Water Cycle - Oceans (2)

  • Distinguishing polluted, dirty, and clean water.
  • Using the microscope to test samples of water. 
  •  dissolve
  •  pollute   
  •  sediment

Students look at drops of water under the microscope.



Water is an important resource for all people in the world.  People can die from lack of clean water to drink.  Most students do not think about water because in the United States it is almost an unwritten rule that cities, counties, states and the federal government will provide this resource.  Early in our country this was not so.  Many people died because the rain did not bring water or that sewage from a city polluted the waterways.  The United States is aware of the dangers of polluted water and have one of the strictest laws in the world.  Not all nations in this world have water privileges that Americans have. 

The world’s oceans have always been a “dumping” ground for pollution.  In many areas raw sewage and other wastes are put into the oceans.  Many humans see the oceans as such a vast place that it could never get polluted.  But this is wrong.  Currents in the oceans move the pollution away from the land, but it still remains in the system.  Some wastes are sometimes used by plants and animals in the oceans to help them grow, but too much will upset the natural balance.

There are some substances that will dissolve and others that will remain in the system.  For instance, plastic will not degrade and remains floating on the world’s oceans.  Other substances like phosphorous (from soaps) can be used by small plants in the oceans as fertilizer.  

Pollution is a term used by the media and general public frequently.  However, most children do not understand how the word differs from dirty.  Pollution is when water (or any other part of the environment) becomes offensive or harmful to organisms.  Fresh and salt water can become polluted. However, seawater is not polluted just because it is salty.  

Salt water, although not useful to drink by humans, is not polluted or dirty; it has mineral salts dissolved in it.  This lab has the students think about the difference between dirty, polluted, and clean water. 

  1. Brainstorm with students and make a list  of polluted and dirty components of water.  

    POLLUTED:  oil, harmful chemicals (like mercury, lead), too many dead animals, plastic bags, metal

    DIRTY:  wood, mud, rocks, algae (kelp)
  2. Each group of students should have two jars for Exercise I.  Students should fill up each jar with 50 ml of water and mix one with 25 ml of vinegar and the other with 2 ml of sand.  Students should shake the jars  and determine which jar is dirty or polluted.  The sand jar is dirty because the sand will settle out, however, the vinegar cannot be removed easily and the solution is therefore polluted.
  3. Pre-mix 5 containers (baby food jars work well) and have students look at one or two drops of each of the containers under the microscope.  You may want to label each jar as UNKNOWN 1, UNKNOWN 2, etc. Below are suggested contents:
    jar 1 = 1/4 water + soil  

    jar 2 = 1/4 water + 2 drops of food coloring
    jar 3 = 1/4 water + 3 drops of oil
    jar 4 = 1/4 water + 3 drops of soap
    jar 5 = 1/4 water + salt
  4. Students should figure out if the water is polluted or dirty and record the observations on the sheet. Use the microscope to look at a drop of each of the water to see if students can identify particles in the water. You must remember that polluted or dirty water sometimes depends on the type of animal using that water.  What may not be toxic to humans, may be toxic to little animals, or vice versa.  For instance, soap in water is not polluted if we wash our face, but if we had to drink soapy water it would be polluted. Students should be encouraged to justify their answers.  Consider it correct if their justification is logical.

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