What Is Active Transport?<\/h1>\r\n<\/div>\r\nSome substances can pass into or out of a cell across the\u00a0[pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary]\u00a0without any\u00a0[pb_glossary id=\"5753\"]energy[\/pb_glossary]\u00a0required because they are moving from an area of higher\u00a0concentration\u00a0to an area of lower concentration. This type of transport is called\u00a0[pb_glossary id=\"5705\"]passive transport[\/pb_glossary]<\/strong>. Other substances require energy to cross a\u00a0plasma membrane, often because they are moving from an area of lower\u00a0concentration\u00a0to an area of higher concentration, against<\/em> the concentration gradient. This type of transport is called\u00a0[pb_glossary id=\"5689\"]active transport[\/pb_glossary]<\/strong>. The energy for active transport comes from the energy-carrying molecule called [pb_glossary id=\"5549\"]ATP[\/pb_glossary] (adenosine triphosphate). Active transport may also require\u00a0proteins\u00a0called pumps,\u00a0which are embedded in the plasma membrane. Two types of active transport are\u00a0membrane pumps (such as the\u00a0sodium-potassium pump) and vesicle transport.\r\n\r\nThe\u00a0Sodium-Potassium Pump<\/h2>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary]<\/strong> is a mechanism of [pb_glossary id=\"5689\"]active transport[\/pb_glossary] that moves sodium ions out of the cell and potassium ions into the cells \u2014 in all the trillions of [pb_glossary id=\"5665\"]cells[\/pb_glossary] in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this \"uphill\" process. The energy is provided by [pb_glossary id=\"5549\"]ATP[\/pb_glossary]. The sodium-potassium pump also requires [pb_glossary id=\"5701\"]carrier proteins[\/pb_glossary]. Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.\r\n\r\n[caption id=\"attachment_1674\" align=\"aligncenter\" width=\"819\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Sodium-Potassium-Pump-1-2.png\")
Figure 4.8.2 The sodium-potassium pump moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. First, three sodium ions bind with a carrier protein in the cell membrane. The carrier protein then changes shape, powered by energy from ATP, and as it does, it pumps the three sodium ions out of the cell. At that point, two potassium ions bind to the carrier protein. The process is reversed, and the potassium ions are pumped into the cell.<\/em>[\/caption]\r\n\r\n\r\n\r\nTo appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.<\/span>\r\n\r\n<\/div>\r\n\r\n \t- Sodium is the principal\u00a0ion\u00a0in the fluid outside of\u00a0cells. Normal sodium concentrations are about ten times higher outside of cells<\/em> than inside of cells.\u00a0 To move sodium out of the cell is moving it against the concentration gradient<\/li>\r\n \t
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\r\n<\/ul>\r\nThese differences in concentration create an electrical and chemical gradient across the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary], called the\u00a0[pb_glossary id=\"5699\"]membrane potential[\/pb_glossary]<\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of [pb_glossary id=\"5697\"]nerve impulses[\/pb_glossary] and contraction of muscles. A large percentage of the body's energy goes to maintaining this potential across the membranes of its trillions of cells with the [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary].\r\n\r\n
Vesicle Transport<\/h2>\r\n<\/div>\r\nSome molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called\u00a0[pb_glossary id=\"5695\"]vesicle transport[\/pb_glossary]<\/strong>. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.\r\n\r\n[caption id=\"attachment_1678\" align=\"alignnone\" width=\"1024\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Cytosis-2.jpg\")
Figure 4.8.3 Large molecules can enter and exit the cell with the help of vesicles. On the left side of the diagram you can see exocytosis, as large molecules exit the cell through the plasma membrane. On the right side of the diagram you can see endocytosis, as large molecules enter the cell through the plasma membrane, via vesicle formation.<\/em>[\/caption]\r\nEndocytosis<\/h3>\r\n[pb_glossary id=\"5611\"]Endocytosis[\/pb_glossary]<\/strong>\u00a0is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other\u00a0solid\u00a0particle is engulfed, the process is called\u00a0[pb_glossary id=\"1680\"]phagocytosis[\/pb_glossary].<\/strong>\u00a0When fluid is engulfed, the process is called\u00a0[pb_glossary id=\"1681\"]pinocytosis[\/pb_glossary]<\/strong>.\r\nExocytosis<\/h3>\r\n[pb_glossary id=\"1682\"]Exocytosis[\/pb_glossary]<\/strong>\u00a0is a type of vesicle transport that moves a substance out of the cell (exo-, like \"exit\"). A vesicle containing the substance moves through the cytoplasm to the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary].\u00a0Because the vesicle\u00a0membrane\u00a0is a\u00a0[pb_glossary id=\"5597\"]phospholipid bilayer[\/pb_glossary]\u00a0like the plasma membrane, the vesicle membrane fuses with the\u00a0cell membrane, and the substance is released outside the cell.\r\n\r\n[caption id=\"attachment_1685\" align=\"aligncenter\" width=\"703\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Endocytosis-and-Exocytosis-2.png\")
Figure 4.8.4 Endocytosis brings substances into the cell via vesicle formation. Exocytosis allows substances to exit the cell by merging a transport vesicle with the cell membrane.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My Human Body<\/span>\r\n\r\n<\/div>\r\nMaintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it's no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high\u00a0blood pressure<\/a>,\u00a0heart\u00a0disease<\/a>,\u00a0diabetes<\/a>, and other disorders.\r\n\r\nIf you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:\r\n\r\n \t- Total sodium intake should be less than 2,300 mg\/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg\/serving (or 5 per cent daily value).<\/li>\r\n \t
- Total potassium intake should be 4,700 mg\/day. It's easy to add potassium to the diet by choosing the right foods \u2014 and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.<\/li>\r\n<\/ul>\r\n
