1. Cell Transport Movement through the Membrane

2. Crossing the Cell Membrane To stay alive, a cell must exchange materials such as food and wastes with its environment. These materials must cross the cell membrane. The plasma membrane must regulate the movement of dissolved molecules on one side of the membrane to the liquid on the other side. Small molecules go in and out freely while large molecules such as proteins and carbohydrates cannot. Semi-permeable membrane. Only allows certain molecules to pass in and out of cell.

3. Substances That Are Let IN & OUT IN Water Glucose (a type of sugar) Lipids (fats) Amino Acids (the building blocks of protein) OUT Water Byproducts (waste) of glucose, lipids, and amino acids Other waste products

4. Fluid Mosaic Model The composition of all cell membranes is typically a double-layered sheet called a lipid bilayer. A phospholipid molecule has two parts: – 1) Phosphate group (PO4) – 2) Glycerol (the lipid) Carbohydrate Chain Protein Channel Lipid Bilayer Inside of Cell (Cytoplasm) Outside of Cell

5. Phospholipid Molecule (Cont’d) The bilayer of phospholipid molecules are arranged: – With the polar phosphate groups touching the external environment and inside of the cell (the cytoplasm) – With the two fatty acid tails facing each other The plasma membrane is not just a bilayer of pure phospholipds – Inside of the bilayer: Cholesterol – prevents fatty acid chains from sticking together Transmembrane proteins – act as transport channels to move substances into and out of the cell

6. Simple Diffusion (Passive Transport) Passing of particles through a cell membrane Diffusion. Particles move from higher concentration  lower concentration. “It does not require energy” Concentration. The mass of solute in a given volume of solution. ( 12g of salt in 3 liters of water, concentration would be 4g/L) Diffusion ends when the molecules are dispersed evenly Homeostasis or equilibrium is reached Homeostasis. A process at which organisms maintain an internal stable environment.

7. Explaining Concentration Solute – A substance that is dissolved in solvent to make a solution. Solvent – Substance in which a solute is dissolved in to form a solution. Solution – Mixture of 2 or more substances in which molecules of the substances are evenly distributed.

8. Concentration Gradient Difference between the concentration of a particular molecule in one area and the concentration in an adjacent area Diffusion always occurs down a gradient – From higher concentration to lower concentration At equilibrium the gradient is no longer present

9. Osmosis (Passive Transport) The diffusion of WATER across a selectively- permeable membrane. Occurs in response to the solutes dissolved in the water. Water moves from where there is more water to where there is lower water. Another thought- water moves from where there are less particles (solutes) to where there are more particles. Ex: Contractile vacuoles. Cavities in cytoplasm that are specialized to collect water.

10. Hypertonic Solution Concentration of solutes in the solution is higher than the concentration of solutes inside the cell “Above Strength” Water will diffuse out of the cell Cell will shrivel and shrink Cell will die Ex. Lettuce in salt water. Lettuce wilts in a few minutes because cells have lost their water to the salty, hypertonic environment

11. Hypotonic solution Concentration of solutes is lower in the solution than the concentration of solutes inside the cell. “Below Strength” Water flows into the cell Causes the cell to swell Will not occur in plant cells due to cell wall Ex. Distilled water has no solutes Ex. Lettuce in distilled water stays crisp

12. Isotonic Solution Equal amount of solutes IV in hospitals is isotonic, replenishes fluids only (osmosis does not occur)

13. Facilitated Diffusion (Passive Transport) Used when molecules can’t cross by simple diffusion Some molecules must be facilitated with other molecules. “Carrier Proteins” must carry molecules across the membrane Ex: Molecules such as glucose, that cannot diffuse across the cell membrane’s lipid bilayer on their own move through protein channels instead.

14. Active Transport Moving against a concentration gradient Low concentration to high concentration Requires Energy! Often involves carrier proteins Important in animals (homeostasis) Important in plants to absorb nutrients from soil

15. Bulk Transport (Active Transport) Large molecules, food and other substances are packaged in membrane bound sacs and moved across the membrane 4 Types: 1.Endocytosis- bringing into the cell 2.Pinosytosis- drinking (endocytosis) 3.Phagocytosis- eating (endocytosis) 4.Exocytosis- opposite of endocytosis, wastes leave the cell http://www.maxanim.com/physiology/Endocytosis%20and%20Exocytosis/ee4.swf

16. Additional Terms Transport Protein – Assist in the movement of substances by facilitated diffusion or active transport Types: channels, carriers, and pumps Turgor Pressure – The pressure exerted by water inside the cell against the cell wall. Vesicle – Vesicles are small organelles present in cells. Are membrane enclosed sacs which store and transport substances to and from. Permeable – Capable of being permeated or passed through Ex. Wood is permeable to oil Impermeable – Not permeable or passable.