Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
SNARE (protein) wikipedia , lookup
Lipid bilayer wikipedia , lookup
Cell encapsulation wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Cytokinesis wikipedia , lookup
Membrane potential wikipedia , lookup
Signal transduction wikipedia , lookup
Endomembrane system wikipedia , lookup
Passive Transport: Diffusion, Facilitated Diffusion & Osmosis Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high-quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks). Copyright © 2015 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/about/ terms-of-use. Printed: July 13, 2015 www.ck12.org Chapter 1. Passive Transport: Diffusion, Facilitated Diffusion & Osmosis C HAPTER 1 Passive Transport: Diffusion, Facilitated Diffusion & Osmosis • • • • Describe a concentration gradient. Define diffusion. Distinguish between diffusion and osmosis. Differentiate between hypertonic, hypotonic, and isotonic solutions. What happens if you put a few drops of food coloring in water? Over time, the molecules of color spread out through the rest of the water. When the molecules are evenly spread throughout the space, the water will become an even color. This process of molecules moving from an area where there are lots of the same molecules to an area where there are fewer of these same molecules is known as diffusion. 1 www.ck12.org Passive Transport Recall that the cell membrane is semipermeable. It does not allow everything to pass through. Some molecules can pass easily through your cell membranes, while others have more difficulty. Some molecules even need an input of energy to help get them across the cell membrane. The movement of molecules across a membrane without the input of energy is known as passive transport. When energy is needed, the movement is known as active transport. Diffusion One example of passive transport is diffusion, when molecules move from an area of high concentration (large amount) to an area of low concentration (low amount). The amount of a substance in relation to the total volume is the concentration. They will continue to move in this way until equilibrium is reached or when the particles are equally disbursed throughout the area. In other words, there is no longer an area of high concentration or low concentration. This is a natural process and does not require energy because molecules are always in motion. Diffusion can occur across a semipermeable membrane, or a membrane that allows some things to cross such as water and oxygen but not allow other things to cross such as sugar. In diffusion, molecules that are small and uncharged like water and oxygen can freely diffuse across a cell membrane. They simply flow through the cell membrane. Other larger or charged molecules that diffuse across a membrane may need assistance from a protein doorway. As stated, oxygen is a molecule that can freely diffuse across a cell membrane. For example, an oxygen molecule can diffuse out of the air sacs in your lungs into your bloodstream because oxygen is more concentrated in your lungs than in your blood. Oxygen moves from the high concentration in your lungs to the low concentration of oxygen in your bloodstream. FIGURE 1.1 The figure on top shows a high concentration of particles on the left and a low concentration on the right. The particles will move from left to right until they reach equilibrium which is pictured on the bottom. In this case, the particles are evenly spread across the area. Facilitated Diffusion As was stated in the previous section, a semipermeable membrane allows small particles like oxygen and water to pass right through the cell membrane. Particles such as sugar and amino acids are too large to fit through the semipermeable cell membrane and need to find a passage way through the membrane. In facilitated diffusion, a protein doorway in the membrane allows these larger molecules to cross the membrane. Even though these larger molecules move through a protein doorway, they still are moving from an area of higher concentration to lower concentration so they are not using energy. 2 www.ck12.org Chapter 1. Passive Transport: Diffusion, Facilitated Diffusion & Osmosis FIGURE 1.2 This is an example of facilitated diffusion. On the left is a protein doorway that is called a pore. The pore is large enough to allow bigger molecules passageway through the cell membrane. The one to the right is a protein doorway that allows one molecule to pass at a time. Osmosis The diffusion of water, and water only, across a membrane because of a difference in concentration is called osmosis. Applications of Osmosis How do marine animals keep their cells from shrinking? Marine animals live in salt water, which is an environment where there is more salt in the water than in their cells. To prevent losing too much water from their bodies, these animals intake large quantities of salt water and then secrete the excess salt. ( Figure below ). Vocabulary • Active Transport: The movement of molecules across a membrane which requires energy. • Concentration: The amount of a substance in relation to the total volume • Diffusion: The movement of molecules from an area of high concentration through a membrane to an area of low concentration. • Equilibrium: A situation where molecules are evenly distributed in an area. 3 www.ck12.org FIGURE 1.3 Osmosis causes fish cells to exchange fresh water and salt by losing or gaining water. • Facilitated Diffusion: The movement of larger particles through a protein doorway from an area of high concentration to low concentration. • Osmosis: A special case of diffusion where water moves across a semi-permeable membrane. • Passive Transport: The movement of molecules across a membrane without the input of energy • Semi-permeable membrane: A membrane that allows certain things to cross and does not let other things to cross. Summary • Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. • Osmosis is a special case of diffusion. When water crosses a semipermeable membrane from an area of high concentration to an area of low concentration, this is called osmosis. Explore More Use the resource below to answer the following questions. • Osmosis at http://www.youtube.com/watch?v=7-QJ-UUX0iY (5:07) MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/flx/render/embeddedobject/57351 1. What is osmosis? 2. How would a salt solution affect a cell? How could this affect cellular processes? Review 1. Describe the process of diffusion. 4 www.ck12.org Chapter 1. Passive Transport: Diffusion, Facilitated Diffusion & Osmosis 2. Define osmosis. 3. Why doesn’t diffusion or osmosis require energy to occur? 4. If a plant cell is placed in a solution and the cell shrivels up, what type of solution was it placed in? How do you know? References 1. Mariana Ruiz Villarreal (LadyofHats). Fish cells and osmosis . 5