A Bag Full of Jell-O<\/h1>\r\n<\/div>\r\nThe simple cut-away model of an animal [pb_glossary id=\"5665\"]cell[\/pb_glossary] (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] filled with [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary]. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a [pb_glossary id=\"5797\"]nucleus[\/pb_glossary] and other [pb_glossary id=\"5557\"]organelles[\/pb_glossary]. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use [pb_glossary id=\"5753\"]energy[\/pb_glossary], respond to the environment, and [pb_glossary id=\"5807\"]reproduce[\/pb_glossary]. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary].\r\n\r\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the [pb_glossary id=\"5665\"]cell[\/pb_glossary] and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.\r\n\r\nPhospholipid Bilayer<\/h2>\r\n<\/div>\r\nThe plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0[pb_glossary id=\"5597\"]phospholipid bilayer[\/pb_glossary]<\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water ([pb_glossary id=\"5677\"]hydrophilic[\/pb_glossary]) and the tails \u201chate\u201d water ([pb_glossary id=\"5675\"]hydrophobic[\/pb_glossary]). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).\r\n\r\n[pb_glossary id=\"5675\"]Hydrophobic[\/pb_glossary] molecules can easily pass through the [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] if they are small enough, because they are water-hating like the interior of the membrane. [pb_glossary id=\"5677\"]Hydrophilic[\/pb_glossary] molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.\r\n\r\n[caption id=\"attachment_1592\" align=\"aligncenter\" width=\"457\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Phospholipid_Bilayer-5.jpg\")
Figure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em>[\/caption]\r\n\r\n\r\nOther Molecules in the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe plasma membrane also contains other molecules, primarily other [pb_glossary id=\"5651\"]lipids[\/pb_glossary] and [pb_glossary id=\"5813\"]proteins[\/pb_glossary]. The yellow molecules in the diagram here, for example, are the [pb_glossary id=\"5651\"]lipid[\/pb_glossary] cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport [pb_glossary id=\"5813\"]proteins[\/pb_glossary] that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.\r\n\r\n[caption id=\"attachment_1595\" align=\"aligncenter\" width=\"610\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Lipid-bilayer-2.jpg\")
Figure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em>[\/caption]\r\n\r\n\r\nAdditional Functions of the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] may have extensions, such as whip-like [pb_glossary id=\"5607\"]flagella[\/pb_glossary] (singular flagellum) or brush-like [pb_glossary id=\"1597\"]cilia[\/pb_glossary] (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.\r\n\r\n[caption id=\"attachment_1598\" align=\"aligncenter\" width=\"379\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Spermatozoa-human-3140x-2.jpg\")
Figure 4.4.5 Human sperm with their long, whip-like flagella.<\/em>[\/caption]\r\n\r\n[caption id=\"attachment_1599\" align=\"aligncenter\" width=\"369\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Cilia-2.jpg\")
Figure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My\u00a0<\/strong>Human Body<\/strong>\r\n\r\n<\/div>\r\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here's a good one.\u00a0We usually think of lung\u00a0[pb_glossary id=\"5605\"]cancer[\/pb_glossary]\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body's ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.\r\n\r\n[caption id=\"attachment_5940\" align=\"aligncenter\" width=\"672\"]![\"4.4.7](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/1024px-Adverse_effects_of_vaping_raster-2.png\")
Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal - results of vaping.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"1597\"]Cilia[\/pb_glossary] are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.\r\n\r\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.\r\n\r\n4.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\nBetts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\nGhosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Animal_Cell_Unannotated.svg_-2.png\")
Figure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/jello-mold-2.jpg\")
Figure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n\nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\nThe plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\nHydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\nFigure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n\nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\nFigure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n\nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\nFigure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\nFigure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n\nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\nFigure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\nCilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n4.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n4.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
