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Transcript
Cell Transport Movement through the Membrane 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. 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 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 Outside of Cell Protein Channel Inside of Cell (Cytoplasm) Lipid Bilayer 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 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. 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. 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 Osmosis (Passive Transport) • The diffusion of WATER across a selectivelypermeable 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. 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 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 Isotonic Solution • Equal amount of solutes • IV in hospitals is isotonic, replenishes fluids only (osmosis does not occur) 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. 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 Bulk Transport (Active Transport) • Large molecules, food and other substances are packaged in membrane bound sacs and moved across the membrane 4 Types: 1. 2. 3. 4. Endocytosis- bringing into the cell Pinosytosis- drinking (endocytosis) Phagocytosis- eating (endocytosis) Exocytosis- opposite of endocytosis, wastes leave the cell http://www.maxanim.com/physiology/Endocytosis%20and%20Exocytosis/ee4.swf 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.