Welcome to our video lecture on topic a1.1 water our guiding questions for today what physical and chemical properties of water make it essential for life and what are the challenges and opportunities of water as a habitat our objectives today we're going to look at how water is the medium of life we're going to talk about the properties of water that are the result of its polarity and hydrogen bonding we're going to look at how water provides some benefits and some challenges as a habitat we're going to wrap up with a look at the origin of water here on Earth and how it was so essential for the evolution of life first up we're going to talk about how water is the medium for Life water is basically what all of us are dissolved in um Darwin said quite a bit ago that the first organisms must have appeared in some warm Little Pond we're pretty sure now it wasn't little it wasn't a pond it was probably an ocean but it was quite warm and then in the water phospholipids build these beautiful little bubbles called my cells substances dissolved inside those micelles were more concentrated because they were stuck inside the micelle and so reactions were more easily able to occur today most of our our molecules of Life all the stuff that happens biochemically still is happening dissolved in water and so water is our medium for life most of the magical properties of water that we're going to talk about are due to hydrogen bonding that can form between water molecules so we're going to do a little bit of a chemistry review here and talk about what even is hydrogen bonding remember that water H2O2 hydrogen atoms and an oxygen atom is covalently bonded so we have some covalent bonds here that covalent bonds are due to the sharing of electrons we have a pair of electrons being shared here between the oxygen and the hydrogen another pair being shared here pair of electrons being shared here but what's interesting about oxygen and hydrogen is that oxygen is more electronegative electronegative this means that the oxygen nucleus can pull on that shared pair of electrons more strongly than can hydrogen so those electrons get pulled a little bit closer to the oxygen these electrons get pulled a little bit more strongly to the oxygen oxygen also has two non-bonding pairs of electrons and this means that the oxygen side has a whole lot more electrons hanging out with it than do the hydrogen signs and so the oxygen side of the water molecule ends up being partially negative partially negative not totally negative like in an ionic bond but a little bit negative and then the hydrogen side because the electrons are not hanging out with hydrogen quite as much the hydrogen side ends up to be partially positive this bond is a polar bond because we are not sharing those electrons fairly the molecule is also polar because we have that partial negative side on one part of the molecule and partially positive on the other side of the molecule what's super cool about this is when this water molecule gets close to another water molecule The partially positive hydrogen side of one water molecule The partially negative side of another water molecule those guys are attracted to each other Opposites Attract right and so this force of attraction between these partially positive and partially negative pieces of different molecules is called hydrogen bonding this happens between water molecules because we have hydrogen on the oxygen hydrogen bonding can form only when we have hydrogen bound to oxygen or fluorine or nitrogen since I have oxygen here we have some hydrogen bonds this is just a force of attraction it is not a true chemical bond this is not nearly as strong as these covalent bonds between the oxygens and the hydrogens we but it makes water molecules kind of sticky and that stickiness allows us to do all kinds of cool stuff with water the first couple properties that we're going to look at that are due to water's polarity and hydrogen bonding that can form our cohesion and adhesion cohesion is exactly what we're looking at on the previous line cohesion forms between water molecules The partially positive piece of one water molecule The partially negative piece of another water molecule Opposites Attract just like little magnets right north south magnets are attracted to each other partial positive partial negative pieces of water attracted to each other that is cohesion what's pretty cool though is that lots of stuff in the world is also Polar Polar or sometimes even fully charged like ionic compounds and because of water's polarity water will be attracted to other stuff not just water and so I could have something that's ionic here something that's quite polar here and those opposites partial positive here partial negative here or fully positive here and an Oxygen's partial negative here we're going to have again those forces of attraction opposites will attract if I add something that's not water to the mix it's adhesion that's how I remember the difference between cohesion and adhesion cohesion water water adhesion we've added something extra that's not water to the mix and that's adhesion one example of how cohesion helps to support life here on Earth is through the xylem of plants some plants have circulatory systems kind of like us humans have our circulatory systems plants don't have blood but they do have water and minerals and sap that flow through their bodies and the xylem is a specialized transport vessel in plants that transports water and minerals that water moves up against the force of gravity through the xylem because of cohesion here's one water molecule inside the xylem it gets pulled up against the force of gravity because this guy is pulling it up as this guy gets pulled up it pulls this one and does this one is getting pulled up it pulls this one behind it and so we have this continuous column of water moving up the tree or up the plant against the force of gravity we call this the transpiration stream because water is cohesive it's going to move up up up each water