[h5p id=\"475\"]<\/p>\r\nFigure 4.8.5 Potassium power!\u00a0<\/em>\r\n\r\n\r\n4.8 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"5689\"]Active transport[\/pb_glossary] requires [pb_glossary id=\"5753\"]energy[\/pb_glossary] to move substances across a [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary], often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\r\n \t
- The [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary] is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\r\n \t
- [pb_glossary id=\"5695\"]Vesicle transport[\/pb_glossary] is a type of active transport that uses [pb_glossary id=\"5825\"]vesicles[\/pb_glossary]\u00a0to move large molecules into or out of cells.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define active transport.<\/li>\r\n \t
- [h5p id=\"476\"]<\/li>\r\n \t
- What is the sodium-potassium pump? Why is it so important?<\/li>\r\n \t
- The drawing below shows the fluid inside and outside of a cell. The dots represent molecules of a substance needed by the cell. Explain which type of transport \u2014 active or passive \u2014 is needed to move the molecules into the cell.\r\n\r\n[caption id=\"attachment_2343\" align=\"alignnone\" width=\"317\"]
![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Active-Transport-2.png\")
Figure 4.8.6 Use this image to answer question #4[\/caption]<\/li>\r\n \t - What are the similarities and differences between phagocytosis and pinocytosis?<\/li>\r\n \t
- What is the functional significance of the shape change of the carrier protein in the sodium-potassium pump after the sodium ions bind?<\/li>\r\n \t
- A potentially deadly poison derived from plants called ouabain<\/a> blocks the sodium-potassium pump and prevents it from working. What do you think this does to the sodium and potassium balance in cells? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.8 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Z_mXDvZQ6dU&feature=emb_logo\r\nNeutrophil Phagocytosis - White Blood Cell Eats Staphylococcus Aureus Bacteria,\r\nImmiflexImmuneSystem, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Ptmlvtei8hw\r\n
Cell Transport, The Amoeba Sisters, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.8.1<\/strong>\r\n\r\nHumvee challenge<\/a> by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.8.2<\/strong>\r\n\r\nSodium Potassium Pump by Christine Miller is used under a\u00a0CC BY 4.0<\/a>\u00a0 (<\/span>https:\/\/creativecommons.org\/licenses\/by\/4.0\/) license.<\/span>\r\n\r\nFigure 4.8.3<\/strong>\r\n\r\nCytosis<\/a> by Manu5<\/a>\u00a0on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 4.8.4\u00a0<\/strong>\r\n\r\nEndocytosis and Exocytosis by Christine Miller is used under a\u00a0CC BY 4.0<\/a>\u00a0 (<\/span>https:\/\/creativecommons.org\/licenses\/by\/4.0\/) license. <\/span>\r\n\r\nFigure 4.8.5<\/strong>\r\n\r\n \t- Canteloupes. Image Number K7355-11<\/a> by Scott Bauer\/ USDA<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/li>\r\n \t
- Spinach<\/a> by chiara conti<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Eleven long purple eggplants<\/a> by JVRKPRASAD<\/a> on Wikimedia commons is used under a\u00a0 CC BY-SA 4.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Bananas<\/a> by Marco Antonio Victorino<\/a> on Pexels<\/a> is used under the Pexels license<\/a> (https:\/\/www.pexels.com\/license\/).<\/li>\r\n \t
- Potato picking<\/a> by Nic D<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Maldives<\/a> by Sebastian Pena Lambarri<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n<\/ul>\r\nFigure 4.8.6<\/strong>\r\n\r\nActive Transport by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n
References<\/h2>\r\n
Amoeba Sisters. (2016, June 24). Cell transport [digital image]. YouTube. https:\/\/www.youtube.com\/watch?v=Ptmlvtei8hw&feature=youtu.be<\/p>\r\n
ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis - White blood cell eats staphylococcus aureus bacteria. YouTube. https:\/\/www.youtube.com\/watch?v=Z_mXDvZQ6dU<\/p>\r\n
Mayo Clinic Staff. (n.d.). Diabetes [online]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/diabetes\/symptoms-causes\/syc-20371444<\/p>\r\n
Mayo Clinic Staff. (n.d.). High blood pressure (hypertension) [online]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/high-blood-pressure\/symptoms-causes\/syc-20373410<\/p>\r\n
Mayo Clinic Staff. (n.d.). Heart disease [online]. MayoClinic.org.\u00a0 https:\/\/www.mayoclinic.org\/diseases-conditions\/heart-disease\/symptoms-causes\/syc-20353118<\/p>\r\n
Wikipedia contributors. (2020, June 19). Ouabain. In\u00a0Wikipedia. <\/i>\u00a0https:\/\/en.wikipedia.org\/w\/index.php?title=Ouabain&oldid=963440756<\/p>","rendered":"
<\/p>\n![\"Four](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Humvee-challenge-e1585588086447-2.jpg\")
Figure 4.8.1 The Humvee challenge – Active transport.<\/em><\/figcaption><\/figure>\nLike Pushing a Humvee Uphill<\/h1>\n
You can tell by their faces that these airmen (Figure 4.8.1) are expending a lot of energy<\/a> trying to push this Humvee up a slope. The men are participating in a competition that tests their brute strength against that of other teams. The Humvee weighs about 13 thousand pounds (about 5,897 kilograms), so it takes every ounce of energy they can muster to move it uphill against the force of gravity. Transport of some substances across a plasma membrane<\/a> is a little like pushing a Humvee uphill \u2014 it can’t be done without adding energy.<\/p>\n\nWhat Is Active Transport?<\/h1>\n<\/div>\n
Some substances can pass into or out of a cell across the\u00a0plasma membrane<\/a>\u00a0without any\u00a0energy<\/a>\u00a0required because they are moving from an area of higher\u00a0concentration\u00a0to an area of lower concentration. This type of transport is called\u00a0passive transport<\/a><\/strong>. Other substances require energy to cross a\u00a0plasma membrane, often because they are moving from an area of lower\u00a0concentration\u00a0to an area of higher concentration, against<\/em> the concentration gradient. This type of transport is called\u00a0active transport<\/a><\/strong>. The energy for active transport comes from the energy-carrying molecule called ATP<\/a> (adenosine triphosphate). Active transport may also require\u00a0proteins\u00a0called pumps,\u00a0which are embedded in the plasma membrane. Two types of active transport are\u00a0membrane pumps (such as the\u00a0sodium-potassium pump) and vesicle transport.<\/p>\n\nThe\u00a0Sodium-Potassium Pump<\/h2>\n<\/div>\n
