The Blue Marble<\/h1>\r\nIt's often called the \"water planet,\" and it's been given the nickname \"the blue marble.\" You probably just call it \"home.\" Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span>\r\n\r\n<\/div>\r\n\r\n\r\n[caption id=\"attachment_1069\" align=\"alignright\" width=\"355\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Total-water-on-earth-2.png\")
Figure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em>[\/caption]\r\nWater, Water Everywhere<\/h1>\r\n<\/div>\r\nIf you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).\r\n\r\nStructure and Properties of Water<\/h1>\r\n<\/div>\r\nYou are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.\r\nChemical\u00a0Structure of Water<\/h2>\r\n[caption id=\"attachment_1080\" align=\"alignleft\" width=\"259\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/POlarity-of-water-2.png\")
Figure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em>[\/caption]\r\n\r\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0[pb_glossary id=\"5711\"]atom[\/pb_glossary]\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts [pb_glossary id=\"5751\"]electrons[\/pb_glossary] more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0[pb_glossary id=\"5627\"]polarity[\/pb_glossary]<\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.\r\n\r\n \r\n\r\n\r\n \r\n\r\n<\/div>\r\n\r\n[caption id=\"attachment_1083\" align=\"alignright\" width=\"282\"]![\"Diagram](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Hydrogen-bonds-2.jpg\")
Figure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em>[\/caption]\r\n\r\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a [pb_glossary id=\"1082\"]hydrogen bond[\/pb_glossary]<\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.\r\n\r\n\r\nHow do you think hydrogen bonding affects water's properties?\r\n\r\n<\/div>\r\nProperties of Water<\/h2>\r\n[caption id=\"attachment_1142\" align=\"alignleft\" width=\"393\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Dew-2-scaled.jpg\")
Figure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em>[\/caption]\r\n\r\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to \"stick\" together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.\r\n<\/div>\r\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0[pb_glossary id=\"5753\"]energy[\/pb_glossary]\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.\r\n\r\nWatch the video below to hear more about hydrogen bonding and it's effects on the properties of water:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=UukRgqzk-KE\r\n\r\nWhy does ice float in water? - George Zaidan and Charles Morton, TED-ED, 2013.<\/p>\r\n\r\n
Water and Living Things<\/h2>\r\n<\/div>\r\nThe human body is about 70 per cent water (not counting the water in body fat, which varies from person to person). The body needs all this water to function normally. Just why is so much water required by human beings and other organisms? Water can dissolve many substances that organisms need. Water's polarity helps it dissolve other polar substances. Water is also necessary for many biochemical reactions. The examples below are among the most important biochemical processes that occur in living things, but they are just two of the many ways that water is involved in biochemical reactions.\r\n\r\n \t- Photosynthesis<\/strong>:<\/strong>\u00a0In this process,\u00a0cells\u00a0use the\u00a0energy\u00a0in sunlight to change carbon dioxide and water to glucose and oxygen. The reactions of\u00a0[pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\n6CO2<\/sub>\u00a0+ 6H2<\/sub>O +\u00a0Energy<\/strong><\/span>\u00a0\u2192 C6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\r\n
\r\n \t- Cellular respiration<\/strong>:\u00a0<\/strong>In this process,\u00a0cells\u00a0break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of\u00a0[pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\nC6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\u00a0\u2192 6CO2<\/sub>\u00a0+ 6H2<\/sub>O + Energy<\/span><\/strong>\r\n\r\nWater is involved in many other\u00a0biochemical reactions and\u00a0almost all life processes depend on water.\r\n\r\n
Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_1146\" align=\"aligncenter\" width=\"400\"]![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Wheelchair-marathoner-2-scaled.jpg\")
Figure 3.11.6. Endurance athletes are at risk for water intoxication.<\/em>[\/caption]\r\n\r\nAre you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate? If you answered \"yes\" to either question, you may be at risk of water intoxication.\r\n\r\nWater is considered the least toxic chemical\u00a0compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called\u00a0[pb_glossary id=\"5671\"]hyponatremia[\/pb_glossary]<\/strong>, which refers to a lower-than-normal level of sodium in the\u00a0blood\u00a0that occurs when more water is entering than leaving the body.\r\n\r\nAs excessive water is consumed, fluid outside the\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary]\u00a0decreases in its\u00a0concentration\u00a0of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by\u00a0[pb_glossary id=\"5663\"]osmosis[\/pb_glossary]<\/strong>\u00a0to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty\u00a0breathing during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where\u00a0blood\u00a0flow is interrupted or pressure is applied to the brain stem. This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.\r\n\r\nUnder normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13 per cent of the runners finished the race with water intoxication (Almond, et al., 2005). The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.\r\n\r\nBecause of the publicity water intoxication has received lately, sports experts have\u00a0lowered\u00a0their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to \"stay ahead of thirst,\" which they\u00a0recommended previously. Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce\u00a0blood\u00a0volume. Serious water intoxication should be considered a true medical emergency.\r\n\r\n3.11 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.<\/li>\r\n \t
- Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to \"stick\" together.<\/li>\r\n \t
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including [pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary] and [pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary].<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n3.11 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Where is most of Earth's fresh water found?<\/li>\r\n \t
- Identify properties of water.<\/li>\r\n \t
- What is polarity? Explain why water molecules are polar.<\/li>\r\n \t
- Why do water molecules tend to \"stick\" together?<\/li>\r\n \t
- What role does water play in photosynthesis and cellular respiration?<\/li>\r\n \t
- Which do you think is stronger: the bonds between the hydrogen and oxygen atoms\u00a0within\u00a0<\/em>a water molecule, or the bonds between the hydrogen and oxygen atoms\u00a0between<\/em>\u00a0water molecules? Explain your answer.<\/li>\r\n \t
- Given what you\u2019ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.<\/li>\r\n \t
- What is the name for the bonds that form between water molecules?<\/li>\r\n \t
- Explain why water can dissolve other\u00a0polar molecules.<\/li>\r\n \t
- If there is\u00a0pollution\u00a0in the ocean that causes the water to become more cloudy or opaque, how do you think\u00a0the ocean's\u00a0photosynthetic organisms will be affected? Explain your answer.<\/li>\r\n \t
- Describe one way in which your body gets rid of excess water.<\/li>\r\n \t
- True or False:\u00a0<\/em>Ice floats on top of water because it is denser than water.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n3.11 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=3jwAGWky98c&t=14s\r\nProperties of Water, by The Amoeba Sisters, 2016.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&t=84s\r\n
