The Cells Plasma Membrane The Plasma Membrane Is

The Cell’s Plasma Membrane

The Plasma Membrane Is Selectively Permeable Won’t Allow just anything in or out Waste Removal Maintains Homeostasis Selective about what crosses the membrane Small particles diffuse across; Large have to be “helped” Balance of water , glucose, amino acids, lipids regardless internal and external cell conditions. Excess nutrients and materials when concentration is too high

Structure of the Plasma (Cell) Membrane *Referred to as a phospholipid bilayer (2 layers of phospholipids) in a fluid mosaic **Phospholipids with a phosphate head. Phosphate Polar heads “love” water; hydrophilic Non-Polar, lipid Tails – “hate” water and keep extra water out of the cell; hydrophobic

Other components of the plasma membrane: Cholesterol prevents fatty acid chains of the phospholipids from sticking together and collapsing the membrane! Phospholipid Cholesterol Molecule

Carrier proteins will “carry” specific particles, particularly ions, across membrane Channel Proteins allows small things like polar molecules directly through the membrane Cholesterol Stabilizes membrane; prevents fatty acid chains of phospholipids from sticking together Carbohydrates Helps cells identify each other Channel Proteins Carbohydrates Cholesterol Carrier Proteins

Transport Across the Semi. Permeable Membrane

Transport Across the Plasma Membrane Transport of Materials Across The Plasma (Cell) Membrane 2 Kinds: * Passive (No energy required) *Active (Energy in the form of ATP is Required)

Passive Transport

Proteins and Diffusion

Facilitated Diffusion Requires Proteins

Channel Proteins Like a hollow tube. Allows very small molecules diffuse down a concentration gradient (high concentration to low concentration)

Carrier Proteins **Polar molecules and charged ions can not diffuse freely across the plasma membrane hydrophobic nature of the fatty acid tails **Carrier Proteins “help” these through the membrane without using any ATP ** The molecule changes the shape of protein http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 2/animation__how_facilitated_diffusion_ works. html

Passive Transport Continued: NO Proteins Required in Simple Diffusion and Osmosis

Passive Transport That Requires NO Proteins Osmosis – water simply diffuses across the plasma membrane without any help Simple Diffusion – Small molecules such as O 2 and CO 2 will readily diffuse as well Both depend on Solute Concentration!!

Diffusion and Osmosis **Goes WITH the concentration gradient – High to low Plasma membrane

A Little Vocab……………. . SOLVENT: A usually liquid substance (such as water) that is capable of dissolving or dispersing one or more substances. Water is the universal solvent SOLUTE: A substance (such as salt) that dissolves in a solvent. SOLUTION: The combination of a solute with a solvent, when the solute has been evenly dissolved in the solvent. Such as saline solution for contact lenses

Tonicity Drives Osmosis

Tonicity � Solutions In Which Cells are in (Extra-Cellular Fluid) can be: � Hypertonic � Hypotonic � Isotonic

A Cell in a Hypertonic Solution Solute concentration of a solution is higher OUTSIDE of the cell than inside cell Causes water to diffuse OUT of the cell The sell shrinks

A Cell in Hypotonic Solution Solute concentration of solution is low thus MORE H 2 O!! Causes water to diffuse INTO the cell The cell swells

A Cell in an Isotonic Solution Solute concentration of solution equal to that of cell No net movement of water Dynamic Equilibrium

Tonicity Things to remember: If: It’s hypertonic OUTSIDE of the cell, the CELL itself is considered to be hypotonic If: It’s hypotonic OUTSIDE of the cell, the CELL itself is considered to be hypertonic Water would flow from HYPO- to HYPER

Osmotic Pressure

Osmotic Pressure Osmosis always moves a solvent in one direction only, from a less concentrated solution to a more concentrated solution (Hypo – to Hyper - ) As osmosis proceeds, pressure builds up on the side of the membrane where volume has increased. Ultimately, this pressure prevents more water from and osmosis stops. THUS, Osmotic Pressure of a solution is the pressure needed to be applied to the solution in order to STOP osmosis!!

Solutions with LOW Osmotic Pressure These are cells are in a hypotonic solution The SOLUTION has a low osmotic pressure. SOLUTIONS with low osmotic pressure have a tendency to LOSE water Water enters the cells!!

Solutions with HIGH Osmotic Pressure These are cells in a hypertonic solutions. The solution OUTSIDE the cell has a high osmotic pressure. Solutions with a high osmotic pressure have a tendency to GAIN water The cell itself has a LOW osmotic pressure Not enough pressure to stop water from leaving (osmosis) The cells shrink!!

Isotonic Solution The solution and the cell both have equal osmotic pressures. No net movement of water

Osmotic Pressure – Gummy Bear

Osmotic Pressure – U Tube

Facilitated Diffusion Passive Transport Carrier proteins “help” molecules across

Classwork/Homework Time!! Diffusion and Osmosis Crossword Answer “Science Organizer” questions about passive transport. Use terms we’ve used in class; hypertonic, hypotonic, isotonic, solute, solvent, diffusion, osmosis, concentration gradient etc. Use a separate sheet of paper if you run out of room!!

Active Transport NEEDS ENERGY (ATP)

Active Transport In some cases, particles such as ions (charged particles) move AGAINST the concentration gradients going from low to high!!! Requires Transport (carrier) proteins and ATP

Active Transport In some cases, ions such as K+ (potassium ion), must move across the membrane from LOW concentration to HIGH concentration Called going against the concentration gradient http: //www. wisconline. com/objects/View. Object. aspx? ID=AP 11203

Active Transport Brain. Pop www. brainpop. com

Cells Maintain Homeostasis – A Steady Internal Environment Maintain p. H levels Temperature Active and Passive Transport of particles Water balance Glucose balance

Buffers and Maintaining p. H balance Acids and bases. Remember them? ? ? Buffers are used A buffer is an aqueous solution (a chemical dissolved in water) that resists major changes in the p. H of the solution. Acidosis occurs when acid builds up Alkalosis occurs when bases build up Blood maintains a p. H between 7. 38 and 7. 42 (slightly above neutral)

p. H – Remember Acids and Bases? ? An acid is basically a solution with numerous hydrogen ions (H+) A base is a solution with hydroxide (OH-) ions Blood p. H is regulated by the lungs and the kidneys Blood contains large amounts of carbonic acid, a weak acid, and bicarbonate, a base. If blood p. H falls below 6. 8 or rises above 7. 8, one can become sick or die. The bicarbonate neutralizes excess acids in the blood while the carbonic acid neutralizes excess bases.

High Blood Temperature If blood temperature rises too high, blood vessels dilate, more blood flows close to the body surface and excess heat radiates from the body. If it doesn’t cool enough, the brains induces sweating

Low Blood Temperature If the blood temperature falls too low, arteries that supply blood to the skin constrict and warm blood is retained. If it gets too cold, the brain activates shivering. Each muscle tremor in shivering releases heat energy and helps warm the body.

Glucose Levels Monitored by cells in the pancreas Hormones chemicals that carry messages from organs of your body to your cells. Work in large part to keep the body’s natural balance in check. Glucagon secreted by the pancreas – RAISE blood glucose levels Insulin – Helps to LOWER blood glucose levels