molecule pulls another guy up with it at the very top of that stream that water molecule is evaporating out of the leaf of the plant and when it moves the next guy moves up the next guy moves up and they move up and they move up and we have this constant column of water moving up the plant against the force of gravity this is due to cohesion and adhesion we'll talk about that in a little bit cohesion also results in forces of attraction between water molecules on the surface of a body of water we call that surface tension surface tension is that force of attraction between water molecules at the surface it allows things like this spider to literally walk on water this guy is called a raft spider and it hangs out at the surface of the water like this you can see how it like just barely puts little divots into the surface of the water and again that's due to surface tension those water molecules that are holding on to each other and the stickiness between the water molecules at the surface it allows that spider to hang out at the surface and it feeds on mosquito larvae that are just under the surface of the water we're going to look now at some adhesion that helps to support life on Earth so water molecules because they're polar are attracted to Polar and charged soil particles as well because it's not water attracted more water which is cohesion we have water being attracted to soil particles this is adhesion we've added something that's not water is going to move up against the force of gravity because it's attracted to soil particles attracted to soil particles if I have very small pieces of soil that water can move up higher because there are just more pieces of surface area and so we're able to move that water up higher against the force of gravity this allows us to move water from the water table we can draw it up through the soil to where the plant roots are and where we dig our wells so that we can access that water this movement of water against the force of gravity against the force of gravity against the force of gravity in these small spaces is known as capillary action capillaries are super small tubes the smaller the tube the higher we can get that water to move due to those forces of adhesion in plants plants take advantage of both cohesion and adhesion to move that water up against the force of gravity due to capillary action remember from the couple slides ago we call that transpiration transpiration stream that column of water that moves up the plant the water evaporates out of the leaf that pulls water up pulls water up pulls water up this is due to capillary action that movement of water up a tube against the force of gravity due to cohesion between water molecules and also adhesion of the inside of the tube what's super cool is it in Plants this results also in mass flow so again we have water molecules moving out of a leaf which pulls up more water more water more water more water into the Roots the Roots are pulling water out of the soil away from those soil particles when this water molecule gets pulled away from the soil and into the water oh sorry into this the plant another water molecule gets pulled toward the plant because this guy moves this way it pulls this guy this way which pulls this guy this way and so water is moving towards the plant roots all the time as the water moves into the root it pulls the next water nearer which pulls the next water mirror which pulls the next water nearer we call this mass flow water will flow toward the plant roots because of cohesion and adhesion which is pretty amazing we're going to look at one more example of adhesion adhesion helps to support life on Earth this is a zoomed in version of some Moss some mosses have these super cool little structures called paraphilia paraphilia are these tubes of cell walls cell walls in plants are composed of a substance called cellulose cellulose is a carbohydrate that is a little bit polar which means of course that water is going to be attracted to it water vapor molecules in the air that's there from fog or just regular old humidity these water molecules are going to be attracted to the polarity of the cellulose and the cell walls of these periphelia the water is going to move into the tube and due to more capillary action adhesion and cohesion the water molecules are going to travel through the paraphilia again we're pulling the water molecules out of fog or humid air and then that water just kind of hangs out inside those paraphilia until the plant needs it for photosynthesis or some other kind of metabolic function super crazy cool because of that adhesive property of water because water is attracted to other things that have charges water is a really good solvent so we're going to talk here about how water is a solvent solvents are things that dissolve other things water is really good at dissolving stuff sometimes we call it the universal solvent this isn't the greatest name because it doesn't dissolve the whole entire universe but it dissolves a lot of stuff it does dissolve water dissolves most polar or hydrophilic substances remember that hydrophilic means it's attracted to water polar things are attracted to water because water is polar most things that are polar are soluble in water there are some exceptions cellulose that we talked about a little bit ago cellulose in plant cell walls is not soluble even though it is polar it's really really really really big it's structure that we'll look at when we get to our unit our lesson on carbohydrates we'll talk about why it is insoluble but most things that are polar are soluble we're going to look here at a substance that is not just polar it's so polar it's ionic we've got some salt crystals here sodium chloride salt remember that these ionic compounds are composed of oppositely charged ions we've got some sodium cations that are positively charged we have some chloride anions that are negatively charged because water is partially negative and partially positive opposites are going to attract and so