The\u00a0sodium-potassium pump<\/a><\/strong> is a mechanism of active transport<\/a> that moves sodium ions out of the cell and potassium ions into the cells \u2014 in all the trillions of cells<\/a> in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this “uphill” process. The energy is provided by ATP<\/a>. The sodium-potassium pump also requires carrier proteins<\/a>. Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.<\/p>\nFigure 4.8.2 The sodium-potassium pump moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. First, three sodium ions bind with a carrier protein in the cell membrane. The carrier protein then changes shape, powered by energy from ATP, and as it does, it pumps the three sodium ions out of the cell. At that point, two potassium ions bind to the carrier protein. The process is reversed, and the potassium ions are pumped into the cell.<\/em><\/figcaption><\/figure>\n\nTo appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.<\/span><\/p>\n<\/div>\n\n- Sodium is the principal\u00a0ion\u00a0in the fluid outside of\u00a0cells. Normal sodium concentrations are about ten times higher outside of cells<\/em> than inside of cells.\u00a0 To move sodium out of the cell is moving it against the concentration gradient<\/li>\n
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\n<\/ul>\n
These differences in concentration create an electrical and chemical gradient across the\u00a0cell membrane<\/a>, called the\u00a0membrane potential<\/a><\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of nerve impulses<\/a> and contraction of muscles. A large percentage of the body’s energy goes to maintaining this potential across the membranes of its trillions of cells with the sodium-potassium pump<\/a>.<\/p>\n\nVesicle Transport<\/h2>\n<\/div>\n
Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called\u00a0vesicle transport<\/a><\/strong>. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.<\/p>\nFigure 4.8.3 Large molecules can enter and exit the cell with the help of vesicles. On the left side of the diagram you can see exocytosis, as large molecules exit the cell through the plasma membrane. On the right side of the diagram you can see endocytosis, as large molecules enter the cell through the plasma membrane, via vesicle formation.<\/em><\/figcaption><\/figure>\nEndocytosis<\/h3>\n
Endocytosis<\/a><\/strong>\u00a0is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other\u00a0solid\u00a0particle is engulfed, the process is called\u00a0phagocytosis<\/a>.<\/strong>\u00a0When fluid is engulfed, the process is called\u00a0pinocytosis<\/a><\/strong>.<\/p>\nExocytosis<\/h3>\n
Exocytosis<\/a><\/strong>\u00a0is a type of vesicle transport that moves a substance out of the cell (exo-, like “exit”). A vesicle containing the substance moves through the cytoplasm to the\u00a0cell membrane<\/a>.\u00a0Because the vesicle\u00a0membrane\u00a0is a\u00a0phospholipid bilayer<\/a>\u00a0like the plasma membrane, the vesicle membrane fuses with the\u00a0cell membrane, and the substance is released outside the cell.<\/p>\nFigure 4.8.4 Endocytosis brings substances into the cell via vesicle formation. Exocytosis allows substances to exit the cell by merging a transport vesicle with the cell membrane.<\/em><\/figcaption><\/figure>\n\nFeature: My Human Body<\/span><\/p>\n<\/div>\nMaintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it’s no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high\u00a0blood pressure<\/a>,\u00a0heart\u00a0disease<\/a>,\u00a0diabetes<\/a>, and other disorders.<\/p>\nIf you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:<\/p>\n
\n- Total sodium intake should be less than 2,300 mg\/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg\/serving (or 5 per cent daily value).<\/li>\n
- Total potassium intake should be 4,700 mg\/day. It’s easy to add potassium to the diet by choosing the right foods \u2014 and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.<\/li>\n<\/ul>\n
\n
\n<\/div>\n<\/div>\nFigure 4.8.5 Potassium power!\u00a0<\/em><\/p>\n\n\n\n4.8 Summary<\/span><\/h1>\n<\/header>\n\n\n- Active transport<\/a> requires energy<\/a> to move substances across a plasma membrane<\/a>, often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\n
- The sodium-potassium pump<\/a> is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\n
- Vesicle transport<\/a> is a type of active transport that uses vesicles<\/a>\u00a0to move large molecules into or out of cells.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n\n
\n4.8 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- Define active transport.<\/li>\n
- \n\n
The\u00a0Sodium-Potassium Pump<\/h2>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary]<\/strong> is a mechanism of [pb_glossary id=\"5689\"]active transport[\/pb_glossary] that moves sodium ions out of the cell and potassium ions into the cells \u2014 in all the trillions of [pb_glossary id=\"5665\"]cells[\/pb_glossary] in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this \"uphill\" process. The energy is provided by [pb_glossary id=\"5549\"]ATP[\/pb_glossary]. The sodium-potassium pump also requires [pb_glossary id=\"5701\"]carrier proteins[\/pb_glossary]. Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.\r\n\r\n[caption id=\"attachment_1674\" align=\"aligncenter\" width=\"819\"] Figure 4.8.2 The sodium-potassium pump moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. First, three sodium ions bind with a carrier protein in the cell membrane. The carrier protein then changes shape, powered by energy from ATP, and as it does, it pumps the three sodium ions out of the cell. At that point, two potassium ions bind to the carrier protein. The process is reversed, and the potassium ions are pumped into the cell.<\/em>[\/caption]\r\n\r\n\r\n\r\nTo appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.<\/span>\r\n\r\n<\/div>\r\n\r\n \t- Sodium is the principal\u00a0ion\u00a0in the fluid outside of\u00a0cells. Normal sodium concentrations are about ten times higher outside of cells<\/em> than inside of cells.\u00a0 To move sodium out of the cell is moving it against the concentration gradient<\/li>\r\n \t
