Table of Contents

Growing Food on Mars

Teacher's Notes

Living and working in a closed environment

Transparency Master

This unit is an introduction to the stability of ecosystems.

Long term survival on the planet Mars requires the construction of a stable habitat, able to support an agriculture suitable for food (and possibly oxygen) production for its human inhabitants.

On Mars there is no corner store. There is no readily available source of liquid water. There is no breathable air... you can never open a window! One must live in a totally closed and sealed environment within which one must arrange to provide all the elements essential to human survival.

In this activity students are challenged to build a small stable biosphere and to investigate the conditions which predicate success or failure of their biosphere.

Things to emphasize

1. There is only one known stable biosphere in the Universe. It is called the planet Earth;

2. Nature cannot easily re-create raw materials, therefore almost everything must be recycled;

3. A biosphere's stability depends completely upon natural "feedback" mechanisms for its survival;

4. The perfect biosphere will achieve a state of dynamic equilibrium whereby some species within the biosphere consume resources at exactly the same rate that other species within the biosphere recycle those resources;

5. The larger and more varied a biosphere is, the more resistant it is to catastrophic failure from a given internal or external influence;

6. The larger and more varied a biosphere is, the longer it takes to achieve catastrophic failure from a given internal or external influence;

7. The larger and more varied a biosphere is, the more difficult it is to reverse catastrophic failure from a given internal or external influence once it has begun;

8. 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.

Building the "Biosphere"

A biosphere is not a terrarium.

In this project the main idea is to design and build a stable ecologically-closed system. This is called a biosphere. You cannot "open" a biosphere to add material, remove material or otherwise modify the system.

A terrarium, on the other hand, is kept "open" so that environmental conditions within the terrarium can be adjusted as required to keep the system healthy and prosperous.

Transparency Master

Equipment List

You will need:

1. A large wide-mouth condiment jar (about 4 L or larger), with lid (label removed). The kind that cafeterias or restaurants use for pickles or mustard is ideal.

2. Crushed limestone or gravel.

3. Charcoal in barbeque briquettes or wood fragments.

4. Peat moss or humus-rich soil.

5. An assortment of green plants, mosses, and fungi.

6. Water.

7. A small amount of general purpose plant fertilizer.

8. An identification label.

The Procedure

The procedure is simple. Begin with a large wide mouth jar.

1. Place a 2-4 cm layer of stone in the bottom.

2. Overlay the stone with 2-3 cm of charcoal. (Crush big chunks into smaller pieces first).

3. The soil layer should be rich in humus. About 5-6 cm depth should suffice.

4. Select a wide variety of small green plants. Small moss and fungi covered sticks can be included.

5. Create a solution of water and plant fertilizer according to the directions on the fertilizer container. Add enough to just cover the stones in the bottom of the jar.

6. Seal the container, create a label itemizing the contents of your biosphere, and glue the label to the lid.

7. Set the biosphere in a moderately warm and bright location.

8. Record observations.

Tips 'n Hints

1. Plan a field trip to collect the plants and soil(s) required for each biosphere.

2. Some biospheres will fail quickly, while others may last for years. It is very important to document as much detail about the contents of each biosphere as possible in order to make inferences explaining the success (or lack of success) of each experiment.

3. Use soil and plants from the same location and growing conditions.

4. Try not to change the biosphere's location too frequently since this inhibits the plants' ability to acclimatize to their new environment.

5. Never open the biosphere. You risk destroying the system's ability to form a stable equilibrium.

6. Warning: Avoid long exposures to direct sunlight.

Observations

Observation Blackline Master

Key Ideas

1. Your biosphere needs energy.

Energy, in the form of visible (short wavelength) sunlight, must enter the biosphere at the same rate at which infrared (long wavelength light) energy is radiated out by your biosphere. If this does not happen your biosphere will get hotter and hotter (energy in exceeds energy out) or colder and colder (energy out exceed energy in).

2. The total amount of material within the biosphere is constant

This biosphere requires water, oxygen and carbon dioxide for its survival. Because the biosphere is a closed system the total amount of material in the system never changes. This can be verified by occasionally weighing the biosphere. However, the plants inside this biosphere are consuming carbon dioxide, water, and nutrients from the soil. The green plants are using these materials to produce oxygen and complex organic molecules such as sugar. If the green plants do this for a long enough time they will eventually run out of at least one of these ingredients.

While the green plants are using up water and carbon dioxide, bacteria and non-green plants such as fungi are using up oxygen and the complex organic molecules created by the green plants to release carbon dioxide and water.

3. The biosphere need to achieve a state of dynamic equilibrium

In a perfect biosphere the aerobic (oxygen consuming) bacteria and non-green plants are using the plant produced oxygen to release water and carbon dioxide at the same rate that the green plants are consuming it.

Whenever all the materials being consumed by various species in a system are exactly replaced by other species, the system is said to be in equilibrium, or more exactly, in ecological equilibrium.

Conditions Affecting Equilibrium

(a) Buffers

Buffers are systems which tend to minimize the impact of any change induced in a larger system by absorbing the consequences of the change.

For example, dams on a river act as "flow buffers" which trap flash-flood waters and release these trapped waters slowly.

In this biosphere charcoal acts as atmospheric buffer. A large lump of charcoal on the surface of the biosphere effectively increases the air volume of your container by a factor of ten or more without actually having to use a bigger container. It does this by slowly absorbing and slowly releasing excess amounts of oxygen, carbon dioxide, methane and other gases and therefore prevents radical changes in the composition of the air within the biosphere.

(b) Feedback

Feedback is a mechanism whereby the outcome of a process sends signals back to the process and defines how the process should continue. Feedback can be characterized by three types.

1. Positive feedback: Feedback which causes the process to speed up.

2. Negative feedback: Feedback which causes the process to slow down.

3. Equilibrium feedback: Feedback which causes the process to remain constant.

Activities

1. Ask students to make a chart that lists all the elements of their biosphere and what each consumes and produces. Have students predict the effect of removing each element on the biosphere as a whole.

2. Have students suggest a plant or animal that might be successfully introduced to their biosphere and explain the impact this might have on the biosphere as a whole.

3. What Does It Mean?, Student Activity Master

Topics for Class Discussion

1. A warmer atmosphere implies more evaporation and therefore more water vapour in the Earth's atmosphere. More water vapour results in a cloudier planet. It is well known that clouds strongly reflect sunlight, therefore less energy is able reach the Earth's surface and the lower parts of the Earth's atmosphere.

   1. Ask students to draw a diagram to show this transfer of energy.

   2. Discuss the effect. Is it a negative, positive, or equilibrium feedback mechanism?

2. On a trip to Mars we cannot take a complete ecosystem with us, therefore we will have to rely on machines to help maintain a stable environment within our closed living space.

   1. Check the library to find out how astronauts recycle the air in the space shuttle.

   2. Check the library to find out how waste water is purified in city treatment plants.

3. A human needs to consume about 4 L of water per day (in food and beverages) to stay healthy.

   1. How much would one person need for a 910-day, round-trip, mission to Mars?

   2. How much water (in litres) for a 4 person crew?

   3. How much water (in kilograms) for a 4 person crew?

   4. How much water (in kilograms) for a 4 person crew if one-half of the consumed water can be recycled?

4. Devise a method to recycle the water used by plants in a simple biosphere. Hint: Begin by determining where all the water used in watering plants goes.