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Transcript
The Cell Membrane The barrier to the cell Mrs. Dignan’s Science Class Cell Membrane Physical Description: thin, flexible barrier made of phospholipids around the cell (just inside the cell wall OR the outside border of animal cells) Function: controls what enters and leaves the cell; support and protection Type of Cell: found in all cells Analogy: it is like the security guard of a factory because it controls what enters and leaves the cell Plant Cell Animal Cell Bacterial Cell Why Does The Cell Membrane Matter? What would happen at an airport if there were no security guards and airline checkers? Answer: Dangerous materials could enter, there could be way too many people there at one time and flights would become overcrowded and unable to fly. What if, instead of security guards, we had giant cement walls to keep people out of airports? Answer: No one would be able to fly and the world would come to an end! Selectively Permeable Permeable: something that allows other substances to pass through Selective: choosing or “selecting” Like a security guard, the cell membrane controls what enters and what leaves the cell. They are sometimes also described as “semipermeable”. Permeability has everything to do with the cell membrane’s structure https://www.youtube. com/watch?v=Rl5Em UQdkuI The phospholipid bilayer “Phospho” – the head of the phospholipid is composed of a phosphorus atom, surrounded by other atoms (called a phosphate group). “Lipid” – the tail of the phospholipid is composed of lipids, which are fatty acids like oils, waxes, and fats. Hydrophillic – “hydro” means water, “phillic” means love. Hydrophillic molecules love water and are attracted to it. Hydrophobic – “hydro” means water, “phobic” means fear. Hydrophobic molecules hate water and repel it. Phospholipids have a hydrophillic head and a hydrophobic tail. The cell membrane is composed of a bilayer (two layers) of phospholipids. In both layers, the head is attracted to the water inside and outside of the cell. The tail is repelled and ends up facing it’s counterpart in the other layer. Some shall pass In order for molecules to enter or exit the cell, they must pass through the phospholipid bilayer. Some have an easier time than others…. Fat soluble molecules: Molecules that dissolve easily in fats. They can usually squeeze through the membrane easily because the fatty tails of the phospholipids like them. (Exps – O2, CO2, steroids, Vitamins A, D, E, and K.) Water soluble molecules: Molecules that dissolve easily in water. They are usually repelled by the hydrophobic tails of the phospholipids. (Exps – sugars, sodium, calcium) Water: Surprisingly, water can pass through the phospholipid bilayer relatively easily because it is a very small molecule. Types of Transport Passive Transport: molecules move randomly according to their concentration gradient. Does NOT require energy Happens spontaneously Example: a bad smell diffusing across a room Active Transport: molecules are actively moved by cell organelles. Does require energy Something has to make it happen Example: some movers carrying boxes into the house. Passive transport Diffusion: molecules spread out through a liquid or gas. Molecules always move from an area of higher concentration to less concentration Concentration=the amount of molecules per unit of area New York City has a high concentration of people, Montana has a low concentration of people Diffusion of dye through water Passive transport Osmosis: The diffusion of water molecules across a semi-permeable membrane. A specific type of diffusion. Semi permeable = some things get through, others don’t The cell membrane has small pores. Small molecules like H2O and O2 get through, but bigger molecules like C6H12O6 cannot. Osmosis water is the only thing that moves in osmosis. Solution: a liquid formed when a solute dissolves in a solvent. Solvent: the liquid that the solute is dissolved in (typically water) Solute: the thing that is dissolved in the solvent (sugar, salt, kool-aid, etc.) Passive transport Types of solutions Hypotonic- Low solute concentration compared to the cell (example- pure water) Isotonic- The same solute concentration compared to the cell (example- slightly salty water) hypertonic- High solute concentration compared to the cell (example- very salty water) Osmosis Active transport Active Transport: ATP is used to open and close special proteins in the membrane to let bigger molecules into or out of the cell. Active transport Cytokinesis: ATP is used to actually move the cell membrane around. Cyto=cell Kinesis=movement Endocytosis- the cell membrane engulfs food particles to take them inside the cell Exocytosis-the cell membrane “spits out” waste particles to get rid of them Cytokinesis is also important when the cell reproduces by splitting into two cells. Cell membranes Task: Make a concept diagram that contains the following terms. Hypertonic Transport Solute Endocytosis Osmosis Cell division Passive Transport Cytokinesis Hydrophobic tail Isotonic Solution Cell membrane Solvent Hydrophilic head Phospholipid Proteins hypotonic Active Transport Diffusion Exocytosis Active transport