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\r\n<\/ul>\r\nThese differences in concentration create an electrical and chemical gradient across the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary], called the\u00a0[pb_glossary id=\"5699\"]membrane potential[\/pb_glossary]<\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of [pb_glossary id=\"5697\"]nerve impulses[\/pb_glossary] and contraction of muscles. A large percentage of the body's energy goes to maintaining this potential across the membranes of its trillions of cells with the [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary].\r\n\r\n
Vesicle Transport<\/h2>\r\n<\/div>\r\nSome molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called\u00a0[pb_glossary id=\"5695\"]vesicle transport[\/pb_glossary]<\/strong>. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.\r\n\r\n[caption id=\"attachment_1678\" align=\"alignnone\" width=\"1024\"] Figure 4.8.3 Large molecules can enter and exit the cell with the help of vesicles. On the left side of the diagram you can see exocytosis, as large molecules exit the cell through the plasma membrane. On the right side of the diagram you can see endocytosis, as large molecules enter the cell through the plasma membrane, via vesicle formation.<\/em>[\/caption]\r\nEndocytosis<\/h3>\r\n[pb_glossary id=\"5611\"]Endocytosis[\/pb_glossary]<\/strong>\u00a0is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other\u00a0solid\u00a0particle is engulfed, the process is called\u00a0[pb_glossary id=\"1680\"]phagocytosis[\/pb_glossary].<\/strong>\u00a0When fluid is engulfed, the process is called\u00a0[pb_glossary id=\"1681\"]pinocytosis[\/pb_glossary]<\/strong>.\r\nExocytosis<\/h3>\r\n[pb_glossary id=\"1682\"]Exocytosis[\/pb_glossary]<\/strong>\u00a0is a type of vesicle transport that moves a substance out of the cell (exo-, like \"exit\"). A vesicle containing the substance moves through the cytoplasm to the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary].\u00a0Because the vesicle\u00a0membrane\u00a0is a\u00a0[pb_glossary id=\"5597\"]phospholipid bilayer[\/pb_glossary]\u00a0like the plasma membrane, the vesicle membrane fuses with the\u00a0cell membrane, and the substance is released outside the cell.\r\n\r\n[caption id=\"attachment_1685\" align=\"aligncenter\" width=\"703\"] Figure 4.8.4 Endocytosis brings substances into the cell via vesicle formation. Exocytosis allows substances to exit the cell by merging a transport vesicle with the cell membrane.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My Human Body<\/span>\r\n\r\n<\/div>\r\nMaintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it's no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high\u00a0blood pressure<\/a>,\u00a0heart\u00a0disease<\/a>,\u00a0diabetes<\/a>, and other disorders.\r\n\r\nIf you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:\r\n\r\n \t- Total sodium intake should be less than 2,300 mg\/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg\/serving (or 5 per cent daily value).<\/li>\r\n \t
- Total potassium intake should be 4,700 mg\/day. It's easy to add potassium to the diet by choosing the right foods \u2014 and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.<\/li>\r\n<\/ul>\r\n
[h5p id=\"475\"]<\/p>\r\nFigure 4.8.5 Potassium power!\u00a0<\/em>\r\n\r\n\r\n4.8 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"5689\"]Active transport[\/pb_glossary] requires [pb_glossary id=\"5753\"]energy[\/pb_glossary] to move substances across a [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary], often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\r\n \t
- The [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary] is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\r\n \t
- [pb_glossary id=\"5695\"]Vesicle transport[\/pb_glossary] is a type of active transport that uses [pb_glossary id=\"5825\"]vesicles[\/pb_glossary]\u00a0to move large molecules into or out of cells.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Define active transport.<\/li>\r\n \t
- [h5p id=\"476\"]<\/li>\r\n \t
- What is the sodium-potassium pump? Why is it so important?<\/li>\r\n \t
- The drawing below shows the fluid inside and outside of a cell. The dots represent molecules of a substance needed by the cell. Explain which type of transport \u2014 active or passive \u2014 is needed to move the molecules into the cell.\r\n\r\n[caption id=\"attachment_2343\" align=\"alignnone\" width=\"317\"] Figure 4.8.6 Use this image to answer question #4[\/caption]<\/li>\r\n \t
- What are the similarities and differences between phagocytosis and pinocytosis?<\/li>\r\n \t
- What is the functional significance of the shape change of the carrier protein in the sodium-potassium pump after the sodium ions bind?<\/li>\r\n \t
- A potentially deadly poison derived from plants called ouabain<\/a> blocks the sodium-potassium pump and prevents it from working. What do you think this does to the sodium and potassium balance in cells? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.8 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Z_mXDvZQ6dU&feature=emb_logo\r\nNeutrophil Phagocytosis - White Blood Cell Eats Staphylococcus Aureus Bacteria,\r\nImmiflexImmuneSystem, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Ptmlvtei8hw\r\n
Cell Transport, The Amoeba Sisters, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.8.1<\/strong>\r\n\r\nHumvee challenge<\/a> by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.8.2<\/strong>\r\n\r\nSodium Potassium Pump by Christine Miller is used under a\u00a0CC BY 4.0<\/a>\u00a0 (<\/span>https:\/\/creativecommons.org\/licenses\/by\/4.0\/) license.<\/span>\r\n\r\nFigure 4.8.3<\/strong>\r\n\r\nCytosis<\/a> by Manu5<\/a>\u00a0on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 4.8.4\u00a0<\/strong>\r\n\r\nEndocytosis and Exocytosis by Christine Miller is used under a\u00a0CC BY 4.0<\/a>\u00a0 (<\/span>https:\/\/creativecommons.org\/licenses\/by\/4.0\/) license. <\/span>\r\n\r\nFigure 4.8.5<\/strong>\r\n\r\n \t- Canteloupes. Image Number K7355-11<\/a> by Scott Bauer\/ USDA<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/li>\r\n \t
