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Air and Water in the Environment
Teacher's Notes
Searching for water on the Martian surface
This unit is an introduction to the water cycle. On Earth the water cycle seems relatively complex because of the large diversity of natural processes which involve water.
In this unit students explore the role of green plants in the water cycle.
In a closed environment, such as a space habitat, plants will be essential elements of the water cycle.
On Mars water is rare. It may, however, be abundant in some underground locations as a permafrost layer. Until Mars is more fully explored it is not known whether or not this is the case.
Things to Emphasize
Water is essential for plant and animal survival;
On a voyage to Mars astronauts will need to carry their water supply with them;
On Mars water is a very scarce resource;
Water must be recycled in the environment;
Water vapour is an invisible gas;
Plants have the ability to use slightly "polluted" water and release it into the air as "pure" water (vapour);
Science investigation involves a multi-step inquiry process: ask an initial question, plan the investigation, record observations and collect data, analyze data to draw a conclusion, and communicate the findings.
Extracting Water from the Air
This set up is somewhat self-explanatory. It requires six large, clean, glass jars. Each jar is set up as shown below.
Each pair of jars is placed neck-to-neck so that air can circulate freely inside each of them. Use ample duct tape to insure an air tight seal. This will prevent air from the room leaking into the jar and air from the jar leaking into the room.
The duct tape also prevents the top jar from toppling off the of the lower jar.
The top of each system is chilled using ordinary water ice, which is placed in a bottomless plastic margarine container as shown. A ring of silicon around the edge of the container prevents water from the melted ice from running down the sides of the jars.
Hint: Set this experiment up a few hours prior to your demonstration. Let the three systems stand a few hours before adding any ice.
How it Happens
The ice creates the same effect that you would observe in the atmosphere; namely, as you go higher into the air (in an airplane, perhaps), the temperature goes down.
Even after just a few minutes students will begin to notice that water droplets are forming on the inside of the top jar(s). Left for a few hours, the amount of water that forms at the top in each system will show dramatic differences in quantity.
The system with the plant will generally produce much more condensed water than either the system containing the soil or the system containing only air. This is because plants actively transpire water vapour.
The Earth, just like the systems in the jars, is a closed system. The condensed water from all sources of water vapour falls back to earth as rain or snow. If this did not happen, the Earth would eventually run out of water!
Activities
What We Did, Student Activity Master
What We Saw, Student Activity Master
Words We Know, Student Activity Master
How Many Plants?, Student Activity Master
How Many Drops?, Student Activity Master
Topics for Discussion
Which of the systems above most closely resembles the Earth?
Which of the systems above most closely resembles the Earth's deserts?
Which of the systems above most closely resembles the planet Mars?
Clouds are really just made up of millions and millions of tiny water droplets. Why don't all clouds simply fall out of the sky either as rain or snow?
Humans (and most other land animals) cannot drink sea water because of the salt which is dissolved in the water. Yet sailors on long sea voyages often collect rain water for cooking and drinking. This rain water they collect comes from the sea. Why is it that they can drink this rain water?
Hint: Build a system as shown above, but place a dish of clean salty water in the bottom. Have students dip a clean Q-tip (one per student) into the solution and let them taste it before sealing up the system. After condensing water with ice on the inside of the top jar, open up the system and, using new clean Q-tips (one per student), have them taste the condensed water.
Finally, allow the dish of salt water to completely evaporate (this may take a few days). Have students examine the residue.
for the Canadian Space Agency.