what happens is these sodium cations get surrounded by water molecules sodium is positively charged and so it's going to be attracted to the partially negative oxygen side of a bunch of water molecules and so we can build this whole bubble of water around the sodium cation the same but opposite happens with the chloride chloride is negatively charged a bubble of water molecules forms around it but instead of having the oxygen side pointed toward the sodium now we have the partially positive hydrogen signs of a bunch of water molecules being attracted to that chloride anion and then this guy can float around all the other water molecules because it's surrounded by water molecules same thing happens here we call this the process of solvation solvation is that process of being dissolved water is really good at dissolving things that are polar and hydrophilic there are exceptions like cellulose most non-polar substances or hydrophobic substances are not soluble in water there are some exceptions to this as well oxygen gas is nonpolar but it's super tiny and so it dissolves kind of sort of a little bit well in water not super great not as good as salt does but it can dissolve in water because it's so so so small metabolism can occur only when things are dissolved in water metabolism is the sum of enzyme catalyzed chemical reactions in a biological system it is the biochemistry it is all of our chemical reactions it is the reactions that plants do to make glucose and photosynthesis it is the chemical reactions of us digesting the Apple that we just ate metabolism is all the chemical reactions the enzyme catalyzed chemical reactions that happen in a biological system one example of metabolism is here we have an enzyme that's called sucrase I have this thing that's the substrate substrate is the thing that the enzyme acts on in this instance it's sucrose which is sugar we need to break the sugar down the sucrose down into glucose and fructose that we can use glucose in cellular respiration so we've got this enzyme sucrase and when the enzyme sucrase runs into sucrose it's able to break that bond between the glucose and the fructose and then we have our products in order for this chemical reaction to occur this enzyme and the substrate that the enzyme acts on they need to run into each other if I don't have any water if this guy's just sitting here and this guy's just sitting here this Collision is never going to occur which means that the chemical reaction is never going to occur when things are dissolved in the water because water is such a good solvent metabolism can occur the water will allow this guy to flow toward the enzyme the enzyme in the substrate can Collide and that chemical reaction can occur if we do not have our metabolites metabolites are things that we use in metabolism if we don't have our metabolites dissolved in water these collisions do not occur and we don't have chemical reactions happening no chemical reactions no life water is the medium of life toward the beginning of the lecture we looked at xylem in plants and we talked about cohesion how those water molecules get pulled up against the force of gravity through the xylem due to cohesion and then there's also some adhesion that capillary action that occurs because the cellulose that makes up the cell walls of the plants is also polar water molecules are attracted to the cell walls inside the xylem as well as to each other and then capillary action water moves up against the force of gravity through the plant we call this transpiration and transpiration again occurs in the xylem of plants this is how plants transport water and minerals in the xylem water and minerals are not the only thing that need to be transported around plants though plants that have xylem also have phloem phloem is another kind of Transport vessel in many plants and this is where the sucrose and other organic molecules that are produced during photosynthesis and other pieces of metabolism are transported around the plant photosynthesis happens in the chloroplasts and some specialized cells that have lots of chloroplasts and then that sap that sucrose sugar gets loaded into this stuff called phloem the phloem can then transport the sugar the sucrose and other stuff because it's dissolved in water so we are able to transport substances around the plant body because lots of cool stuff like sucrose and minerals are dissolved in water we humans also need to transport stuff around our bodies we do this with blood our blood is composed more than half of it of water which we call plasma lots and lots of water in our blood that water because it's polar is able to dissolve all kinds of cool stuff that we can then transport around our circulatory system some of the things that we can dissolve in the water sodium chloride salt we also have another kind of salt potassium so sodium and potassium and chloride definitely dissolved in our blood we can also dissolve polar amino acids these are the building blocks of proteins so we can send lots of proteins around our blood pieces of proteins in the form of amino acids that are quite polar glucose sugar that we need for respiration to make some ATP also polar all of these things are polar because they're polar they'll dissolve in the water and we can transport them around our bodies there are some other things like oxygen gas it's nonpolar but because it's such a tiny little molecule we can dissolve it a little bit in the water the plasma of our blood we can't dissolve enough of it though to support respiration and so we have the amazing red blood cells that are also called erythrocytes and they have a protein stuck to them called hemoglobin and that hemoglobin is really good at grabbing onto oxygen gas so we can dissolve a little bit in the plasma of our blood but most of our oxygen does get carried by the hemoglobin on our red blood cells other things that are non-polar and that are big like triglycerides and cholesterol these guys don't do super great dissolving in the plasma the water