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Transcript
General Biology – Chapter 5 Notes on Active Transport Systems (day 2) Objectives: 1. Recognize that these cellular transport systems require energy and therefore considered uphill processes. 2. Recognize and explain the sodium /potassium pump. Know that there are many other active pump systems a cell utilizes but that we will only look at this one. 3. Identify and articulate endocytosis and exocytosis. Endocytosis has two divisions. They are phagocytosis and pinocytosis. Be able to delineate them. Notes. We will be looking at only 3 active cellular transport systems. They are the Sodium Potassium Pump, Endocytosis and exocytosis. Na+/K+ Pump Because these are ions you might expect them to move through a cell membrane by ionic channel diffusion, a passive transport system we talked about yesterday, in order to function properly some cells require a higher concentration of sodium outside the cell and a higher concentration of potassium inside the cell. These concentration gradients are maintained for these to ions by the so called sodium /potassium pump. Essentially, this works just like facilitated diffusion in conjunction with a carrier protein. The difference is that Sodium and potassium move against the concentration gradients so that for every three sodium ions being pump outside the cell, there are two potassium ions being pumped into the cell. Because these ions are being pumped against their concentration gradient, the cell must use energy (ATP) to make it happen. Refer to the reference transparency in your book. You must be able to describe the details of this cellular transport system. Endocytosis/Exocytosis : For molecules and sometimes whole organisms (bacteria) that are too big to pass through the cell membrane by facilitated diffusion, an Active process called endocytosis is employed by the cell. If the molecule to be brought into the cell is something big like a protein or viral particle the term we use to describe endocytosis is phagocytosis. If the molecule or particle to be brought into the cell is smaller and there is lots of water with it, the term we use to describe endocytosis is pinocytosis. White blood cells employ phagocytosis all the time. They actually prefer to bring bacteria into their interior parts and destroy them there. See the diagram in your book for differences. You must be able to spot endocytosis and exocytosis in action. Note that exocytosis is the reverse of endocytosis and there are no addition terms to describe exocytosis. Waste molecules and particles that are too big to pass through the cell membrane by facilitated diffusion will be expelled from the cell by exocytosis. See the diagram below. Note that the newly formed vesicle is actually made from a piece of the cell membrane. The molecules brought into the cell are most likely nutrient molecules and will be delivered to the appropriate cellular organelle for processing. Exocytosis is shown below and is nothing more than the reverse of endocytosis.