What is<\/strong> the Plasma Membrane?<\/strong><\/h1>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the [pb_glossary id=\"5665\"]cell[\/pb_glossary] and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.\r\n\r\nPhospholipid Bilayer<\/h2>\r\n<\/div>\r\nThe plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0[pb_glossary id=\"5597\"]phospholipid bilayer[\/pb_glossary]<\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water ([pb_glossary id=\"5677\"]hydrophilic[\/pb_glossary]) and the tails \u201chate\u201d water ([pb_glossary id=\"5675\"]hydrophobic[\/pb_glossary]). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).\r\n\r\n[pb_glossary id=\"5675\"]Hydrophobic[\/pb_glossary] molecules can easily pass through the [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] if they are small enough, because they are water-hating like the interior of the membrane. [pb_glossary id=\"5677\"]Hydrophilic[\/pb_glossary] molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.\r\n\r\n[caption id=\"attachment_1592\" align=\"aligncenter\" width=\"457\"] Figure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em>[\/caption]\r\n\r\n\r\nOther Molecules in the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe plasma membrane also contains other molecules, primarily other [pb_glossary id=\"5651\"]lipids[\/pb_glossary] and [pb_glossary id=\"5813\"]proteins[\/pb_glossary]. The yellow molecules in the diagram here, for example, are the [pb_glossary id=\"5651\"]lipid[\/pb_glossary] cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport [pb_glossary id=\"5813\"]proteins[\/pb_glossary] that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.\r\n\r\n[caption id=\"attachment_1595\" align=\"aligncenter\" width=\"610\"] Figure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em>[\/caption]\r\n\r\n\r\nAdditional Functions of the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] may have extensions, such as whip-like [pb_glossary id=\"5607\"]flagella[\/pb_glossary] (singular flagellum) or brush-like [pb_glossary id=\"1597\"]cilia[\/pb_glossary] (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.\r\n\r\n[caption id=\"attachment_1598\" align=\"aligncenter\" width=\"379\"] Figure 4.4.5 Human sperm with their long, whip-like flagella.<\/em>[\/caption]\r\n\r\n[caption id=\"attachment_1599\" align=\"aligncenter\" width=\"369\"] Figure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My\u00a0<\/strong>Human Body<\/strong>\r\n\r\n<\/div>\r\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here's a good one.\u00a0We usually think of lung\u00a0[pb_glossary id=\"5605\"]cancer[\/pb_glossary]\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body's ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.\r\n\r\n[caption id=\"attachment_5940\" align=\"aligncenter\" width=\"672\"] Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal - results of vaping.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"1597\"]Cilia[\/pb_glossary] are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.\r\n\r\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.\r\n\r\n4.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\nBetts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\nGhosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\nFigure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n\nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\nThe plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\nHydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\nFigure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n\nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\nFigure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n\nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\nFigure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\nFigure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n\nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\nFigure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\nCilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n4.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n4.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
Phospholipid Bilayer<\/h2>\r\n<\/div>\r\nThe plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0[pb_glossary id=\"5597\"]phospholipid bilayer[\/pb_glossary]<\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water ([pb_glossary id=\"5677\"]hydrophilic[\/pb_glossary]) and the tails \u201chate\u201d water ([pb_glossary id=\"5675\"]hydrophobic[\/pb_glossary]). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).\r\n\r\n[pb_glossary id=\"5675\"]Hydrophobic[\/pb_glossary] molecules can easily pass through the [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] if they are small enough, because they are water-hating like the interior of the membrane. [pb_glossary id=\"5677\"]Hydrophilic[\/pb_glossary] molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.\r\n\r\n[caption id=\"attachment_1592\" align=\"aligncenter\" width=\"457\"] Figure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em>[\/caption]\r\n\r\n\r\nOther Molecules in the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe plasma membrane also contains other molecules, primarily other [pb_glossary id=\"5651\"]lipids[\/pb_glossary] and [pb_glossary id=\"5813\"]proteins[\/pb_glossary]. The yellow molecules in the diagram here, for example, are the [pb_glossary id=\"5651\"]lipid[\/pb_glossary] cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport [pb_glossary id=\"5813\"]proteins[\/pb_glossary] that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.\r\n\r\n[caption id=\"attachment_1595\" align=\"aligncenter\" width=\"610\"] Figure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em>[\/caption]\r\n\r\n\r\nAdditional Functions of the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] may have extensions, such as whip-like [pb_glossary id=\"5607\"]flagella[\/pb_glossary] (singular flagellum) or brush-like [pb_glossary id=\"1597\"]cilia[\/pb_glossary] (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.\r\n\r\n[caption id=\"attachment_1598\" align=\"aligncenter\" width=\"379\"] Figure 4.4.5 Human sperm with their long, whip-like flagella.<\/em>[\/caption]\r\n\r\n[caption id=\"attachment_1599\" align=\"aligncenter\" width=\"369\"] Figure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My\u00a0<\/strong>Human Body<\/strong>\r\n\r\n<\/div>\r\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here's a good one.\u00a0We usually think of lung\u00a0[pb_glossary id=\"5605\"]cancer[\/pb_glossary]\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body's ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.\r\n\r\n[caption id=\"attachment_5940\" align=\"aligncenter\" width=\"672\"] Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal - results of vaping.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"1597\"]Cilia[\/pb_glossary] are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.\r\n\r\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.\r\n\r\n4.