How polarity makes water behave strangely - Christina Kleinberg,\u00a0 TED-Ed, 2013.<\/p>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 3.11.1<\/strong>\r\n\r\nPlanet Earth<\/a> by NASA<\/a> (<\/i>photo taken by either Harrison Schmitt<\/a>\u00a0 or Ron Evans<\/a> (of the Apollo 17<\/a> crew), on Wikimedia Commons, is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 3.11.2<\/strong>\r\n\r\nTotal water on earth<\/a> by\u00a0LadyofHats at CK12<\/a>, is used under a <\/span><\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\u00a0<\/span><\/span>\r\n\r\nFigure 3.11.3<\/strong>\r\n\r\nPolarity of water by Christine Miller is released into the Public Domain<\/a> (https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/).\r\n\r\nFigure 3.11.4<\/strong>\r\n\r\nHydrogen bonds<\/a>, translated by Michal Ma\u0148as (User:snek01<\/a>) is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original<\/a> uploader was Qwerter<\/a>\u00a0at\u00a0Czech Wikipedia<\/a>.)\r\n\r\nFigure 3.11.5<\/strong>\r\n\r\nDew<\/a> by\u00a0Pascal Chanel<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n\r\nFigure 3.11.6<\/strong>\r\n\r\nWoman in a wheelchair marathon<\/a> by Kevin Andr\u00e9<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReferences<\/h2>\r\n
Almond, C.S., Shin, A.Y., Fortescue, E.B. et al. (2005, April). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine,<\/em> 352 (15), 1550\u20131624. doi:10.1056\/NEJMoa043901. PMID 15829535.<\/p>\r\nAmoeba Sisters. (2016, July 26). Properties of Water. YouTube. https:\/\/www.youtube.com\/watch?v=3jwAGWky98c&feature=youtu.be<\/p>\r\n
Ruiz Villarreal, M. (LadyofHats). (2016, August 15). Figure 2. Total water on earth [digital image]. In Brainard, J., Henderson, R., CK-12's College Human Biology FlexBook<\/em>\u00ae (section 3.11). CK12 Foundation. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/<\/p>\r\nTED-Ed. (2013, February 4). How polarity makes water behave strangely - Christina Kleinberg. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&feature=youtu.be<\/p>\r\n
TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton. YouTube. https:\/\/www.youtube.com\/watch?v=UukRgqzk-KE&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
<\/p>\n![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Planet-Earth-2.jpg\")
Figure 3.11.1. The Blue Marble: 71% of the earth’s surface is covered by water.<\/em><\/figcaption><\/figure>\n\nThe Blue Marble<\/h1>\n
It’s often called the “water planet,” and it’s been given the nickname “the blue marble.” You probably just call it “home.” Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span><\/p>\n<\/div>\n\nFigure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em><\/figcaption><\/figure>\nWater, Water Everywhere<\/h1>\n<\/div>\n
If you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).<\/p>\n\nStructure and Properties of Water<\/h1>\n<\/div>\n
You are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.<\/p>\n
Chemical\u00a0Structure of Water<\/h2>\nFigure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em><\/figcaption><\/figure>\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0atom<\/a>\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts electrons<\/a> more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0polarity<\/a><\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.<\/p>\n <\/p>\n
\n <\/p>\n<\/div>\nFigure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em><\/figcaption><\/figure>\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a hydrogen bond<\/a><\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.<\/p>\n\nHow do you think hydrogen bonding affects water’s properties?<\/p>\n<\/div>\n
Properties of Water<\/h2>\nFigure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em><\/figcaption><\/figure>\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to “stick” together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.<\/p>\n
<\/div>\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0energy<\/a>\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.<\/p>\nWatch the video below to hear more about hydrogen bonding and it’s effects on the properties of water:<\/p>\n
Figure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em>[\/caption]\r\nWater, Water Everywhere<\/h1>\r\n<\/div>\r\nIf you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).\r\n\r\nStructure and Properties of Water<\/h1>\r\n<\/div>\r\nYou are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.\r\nChemical\u00a0Structure of Water<\/h2>\r\n[caption id=\"attachment_1080\" align=\"alignleft\" width=\"259\"] Figure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em>[\/caption]\r\n\r\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0[pb_glossary id=\"5711\"]atom[\/pb_glossary]\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts [pb_glossary id=\"5751\"]electrons[\/pb_glossary] more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0[pb_glossary id=\"5627\"]polarity[\/pb_glossary]<\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.\r\n\r\n \r\n\r\n\r\n \r\n\r\n<\/div>\r\n\r\n[caption id=\"attachment_1083\" align=\"alignright\" width=\"282\"] Figure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em>[\/caption]\r\n\r\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a [pb_glossary id=\"1082\"]hydrogen bond[\/pb_glossary]<\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.\r\n\r\n\r\nHow do you think hydrogen bonding affects water's properties?\r\n\r\n<\/div>\r\nProperties of Water<\/h2>\r\n[caption id=\"attachment_1142\" align=\"alignleft\" width=\"393\"] Figure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em>[\/caption]\r\n\r\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to \"stick\" together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.\r\n<\/div>\r\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0[pb_glossary id=\"5753\"]energy[\/pb_glossary]\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.\r\n\r\nWatch the video below to hear more about hydrogen bonding and it's effects on the properties of water:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=UukRgqzk-KE\r\n\r\nWhy does ice float in water? - George Zaidan and Charles Morton, TED-ED, 2013.<\/p>\r\n\r\n
Water and Living Things<\/h2>\r\n<\/div>\r\nThe human body is about 70 per cent water (not counting the water in body fat, which varies from person to person). The body needs all this water to function normally. Just why is so much water required by human beings and other organisms? Water can dissolve many substances that organisms need. Water's polarity helps it dissolve other polar substances. Water is also necessary for many biochemical reactions. The examples below are among the most important biochemical processes that occur in living things, but they are just two of the many ways that water is involved in biochemical reactions.\r\n\r\n \t- Photosynthesis<\/strong>:<\/strong>\u00a0In this process,\u00a0cells\u00a0use the\u00a0energy\u00a0in sunlight to change carbon dioxide and water to glucose and oxygen. The reactions of\u00a0[pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\n6CO2<\/sub>\u00a0+ 6H2<\/sub>O +\u00a0Energy<\/strong><\/span>\u00a0\u2192 C6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\r\n
\r\n \t- Cellular respiration<\/strong>:\u00a0<\/strong>In this process,\u00a0cells\u00a0break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of\u00a0[pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\nC6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\u00a0\u2192 6CO2<\/sub>\u00a0+ 6H2<\/sub>O + Energy<\/span><\/strong>\r\n\r\nWater is involved in many other\u00a0biochemical reactions and\u00a0almost all life processes depend on water.\r\n\r\n
Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_1146\" align=\"aligncenter\" width=\"400\"] Figure 3.11.6. Endurance athletes are at risk for water intoxication.<\/em>[\/caption]\r\n\r\nAre you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate? If you answered \"yes\" to either question, you may be at risk of water intoxication.\r\n\r\nWater is considered the least toxic chemical\u00a0compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called\u00a0[pb_glossary id=\"5671\"]hyponatremia[\/pb_glossary]<\/strong>, which refers to a lower-than-normal level of sodium in the\u00a0blood\u00a0that occurs when more water is entering than leaving the body.\r\n\r\nAs excessive water is consumed, fluid outside the\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary]\u00a0decreases in its\u00a0concentration\u00a0of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by\u00a0[pb_glossary id=\"5663\"]osmosis[\/pb_glossary]<\/strong>\u00a0to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty\u00a0breathing during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where\u00a0blood\u00a0flow is interrupted or pressure is applied to the brain stem. This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.\r\n\r\nUnder normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13 per cent of the runners finished the race with water intoxication (Almond, et al., 2005). The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.\r\n\r\nBecause of the publicity water intoxication has received lately, sports experts have\u00a0lowered\u00a0their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to \"stay ahead of thirst,\" which they\u00a0recommended previously. Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce\u00a0blood\u00a0volume. Serious water intoxication should be considered a true medical emergency.\r\n\r\n3.11 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.<\/li>\r\n \t
- Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to \"stick\" together.<\/li>\r\n \t
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including [pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary] and [pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary].<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n3.11 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Where is most of Earth's fresh water found?<\/li>\r\n \t
- Identify properties of water.<\/li>\r\n \t
- What is polarity? Explain why water molecules are polar.<\/li>\r\n \t
- Why do water molecules tend to \"stick\" together?<\/li>\r\n \t
- What role does water play in photosynthesis and cellular respiration?<\/li>\r\n \t
- Which do you think is stronger: the bonds between the hydrogen and oxygen atoms\u00a0within\u00a0<\/em>a water molecule, or the bonds between the hydrogen and oxygen atoms\u00a0between<\/em>\u00a0water molecules? Explain your answer.<\/li>\r\n \t
- Given what you\u2019ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.<\/li>\r\n \t
- What is the name for the bonds that form between water molecules?<\/li>\r\n \t
- Explain why water can dissolve other\u00a0polar molecules.<\/li>\r\n \t
- If there is\u00a0pollution\u00a0in the ocean that causes the water to become more cloudy or opaque, how do you think\u00a0the ocean's\u00a0photosynthetic organisms will be affected? Explain your answer.<\/li>\r\n \t
- Describe one way in which your body gets rid of excess water.<\/li>\r\n \t
- True or False:\u00a0<\/em>Ice floats on top of water because it is denser than water.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n3.11 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=3jwAGWky98c&t=14s\r\nProperties of Water, by The Amoeba Sisters, 2016.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&t=84s\r\n
How polarity makes water behave strangely - Christina Kleinberg,\u00a0 TED-Ed, 2013.<\/p>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 3.11.1<\/strong>\r\n\r\nPlanet Earth<\/a> by NASA<\/a> (<\/i>photo taken by either Harrison Schmitt<\/a>\u00a0 or Ron Evans<\/a> (of the Apollo 17<\/a> crew), on Wikimedia Commons, is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 3.11.2<\/strong>\r\n\r\nTotal water on earth<\/a> by\u00a0LadyofHats at CK12<\/a>, is used under a <\/span><\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\u00a0<\/span><\/span>\r\n\r\nFigure 3.11.3<\/strong>\r\n\r\nPolarity of water by Christine Miller is released into the Public Domain<\/a> (https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/).\r\n\r\nFigure 3.11.4<\/strong>\r\n\r\nHydrogen bonds<\/a>, translated by Michal Ma\u0148as (User:snek01<\/a>) is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original<\/a> uploader was Qwerter<\/a>\u00a0at\u00a0Czech Wikipedia<\/a>.)\r\n\r\nFigure 3.11.5<\/strong>\r\n\r\nDew<\/a> by\u00a0Pascal Chanel<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n\r\nFigure 3.11.6<\/strong>\r\n\r\nWoman in a wheelchair marathon<\/a> by Kevin Andr\u00e9<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReferences<\/h2>\r\n
Almond, C.S., Shin, A.Y., Fortescue, E.B. et al. (2005, April). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine,<\/em> 352 (15), 1550\u20131624. doi:10.1056\/NEJMoa043901. PMID 15829535.<\/p>\r\nAmoeba Sisters. (2016, July 26). Properties of Water. YouTube. https:\/\/www.youtube.com\/watch?v=3jwAGWky98c&feature=youtu.be<\/p>\r\n
Ruiz Villarreal, M. (LadyofHats). (2016, August 15). Figure 2. Total water on earth [digital image]. In Brainard, J., Henderson, R., CK-12's College Human Biology FlexBook<\/em>\u00ae (section 3.11). CK12 Foundation. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/<\/p>\r\nTED-Ed. (2013, February 4). How polarity makes water behave strangely - Christina Kleinberg. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&feature=youtu.be<\/p>\r\n
TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton. YouTube. https:\/\/www.youtube.com\/watch?v=UukRgqzk-KE&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
<\/p>\nFigure 3.11.1. The Blue Marble: 71% of the earth’s surface is covered by water.<\/em><\/figcaption><\/figure>\n\nThe Blue Marble<\/h1>\n
It’s often called the “water planet,” and it’s been given the nickname “the blue marble.” You probably just call it “home.” Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span><\/p>\n<\/div>\n\nFigure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em><\/figcaption><\/figure>\nWater, Water Everywhere<\/h1>\n<\/div>\n
If you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).<\/p>\n\nStructure and Properties of Water<\/h1>\n<\/div>\n
You are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.<\/p>\n
Chemical\u00a0Structure of Water<\/h2>\nFigure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em><\/figcaption><\/figure>\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0atom<\/a>\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts electrons<\/a> more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0polarity<\/a><\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.<\/p>\n <\/p>\n
\n <\/p>\n<\/div>\nFigure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em><\/figcaption><\/figure>\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a hydrogen bond<\/a><\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.<\/p>\n\nHow do you think hydrogen bonding affects water’s properties?<\/p>\n<\/div>\n
Properties of Water<\/h2>\nFigure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em><\/figcaption><\/figure>\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to “stick” together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.<\/p>\n
<\/div>\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0energy<\/a>\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.<\/p>\nWatch the video below to hear more about hydrogen bonding and it’s effects on the properties of water:<\/p>\n
Structure and Properties of Water<\/h1>\r\n<\/div>\r\nYou are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.\r\nChemical\u00a0Structure of Water<\/h2>\r\n[caption id=\"attachment_1080\" align=\"alignleft\" width=\"259\"] Figure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em>[\/caption]\r\n\r\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0[pb_glossary id=\"5711\"]atom[\/pb_glossary]\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts [pb_glossary id=\"5751\"]electrons[\/pb_glossary] more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0[pb_glossary id=\"5627\"]polarity[\/pb_glossary]<\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.\r\n\r\n \r\n\r\n\r\n \r\n\r\n<\/div>\r\n\r\n[caption id=\"attachment_1083\" align=\"alignright\" width=\"282\"] Figure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em>[\/caption]\r\n\r\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a [pb_glossary id=\"1082\"]hydrogen bond[\/pb_glossary]<\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.\r\n\r\n\r\nHow do you think hydrogen bonding affects water's properties?\r\n\r\n<\/div>\r\nProperties of Water<\/h2>\r\n[caption id=\"attachment_1142\" align=\"alignleft\" width=\"393\"] Figure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em>[\/caption]\r\n\r\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to \"stick\" together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.\r\n<\/div>\r\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0[pb_glossary id=\"5753\"]energy[\/pb_glossary]\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.\r\n\r\nWatch the video below to hear more about hydrogen bonding and it's effects on the properties of water:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=UukRgqzk-KE\r\n\r\nWhy does ice float in water? - George Zaidan and Charles Morton, TED-ED, 2013.<\/p>\r\n\r\n
