In the second half of chapter 2, we start to talk about biochemistry. Water is a big part of that, but there are other things that we'll be discussing within the biochemistry portion as well. Biochemistry studies the chemical makeup of living things, essentially, and the reactions that take place in those living things.
There are two types of chemicals in the body and in living things. Those that are considered inorganic, and by definition inorganic means they do not contain carbon. There are exceptions to that. And there are other compounds that are called organic.
Organic compounds most certainly means that carbon is one of the central atoms within those compounds. The two classes of biochemical compounds are very important, but in different ways to living organisms. As far as inorganic compounds are concerned, we're going to first look at water, then we'll move on to salts, and then finally talk about acids and bases and their properties. When we look at the organic compounds, we're going to focus on the four types of organic compounds.
which are often referred to as macro molecules because they're very large molecules but we're going to focus on carbohydrates lipids proteins and nucleic acids so as we're going through each of these different types of inorganic and organic compounds pay special attention to their role within the biological world so we're going to begin our discussion of biochemistry talking about water and this video segment will focus primarily on water water is a very important molecule on this earth without water we could not function we could not live but you may not be aware of why water is such an important molecule that supports our life in so many different ways living organisms require more water than any other substance within their body and we'll talk later in unit three about how your cells make their own water it's called molecular or cellular water so when you look at the cellular level at any organism or even an organism that's single-celled they're essentially 70 to 95 water Not only is water inside of them, they're surrounded by an aqueous environment as well. So there's a reason that water is very abundant and why our planet is so habitable by us because of water. So if you look at any picture of the globe, the Earth, you're going to see that the majority of the Earth's surface is covered by water.
And that helps to support all the different life forms that are on our planet. So water and its ability to provide so many different things for our living world goes all the way back to its chemistry. So as we just finished talking about the basics of chemistry, we have to go back to the chemistry of water.
Water is a polar molecule. The way that water is formed is through polar covalent bonding, which creates partial charges on different regions of the water molecules. So as we discussed previously, the bonds that hold oxygen and hydrogen together in an individual water molecule are polar covalent bonding, which again means sharing of electrons, but in an unequal fashion.
creating partial charges on different regions of the molecule. Because the oxygen is so electronegative, it keeps the electrons a majority of the time, giving it a partial negative. The hydrogens are left without the electrons the majority of the time, giving them partial positive charges.
So this water molecule, because of the way that it's formed, has this partial charge to it which is considered to be a polarity it has a positive side and a negative side it's not a full positive or negative but it's a strong positive and negative and that allows for adjacent water molecules to be attached via hydrogen bonding, which is a much weaker type of bond than a polar covalent bond, but it allows for these water molecules to have this loose kind of association with each other. Because of water's chemistry, both the polar covalent bonding within the molecule that creates these partial charges and its ability to hydrogen bond and connect with other water molecules. This gives water unique chemical properties that allows it to do the things that it does within our biological world.
We are going to focus on four of water's major properties that help facilitate life. So how is water so crucial to us? What can water do? that enables it to be such a molecule that we absolutely cannot live without. So we'll start with its cohesiveness.
Then we'll talk a little bit about temperature-related things with water, its ability to both moderate temperature and expand when it's frozen. And then we'll talk about its ability to dissolve things as a solvent. So let's start with its cohesive behavior.
Water is capable of something called cohesion. Cohesion is what allows the water molecules to attach to each other. So through those hydrogen bonding, they can cohesively attach.
But it also allows water to attach to other surfaces as well. Cohesion is the primary reason that water is able to be transported up inside of a plant. I mean think about it for a second in order for a tree and all the components that make up the part of the tree that's above ground to get water it has to come in and be transported in from the roots that is going against gravity it's going against the natural flow so in order to make that happen without requiring an enormous amount of energy to do so basically the water kind of walks up inside of the plant cell walls walks up inside of the xylem inside of there we'll talk about xylem at a later date but that's probably a term you've heard in your past before this cohesion also enables water to have surface tension surface tension example if i find my picture here is this bug here called a water strider that's appearing to basically walk on water and how it's able to do that is because of the surface tension created in between the hydrogen bonds of adjacent water molecules essentially then this image here is showing capillary action with waters cohesive nature so a capillary tube is a very very thin glass tube that in order to get water up into the tube you basically just take it it's like a skinny straw and put it on top of water and it naturally gets sucked up inside and how it does that is through adhering to the inside of the capillary wall the chemical nature of the water molecules adheres to the chemical nature of the glass and that allows it to go up inside of the capillary tube Next, water is able to moderate temperature. Water is able to absorb enormous amounts of heat and release enormous amounts of heat. And it's able to do so in such a way that it only changes its temperature very slightly.
