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in this video we'll talk about
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properties of water and this is all
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standard level or Core
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Curriculum at most temperatures on earth
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water is in a liquid state and that's
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going to be really important because
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almost all of the metabolic reactions
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that happen in our cells um take place
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with molecules that are dissolved in
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solution so amongst these water
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molecules um and that's a very important
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quality of water to keep an eye
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on now when we're drawing a water
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molecule we really want to draw it in
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this form here and I can even label this
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this is an oxygen and two hydrogens
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that's how we get H2O but it's useful to
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look at more of a a chemistry diagram if
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you will so the oxygen and the hydrogen
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are bound together through a calent bond
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but there's an unequal sharing of
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electrons and those electrons um are
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pulled a little closer to this um oxygen
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than to the hydrogen and that results in
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part partial
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charges so this is how we would write
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those partial charges oxygen is going to
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have a partially negative charge and
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hydrogen ends are going to have a
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partially positive charge so this is the
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way that I would want to draw a single
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water
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molecule now notice that I've chosen to
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draw that coal bond with a solid line
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that's the proper notation that um
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consists of a bond within a water
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molecule between two separate water
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molecules we're going to have a special
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type of bond called a hydrogen bond and
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we use a dashed or dotted line for a
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hydrogen bond and a hydrogen bond is an
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attraction between the partially
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negative end of one molecule and the
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partially positive end of a different
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molecule and so that's very important
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here if I have to draw multiple water
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molecules I want to be able to not only
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draw their partial charges and not only
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draw what atoms exist in there that's a
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little tough to read there but I also
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want to be able to draw that hydrogen
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bond that is going to exist between them
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and that hydrogen bond gives water some
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very special
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properties and that includes cohesion so
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cohesion um is an attraction between two
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molecules that are the same so water
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being attracted or sticking to other
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water molecules and that is a result of
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this hydrogen bonding that we're seeing
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here between these water molecules so
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cohesion water sticking to other water
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molecules and that's very important for
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a few reasons one of which um being what
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we call transpiration and this is a
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process that happens in the xylm of
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plants so the xylem is a tube that goes
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through a plant and it's the way in
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which water and other dissolved minerals
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is going to travel up through the plant
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and it really starts with evaporation
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from the stamat so we'll learn more
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about that in another chapter or sorry
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another topic um but these stamata are
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little openings in the plant leaf and
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when water evaporates from that plant
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it's also going to pull other water
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molecules up through the xylem due to
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cohesion so if you can imagine a water
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molecule up here pulling another water
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molecule up with it and that's going to
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create this tension this pulling force
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and that's going to pull water all the
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way up through the xylm of the plant as
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long as we have a continuous water
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column so as long as one water molecule
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is in contact with the water molecule
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right beneath it it's going to be able
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to create that tension force and pull
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the water up through the xylem of the
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plant all due to
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cohesion now not only is cohesion
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important for the insides of some
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organisms but it's important in creating
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habitat space for others so here we can
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see um this insect living on top of the
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water it's not floating in the water
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like you and I might float in a swimming
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pool it's not getting wet it's not even
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breaking the surface of the water so
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what that looks like is something like
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like this where the water molecules
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actually Bend um when coming in contact
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with like the foot of the insect I have
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no idea what this insect's foot looks
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like um but that's all due to this force
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of cohesion right these water molecules
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are hanging on to each other so tightly
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that hydrogen bond is so strong that
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that water doesn't even break and now
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this organism can utilize the surface of
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the water as a habitat
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space now you may have noticed when you
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put water into a tube like a graduated
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cylinder it doesn't form a line straight
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across but rather this like u-shaped bit
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here right so it looks more like this we
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call this the meniscus and this is all
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due to something called capillary action
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and capillary action is a result of
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adhesion so adhesion is the attraction
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between water molecules and a solid
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surface so in this case an attraction
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between the water molecules and the side
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of your tube and what that's doing is
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that's pulling the water up well as you
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can imagine that's also very important
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in transpiration for plants so not only
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is cohesion water pulling water
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important but also adhesion water
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sticking to the sides of this xylem
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that's super important because that
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helps pull water up against the force of
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gravity maintaining that moisture
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content in plants and helping plants
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move water from the soil up through
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their
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xylem another important quality of water
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is its ability to act as a solvent okay
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so just some quick vocabulary practice
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here a solute is what is being dissolved
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a solvent is usually a liquid acting as
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whatever we're dissolving something into
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and the solution is the resulting
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homogeneous mixture of these two
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now some things make better solvents
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than others water is not the universal
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solvent okay it's a very very good
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solvent but it cannot dissolve
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everything it can only dissolve things
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that are
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hydrophilic so Hydro meaning water and
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filic meaning love these are water
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loving things and these are going to be
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either polar molecules like glucose or
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ions things that have a charge so water
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is polar it loves other things that are
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also polar or have a charge that's in
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stark contrast to hydrophobic Hydro
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meaning water phobic meaning hating
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these are water hating substances so
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these are going to be nonpolar things so
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things like lipids or things um like an
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oxygen molecule um that have very low
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solubility in water
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now metabolism all of those reactions
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that happen in our cells requires things
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to be in solution so the fact that water
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is able to dissolve so many types of
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things makes it a really good medium for
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life and again this is all because water
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is polar so what we want to do is start
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associating the property being a good
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solvent with the property of water which
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is water is polar so that we can start
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to see the connection between what
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physical properties water has and how
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that's helpful to living
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things because water is such a good
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solvent that makes it an ideal transport
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medium in both plants and in animals so
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in that plant we're going to have two
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tubes we talked a little bit about the
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xylem so the xylem is going to carry