Water and Living Things<\/h2>\r\n<\/div>\r\nThe human body is about 70 per cent water (not counting the water in body fat, which varies from person to person). The body needs all this water to function normally. Just why is so much water required by human beings and other organisms? Water can dissolve many substances that organisms need. Water's polarity helps it dissolve other polar substances. Water is also necessary for many biochemical reactions. The examples below are among the most important biochemical processes that occur in living things, but they are just two of the many ways that water is involved in biochemical reactions.\r\n\r\n \t- Photosynthesis<\/strong>:<\/strong>\u00a0In this process,\u00a0cells\u00a0use the\u00a0energy\u00a0in sunlight to change carbon dioxide and water to glucose and oxygen. The reactions of\u00a0[pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\n6CO2<\/sub>\u00a0+ 6H2<\/sub>O +\u00a0Energy<\/strong><\/span>\u00a0\u2192 C6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\r\n
\r\n \t- Cellular respiration<\/strong>:\u00a0<\/strong>In this process,\u00a0cells\u00a0break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of\u00a0[pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\nC6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\u00a0\u2192 6CO2<\/sub>\u00a0+ 6H2<\/sub>O + Energy<\/span><\/strong>\r\n\r\nWater is involved in many other\u00a0biochemical reactions and\u00a0almost all life processes depend on water.\r\n\r\n
Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_1146\" align=\"aligncenter\" width=\"400\"] Figure 3.11.6. Endurance athletes are at risk for water intoxication.<\/em>[\/caption]\r\n\r\nAre you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate? If you answered \"yes\" to either question, you may be at risk of water intoxication.\r\n\r\nWater is considered the least toxic chemical\u00a0compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called\u00a0[pb_glossary id=\"5671\"]hyponatremia[\/pb_glossary]<\/strong>, which refers to a lower-than-normal level of sodium in the\u00a0blood\u00a0that occurs when more water is entering than leaving the body.\r\n\r\nAs excessive water is consumed, fluid outside the\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary]\u00a0decreases in its\u00a0concentration\u00a0of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by\u00a0[pb_glossary id=\"5663\"]osmosis[\/pb_glossary]<\/strong>\u00a0to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty\u00a0breathing during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where\u00a0blood\u00a0flow is interrupted or pressure is applied to the brain stem. This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.\r\n\r\nUnder normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13 per cent of the runners finished the race with water intoxication (Almond, et al., 2005). The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.\r\n\r\nBecause of the publicity water intoxication has received lately, sports experts have\u00a0lowered\u00a0their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to \"stay ahead of thirst,\" which they\u00a0recommended previously. Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce\u00a0blood\u00a0volume. Serious water intoxication should be considered a true medical emergency.\r\n\r\n3.11 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.<\/li>\r\n \t
- Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to \"stick\" together.<\/li>\r\n \t
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including [pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary] and [pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary].<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n3.11 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Where is most of Earth's fresh water found?<\/li>\r\n \t
- Identify properties of water.<\/li>\r\n \t
- What is polarity? Explain why water molecules are polar.<\/li>\r\n \t
- Why do water molecules tend to \"stick\" together?<\/li>\r\n \t
- What role does water play in photosynthesis and cellular respiration?<\/li>\r\n \t
- Which do you think is stronger: the bonds between the hydrogen and oxygen atoms\u00a0within\u00a0<\/em>a water molecule, or the bonds between the hydrogen and oxygen atoms\u00a0between<\/em>\u00a0water molecules? Explain your answer.<\/li>\r\n \t
- Given what you\u2019ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.<\/li>\r\n \t
- What is the name for the bonds that form between water molecules?<\/li>\r\n \t
- Explain why water can dissolve other\u00a0polar molecules.<\/li>\r\n \t
- If there is\u00a0pollution\u00a0in the ocean that causes the water to become more cloudy or opaque, how do you think\u00a0the ocean's\u00a0photosynthetic organisms will be affected? Explain your answer.<\/li>\r\n \t
- Describe one way in which your body gets rid of excess water.<\/li>\r\n \t
- True or False:\u00a0<\/em>Ice floats on top of water because it is denser than water.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n3.11 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=3jwAGWky98c&t=14s\r\nProperties of Water, by The Amoeba Sisters, 2016.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&t=84s\r\n
How polarity makes water behave strangely - Christina Kleinberg,\u00a0 TED-Ed, 2013.<\/p>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 3.11.1<\/strong>\r\n\r\nPlanet Earth<\/a> by NASA<\/a> (<\/i>photo taken by either Harrison Schmitt<\/a>\u00a0 or Ron Evans<\/a> (of the Apollo 17<\/a> crew), on Wikimedia Commons, is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 3.11.2<\/strong>\r\n\r\nTotal water on earth<\/a> by\u00a0LadyofHats at CK12<\/a>, is used under a <\/span><\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\u00a0<\/span><\/span>\r\n\r\nFigure 3.11.3<\/strong>\r\n\r\nPolarity of water by Christine Miller is released into the Public Domain<\/a> (https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/).\r\n\r\nFigure 3.11.4<\/strong>\r\n\r\nHydrogen bonds<\/a>, translated by Michal Ma\u0148as (User:snek01<\/a>) is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original<\/a> uploader was Qwerter<\/a>\u00a0at\u00a0Czech Wikipedia<\/a>.)\r\n\r\nFigure 3.11.5<\/strong>\r\n\r\nDew<\/a> by\u00a0Pascal Chanel<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n\r\nFigure 3.11.6<\/strong>\r\n\r\nWoman in a wheelchair marathon<\/a> by Kevin Andr\u00e9<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReferences<\/h2>\r\n
Almond, C.S., Shin, A.Y., Fortescue, E.B. et al. (2005, April). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine,<\/em> 352 (15), 1550\u20131624. doi:10.1056\/NEJMoa043901. PMID 15829535.<\/p>\r\nAmoeba Sisters. (2016, July 26). Properties of Water. YouTube. https:\/\/www.youtube.com\/watch?v=3jwAGWky98c&feature=youtu.be<\/p>\r\n
Ruiz Villarreal, M. (LadyofHats). (2016, August 15). Figure 2. Total water on earth [digital image]. In Brainard, J., Henderson, R., CK-12's College Human Biology FlexBook<\/em>\u00ae (section 3.11). CK12 Foundation. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/<\/p>\r\nTED-Ed. (2013, February 4). How polarity makes water behave strangely - Christina Kleinberg. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&feature=youtu.be<\/p>\r\n
TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton. YouTube. https:\/\/www.youtube.com\/watch?v=UukRgqzk-KE&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
<\/p>\nFigure 3.11.1. The Blue Marble: 71% of the earth’s surface is covered by water.<\/em><\/figcaption><\/figure>\n\nThe Blue Marble<\/h1>\n
It’s often called the “water planet,” and it’s been given the nickname “the blue marble.” You probably just call it “home.” Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span><\/p>\n<\/div>\n\nFigure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em><\/figcaption><\/figure>\nWater, Water Everywhere<\/h1>\n<\/div>\n
If you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).<\/p>\n\nStructure and Properties of Water<\/h1>\n<\/div>\n
You are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.<\/p>\n
Chemical\u00a0Structure of Water<\/h2>\nFigure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em><\/figcaption><\/figure>\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0atom<\/a>\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts electrons<\/a> more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0polarity<\/a><\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.<\/p>\n <\/p>\n
\n <\/p>\n<\/div>\nFigure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em><\/figcaption><\/figure>\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a hydrogen bond<\/a><\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.<\/p>\n\nHow do you think hydrogen bonding affects water’s properties?<\/p>\n<\/div>\n
Properties of Water<\/h2>\nFigure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em><\/figcaption><\/figure>\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to “stick” together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.<\/p>\n
<\/div>\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0energy<\/a>\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.<\/p>\nWatch the video below to hear more about hydrogen bonding and it’s effects on the properties of water:<\/p>\n
Figure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em>[\/caption]\r\n\r\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0[pb_glossary id=\"5711\"]atom[\/pb_glossary]\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts [pb_glossary id=\"5751\"]electrons[\/pb_glossary] more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0[pb_glossary id=\"5627\"]polarity[\/pb_glossary]<\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.\r\n\r\n \r\n Figure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em>[\/caption]\r\n\r\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a [pb_glossary id=\"1082\"]hydrogen bond[\/pb_glossary]<\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.\r\nProperties of Water<\/h2>\r\n[caption id=\"attachment_1142\" align=\"alignleft\" width=\"393\"] Figure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em>[\/caption]\r\n\r\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to \"stick\" together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.\r\n<\/div>\r\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0[pb_glossary id=\"5753\"]energy[\/pb_glossary]\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.\r\n\r\nWatch the video below to hear more about hydrogen bonding and it's effects on the properties of water:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=UukRgqzk-KE\r\n\r\nWhy does ice float in water? - George Zaidan and Charles Morton, TED-ED, 2013.<\/p>\r\n\r\n
Water and Living Things<\/h2>\r\n<\/div>\r\nThe human body is about 70 per cent water (not counting the water in body fat, which varies from person to person). The body needs all this water to function normally. Just why is so much water required by human beings and other organisms? Water can dissolve many substances that organisms need. Water's polarity helps it dissolve other polar substances. Water is also necessary for many biochemical reactions. The examples below are among the most important biochemical processes that occur in living things, but they are just two of the many ways that water is involved in biochemical reactions.\r\n\r\n \t- Photosynthesis<\/strong>:<\/strong>\u00a0In this process,\u00a0cells\u00a0use the\u00a0energy\u00a0in sunlight to change carbon dioxide and water to glucose and oxygen. The reactions of\u00a0[pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\n6CO2<\/sub>\u00a0+ 6H2<\/sub>O +\u00a0Energy<\/strong><\/span>\u00a0\u2192 C6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\r\n
\r\n \t- Cellular respiration<\/strong>:\u00a0<\/strong>In this process,\u00a0cells\u00a0break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of\u00a0[pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\nC6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\u00a0\u2192 6CO2<\/sub>\u00a0+ 6H2<\/sub>O + Energy<\/span><\/strong>\r\n\r\nWater is involved in many other\u00a0biochemical reactions and\u00a0almost all life processes depend on water.\r\n\r\n
Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_1146\" align=\"aligncenter\" width=\"400\"] Figure 3.11.6. Endurance athletes are at risk for water intoxication.<\/em>[\/caption]\r\n\r\nAre you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate? If you answered \"yes\" to either question, you may be at risk of water intoxication.\r\n\r\nWater is considered the least toxic chemical\u00a0compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called\u00a0[pb_glossary id=\"5671\"]hyponatremia[\/pb_glossary]<\/strong>, which refers to a lower-than-normal level of sodium in the\u00a0blood\u00a0that occurs when more water is entering than leaving the body.\r\n\r\nAs excessive water is consumed, fluid outside the\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary]\u00a0decreases in its\u00a0concentration\u00a0of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by\u00a0[pb_glossary id=\"5663\"]osmosis[\/pb_glossary]<\/strong>\u00a0to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty\u00a0breathing during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where\u00a0blood\u00a0flow is interrupted or pressure is applied to the brain stem. This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.\r\n\r\nUnder normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13 per cent of the runners finished the race with water intoxication (Almond, et al., 2005). The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.\r\n\r\nBecause of the publicity water intoxication has received lately, sports experts have\u00a0lowered\u00a0their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to \"stay ahead of thirst,\" which they\u00a0recommended previously. Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce\u00a0blood\u00a0volume. Serious water intoxication should be considered a true medical emergency.\r\n\r\n3.11 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.<\/li>\r\n \t
- Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to \"stick\" together.<\/li>\r\n \t
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including [pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary] and [pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary].<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n3.11 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Where is most of Earth's fresh water found?<\/li>\r\n \t
- Identify properties of water.<\/li>\r\n \t
- What is polarity? Explain why water molecules are polar.<\/li>\r\n \t
- Why do water molecules tend to \"stick\" together?<\/li>\r\n \t
- What role does water play in photosynthesis and cellular respiration?<\/li>\r\n \t
- Which do you think is stronger: the bonds between the hydrogen and oxygen atoms\u00a0within\u00a0<\/em>a water molecule, or the bonds between the hydrogen and oxygen atoms\u00a0between<\/em>\u00a0water molecules? Explain your answer.<\/li>\r\n \t
- Given what you\u2019ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.<\/li>\r\n \t
- What is the name for the bonds that form between water molecules?<\/li>\r\n \t
- Explain why water can dissolve other\u00a0polar molecules.<\/li>\r\n \t