of our blood and so instead we have these super cool things called lipoprotein complexes that are kind of like the micelles that we talked about those protocells when cell membranes first started forming so in these little protein complexes what we have are some phospholipids but we have a phospholipid mono layer not a bilayer the phospholipid polar heads are out here toward the plasma of the blood stick inside this bubble this lipoprotein complex and this is where the other nonpolar things like cholesterol and triglycerides hang out we have some very low density lipoproteins we have some low density level proteins we also have some high density lipoproteins these are the things that our doctors are looking at when they check our cholesterol levels HDL high density lipoproteins this is our good cholesterol this is good for us these giant very low density lipoproteins oh this is bad this is when our doctors are like you need to stop eating so much ice cream so anyhow when you're like what even are you talking about my cholesterol is good and my cholesterol is bad it is these lipoprotein complexes that float around our bloodstreams um because they have phosphate heads polar on the outside and so they're super easy to move around with the water those phosphate heads are attracted to the water um this is what our doctors are looking at when they're checking our cholesterol we're going to switch things up here a little bit and talk about buoyancy buoyancy is the force that water exerts on other objects that are in it that cohesion of water water wants to stick to itself and so it doesn't really want other things to get in between its hydrogen bonds but of course if something is very heavy if it has a lot of force getting pulled down toward gravity it can break those hydrogen bonds and then sink through the water the water's force of buoyancy pushes things up gravity pulls it down the density of water is about one gram per cubic centimeter a cubic centimeter is the same thing as a milliliter so one gram per milliliter one gram per cubic centimeter what's super cool our bodies the combinations of our bones which are pretty dense and our fat which is not very dense at all makes us to be pretty similar to one gram per cubic centimeter so we kind of match the density of water pretty well some organisms that live in the water need to float a little bit better this is cyanobacteria cyanobacteria is a photosynthetic bacteria and they build these super cool gas vesicles they have gas vesicles that are filled with you guessed it gas and that air is so much less dense than water it helps for these chains of cyanobacteria these photosynthetic bacteria to float to stay up toward the surface of the water they need to be at the surface of the water because that's where all the sunshine is so that they can carry out all their magical photosynthesis other organisms that live in the water like these fish they have these super cool things called Swim bladders swim bladders it is here in the fish it's here out of the fish and these are also filled with air to help the fish be more buoyant so that it can stay up a little bit more not have to work so hard to swim toward the surface of the water viscosity is another property of fluids and of water because it's a fluid viscosity is the stickiness of fluids and its resistance to flow things that are highly viscous like syrup they flow very slowly things that have low viscosity like alcohol they flow super super fast this viscosity the stickiness is due to friction some molecules stick to each other a little bit better and so they have higher viscosity they have more friction when they flow things that have less polarity that low friction like alcohol flow a little bit more easily what's super interesting is we've got the viscosity of water here when I start dissolving things like sodium and chloride and potassium and glucose all of these things are also polar they stick to each other a little bit more that stickiness increases the viscosity of this stuff hematocrit this is how we're looking at more and more um blood cells in the plasma so you can see here that the viscosity as we add cells is going to also increase this is a concern for us humans and our health because the more viscous stuff is the more viscous our blood is the higher our blood pressure and we don't want to have super super high blood pressure and we also don't want to have super super low blood pressure and so just the right amount of blood and plasma and stuff dissolved in our plasma helps to keep that blood pressure just right what's interesting is if we think of plasma as being similar to seawater so when we have ocean water saline Marine salty water its viscosity is greater than that of pure water and so it does take more energy for organisms to swim in seawater than it does for organisms to swim in fresh water because there's just so much more stuff dissolved in it it's more viscous it's stickier more energy is required to swim thermal conductivity is the rate at which heat passes through a substance water is an okay thermal conductor but lipids are way worse so lipids have a rate of only 25 percent of water so heat can pass through lip it's about a fourth as fast as it passes through water this is why a lot of our organisms that live at the poles north North Pole South Pole have a lot of blubber a lot of lipid to help insulate their bodies keep the insides of their bodies warm when they are in the super cold water air as an even better insulator its rate is only five percent that of water and so organisms that live in water are at a greater risk of losing heat to the surroundings than our organisms that live in the air because the air just doesn't conduct that that um heat energy as well as does water but that's a really high heat of vaporization this sweet baby is panting because water molecules on its tongue are evaporating into the air water has a super high heat of vaporization 41 kilojoules for every mole of water evaporated is being absorbed and so as water