welcome to ap biology i'm margaret evans from woodbridge virginia home of the woodbridge senior high school vikings and i will be your instructor for this lesson on topic 1.1 structure of water and hydrogen bonding so let's get ready to science what will we learn in this video we will learn about the chemical structure of water how that structure is resulting in something called polarity how does water's polarity result in cohesion and adhesion through hydrogen bond interactions what chemical characteristics of water result in its cohesive and adhesive properties and how do living systems depend on the chemical properties of water let's begin it's important to understand that the subcomponents of biological molecules determine the properties of that molecule and as it relates to the components of water water is composed of two elements oxygen and hydrogen as you can see from the diagram that just appeared and a one to two one to two ratio respectively covalent bonds are the bond types that are involved in a water molecule oxygen is sharing electrons with hydrogen however that sharing is not done equally because oxygen is more electronegative compared to hydrogen and this will result in something called polarity and so i'm going to add a negative sign near the oxygen portion of the molecule indicating that the electrons are being pulled closer to the oxygen and then that leaves the hydrogen area more positive and once again this dual property of charges on a molecule is referred to as polarity since this is a covalent bond that results in polarity we can also call it a polar covalent bond hydrogen bonds are weak interactions between the negative and positive regions of two molecules and considering that water is polar then it has the opportunity to participate in forming hydrogen bonds with other water molecules or with other molecules that have a charge when you have two of the same molecules forming hydrogen bonds between them we call this cohesion an example here would be a water molecule bonding with another water molecule and as you can see i have these molecules positioned so that the negative side of one water molecule is positioned near the positive side of the other and thus they can form a hydrogen bond in between when you have two different molecules forming hydrogen bonds with each other this is called adhesion and so my example here would be an amino acid and a water molecule and as you can see the amino acid also has that dual polarity property and so the negative side of that amino acid will be positioned near the hydrogen's positive side and a hydrogen bond would be able to form between the two of them as well living systems depend upon these properties of water that derive out of its polarity and so hydrogen bonds between water molecules can result in something called surface tension which we'll talk about a little bit more in the next slide and so cohesion adhesion and surface tension allow for water to demonstrate additional chemical behaviors or properties known as the emergent properties and we'll get into looking at several example of examples of those life depends upon these uh properties of water and let's take a look at the first one which would be surface tension surface tension is a result of increased hydrogen bond interactions between water molecules only at the surface and so the classic example would be a water droplet on a penny and i have a video here that will show you a leaf floating on the surface tension of water and how could this be important to living things well leaves of aquatic plants oftentimes rest on the surface of water allowing them to have more access to sunlight for processes like photosynthesis the next example we're going to look at is water solvency abilities now no we're tempted to say that water is a universal solvent and that is inaccurate however water does have very high solvency abilities in its liquid state so take a look here at this video that shows some salt being dissolved in water now why is this an important property that life depends upon because organisms must obtain key nutrients from their environment considering that living things are made up of 70 water dissolved materials in the water allow for easy access by cells our next property we're going to look at is the ability of ice to float now water's cohesive properties allow for unique bonding interactions in water solid state and this makes water um as a solid less dense than water as a liquid and here we can see in the video uh with the ice being added we notice that it floats leaving liquid water underneath now how is this an important property for living things well aquatic organisms are still able to live in water in freezing climates because the water will freeze on the surface leaving liquid water underneath for those organisms to still thrive next we're going to take a look at water's high heat capacity water has the ability to absorb a lot of thermal energy before it changes chemical states it resists sudden changes in temperature and so or organisms like my friend here my little fish friend here lives in a water environment and so many aquatic organisms like the fish will depend upon this property of water so that they can maintain appropriate temperature regulations of their of their bodies lastly we're going to take a look at capillary action capillary actions result of the adhesive and cohesive properties of water and in this video here you'll see that as i add a thin tube into the liquid the liquid automatically goes up into the tube now how is this property important for living things well plants can access water from the soil through this capillary action ability into their roots so let's practice our skill for this video which is a describe in which we're going to use a visual representation to describe characteristics of biological concepts concepts processes or models represented visually so here is our question that i would like for you to consider so pause your video at this moment read through that question and we'll come back in a second to see what your answer is all right so we're looking at describing the property of water illustrated by this graph and so the answer that i have is that the graph shows the water temperature remaining relatively the same as the air temperature increases over the six day period and this is demonstrating water's high heat capacity now if you notice it is it is a describe so you must describe how this visual represents that opposed to just saying it's representing high heat capacity and that's the difference between an identify and a describe and we're also asked to describe how life uh such as micropis samoides uh which is a fish species would depend upon it and so once again the fish's ability to maintain optimum body temperature is dependent upon water's ability to absorb heat and resist those temperature changes so what should we take away from this video once again we have to understand that the chemical components of water do influence how water interacts and that the oxygen and the hydrogens within the molecule do uh result in polarity due to the unequal sharing of electrons and this results in water's ability to form hydrogen bonds and exhibit some abilities like cohesion and adhesion and surface tension always remember science is not a class it's a mindset so set your mind on science and make sure that you continue to take a look at the videos that we offer biology out