- Spinach<\/a> by chiara conti<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Eleven long purple eggplants<\/a> by JVRKPRASAD<\/a> on Wikimedia commons is used under a\u00a0 CC BY-SA 4.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Bananas<\/a> by Marco Antonio Victorino<\/a> on Pexels<\/a> is used under the Pexels license<\/a> (https:\/\/www.pexels.com\/license\/).<\/li>\r\n \t
- Potato picking<\/a> by Nic D<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Maldives<\/a> by Sebastian Pena Lambarri<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n<\/ul>\r\nFigure 4.8.6<\/strong>\r\n\r\nActive Transport by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n
References<\/h2>\r\n
Amoeba Sisters. (2016, June 24). Cell transport [digital image]. YouTube. https:\/\/www.youtube.com\/watch?v=Ptmlvtei8hw&feature=youtu.be<\/p>\r\n
ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis - White blood cell eats staphylococcus aureus bacteria. YouTube. https:\/\/www.youtube.com\/watch?v=Z_mXDvZQ6dU<\/p>\r\n
Mayo Clinic Staff. (n.d.). Diabetes [online]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/diabetes\/symptoms-causes\/syc-20371444<\/p>\r\n
Mayo Clinic Staff. (n.d.). High blood pressure (hypertension) [online]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/high-blood-pressure\/symptoms-causes\/syc-20373410<\/p>\r\n
Mayo Clinic Staff. (n.d.). Heart disease [online]. MayoClinic.org.\u00a0 https:\/\/www.mayoclinic.org\/diseases-conditions\/heart-disease\/symptoms-causes\/syc-20353118<\/p>\r\n
Wikipedia contributors. (2020, June 19). Ouabain. In\u00a0Wikipedia. <\/i>\u00a0https:\/\/en.wikipedia.org\/w\/index.php?title=Ouabain&oldid=963440756<\/p>","rendered":"
<\/p>\nFigure 4.8.1 The Humvee challenge – Active transport.<\/em><\/figcaption><\/figure>\nLike Pushing a Humvee Uphill<\/h1>\n
You can tell by their faces that these airmen (Figure 4.8.1) are expending a lot of energy<\/a> trying to push this Humvee up a slope. The men are participating in a competition that tests their brute strength against that of other teams. The Humvee weighs about 13 thousand pounds (about 5,897 kilograms), so it takes every ounce of energy they can muster to move it uphill against the force of gravity. Transport of some substances across a plasma membrane<\/a> is a little like pushing a Humvee uphill \u2014 it can’t be done without adding energy.<\/p>\n\nWhat Is Active Transport?<\/h1>\n<\/div>\n
Some substances can pass into or out of a cell across the\u00a0plasma membrane<\/a>\u00a0without any\u00a0energy<\/a>\u00a0required because they are moving from an area of higher\u00a0concentration\u00a0to an area of lower concentration. This type of transport is called\u00a0passive transport<\/a><\/strong>. Other substances require energy to cross a\u00a0plasma membrane, often because they are moving from an area of lower\u00a0concentration\u00a0to an area of higher concentration, against<\/em> the concentration gradient. This type of transport is called\u00a0active transport<\/a><\/strong>. The energy for active transport comes from the energy-carrying molecule called ATP<\/a> (adenosine triphosphate). Active transport may also require\u00a0proteins\u00a0called pumps,\u00a0which are embedded in the plasma membrane. Two types of active transport are\u00a0membrane pumps (such as the\u00a0sodium-potassium pump) and vesicle transport.<\/p>\n\nThe\u00a0Sodium-Potassium Pump<\/h2>\n<\/div>\n
The\u00a0sodium-potassium pump<\/a><\/strong> is a mechanism of active transport<\/a> that moves sodium ions out of the cell and potassium ions into the cells \u2014 in all the trillions of cells<\/a> in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this “uphill” process. The energy is provided by ATP<\/a>. The sodium-potassium pump also requires carrier proteins<\/a>. Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.<\/p>\nFigure 4.8.2 The sodium-potassium pump moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. First, three sodium ions bind with a carrier protein in the cell membrane. The carrier protein then changes shape, powered by energy from ATP, and as it does, it pumps the three sodium ions out of the cell. At that point, two potassium ions bind to the carrier protein. The process is reversed, and the potassium ions are pumped into the cell.<\/em><\/figcaption><\/figure>\n\nTo appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.<\/span><\/p>\n<\/div>\n\n- Sodium is the principal\u00a0ion\u00a0in the fluid outside of\u00a0cells. Normal sodium concentrations are about ten times higher outside of cells<\/em> than inside of cells.\u00a0 To move sodium out of the cell is moving it against the concentration gradient<\/li>\n
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\n<\/ul>\n
These differences in concentration create an electrical and chemical gradient across the\u00a0cell membrane<\/a>, called the\u00a0membrane potential<\/a><\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of nerve impulses<\/a> and contraction of muscles. A large percentage of the body’s energy goes to maintaining this potential across the membranes of its trillions of cells with the sodium-potassium pump<\/a>.<\/p>\n\nVesicle Transport<\/h2>\n<\/div>\n
Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called\u00a0vesicle transport<\/a><\/strong>. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.<\/p>\nFigure 4.8.3 Large molecules can enter and exit the cell with the help of vesicles. On the left side of the diagram you can see exocytosis, as large molecules exit the cell through the plasma membrane. On the right side of the diagram you can see endocytosis, as large molecules enter the cell through the plasma membrane, via vesicle formation.<\/em><\/figcaption><\/figure>\nEndocytosis<\/h3>\n
Endocytosis<\/a><\/strong>\u00a0is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other\u00a0solid\u00a0particle is engulfed, the process is called\u00a0phagocytosis<\/a>.<\/strong>\u00a0When fluid is engulfed, the process is called\u00a0pinocytosis<\/a><\/strong>.<\/p>\nExocytosis<\/h3>\n