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\nBetts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\nGhosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\nFigure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n\nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\nThe plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\nHydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\nFigure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n\nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\nFigure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n\nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\nFigure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\nFigure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n\nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\nFigure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\nCilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n4.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n4.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
Other Molecules in the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe plasma membrane also contains other molecules, primarily other [pb_glossary id=\"5651\"]lipids[\/pb_glossary] and [pb_glossary id=\"5813\"]proteins[\/pb_glossary]. The yellow molecules in the diagram here, for example, are the [pb_glossary id=\"5651\"]lipid[\/pb_glossary] cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport [pb_glossary id=\"5813\"]proteins[\/pb_glossary] that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.\r\n\r\n[caption id=\"attachment_1595\" align=\"aligncenter\" width=\"610\"] Figure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em>[\/caption]\r\n\r\n\r\nAdditional Functions of the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] may have extensions, such as whip-like [pb_glossary id=\"5607\"]flagella[\/pb_glossary] (singular flagellum) or brush-like [pb_glossary id=\"1597\"]cilia[\/pb_glossary] (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.\r\n\r\n[caption id=\"attachment_1598\" align=\"aligncenter\" width=\"379\"] Figure 4.4.5 Human sperm with their long, whip-like flagella.<\/em>[\/caption]\r\n\r\n[caption id=\"attachment_1599\" align=\"aligncenter\" width=\"369\"] Figure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My\u00a0<\/strong>Human Body<\/strong>\r\n\r\n<\/div>\r\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here's a good one.\u00a0We usually think of lung\u00a0[pb_glossary id=\"5605\"]cancer[\/pb_glossary]\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body's ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.\r\n\r\n[caption id=\"attachment_5940\" align=\"aligncenter\" width=\"672\"] Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal - results of vaping.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"1597\"]Cilia[\/pb_glossary] are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.\r\n\r\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.\r\n\r\n4.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\nBetts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\nGhosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\nFigure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n\nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\nThe plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\nHydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\nFigure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n\nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\nFigure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n\nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\nFigure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\nFigure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n\nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\nFigure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\nCilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n4.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n4.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
Additional Functions of the Plasma Membrane<\/h2>\r\n<\/div>\r\nThe [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] may have extensions, such as whip-like [pb_glossary id=\"5607\"]flagella[\/pb_glossary] (singular flagellum) or brush-like [pb_glossary id=\"1597\"]cilia[\/pb_glossary] (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.\r\n\r\n[caption id=\"attachment_1598\" align=\"aligncenter\" width=\"379\"] Figure 4.4.5 Human sperm with their long, whip-like flagella.<\/em>[\/caption]\r\n\r\n[caption id=\"attachment_1599\" align=\"aligncenter\" width=\"369\"] Figure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em>[\/caption]\r\n\r\n\r\n\r\nFeature: My\u00a0<\/strong>Human Body<\/strong>\r\n\r\n<\/div>\r\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here's a good one.\u00a0We usually think of lung\u00a0[pb_glossary id=\"5605\"]cancer[\/pb_glossary]\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body's ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.\r\n\r\n[caption id=\"attachment_5940\" align=\"aligncenter\" width=\"672\"] Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal - results of vaping.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"1597\"]Cilia[\/pb_glossary] are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.\r\n\r\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.\r\n\r\n4.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\nBetts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\nGhosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\nFigure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n\nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\nThe plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\nHydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\nFigure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n\nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\nFigure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n\nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\nFigure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\nFigure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n\nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\nFigure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\nCilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n4.