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water and dissolved minerals the phum is
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going to carry things like sucrose or
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other carbo hydrates but they have to be
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in solution so when we say in solution
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they have to be dissolved in water so
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water is a very good medium for
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dissolving things and getting them to
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flow through the different parts of the
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plant same thing happens with animals um
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we have a blood transport system and
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water makes up the primary component of
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what we call our blood plasma so our
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blood plasma is the liquidy part of our
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blood and it is primarily made up of
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water so that means it's going to be a
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very good solvent for things like ions
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glucose amino acids things that are
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hydrophilic things like oxygen or things
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like fats or cholesterol they have to be
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carried by things like cells or proteins
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because they are not very soluble in
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water so we'll replace that terminology
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here okay things that are hydrophilic
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are soluble and we are going to find
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them um in the blood plasma okay and
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things that are not soluble we're going
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to find them attached to things like
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proteins or cell components so that they
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can be
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transported another important physical
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property of water is buoyancy so gravity
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or gravitational force is going to be
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exerted downward it is buoyancy that is
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the force moving in the upward Direction
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so a force exerted upwards on an object
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by that water and so if done correctly
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or if in the right balance this leads to
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objects or organisms being able to float
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so less dense objects are going to be
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able to float on water the buoyancy of
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water is greater than the force of
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gravity exerted on the water and so
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those will float denser objects will
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sink most aquatic organisms are going to
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have about the same density of water and
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they don't want to be really stuck at
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the bottom or always really up at the
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top but some organisms can actually
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adjust their buoyancy so for example
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this is what's called a swim bladder in
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a fish and this fish can fill this swim
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bladder up with air when it does that it
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becomes less dense and it starts to
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float if it deflates its swim bladder it
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becomes more dense and starts to sink in
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the water so adjusting its own um
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density to either rise or fall in water
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all due to Water's
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buoyancy now let's talk about viscosity
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or water's resistance to flow so think
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about a fish swimming through the water
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we need some resistance from the water
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when the fin is moving in order for that
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fin to help the fish Propel itself
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forward there are also some um
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implications here for water being used
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as a transport medium so the more
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solutes that are dissolved in the water
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the higher the viscosity so we need to
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keep that in mind um there are limits to
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how much we can dissolve into things
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like blood um before it becomes very
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resistant to
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flow the next physical property that
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deserves our attention is what's called
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thermal
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conductivity water is a very good
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conductor of heat so heat can transfer
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easily through water that can be good or
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that can be bad um it just depends on
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the scenario so sometimes it's great if
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there's a lot of metabolic activity
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happening in our cells some of that
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blood plasma right that watery based
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solution that we talked about just a bit
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ago can pick up some of that water and
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then transport that heat maybe to the
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surface of our skin okay but having that
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heat energy enter that water very easily
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and then be transported in that way can
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be great it can also have some dire
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consequences if I'm um falling into an
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icy Pond um or a very cold body of water
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that water again is a good thermal
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conductor it can take the heat from my
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body and that heat will then be
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transferred into that water so in that
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case it can be bad so when we say the
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consequences for animals in aquatic
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habitats um sometimes that's great and
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sometimes that's not so we just need to
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consider um water is a very good thermal
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conductor and organisms will have to
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have adaptations to either take
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advantage of that or to prevent losing
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too much body heat um into that
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water although water is a good thermal
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conductor um it doesn't actually change
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temperatures very easily so water has
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what's called a high specific heat
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capacity and that means that it can
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actually absorb a lot of heat energy
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without a drastic change in energy so it
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has a high specific heat capacity it
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doesn't change temperatures as easily as
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other things like an alcohol or methane
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or something like that this is great if
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you are an aquatic organism so it has
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what's called a moderating effect I
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would definitely put that in my memory
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bank a moderating effect means that you
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can have lots of temperature variation
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in the air it can go from being a warm
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sunny day to a nice chilly night and the
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temperature of the water water won't
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actually change that much so it's
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moderating it's keeping that temperature
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range for that body of water in a
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relatively narrow range so that's great
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for aquatic organisms that live in there
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it can also be great for the maintenance
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of body temperature so like we just
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talked about your cells um can produce a
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lot of heat with um different metabolic
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reactions so that heat energy can enter
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the watery parts of your cells the
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cytoplasm or even the water-based fluid
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the plasma in your blood and that won't
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change temperature very much again
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you'll see some organisms that live in
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really hot areas um like this African
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elephant the reason that they have
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really big ears is to be able to expose
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those ears and the blood that's inside
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them to the outside air so yes water is
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a good thermal conductor it can exchange
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heat with the environment but the actual
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water itself so the blood plasma won't
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change temperatures um
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drastically so what does this look like
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in practicality well let's talk first
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about this ringed seal this ringed seal
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lives mostly in the water and water is
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very buoyant so that's great the seal
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can float and it doesn't have to expend
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a lot of energy to do that but water is
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very viscous so in order to move through
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it it does have to expend energy that
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way
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water is also a very good thermal
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conductor so what you're going to see
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here on seals is a large amount of
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blubber or fat that helps prevent some
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of the body heat from inside of the seal
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um being transmitted to the water in the
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environment so different adaptations for
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different environments this is the
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Arctic loon and it's evolved to live in
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the air air is less buoyant than water
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so that loon has to expend a lot of
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energy in order to stay um a loft to
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stay in the air but air is less viscous
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than water so it doesn't take as much
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energy to move through that air okay air
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is also not as um great of a thermal
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conductor so we're going to find less
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things like blubber on that bird but
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great examples of the ways in which
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organisms and especially animals in and
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near these aqu habitats have different
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adaptations to deal with the pros and
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the cons of these physical properties of
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water