Exocytosis<\/a><\/strong>\u00a0is a type of vesicle transport that moves a substance out of the cell (exo-, like “exit”). A vesicle containing the substance moves through the cytoplasm to the\u00a0cell membrane<\/a>.\u00a0Because the vesicle\u00a0membrane\u00a0is a\u00a0phospholipid bilayer<\/a>\u00a0like the plasma membrane, the vesicle membrane fuses with the\u00a0cell membrane, and the substance is released outside the cell.<\/p>\nFigure 4.8.4 Endocytosis brings substances into the cell via vesicle formation. Exocytosis allows substances to exit the cell by merging a transport vesicle with the cell membrane.<\/em><\/figcaption><\/figure>\n\nFeature: My Human Body<\/span><\/p>\n<\/div>\nMaintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it’s no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high\u00a0blood pressure<\/a>,\u00a0heart\u00a0disease<\/a>,\u00a0diabetes<\/a>, and other disorders.<\/p>\nIf you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:<\/p>\n
\n- Total sodium intake should be less than 2,300 mg\/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg\/serving (or 5 per cent daily value).<\/li>\n
- Total potassium intake should be 4,700 mg\/day. It’s easy to add potassium to the diet by choosing the right foods \u2014 and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.<\/li>\n<\/ul>\n
\n
\n<\/div>\n<\/div>\nFigure 4.8.5 Potassium power!\u00a0<\/em><\/p>\n\n\n\n4.8 Summary<\/span><\/h1>\n<\/header>\n\n\n- Active transport<\/a> requires energy<\/a> to move substances across a plasma membrane<\/a>, often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\n
- The sodium-potassium pump<\/a> is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\n
- Vesicle transport<\/a> is a type of active transport that uses vesicles<\/a>\u00a0to move large molecules into or out of cells.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n\n
\n4.8 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- Define active transport.<\/li>\n
- \n\n
- \r\n \t
- Sodium is the principal\u00a0ion\u00a0in the fluid outside of\u00a0cells. Normal sodium concentrations are about ten times higher outside of cells<\/em> than inside of cells.\u00a0 To move sodium out of the cell is moving it against the concentration gradient<\/li>\r\n \t
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\r\n<\/ul>\r\nThese differences in concentration create an electrical and chemical gradient across the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary], called the\u00a0[pb_glossary id=\"5699\"]membrane potential[\/pb_glossary]<\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of [pb_glossary id=\"5697\"]nerve impulses[\/pb_glossary] and contraction of muscles. A large percentage of the body's energy goes to maintaining this potential across the membranes of its trillions of cells with the [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary].\r\n
\r\nVesicle Transport<\/h2>\r\n<\/div>\r\nSome molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called\u00a0[pb_glossary id=\"5695\"]vesicle transport[\/pb_glossary]<\/strong>. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.\r\n\r\n[caption id=\"attachment_1678\" align=\"alignnone\" width=\"1024\"]
Figure 4.8.3 Large molecules can enter and exit the cell with the help of vesicles. On the left side of the diagram you can see exocytosis, as large molecules exit the cell through the plasma membrane. On the right side of the diagram you can see endocytosis, as large molecules enter the cell through the plasma membrane, via vesicle formation.<\/em>[\/caption]\r\nEndocytosis<\/h3>\r\n[pb_glossary id=\"5611\"]Endocytosis[\/pb_glossary]<\/strong>\u00a0is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other\u00a0solid\u00a0particle is engulfed, the process is called\u00a0[pb_glossary id=\"1680\"]phagocytosis[\/pb_glossary].<\/strong>\u00a0When fluid is engulfed, the process is called\u00a0[pb_glossary id=\"1681\"]pinocytosis[\/pb_glossary]<\/strong>.\r\n
Exocytosis<\/h3>\r\n[pb_glossary id=\"1682\"]Exocytosis[\/pb_glossary]<\/strong>\u00a0is a type of vesicle transport that moves a substance out of the cell (exo-, like \"exit\"). A vesicle containing the substance moves through the cytoplasm to the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary].\u00a0Because the vesicle\u00a0membrane\u00a0is a\u00a0[pb_glossary id=\"5597\"]phospholipid bilayer[\/pb_glossary]\u00a0like the plasma membrane, the vesicle membrane fuses with the\u00a0cell membrane, and the substance is released outside the cell.\r\n\r\n[caption id=\"attachment_1685\" align=\"aligncenter\" width=\"703\"]
Figure 4.8.4 Endocytosis brings substances into the cell via vesicle formation. Exocytosis allows substances to exit the cell by merging a transport vesicle with the cell membrane.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My Human Body<\/span>\r\n\r\n<\/div>\r\nMaintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it's no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high\u00a0blood pressure<\/a>,\u00a0heart\u00a0disease<\/a>,\u00a0diabetes<\/a>, and other disorders.\r\n\r\nIf you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:\r\n- \r\n \t
- Total sodium intake should be less than 2,300 mg\/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg\/serving (or 5 per cent daily value).<\/li>\r\n \t
- Total potassium intake should be 4,700 mg\/day. It's easy to add potassium to the diet by choosing the right foods \u2014 and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.<\/li>\r\n<\/ul>\r\n
[h5p id=\"475\"]<\/p>\r\nFigure 4.8.5 Potassium power!\u00a0<\/em>\r\n
\r\n\r\n 4.8 Summary<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- [pb_glossary id=\"5689\"]Active transport[\/pb_glossary] requires [pb_glossary id=\"5753\"]energy[\/pb_glossary] to move substances across a [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary], often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\r\n \t
- The [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary] is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\r\n \t