If you think about boiling water, for instance. So you've got your pot. and it's on top of your stove eye okay and you've got water inside of that pot all right so when you think about as your heating element is heating up that pot if you were to feel the pot before the water starts boiling i guarantee you the hot is in the pot is incredibly hot and that's because the material used to make the pot only absorbs small amounts of heat before getting super hot. The water itself is able to absorb a lot of heat before it actually changes its temperature.
So of course it takes a while for water to boil inside of a pot. It doesn't take long for a pot to get hot at all, but it does take a while for the... water inside to get hot.
Water is able to absorb heat from warmer air and release heat into cooler air. So from a large body of water, like an ocean or even a very large lake, water is able to moderate the air temperature by taking heat either out of the air or putting heat into the air. Heat, just to kind of refresh you a little bit on some terms here to do with heat. Heat is basically a measure of the total amount of kinetic energy going on in a substance.
So kinetic energy, again, is energy in motion. So the more motion, the more movement you have, the more heat you have. So whenever the temperature goes up, temperature is a measure.
of heat because of kinetic energy. The more the temperature goes up, that means you have more heat because you have more kinetic energy. For temperature, the standard international unit is Celsius, just like we've been discussing in lab. Whenever you get into chemistry or even a physics course, you may talk a little bit about calories, kilocalories, and joules.
or even like a class that talks about energy and how it's expended like for a muscle physiology class you might get into calorie and kilocalorie and joule i just kind of wanted to bring those onto the page just so you'll be familiar with them not that you'll be tested on those the specific heat of water is very high this goes to waters you know my little you pot example. It takes a lot of heat in order for water to change its temperature. So specific heat is defined as the amount of heat that must be absorbed or lost for one gram of a substance, like one gram of water, to change its temperature by one degree Celsius. And it takes a lot for water to change its temperature by one degree.
The specific heat of metals such as aluminum or things like that are actually quite low. It doesn't take much heat to get those hot at all. So water is able to resist changes in temperature because of its high specific heat. Whenever heat is absorbed by water, the hydrogen bonds between water molecules break and whenever heat is released by water it's because hydrogen bonds are forming.
So the formation of bonds releases heat and the breaking of bonds absorbs heat. Because of water's high specific heat, this enables it to basically minimize the amount that it fluctuates, which allows organisms to live in it so well. I mean, if you think about how hot it is, you know, towards the equator, If the water in that area absorbed all that heat and got hot instantly, it would pretty much boil all of the life within those bodies of water. So water is able to resist that very effectively. This diagram shows water's ability to change the air temperature.
So if you've ever been to a coastal area, this is showing West Coast in California. But even if you've been to the east coast, to let's say Myrtle Beach or Virginia Beach or maybe one of the beaches in Florida, if you've ever been to a coastal area, you will experience the fact that as you go towards the coast, the air temperature feels cooler, especially in the summer. If you go just a little bit inland, Like here it's showing Los Angeles is at 75, but San Bernardino is at 100. So the further you get away from the water, the less able the water is to absorb the heat within the air.
Now the opposite would happen during the wintertime. During the wintertime, you would actually have it warmer at the coast than inland. And that's because the heat within the ocean water gets released into the atmosphere and makes the air temperature warmer near the water and it's cooler further in because there's no water available there. So water's abilities and its high specific heat, its ability to moderate temperature has great impacts on our climate. Water has the ability to undergo evaporation.
As it changes from liquid to gas and water evaporates, the heat of vaporization turns water into this gas form and allows water to evaporate from the air, essentially evaporate into the air. But this evaporative cooling effect that water has is also very helpful to organisms to maintain life. We use evaporative cooling to sweat.
Evaporative cooling is how different bodies of water help to stabilize their temperature as they get too hot. The water molecules will evaporate into the air to help get some of that heat out essentially. Water also has the ability to expand upon freezing. And this goes back to water's chemistry yet again.