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n4.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal - results of vaping.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"1597\"]Cilia[\/pb_glossary] are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.\r\n\r\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.\r\n4.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\nBetts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\nGhosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\nFigure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\nFigure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n\nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\nThe plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\nHydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\nFigure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n\nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\nFigure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n\nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\nFigure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\nFigure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n\nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\nIf you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\nFigure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\nCilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\nSmoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n4.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n4.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
- \r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is a structure that forms a barrier between the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\r\n \t
- The [pb_glossary id=\"5489\"]plasma membrane[\/pb_glossary] is composed mainly of a [pb_glossary id=\"5597\"]bilayer of phospholipid[\/pb_glossary] molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\r\n \t
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 4.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- What are the general functions of the plasma membrane?<\/li>\r\n \t
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\r\n \t
- Identify other molecules in the plasma membrane. State their functions.<\/li>\r\n \t
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\r\n \t
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\r\n \t
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\r\n \t
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\r\n \t
- [h5p id=\"472\"]<\/li>\r\n \t
- Steroid hormones can pass directly through cell membranes. Why do you think this is the case?<\/li>\r\n \t
- Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?<\/li>\r\n \t
- What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 4.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=emb_logo\r\nInsights into cell membranes via dish detergent - Ethan Perlstein, TED-Ed, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=qBCVVszQQNs\r\n
Inside the cell membrane, by The Amoeba Sisters, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 4.4.1<\/strong>\r\n\r\nAnimal Cell Unannotated,<\/a> by Kelvin Song<\/a> on Wikimedia Commons is used under a CC0 1.0<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) public domain dedication license.\r\n\r\nFigure 4.4.2<\/strong>\r\n\r\nJello mold at the mexican bakery<\/a> photo by Aim\u00e9e Knight<\/a> on Flickr<\/a> is used under a CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.\r\n\r\nFigure 4.4.3<\/strong>\r\n\r\nPhospholipid_Bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.4<\/strong>\r\n\r\nLipid bilayer<\/a> by OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n\r\nFigure 4.4.5<\/strong>\r\n\r\nSpermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.6<\/strong>\r\n\r\nCilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 4.4.7<\/strong>\r\n\r\nAdverse effects of vaping (raster)<\/a> by Mikael H\u00e4ggstr\u00f6m<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n
References<\/h2>\r\n
Amoeba Sisters. (2018, February 27). Inside the cell membrane. YouTube. https:\/\/www.youtube.com\/watch?v=qBCVVszQQNs&feature=youtu.be<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure 3.3 Phospolipid Bilayer [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/p>\r\n
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E.. Womble, M., DeSaix. P. (2013, April 25). Figure\u00a0<\/span>3.4<\/span>\u00a0<\/span>Cell Membrane<\/span> [digital image]. In Anatomy and Physiology. OpenStax. <\/em>https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-1-the-cell-membrane<\/span><\/p>\r\n
Ghosh, A., Coakley, R. C., Mascenik, T., Rowell, T. R., Davis, E. S., Rogers, K., Webster, M. J., Dang, H., Herring, L. E., Sassano, M. F., Livraghi-Butrico, A., Van Buren, S. K., Graves, L. M., Herman, M. A., Randell, S. H., Alexis, N. E., & Tarran, R. (n.d.). Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome.\u00a0American Journal of Respiratory and Critical \/Care Medicine<\/i>,\u00a0198<\/i>(1), 67\u201376. https:\/\/doi-org.ezproxy.tru.ca\/10.1164\/rccm.201710-2033OC<\/p>\r\n
TED-Ed. (2013, February 26). Insights into cell membranes via dish detergent - Ethan Perlstein. YouTube. https:\/\/www.youtube.com\/watch?v=yAXnYcUjn5k&feature=youtu.be<\/p>\r\n ","rendered":"
<\/p>\n
Figure 4.4.1 Simple cut-away model of an animal cell.\u00a0<\/em><\/figcaption><\/figure>\n Figure 4.4.2 Jello molds containing fruit. <\/em><\/figcaption><\/figure>\n \nA Bag Full of Jell-O<\/h1>\n<\/div>\n
The simple cut-away model of an animal cell<\/a> (Figure 4.4.1) shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane<\/a> filled with cytoplasm<\/a>. Like Jell-O containing mixed fruit (Figure 4.4.2), the cytoplasm of the cell also contains various structures, including a nucleus<\/a> and other organelles<\/a>. Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy<\/a>, respond to the environment, and reproduce<\/a>. How do your cells carry out these basic functions and keep themselves \u2014 and you \u2014 alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane<\/a>.<\/p>\n