- [pb_glossary id=\"5695\"]Vesicle transport[\/pb_glossary] is a type of active transport that uses [pb_glossary id=\"5825\"]vesicles[\/pb_glossary]\u00a0to move large molecules into or out of cells.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n 4.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- Define active transport.<\/li>\r\n \t
- [h5p id=\"476\"]<\/li>\r\n \t
- What is the sodium-potassium pump? Why is it so important?<\/li>\r\n \t
- The drawing below shows the fluid inside and outside of a cell. The dots represent molecules of a substance needed by the cell. Explain which type of transport \u2014 active or passive \u2014 is needed to move the molecules into the cell.\r\n\r\n[caption id=\"attachment_2343\" align=\"alignnone\" width=\"317\"] Figure 4.8.6 Use this image to answer question #4[\/caption]<\/li>\r\n \t
- What are the similarities and differences between phagocytosis and pinocytosis?<\/li>\r\n \t
- What is the functional significance of the shape change of the carrier protein in the sodium-potassium pump after the sodium ions bind?<\/li>\r\n \t
- A potentially deadly poison derived from plants called ouabain<\/a> blocks the sodium-potassium pump and prevents it from working. What do you think this does to the sodium and potassium balance in cells? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 4.8 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Z_mXDvZQ6dU&feature=emb_logo\r\nNeutrophil Phagocytosis - White Blood Cell Eats Staphylococcus Aureus Bacteria,\r\nImmiflexImmuneSystem, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=Ptmlvtei8hw\r\n
Cell Transport, The Amoeba Sisters, 2016.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.8.1<\/strong>\r\n\r\nHumvee challenge<\/a> by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.8.2<\/strong>\r\n\r\nSodium Potassium Pump by Christine Miller is used under a\u00a0CC BY 4.0<\/a>\u00a0 (<\/span>https:\/\/creativecommons.org\/licenses\/by\/4.0\/) license.<\/span>\r\n\r\nFigure 4.8.3<\/strong>\r\n\r\nCytosis<\/a> by Manu5<\/a>\u00a0on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 4.8.4\u00a0<\/strong>\r\n\r\nEndocytosis and Exocytosis by Christine Miller is used under a\u00a0CC BY 4.0<\/a>\u00a0 (<\/span>https:\/\/creativecommons.org\/licenses\/by\/4.0\/) license. <\/span>\r\n\r\nFigure 4.8.5<\/strong>\r\n
- \r\n \t
- Canteloupes. Image Number K7355-11<\/a> by Scott Bauer\/ USDA<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/li>\r\n \t
- Spinach<\/a> by chiara conti<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Eleven long purple eggplants<\/a> by JVRKPRASAD<\/a> on Wikimedia commons is used under a\u00a0 CC BY-SA 4.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/li>\r\n \t
- Bananas<\/a> by Marco Antonio Victorino<\/a> on Pexels<\/a> is used under the Pexels license<\/a> (https:\/\/www.pexels.com\/license\/).<\/li>\r\n \t
- Potato picking<\/a> by Nic D<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Maldives<\/a> by Sebastian Pena Lambarri<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n<\/ul>\r\nFigure 4.8.6<\/strong>\r\n\r\nActive Transport by Christine Miller is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n
References<\/h2>\r\n
Amoeba Sisters. (2016, June 24). Cell transport [digital image]. YouTube. https:\/\/www.youtube.com\/watch?v=Ptmlvtei8hw&feature=youtu.be<\/p>\r\n
ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis - White blood cell eats staphylococcus aureus bacteria. YouTube. https:\/\/www.youtube.com\/watch?v=Z_mXDvZQ6dU<\/p>\r\n
Mayo Clinic Staff. (n.d.). Diabetes [online]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/diabetes\/symptoms-causes\/syc-20371444<\/p>\r\n
Mayo Clinic Staff. (n.d.). High blood pressure (hypertension) [online]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/high-blood-pressure\/symptoms-causes\/syc-20373410<\/p>\r\n
Mayo Clinic Staff. (n.d.). Heart disease [online]. MayoClinic.org.\u00a0 https:\/\/www.mayoclinic.org\/diseases-conditions\/heart-disease\/symptoms-causes\/syc-20353118<\/p>\r\n
Wikipedia contributors. (2020, June 19). Ouabain. In\u00a0Wikipedia. <\/i>\u00a0https:\/\/en.wikipedia.org\/w\/index.php?title=Ouabain&oldid=963440756<\/p>","rendered":"
<\/p>\n
Figure 4.8.1 The Humvee challenge – Active transport.<\/em><\/figcaption><\/figure>\n Like Pushing a Humvee Uphill<\/h1>\n
You can tell by their faces that these airmen (Figure 4.8.1) are expending a lot of energy<\/a> trying to push this Humvee up a slope. The men are participating in a competition that tests their brute strength against that of other teams. The Humvee weighs about 13 thousand pounds (about 5,897 kilograms), so it takes every ounce of energy they can muster to move it uphill against the force of gravity. Transport of some substances across a plasma membrane<\/a> is a little like pushing a Humvee uphill \u2014 it can’t be done without adding energy.<\/p>\n
\nWhat Is Active Transport?<\/h1>\n<\/div>\n
Some substances can pass into or out of a cell across the\u00a0plasma membrane<\/a>\u00a0without any\u00a0energy<\/a>\u00a0required because they are moving from an area of higher\u00a0concentration\u00a0to an area of lower concentration. This type of transport is called\u00a0passive transport<\/a><\/strong>. Other substances require energy to cross a\u00a0plasma membrane, often because they are moving from an area of lower\u00a0concentration\u00a0to an area of higher concentration, against<\/em> the concentration gradient. This type of transport is called\u00a0active transport<\/a><\/strong>. The energy for active transport comes from the energy-carrying molecule called ATP<\/a> (adenosine triphosphate). Active transport may also require\u00a0proteins\u00a0called pumps,\u00a0which are embedded in the plasma membrane. Two types of active transport are\u00a0membrane pumps (such as the\u00a0sodium-potassium pump) and vesicle transport.<\/p>\n
\nThe\u00a0Sodium-Potassium Pump<\/h2>\n<\/div>\n
The\u00a0sodium-potassium pump<\/a><\/strong> is a mechanism of active transport<\/a> that moves sodium ions out of the cell and potassium ions into the cells \u2014 in all the trillions of cells<\/a> in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this “uphill” process. The energy is provided by ATP<\/a>. The sodium-potassium pump also requires carrier proteins<\/a>. Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.<\/p>\n
