General ---------Biology ------------------Online------------------------------ Ch. 3 Water and the fitness of the environment

What would happen to the fish in a shallow pond if water, like most substances, became denser as it froze and sank? 
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Check your answer.

Almost all other substances on earth get denser and denser as they cool; water is very unique.  As water cools it also gets denser and denser, but as it approaches the freezing point, it suddenly begins to expand.  What causes this unusual property of water? 
Explanation:  This  is a model of a water molecule.  Look at the two upcoming arrangements of water molecules, and pick the arrangement that is the lightest, or the least dense.  Click here to see arrangements. 

In the two arrangements of water, a is more dense, and liquid, and b is less dense, and solid (ice).  Ice is less dense than liquid water and will therefore float. 

Assignment: Now, based on the two arrangements you studied, explain why ice is less dense than liquid water? 
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Not only does floating ice keep lakes from freezing from the bottom up, leaving all the fish on the surface to perish, the ice on the surface of a pond forms an insulating barrier that allows sunlight through to warm the water.  The water temperature below the ice on a cold day is much warmer than the air above the ice.  Say its -10 degrees in the air above the ice.  What is the lowest possible temperature of the "liquid" water just below the bottom surface of the ice could be? ____ degrees F. See page 39 of your text for a discussion of Fahrenheit and Celsius scales of measuring temperature.

Assignment:  Draw two graphs; one that illustrate the temperature of the air above the ice, measured every hour for 24 hours, and ditto for the water below the ice. Bring this to class and be prepared to draw on the board.  For blank graphs, click here. 
(There is nothing in your text, or in the online notes, that will provide this answer.  This tests your ability to apply what you have learned to a new situation:  how the temperature of water changes compared to other substances, like air.  Pretend you are sitting in a chair on the ice.  It is 12:01 AM; it is dark and cold.  You look at your thermometer that's measuring the air temperature; it is -10 F five feet above the ice, and another that's measuring the water 5 feet below the ice, you read the temperatures and jot them down. You do this each hour for 24 hours.  Imagine what changes will happen. )

Summary:  Students should write summary statements below as bullet points. 
 
 

Test your knowledge:  Practice Quiz # 2, 12,26, 45.