My notes and thoughts from Biology 111, for Friday, September 5, 2008. The entire series can be found here.
On this day, Tropical Storm Hannah was expected to hit, so the college closed at 1 PM. Although that was well after the end of our scheduled lecture, Doc (if I recall correctly) cut the class a bit short to give folks headed home a little extra time.
So in the previous lecture, we had left off discussing Cohesion and Adhesion, the first of the emergent properties of water on the table for discussion. With this lecture, we picked up with the next emergent property on the list.
2. Moderation of Temperature
Water has a relatively high specific heat, which means that water can absorb and release large amounts of heat with little change in temperature.
To discuss this topic, it helps to first have an understanding of the difference between heat and temperature.
(Lecture Continues Below the Fold)
Heat is the total amount of kinetic energy in a body.
Temperature is the average kinetic energy of the particles in a body.
To illustrate this, we discussed the comparison of a hot cup of coffee to the Arctic Ocean.
While the temperature of the cup of coffee is higher, there are many fewer molecules in that cup than there are in the Arctic Ocean. The Arctic Ocean’s greater number of molecules each have lower amounts of kinetic energy (hence the lower temperature) but the sum, the aggregate, the total amount of heat is higher, simply because a lot of little bits of heat add up.
It takes much change in energy to change the temperature of water due to Hydrogen bonding and the crystalline structure of water (even as a liquid, as hydrogen bonds are formed and broken, water has a basically crystalline structure).
The Hydrogen bonds are strong enough that each of them takes a certain amount of energy to break, so much of the heat coming onto the surface of the ocean from the sun is used in breaking those bonds, leaving less energy to impart to the water molecules directly. This energy absorption helps to keep the sun from baking the planet.
Reformation of the hydrogen bonds in the cold winter releases that heat back into the atmosphere, keeping the planet from freezing over.
This ties into the next part of temperature moderation.
Water has a relatively high heat of vaporization
Heat of vaporization is the amount of energy needed to go from a liquid to a gas. This is also due to Hydrogen bonding.
|Water’s State of Matter|
Evaporation lowers the average temperature of the water left behind.
Evaporative cooling —> We use this technique as sweating. Plants use this in the leaves, which then draws water up through the plant from the ground (remember the Hydrogen bonding thing from the last lecture?).
Rain forests are so rainy because of the vast amount of evaporative cooling, which saturates the local atmosphere. All that water vapor then cools, condenses, and falls as rain because it’s now heavier than the surrounding air.
The ocean temperature close to our shore varies between the low single digits in the winter to the upper twenties in the summer, so that’s a thirty degree temperature difference over the course of the year.
In the desert, the temperature ranges from around zero at night to 50° or more during the day.
Water is a great temperature regulator.
We closed out the lecture with a short discussion of the gulf stream, and how that moderates the climate of the British Islands despite their high latitude. We compared the Emerald Isle specifically to the city of Moscow, Russia, which is at about the same latitude.
From whence came the art:
The first image is of our textbook, Biology, Eighth Edition, by Campbell & Reese et al.
Other images by me and are licensed under the Creative Commons Attribution- NonCommercial- Share Alike 3.0 License.