Figure 4.8.2 The sodium-potassium pump moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. First, three sodium ions bind with a carrier protein in the cell membrane. The carrier protein then changes shape, powered by energy from ATP, and as it does, it pumps the three sodium ions out of the cell. At that point, two potassium ions bind to the carrier protein. The process is reversed, and the potassium ions are pumped into the cell.<\/em><\/figcaption><\/figure>\n \nTo appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.<\/span><\/p>\n<\/div>\n
- \n
- Sodium is the principal\u00a0ion\u00a0in the fluid outside of\u00a0cells. Normal sodium concentrations are about ten times higher outside of cells<\/em> than inside of cells.\u00a0 To move sodium out of the cell is moving it against the concentration gradient<\/li>\n
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\n<\/ul>\n
These differences in concentration create an electrical and chemical gradient across the\u00a0cell membrane<\/a>, called the\u00a0membrane potential<\/a><\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of nerve impulses<\/a> and contraction of muscles. A large percentage of the body’s energy goes to maintaining this potential across the membranes of its trillions of cells with the sodium-potassium pump<\/a>.<\/p>\n
\nVesicle Transport<\/h2>\n<\/div>\n
Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called\u00a0vesicle transport<\/a><\/strong>. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.<\/p>\n
Figure 4.8.3 Large molecules can enter and exit the cell with the help of vesicles. On the left side of the diagram you can see exocytosis, as large molecules exit the cell through the plasma membrane. On the right side of the diagram you can see endocytosis, as large molecules enter the cell through the plasma membrane, via vesicle formation.<\/em><\/figcaption><\/figure>\n Endocytosis<\/h3>\n
Endocytosis<\/a><\/strong>\u00a0is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other\u00a0solid\u00a0particle is engulfed, the process is called\u00a0phagocytosis<\/a>.<\/strong>\u00a0When fluid is engulfed, the process is called\u00a0pinocytosis<\/a><\/strong>.<\/p>\n
Exocytosis<\/h3>\n
Exocytosis<\/a><\/strong>\u00a0is a type of vesicle transport that moves a substance out of the cell (exo-, like “exit”). A vesicle containing the substance moves through the cytoplasm to the\u00a0cell membrane<\/a>.\u00a0Because the vesicle\u00a0membrane\u00a0is a\u00a0phospholipid bilayer<\/a>\u00a0like the plasma membrane, the vesicle membrane fuses with the\u00a0cell membrane, and the substance is released outside the cell.<\/p>\n
Figure 4.8.4 Endocytosis brings substances into the cell via vesicle formation. Exocytosis allows substances to exit the cell by merging a transport vesicle with the cell membrane.<\/em><\/figcaption><\/figure>\n \nFeature: My Human Body<\/span><\/p>\n<\/div>\n
Maintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it’s no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high\u00a0blood pressure<\/a>,\u00a0heart\u00a0disease<\/a>,\u00a0diabetes<\/a>, and other disorders.<\/p>\n
If you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:<\/p>\n
- \n
- Total sodium intake should be less than 2,300 mg\/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg\/serving (or 5 per cent daily value).<\/li>\n
- Total potassium intake should be 4,700 mg\/day. It’s easy to add potassium to the diet by choosing the right foods \u2014 and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.<\/li>\n<\/ul>\n
\n
\n<\/div>\n<\/div>\nFigure 4.8.5 Potassium power!\u00a0<\/em><\/p>\n
\n\n\n 4.8 Summary<\/span><\/h1>\n<\/header>\n
\n- \n
- Active transport<\/a> requires energy<\/a> to move substances across a plasma membrane<\/a>, often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\n
- The sodium-potassium pump<\/a> is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\n
- Vesicle transport<\/a> is a type of active transport that uses vesicles<\/a>\u00a0to move large molecules into or out of cells.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n
\n\n 4.8 Review Questions<\/span><\/h1>\n<\/header>\n
\n- \n
- Define active transport.<\/li>\n
- \n\n
- The sodium-potassium pump<\/a> is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.<\/li>\n
- Active transport<\/a> requires energy<\/a> to move substances across a plasma membrane<\/a>, often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.<\/li>\n
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\n<\/ul>\n
- Spinach<\/a> by chiara conti<\/a> on Unsplash<\/a> is used under the Unsplash license<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t
- Canteloupes. Image Number K7355-11<\/a> by Scott Bauer\/ USDA<\/a> on Wikimedia Commons is in the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/li>\r\n \t
- Potassium is the principal\u00a0ion\u00a0in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells<\/em> than outside of cells. To move potassium into the cell is moving it against the concentration gradient.<\/li>\r\n<\/ul>\r\nThese differences in concentration create an electrical and chemical gradient across the\u00a0[pb_glossary id=\"5621\"]cell membrane[\/pb_glossary], called the\u00a0[pb_glossary id=\"5699\"]membrane potential[\/pb_glossary]<\/strong>. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of [pb_glossary id=\"5697\"]nerve impulses[\/pb_glossary] and contraction of muscles. A large percentage of the body's energy goes to maintaining this potential across the membranes of its trillions of cells with the [pb_glossary id=\"5713\"]sodium-potassium pump[\/pb_glossary].\r\n
![Humvee challenge<\/a> by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the](\"https:\/\/commons.wikimedia.org\/wiki\/File:Defenders_compete_in_Aces_Cop_Combat_Challenge_150605-F-GF295-011.jpg\"){kind=link}
![Cytosis<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Cytosis.jpg\"){kind=link}
![Canteloupes. Image Number K7355-11<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Cantaloupes.jpg\"){kind=link}
![Eleven long purple eggplants<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Eleven_long_purple_eggplants.jpg\"){kind=link}