You all know that whenever water freezes, it floats. Ice floats. So ice will float because as water gets frozen, the hydrogen bonds that hold adjacent water molecules together become more ordered. And they... basically make sort of like a honeycomb structure and this honeycomb structure so there would be water molecules at the ends of each of these, become ordered in such a way, these are hydrogen bonds holding them together, become ordered in such a way that there are these gaps within the structure.
And these gaps make hollow places inside of the water that allows ice to float. Water is most dense at four degrees. That's 4 degrees Celsius, which is basically refrigerator temperature.
And then as it gets closer to zero, it freezes. Water's ability to expand upon freezing, become more buoyant and float is very important to aquatic life that live in cold places. I mean, think about it.
If ice were to sink in places like Antarctica or anywhere that it's colder, then everything that's at the bottom would basically freeze and everything above it would freeze as well. and so that would make life entirely impossible on our planet especially with all the water that we have if the ice all sank the last major property of water for us to discuss is water's ability to be a universal solvent a solvent is something that dissolves a solute solute and solvent are the two parts of any solution solutions are primarily solvent and then they have a smaller amount of solute. Water is an excellent solvent.
It's able to dissolve a majority of substances in our world. It is called an aqueous solution whenever water is used as a solvent. In general, if water can't be used to dissolve something, most of the time alcohol or some sort of an alcohol can be used to dissolve it.
Water's ability to be a universal and versatile solvent is due again to its chemistry, its polarity. And the partial charges which are on the hydrogen and the oxygen of the water molecules enable it to dissolve other substances that are placed within water. Water essentially surrounds these compounds that it's trying to dissolve by creating something called a hydration shell. So imagine you take salt and mix it with water.
You know it takes a while. You kind of have to mix it up. Heating makes it happen faster. But it takes a little while for all the salt, which is just sodium chloride, to get dissolved into water. But eventually what happens is that the individual sodium and chloride that makes up salt will become separated from each other and will be totally surrounded.
by water. That's this notion of a hydration shell. But I want you to notice how the water molecules orient themselves around the chloride is different than how it orients itself around.
So if you'll recall, the hydrogens have a partial positive because of the fact that oxygen is greedy and it keeps those electrons most of the time. I don't know why I put a positive. And so when it's breaking down the chloride, the hydrogens are what orient themselves to the chloride because it's a negatively charged anion.
Then when you look at the cation of sodium. The partially negatively charged oxygen is what orients itself to the sodium with these partially positive hydrogens to the outside. So because of water's polarity due to its polar covalent bonding, it's able to uniquely help break down especially these ionically bonded salts like sodium chloride. And it also helps it to break down other substances as well. So water is able to dissolve not just ionic compounds like salts, but it's able to break down others as well.
If you think about whenever you eat, you put food in your mouth, your saliva mixes with your food. Your saliva is primarily water. The polarity of the water molecules starts to break down proteins, carbohydrates, and other food molecules and helps to start that breakdown process.
With water, because of water's polarity and its chemistry, There are some substances that naturally don't mix well with water, and others that do mix well with water. Things that mix well with water and have an affinity for water are said to be hydrophilic, which translates to water and loving. Things that are the opposite, which would be water-fearing, are hydrophobic.
So hydro, again, water, phobic, fearing. And those pretty much are repelled by water or will repel water themselves. One of the most well-known things for being hydrophobic is oil. And think about it.
If you've seen oil and water together, they don't mix. Oil will naturally make tiny little spherical molecules inside of water. And if you put two of those side by side, they'll mesh together.
So depending on a substance's hydro... nature, whether it's hydrophilic or hydrophobic, it may or may not mix well with water. Colloid is a name for a stable suspension of particles in a liquid.
Water is used very frequently as a solvent to make up a solution. Solutions are made in typically one of two ways, either as a percent solution, like let's say a 10% salt solution, or they're made as a molar solution like 0.1 molar sodium chloride. You'll learn more about these types of solutions as you get into the laboratory, say in a chemistry class, and you're making these solutions. Each of these solution types of solutions has their own place.
In general, percent solutions are used whenever accuracy is not of high importance. Molar solutions are more so used when accuracy is of the most importance. Molar solutions are made based on the chemical formula for a compound and its molecular mass. Percent solutions are based on parts. 10% sodium chloride solution might be one part salt and the other parts water.
So it's less precise, let's say. It's less precise. So it really depends on what type of experiment you're doing in the laboratory as to which one is going to be most beneficial.