusion: the movement of molecules from an area of higher concentration to an area of lower concentration  Concentration Gradient: the difference in the concentration of molecules across a distance

Example of Diffusion

 Sugar water/food coloring example  Goal of diffusion: EQUILIBRIUM  Equilibrium: the concentration of molecules becoming the same throughout the space they occupy Sugar water has reached equilibrium when the sugar is equally distributed throughout the water

REMEMBER  Do not forget…..even at equilibrium, molecules still continue to move

OSMOSIS  Osmosis: the process by which WATER moves across a cell membrane from an area of higher concentration to an area of lower concentration  NO ENERGY REQUIRED!!!

Osmosis, con’t  Solution: made up of 2 parts SOLUTE & SOLVENT SOLUTE: what will be dissolved SOLVENT: what will do the dissolving In the sugar and water example Solute: sugar Solvent: water ***WATER is the universal solvent

3 types of Osmotic Solutions  1. Hypotonic Solution  2. Hypertonic Solution  3. Isotonic Solution

Hypotonic Solution  Osmosis depends upon the direction of the solute!  Table 5-1 on page 99  HYPOTONIC SOLUTION: when the concentration of solute molecules outside the cell are LOWER than the concentration of solute molecule inside the cell

 Water will naturally move into the cell  Result: cell will enlarge  Cytolysis can occur: bursting

Hypertonic Solution  Hypertonic: when the concentration of solute molecules outside the cell is HIGHER than the concentration of solute molecules inside the cell  Water will naturally move OUT!!  Result: cell will SHRINK!  Dehydration

Isotonic  Isotonic: when the concentration of solutes outside the cell equal the concentration of solutes inside the cell  Result: EQUILIBRIUM

Osmosis: CONTRACTILE VACUOLES  Found in Hypotonic solutions:  It is the pressure that water molecules exert against a cell wall  Found in Hypertonic solution:  Cells shrink from the cell wall  Loss of turgor pressure Turgor PressurePlasmolysis

Different cells: RBC  Some cells do not have a contractile vacuole and cell wall  Therefore: the normal shape changes Page 100: picture of RBC

Facilitated Diffusion  Used for molecules too big to cross the membrane  Uses transport proteins!  Still moves molecules from area of high concentration to an area of low concentration  Example: glucose

Facilitated diffusion  Can also move molecules OUT of the cell  If sugar concentration gets too high inside the cell, it can transport those sugar molecules to the outside of the cell  SPECIFIC transport proteins are used for SPECIFIC molecules

Section 2: Active Transport  In many cases, a cell MUST move materials from an area of LOWER concentration to an area of HIGHER concentration.  Therefore: it is UP the concentration gradient, not down.  It requires ENERGY

Transport Proteins  Also called “carrier” proteins: called “pumps”  They move substances from lower to higher concentration

Carrier Protien

Sodium-Potassium Pump

 Transports Na+ and K+ ions UP the concentration gradient  Some cells need a higher concentration of Na+ outside and K+ inside the cell  This pump MAINTAINS this concentration

STEPS: page 104  1. 3 Na+ ions bind to the carrier protein on the inside (cytosol) side of the cell  2. A phosphate group binds to use its energy to fulfill this process  3. This takes energy! ATP becomes ADP: a phosphate is used to do this!

 4. This allows the carrier protein to have the shape it needs to bind with 2 K+ ions from the outside of the cell  5. The phosphate is released  6. The 2 K+ are released inside the cell  The process begins again!

Sodium-Potassium Pump  THIS CREATES AN ELECTRICAL GRADIENT!  Outside: becomes + charged relative to the inside  Inside: becomes - charged relative to the outside  Therefore: like a battery!

Movement in Vesicles Some substances are too large to pass through the cell membrane through diffusion or facilitated diffusion. A carrier protein is too small for the object. To transport LARGE quantitites of molecules: 1. Endocytosis 2. Exocytosis

Endocytosis  Steps:  1. cell membrane forms a pouch  2. materials flow into pouch  3. pouch pinches off from the cell membrane and becomes a membrane bound organelle:  VESICLE  4. vesicle fuses with lysosomes  5. contents digested

Endocytosis  2 types:  1. Phagocytosis Large particles  2. Pinocytosis Large amt. of fluid

Exocytosis:  Process in which substances from the cell through a vesicle are transported OUT of the cell  It is the REVERSE of endocytosis!

 Removes: waste, proteins, toxins, etc. 1. These products placed in vesicles 2. Vesicles fuse with cell membrane 3. Substances are released