- If there is\u00a0pollution\u00a0in the ocean that causes the water to become more cloudy or opaque, how do you think\u00a0the ocean's\u00a0photosynthetic organisms will be affected? Explain your answer.<\/li>\r\n \t
- Describe one way in which your body gets rid of excess water.<\/li>\r\n \t
- True or False:\u00a0<\/em>Ice floats on top of water because it is denser than water.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n3.11 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=3jwAGWky98c&t=14s\r\nProperties of Water, by The Amoeba Sisters, 2016.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&t=84s\r\n
How polarity makes water behave strangely - Christina Kleinberg,\u00a0 TED-Ed, 2013.<\/p>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 3.11.1<\/strong>\r\n\r\nPlanet Earth<\/a> by NASA<\/a> (<\/i>photo taken by either Harrison Schmitt<\/a>\u00a0 or Ron Evans<\/a> (of the Apollo 17<\/a> crew), on Wikimedia Commons, is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 3.11.2<\/strong>\r\n\r\nTotal water on earth<\/a> by\u00a0LadyofHats at CK12<\/a>, is used under a <\/span><\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\u00a0<\/span><\/span>\r\n\r\nFigure 3.11.3<\/strong>\r\n\r\nPolarity of water by Christine Miller is released into the Public Domain<\/a> (https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/).\r\n\r\nFigure 3.11.4<\/strong>\r\n\r\nHydrogen bonds<\/a>, translated by Michal Ma\u0148as (User:snek01<\/a>) is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original<\/a> uploader was Qwerter<\/a>\u00a0at\u00a0Czech Wikipedia<\/a>.)\r\n\r\nFigure 3.11.5<\/strong>\r\n\r\nDew<\/a> by\u00a0Pascal Chanel<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n\r\nFigure 3.11.6<\/strong>\r\n\r\nWoman in a wheelchair marathon<\/a> by Kevin Andr\u00e9<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReferences<\/h2>\r\n
Almond, C.S., Shin, A.Y., Fortescue, E.B. et al. (2005, April). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine,<\/em> 352 (15), 1550\u20131624. doi:10.1056\/NEJMoa043901. PMID 15829535.<\/p>\r\nAmoeba Sisters. (2016, July 26). Properties of Water. YouTube. https:\/\/www.youtube.com\/watch?v=3jwAGWky98c&feature=youtu.be<\/p>\r\n
Ruiz Villarreal, M. (LadyofHats). (2016, August 15). Figure 2. Total water on earth [digital image]. In Brainard, J., Henderson, R., CK-12's College Human Biology FlexBook<\/em>\u00ae (section 3.11). CK12 Foundation. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/<\/p>\r\nTED-Ed. (2013, February 4). How polarity makes water behave strangely - Christina Kleinberg. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&feature=youtu.be<\/p>\r\n
TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton. YouTube. https:\/\/www.youtube.com\/watch?v=UukRgqzk-KE&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
<\/p>\nFigure 3.11.1. The Blue Marble: 71% of the earth’s surface is covered by water.<\/em><\/figcaption><\/figure>\n\nThe Blue Marble<\/h1>\n
It’s often called the “water planet,” and it’s been given the nickname “the blue marble.” You probably just call it “home.” Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span><\/p>\n<\/div>\n\nFigure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em><\/figcaption><\/figure>\nWater, Water Everywhere<\/h1>\n<\/div>\n
If you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).<\/p>\n\nStructure and Properties of Water<\/h1>\n<\/div>\n
You are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.<\/p>\n
Chemical\u00a0Structure of Water<\/h2>\nFigure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em><\/figcaption><\/figure>\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0atom<\/a>\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts electrons<\/a> more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0polarity<\/a><\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.<\/p>\n <\/p>\n
\n <\/p>\n<\/div>\nFigure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em><\/figcaption><\/figure>\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a hydrogen bond<\/a><\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.<\/p>\n\nHow do you think hydrogen bonding affects water’s properties?<\/p>\n<\/div>\n
Properties of Water<\/h2>\nFigure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em><\/figcaption><\/figure>\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to “stick” together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.<\/p>\n
<\/div>\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0energy<\/a>\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.<\/p>\nWatch the video below to hear more about hydrogen bonding and it’s effects on the properties of water:<\/p>\n
Why does ice float in water? - George Zaidan and Charles Morton, TED-ED, 2013.<\/p>\r\n\r\n
Water and Living Things<\/h2>\r\n<\/div>\r\nThe human body is about 70 per cent water (not counting the water in body fat, which varies from person to person). The body needs all this water to function normally. Just why is so much water required by human beings and other organisms? Water can dissolve many substances that organisms need. Water's polarity helps it dissolve other polar substances. Water is also necessary for many biochemical reactions. The examples below are among the most important biochemical processes that occur in living things, but they are just two of the many ways that water is involved in biochemical reactions.\r\n\r\n \t- Photosynthesis<\/strong>:<\/strong>\u00a0In this process,\u00a0cells\u00a0use the\u00a0energy\u00a0in sunlight to change carbon dioxide and water to glucose and oxygen. The reactions of\u00a0[pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\n6CO2<\/sub>\u00a0+ 6H2<\/sub>O +\u00a0Energy<\/strong><\/span>\u00a0\u2192 C6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\r\n
\r\n \t- Cellular respiration<\/strong>:\u00a0<\/strong>In this process,\u00a0cells\u00a0break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of\u00a0[pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\nC6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\u00a0\u2192 6CO2<\/sub>\u00a0+ 6H2<\/sub>O + Energy<\/span><\/strong>\r\n\r\nWater is involved in many other\u00a0biochemical reactions and\u00a0almost all life processes depend on water.\r\n\r\n
Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_1146\" align=\"aligncenter\" width=\"400\"] Figure 3.11.6. Endurance athletes are at risk for water intoxication.<\/em>[\/caption]\r\n\r\nAre you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate? If you answered \"yes\" to either question, you may be at risk of water intoxication.\r\n\r\nWater is considered the least toxic chemical\u00a0compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called\u00a0[pb_glossary id=\"5671\"]hyponatremia[\/pb_glossary]<\/strong>, which refers to a lower-than-normal level of sodium in the\u00a0blood\u00a0that occurs when more water is entering than leaving the body.\r\n\r\nAs excessive water is consumed, fluid outside the\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary]\u00a0decreases in its\u00a0concentration\u00a0of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by\u00a0[pb_glossary id=\"5663\"]osmosis[\/pb_glossary]<\/strong>\u00a0to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty\u00a0breathing during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where\u00a0blood\u00a0flow is interrupted or pressure is applied to the brain stem. This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.\r\n\r\nUnder normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13 per cent of the runners finished the race with water intoxication (Almond, et al., 2005). The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.\r\n\r\nBecause of the publicity water intoxication has received lately, sports experts have\u00a0lowered\u00a0their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to \"stay ahead of thirst,\" which they\u00a0recommended previously. Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce\u00a0blood\u00a0volume. Serious water intoxication should be considered a true medical emergency.\r\n\r\n3.11 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.<\/li>\r\n \t
- Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to \"stick\" together.<\/li>\r\n \t
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including [pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary] and [pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary].<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n3.11 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Where is most of Earth's fresh water found?<\/li>\r\n \t
- Identify properties of water.<\/li>\r\n \t
- What is polarity? Explain why water molecules are polar.<\/li>\r\n \t
- Why do water molecules tend to \"stick\" together?<\/li>\r\n \t
- What role does water play in photosynthesis and cellular respiration?<\/li>\r\n \t
- Which do you think is stronger: the bonds between the hydrogen and oxygen atoms\u00a0within\u00a0<\/em>a water molecule, or the bonds between the hydrogen and oxygen atoms\u00a0between<\/em>\u00a0water molecules? Explain your answer.<\/li>\r\n \t
- Given what you\u2019ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.<\/li>\r\n \t
- What is the name for the bonds that form between water molecules?<\/li>\r\n \t
- Explain why water can dissolve other\u00a0polar molecules.<\/li>\r\n \t
- If there is\u00a0pollution\u00a0in the ocean that causes the water to become more cloudy or opaque, how do you think\u00a0the ocean's\u00a0photosynthetic organisms will be affected? Explain your answer.<\/li>\r\n \t
- Describe one way in which your body gets rid of excess water.<\/li>\r\n \t
- True or False:\u00a0<\/em>Ice floats on top of water because it is denser than water.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n3.11 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=3jwAGWky98c&t=14s\r\nProperties of Water, by The Amoeba Sisters, 2016.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&t=84s\r\n
How polarity makes water behave strangely - Christina Kleinberg,\u00a0 TED-Ed, 2013.<\/p>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 3.11.1<\/strong>\r\n\r\nPlanet Earth<\/a> by NASA<\/a> (<\/i>photo taken by either Harrison Schmitt<\/a>\u00a0 or Ron Evans<\/a> (of the Apollo 17<\/a> crew), on Wikimedia Commons, is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 3.11.2<\/strong>\r\n\r\nTotal water on earth<\/a> by\u00a0LadyofHats at CK12<\/a>, is used under a <\/span><\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\u00a0<\/span><\/span>\r\n\r\nFigure 3.11.3<\/strong>\r\n\r\nPolarity of water by Christine Miller is released into the Public Domain<\/a> (https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/).\r\n\r\nFigure 3.11.4<\/strong>\r\n\r\nHydrogen bonds<\/a>, translated by Michal Ma\u0148as (User:snek01<\/a>) is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original<\/a> uploader was Qwerter<\/a>\u00a0at\u00a0Czech Wikipedia<\/a>.)\r\n\r\nFigure 3.11.5<\/strong>\r\n\r\nDew<\/a> by\u00a0Pascal Chanel<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n\r\nFigure 3.11.6<\/strong>\r\n\r\nWoman in a wheelchair marathon<\/a> by Kevin Andr\u00e9<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReferences<\/h2>\r\n
Almond, C.S., Shin, A.Y., Fortescue, E.B. et al. (2005, April). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine,<\/em> 352 (15), 1550\u20131624. doi:10.1056\/NEJMoa043901. PMID 15829535.<\/p>\r\nAmoeba Sisters. (2016, July 26). Properties of Water. YouTube. https:\/\/www.youtube.com\/watch?v=3jwAGWky98c&feature=youtu.be<\/p>\r\n
Ruiz Villarreal, M. (LadyofHats). (2016, August 15). Figure 2. Total water on earth [digital image]. In Brainard, J., Henderson, R., CK-12's College Human Biology FlexBook<\/em>\u00ae (section 3.11). CK12 Foundation. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/<\/p>\r\nTED-Ed. (2013, February 4). How polarity makes water behave strangely - Christina Kleinberg. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&feature=youtu.be<\/p>\r\n
TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton. YouTube. https:\/\/www.youtube.com\/watch?v=UukRgqzk-KE&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
<\/p>\nFigure 3.11.1. The Blue Marble: 71% of the earth’s surface is covered by water.<\/em><\/figcaption><\/figure>\n\nThe Blue Marble<\/h1>\n
It’s often called the “water planet,” and it’s been given the nickname “the blue marble.” You probably just call it “home.” Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span><\/p>\n<\/div>\n\nFigure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em><\/figcaption><\/figure>\nWater, Water Everywhere<\/h1>\n<\/div>\n
If you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).<\/p>\n\nStructure and Properties of Water<\/h1>\n<\/div>\n
You are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.<\/p>\n
Chemical\u00a0Structure of Water<\/h2>\nFigure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em><\/figcaption><\/figure>\nTo understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0atom<\/a>\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts electrons<\/a> more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0polarity<\/a><\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.<\/p>\n <\/p>\n
\n <\/p>\n<\/div>\nFigure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em><\/figcaption><\/figure>\nWhen it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a hydrogen bond<\/a><\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.<\/p>\n\nHow do you think hydrogen bonding affects water’s properties?<\/p>\n<\/div>\n
Properties of Water<\/h2>\nFigure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em><\/figcaption><\/figure>\nHydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to “stick” together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.<\/p>\n
<\/div>\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0energy<\/a>\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.<\/p>\nWatch the video below to hear more about hydrogen bonding and it’s effects on the properties of water:<\/p>\n
- \r\n \t
- Cellular respiration<\/strong>:\u00a0<\/strong>In this process,\u00a0cells\u00a0break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of\u00a0[pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary]\u00a0can be represented by the chemical equation:<\/li>\r\n<\/ul>\r\nC6<\/sub>H12<\/sub>O6<\/sub>\u00a0+ 6O2<\/sub>\u00a0\u2192 6CO2<\/sub>\u00a0+ 6H2<\/sub>O + Energy<\/span><\/strong>\r\n\r\nWater is involved in many other\u00a0biochemical reactions and\u00a0almost all life processes depend on water.\r\n\r\n
Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_1146\" align=\"aligncenter\" width=\"400\"]
Figure 3.11.6. Endurance athletes are at risk for water intoxication.<\/em>[\/caption]\r\n\r\nAre you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate? If you answered \"yes\" to either question, you may be at risk of water intoxication.\r\n\r\nWater is considered the least toxic chemical\u00a0compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called\u00a0[pb_glossary id=\"5671\"]hyponatremia[\/pb_glossary]<\/strong>, which refers to a lower-than-normal level of sodium in the\u00a0blood\u00a0that occurs when more water is entering than leaving the body.\r\n\r\nAs excessive water is consumed, fluid outside the\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary]\u00a0decreases in its\u00a0concentration\u00a0of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by\u00a0[pb_glossary id=\"5663\"]osmosis[\/pb_glossary]<\/strong>\u00a0to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty\u00a0breathing during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where\u00a0blood\u00a0flow is interrupted or pressure is applied to the brain stem. This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.\r\n\r\nUnder normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13 per cent of the runners finished the race with water intoxication (Almond, et al., 2005). The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.\r\n\r\nBecause of the publicity water intoxication has received lately, sports experts have\u00a0lowered\u00a0their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to \"stay ahead of thirst,\" which they\u00a0recommended previously. Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce\u00a0blood\u00a0volume. Serious water intoxication should be considered a true medical emergency.\r\n\r\n 3.11 Summary<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.<\/li>\r\n \t
- Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to \"stick\" together.<\/li>\r\n \t
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including [pb_glossary id=\"5681\"]photosynthesis[\/pb_glossary] and [pb_glossary id=\"5725\"]cellular respiration[\/pb_glossary].<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n 3.11 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- Where is most of Earth's fresh water found?<\/li>\r\n \t
- Identify properties of water.<\/li>\r\n \t
- What is polarity? Explain why water molecules are polar.<\/li>\r\n \t
- Why do water molecules tend to \"stick\" together?<\/li>\r\n \t
- What role does water play in photosynthesis and cellular respiration?<\/li>\r\n \t
- Which do you think is stronger: the bonds between the hydrogen and oxygen atoms\u00a0within\u00a0<\/em>a water molecule, or the bonds between the hydrogen and oxygen atoms\u00a0between<\/em>\u00a0water molecules? Explain your answer.<\/li>\r\n \t
- Given what you\u2019ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.<\/li>\r\n \t
- What is the name for the bonds that form between water molecules?<\/li>\r\n \t
- Explain why water can dissolve other\u00a0polar molecules.<\/li>\r\n \t
- If there is\u00a0pollution\u00a0in the ocean that causes the water to become more cloudy or opaque, how do you think\u00a0the ocean's\u00a0photosynthetic organisms will be affected? Explain your answer.<\/li>\r\n \t
- Describe one way in which your body gets rid of excess water.<\/li>\r\n \t
- True or False:\u00a0<\/em>Ice floats on top of water because it is denser than water.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n 3.11 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=3jwAGWky98c&t=14s\r\nProperties of Water, by The Amoeba Sisters, 2016.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&t=84s\r\n
How polarity makes water behave strangely - Christina Kleinberg,\u00a0 TED-Ed, 2013.<\/p>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 3.11.1<\/strong>\r\n\r\nPlanet Earth<\/a> by NASA<\/a> (<\/i>photo taken by either Harrison Schmitt<\/a>\u00a0 or Ron Evans<\/a> (of the Apollo 17<\/a> crew), on Wikimedia Commons, is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 3.11.2<\/strong>\r\n\r\nTotal water on earth<\/a> by\u00a0LadyofHats at CK12<\/a>, is used under a <\/span><\/span>CC BY-NC 3.0<\/span><\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\u00a0<\/span><\/span>\r\n\r\nFigure 3.11.3<\/strong>\r\n\r\nPolarity of water by Christine Miller is released into the Public Domain<\/a> (https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/).\r\n\r\nFigure 3.11.4<\/strong>\r\n\r\nHydrogen bonds<\/a>, translated by Michal Ma\u0148as (User:snek01<\/a>) is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original<\/a> uploader was Qwerter<\/a>\u00a0at\u00a0Czech Wikipedia<\/a>.)\r\n\r\nFigure 3.11.5<\/strong>\r\n\r\nDew<\/a> by\u00a0Pascal Chanel<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n\r\nFigure 3.11.6<\/strong>\r\n\r\nWoman in a wheelchair marathon<\/a> by Kevin Andr\u00e9<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n
References<\/h2>\r\n
Almond, C.S., Shin, A.Y., Fortescue, E.B. et al. (2005, April). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine,<\/em> 352 (15), 1550\u20131624. doi:10.1056\/NEJMoa043901. PMID 15829535.<\/p>\r\n
Amoeba Sisters. (2016, July 26). Properties of Water. YouTube. https:\/\/www.youtube.com\/watch?v=3jwAGWky98c&feature=youtu.be<\/p>\r\n
Ruiz Villarreal, M. (LadyofHats). (2016, August 15). Figure 2. Total water on earth [digital image]. In Brainard, J., Henderson, R., CK-12's College Human Biology FlexBook<\/em>\u00ae (section 3.11). CK12 Foundation. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/<\/p>\r\n
TED-Ed. (2013, February 4). How polarity makes water behave strangely - Christina Kleinberg. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=ASLUY2U1M-8&feature=youtu.be<\/p>\r\n
TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton. YouTube. https:\/\/www.youtube.com\/watch?v=UukRgqzk-KE&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
<\/p>\n
Figure 3.11.1. The Blue Marble: 71% of the earth’s surface is covered by water.<\/em><\/figcaption><\/figure>\n \nThe Blue Marble<\/h1>\n
It’s often called the “water planet,” and it’s been given the nickname “the blue marble.” You probably just call it “home.” Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things: it is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms.<\/span><\/p>\n<\/div>\n
\nFigure 3.11.2. Most of the water on Earth consists of saltwater in the oceans. What per cent of Earth\u2019s water is fresh water? Where is most of the fresh water found?<\/em><\/figcaption><\/figure>\n Water, Water Everywhere<\/h1>\n<\/div>\n
If you look at Figure 3.11.2, you will see where Earth\u2019s water is found. The term water\u00a0<\/em>generally refers to its\u00a0liquid\u00a0state, and water is a liquid over a wide range of temperatures on Earth. Water, however, also occurs on Earth as a\u00a0solid\u00a0(ice) and as a\u00a0gas\u00a0(water vapor).<\/p>\n
\nStructure and Properties of Water<\/h1>\n<\/div>\n
You are likely already aware of some of the properties of water. For example, you know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food by photosynthesis.<\/p>\n
Chemical\u00a0Structure of Water<\/h2>\n
Figure 3.11.3. Because of unequal sharing of electrons in the covalent bonds that hold the water molecule together it is considered polar.<\/em><\/figcaption><\/figure>\n To understand some of water\u2019s properties, you need to know more about its chemical structure. Each molecule of water consists of one\u00a0atom<\/a>\u00a0of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts electrons<\/a> more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called\u00a0polarity<\/a><\/strong>. The diagram in Figure 3.11.3 shows water\u2019s polarity.<\/p>\n
<\/p>\n
\n<\/p>\n<\/div>\n
Figure 3.11.4. Hydrogen bonding occurs between adjacent water molecules due to their polarity. A hydrogen bond is a weak intra-molecular force.<\/em><\/figcaption><\/figure>\n When it comes to charged molecules, opposites attract. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure 3.11.4. The type of bond that forms between water molecules is called a hydrogen bond<\/a><\/strong>. Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.<\/p>\n
\nHow do you think hydrogen bonding affects water’s properties?<\/p>\n<\/div>\n
Properties of Water<\/h2>\n
Figure 3.11.5. Dew drops cling to blades of grass in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?<\/em><\/figcaption><\/figure>\n Hydrogen bonds between water molecules explain some of water\u2019s properties \u2014 for example, why water molecules tend to “stick” together. Did you ever watch water drip from a leaky faucet or from a\u00a0melting\u00a0icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured\u00a0to the left\u00a0are another example of water molecules sticking together.<\/p>\n
<\/div>\nHydrogen bonds cause water to have a relatively high\u00a0boiling\u00a0point of 100\u00b0C (212\u00b0F). Extra\u00a0energy<\/a>\u00a0is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a\u00a0liquid\u00a0state, rather than a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake\u00a0animals like\u00a0fish\u00a0to survive the winter by staying in the\u00a0liquid\u00a0water under the ice.<\/p>\n
Watch the video below to hear more about hydrogen bonding and it’s effects on the properties of water:<\/p>\n
![\"Image](\"https:\/\/commons.wikimedia.org\/wiki\/File:The_Blue_Marble_4463x4163.jpg\")
![Hydrogen bonds<\/a>, translated by Michal Ma\u0148as (](\"https:\/\/commons.wikimedia.org\/wiki\/File:3D_model_hydrogen_bonds_in_water.jpg\"){kind=link}
![Original<\/a> uploader was](\"https:\/\/commons.wikimedia.org\/wiki\/File:Vodikove_mustky_kalotovy_model.jpg\"){kind=link}