\nWhat is<\/strong> the Plasma Membrane?<\/strong><\/h1>\n<\/div>\n
The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell<\/a> and\u00a0the environment\u00a0outside the cell. Without the plasma membrane, there would be no cell.\u00a0Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it.\u00a0It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.<\/p>\n
\nPhospholipid Bilayer<\/h2>\n<\/div>\n
The plasma membrane is composed mainly of\u00a0phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a\u00a0phospholipid bilayer<\/a><\/strong>. As shown in the simplified diagram in Figure 4.4.3, each individual\u00a0 phospholipid molecule has a phosphate group head (in red) and two fatty acid tails (in yellow). The head \u201cloves\u201d water (hydrophilic<\/a>) and the tails \u201chate\u201d water (hydrophobic<\/a>). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm (intracellular) or the fluid that surrounds the cell (extracellular).<\/p>\n
Hydrophobic<\/a> molecules can easily pass through the plasma membrane<\/a> if they are small enough, because they are water-hating like the interior of the membrane. Hydrophilic<\/a> molecules, on the other hand, cannot<\/em> pass through the plasma membrane \u2014 at least not without help \u2014 because they are water-loving like the exterior of the membrane.<\/p>\n
Figure 4.4.3 The phospholipid bilayer is made up of two sheets of phospholipids, with the fatty acid tails facing the centre.<\/em><\/figcaption><\/figure>\n \nOther Molecules in the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane also contains other molecules, primarily other lipids<\/a> and proteins<\/a>. The yellow molecules in the diagram here, for example, are the lipid<\/a> cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. Proteins in the plasma membrane (shown blue in Figure 4.4.4) include: transport proteins<\/a> that assist other substances in crossing the cell membrane, receptors that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.<\/p>\n
Figure 4.4.4 The plasma membrane contains many molecules embedded in the lipid bilayer.<\/em><\/figcaption><\/figure>\n \nAdditional Functions of the Plasma Membrane<\/h2>\n<\/div>\n
The plasma membrane<\/a> may have extensions, such as whip-like flagella<\/a> (singular flagellum) or brush-like cilia<\/a> (singular cilium), shown below (Figure 4.4.5), that give it other functions. In single-celled organisms, these membrane extensions may help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose, while the flagellum on a human sperm cell allows it to swim.<\/p>\n
Figure 4.4.5 Human sperm with their long, whip-like flagella.<\/em><\/figcaption><\/figure>\n Figure 4.4.6 Brush-like cilia on lung epithelial cells.<\/em><\/figcaption><\/figure>\n \nFeature: My\u00a0<\/strong>Human Body<\/strong><\/p>\n<\/div>\n
If you smoke or use e-cigarettes (vaping) and need another reason to quit, here’s a good one.\u00a0We usually think of lung\u00a0cancer<\/a>\u00a0as the major disease caused by smoking. But smoking and vaping can have devastating effects on the body’s ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia.<\/p>\n
Figure 4.4.7 Airways of \u201chealthy\u201d vapors are abnormal – results of vaping.<\/em><\/figcaption><\/figure>\n Cilia<\/a> are microscopic, hair-like projects on\u00a0cells\u00a0that line the respiratory, reproductive, and digestive systems. Cilia in the\u00a0respiratory system\u00a0line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that’s what you are doing.<\/p>\n
Smoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can’t sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the\u00a0most recent\u00a0exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.<\/p>\n
\n\n 4.4 Summary<\/span><\/h1>\n<\/header>\n
\n- \n
- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The\u00a0plasma\u00a0membranes of some cells have extensions that have other functions, like flagella to help\u00a0sperm\u00a0move, or cilia to help keep our airways clear.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n
\n\n 4.4 Review Questions<\/span><\/h1>\n<\/header>\n
\n- \n
- What are the general functions of the plasma membrane?<\/li>\n
- Describe the phospholipid bilayer of the plasma membrane.<\/li>\n
- Identify other molecules in the plasma membrane. State their functions.<\/li>\n
- Why do some cells have plasma membrane extensions, like flagella and cilia?<\/li>\n
- Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?<\/li>\n
- Which part of a phospholipid molecule in the plasma membrane is made of fatty\u00a0acid\u00a0chains? Is this part hydrophobic or hydrophilic?<\/li>\n
- The two layers of\u00a0phospholipids\u00a0in the plasma membrane are called a phospholipid ____________.<\/li>\n
- \n\n
- The plasma membrane<\/a> is composed mainly of a bilayer of phospholipid<\/a> molecules. It also contains other molecules, such as the steroid cholesterol, which helps the membrane keep its shape, and transport proteins, which help substances pass through the membrane.<\/li>\n
- The plasma membrane<\/a> is a structure that forms a barrier between the cytoplasm<\/a> inside the cell and\u00a0the environment\u00a0outside the cell. It allows only certain substances to pass in or out of the cell.<\/li>\n
![Animal Cell Unannotated,<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Animal_Cell_Unannotated.svg\"){kind=link}
![Phospholipid_Bilayer<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:0302_Phospholipid_Bilayer.jpg\"){kind=link}
![Lipid bilayer<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:0303_Lipid_Bilayer_With_Various_Components.jpg\"){kind=link}
![Spermatozoa-human-3140x<\/a> by No specific author on Wikimedia Commons is released into the](\"https:\/\/commons.wikimedia.org\/wiki\/File:Spermatozoa-human-3140x.jpg\"){kind=link}
![Cilia\/ Bronchiolar epithelium 3 - SEM<\/a> by Charles Daghlian on Wikimedia Commons is released into the](\"https:\/\/commons.wikimedia.org\/wiki\/File:Bronchiolar_epithelium_3_-_SEM.jpg\"){kind=link}
![Adverse effects of vaping (raster)<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Adverse_effects_of_vaping_(raster).png\"){kind=link}