goes from liquid spit to gas molecule in the air it is sucking all kinds of energy out of the tongue of the doggo which means that sweet baby is going to cool off as that water evaporates same thing for us and our sweat it's a really good coolant water is a really good coolant it is not a really good insulator except it kind of is a really good buffer against temperature changes so water has a really high specific heat this means that a lot of energy is required to change the temperature of one gram of water if I want to raise the temperature of water by one degree Celsius I've got one gram of water it's at 10 degrees Celsius I want to heat it up to make it 11 degrees Celsius I need 4.18 joules of energy if I'm looking at Copper I only need a third of a joule I need more than four joules I only need a third of a joules so water has a really really high specific heat a lot of energy is needed to change the temperature of water and this is due as everything is due to those hydrogen bonds so the hydrogen bonds are holding those water molecules together as the temperature increases those water molecules are moving faster and faster and faster they don't want to move super fast because they're kind of sticky to each other so a lot of energy is needed to change the temperature this buffers big temperature changes in the environment so our bodies do not super fast change temperature if our environment's temperature changes because the water in our bodies changes temperature so very very slowly all of these amazing properties of water lead to some challenges and some opportunities as a habitat we are going to compare and contrast this super cool guy the black-throated Arctic Loom and this beautiful one the ranged seal both of them live near the North Pole they both feed in the water so they have some pieces of their habitats that overlap but of course the birds fly and this guy is a swimmer so when we are flying in the air we need to use a little bit more energy to remain airborne because water has better buoyancy so we don't need as much energy to float in the water as we do in the air but because water is more viscous we need more energy to get through the water than we need through the air more energy needed to stay aloft more energy needed to move through the water and then because air is a better insulator than water we don't need as much energy to maintain our body temperatures but we need to use more energy to resist temperature changes water has a super high specific heat and so it's a really good buffer to energy changes but it's not a good insulator so I need more energy to maintain a high body temperature and so we have some benefits but then we also have some challenges to living in or out of the water we're going to wrap up here with a look at the origins of water on Earth how did water get here and how did it stay we have 1.4 billion cubic kilometers of water on Earth 98 of it is in liquid state the very very early Earth was really hot water would have just boiled away so any water that we started with would not have left so how did water get back here after the earth started to cool down our most commonly accepted theory is that there were lots of asteroids smashing into early Earth far more frequent collisions then than we have now those asteroids smashed into Earth and they brought with them some water the distance from the Sun the distance between Earth and Sun meant that we weren't boiling that water away after you know the iron that was the molten Earth cooled down a little bit we have a pretty strong gravitational pull and so the water vapor was pulled down toward Earth all of that hydrogen bonding meant that water got a little bit sticky and so we ended up collecting and holding on to lots and lots of liquid water which was essential for life to evolve we think that there was also some water on Mars but the high level of surface minerals so much iron at the surface of Mars led to chemical reactions between the water and the iron and so the water just didn't stay in H2O form it reacted and became iron oxide instead and so we here on Earth had some fewer minerals at the surface which meant that there were less chemical reactions which meant we got to keep more water and here we are and we are always on the lookout for more planets like us we are trying to find some exoplanets exoplanets are planets that are outside our solar system that are habitable so we want to find some planets that are habitable that means there needs to be liquid water and so we have this lovely thing called the Goldilocks zone we're looking for planets that are the right distance away from their sons Their Stars of course that distance depends on how powerful how hot those suns are a hotter star we need to be further away a cooler Star we need to be a little bit closer we can't have the planets be too hot or too cold they need to be just right like Earth which is why we call it the Goldilocks zone in order for there to be liquid water on Earth so that life could evolve we have found to date about forty thousand forty thousand exoplanets in the Goldilocks zone um where we have a higher chance of binding extraterrestrial life which is a super amazing Prospect and we did it we are done talking about water we looked at what physical and chemical properties of water make it essential for life and those challenges and opportunities of water as a habitat water is the medium of life we are dissolved in so much water those properties of water are the result of its polarity remember that the hydrogen sides are partially positive the oxygen side is partially negative because of that polarity hydrogen bonding can occur the oxygen side of one water molecule is attracted to the partially positive side of another water molecule water provides lots of benefits and challenges as a habitat because of its viscosity and its buoyancy and its thermal properties and then that origin of water on Earth water getting here and staying here was essential for our Evolution good work today my friends