(CHO) Limiting Factors Lesson
Limiting Factors
All About Water
Now we all know that water is an odorless, tasteless, and colorless fluid essential to all living things. But there's more to water than what meets the eye. Let's look a bit deeper...
Water is... Two Sided!
Water is made up of hydrogen and oxygen atoms bonded together in a 2:1 ratio. This means that there are two hydrogen atoms bound to one oxygen atom. But the hydrogen atoms are not bonded evenly across the oxygen molecule. The hydrogens bond together at one end of the oxygen atom making a sort of like a mouse-looking molecule. Because the hydrogens are not equally shared across the oxygen atom, these water molecules are polar. This means they have an unequal charge distribution and the result is a partially positive end on the hydrogen side and a partially positive end on the oxygen side. Therefore, water has two sides!
Water is... Sticky!
The polarity of water molecules allows it to bond with many other substances. This attraction from the positive and negative ends of the molecule forms hydrogen bonds. Hydrogen bonds occur when the positive end of a water molecule attracts to the negative end of another molecule, or vice versa. Hydrogen bonds allow water molecules to stick to each other substances yielding adhesion and cohesion. When water bonds to other water molecules, they bond at 90o angles. This process is called cohesion. When water molecules bond to other substances, it is called adhesion. The combination of adhesion and cohesion is very important to living things. Capillary action is how water moves throughout the roots, stems, and leaves of plants. Without adhesion and cohesion, capillary action is impossible. Water is…Universal!
Water polarity has also given the water the title of universal solvent. The positive a negative charges found in water allow it to dissolve many ionic compounds. Ionic compounds are substances that have positive or negative charges. When those charges come in contact with the charges in water, the water molecules surround the substance making it dissolve.
Water is... Stable!
One of the most important physical properties of water is its ability to absorb heat. Water has a high specific heat. This means that water resists temperature change by absorbing extraordinary amounts of heat. This allows water to work as an insulator and helps maintain a steady environment for all living things. The heat capacity >of water is 1gm/oC. Heat capacity is the measure of the heat required to raise the temperature of 1 gram of a substance by 1oC. This is one of the highest of all known substances because of the strength and number of hydrogen bonds present in water.
Hydrogen bonds are also the cause for a high latent heat of vaporization. A great deal of energy is required to break the hydrogen bonds that are present in liquid water. Once the hydrogen bonds are broken, the water will evaporate and transform to water vapor. This means that water can take in a lot of heat before it will begin to change phases and evaporate.
High specific heat and high latent heat of vaporization are both especially important to all the creatures that live in and use ocean resources. Imagine if the temperature of ocean changed every time the weather changed…imagine if the ocean started to evaporate every summer!
Water is... Unique!
Water expands as it freezes. When water expands, the volume increases which decreases the density. Therefore, water in the solid form is less dense than the liquid form. In other words, ice floats! Water does not follow a linear pattern when observing the density temperature relationship, rather it follows a curve. As the temperature of water decreases from room temperature to freezing, the water becomes more dense. However, as the water freezes the hydrogen bonds become rigid and cause the liquid to expand. This changes the volume of the solid water and the ice becomes less dense than the liquid water. This property of water is essential to our environment – any change would cause our oceans to freeze from the bottom up!
Sea water is about 96.5% pure water and 3.5% dissolved solids and gases. These dissolved solids change the latent heat of the water by about 4%. In other words, it takes less energy to evaporate sea water than pure water. The dissolved solids also inhibit the formation of the crystal structure during freezing. The saltier the water, the lower the freezing point. Further, as seawater freezes, the ice formed is almost pure water. The remaining salt water is very dense and sits below the ice.
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