Effects of a Closed Environment
on Living Things
Grade Level: 9 - 12
We must understand the interdependent relationships between photosynthesis
and animal respiration before we can proceed in developing systems that
will allow long term survival in space. Utilizing the processes of photosynthesis
and respiration, students investigate living organisms in a closed environment.
- What factors are necessary in order to assure that living things can
survive and function in a closed environment?
- What happens to plants when they are placed in an environment saturated
with carbon dioxide for a period of time?
Varies depending on the expertise of the students.
For each team of students: •
For each student:
- 8 test tubes
- 4 aquatic snails
- 8 stoppers
- bromthymol blue solution
- 4 stalks of Elodea
- 1 or 2 liter bottle of club soda
For the class:
- One photocopy each of "Student Record Sheet," "Analyzing Your Data,"
and "Excess Oxygen Experiment Observations" (masters on the following
- 1 Overhead transparency of "Setting Up the Test Tubes"
A Closed Environment ---------------Student Record Sheet
Table # 2 Solution Color for Test Tubes with Bromthymol Blue
After collecting data, reflect on these questions:
- Which test tubes were used as controls?
- What causes the bromthymol blue solution to turn yellow?
- For each test tube, explain what effects cause the final observed
EXCESS CARBON DIOXIDE EXPERIMENT OBSERVATIONS
Table # 3
Solution Color for Test Tubes Saturated with CO2 & Bromthymol Blue
After you have collected data, reflect on these questions.
- Did any of these tubes go from yellow to clear or blue?
What gas do you suspect replaced the CO2?
- Tube D should remain yellow in color. Tube H should remain blue
in color. Tube L should remain yellow in color. Why will this be the
case for each of the tubes? Be specific.
- Why would each of these tubes (D, L, and H) be considered a control
for its group?
- Which of the three sets of test tubes will be considered the control
group? Why did you say that?
- Did tube I clear? How long did it take? Observe tube K; has it cleared?
Why do you think this happens?
A Closed Environment --------------- Analyzing Your Data
- In your observations of tubes E through H which of the tubes, if any,
- What is the reason bromthymol blue turns yellow in these tubes?
- Are any of the tubes blue in color? What does blue indicate?
- Are any of them clear? What does clear indicate?
- Which of the tube groups ABCD or EFGH is most likely to remain clear?
- What do you think is the relationship between photosynthesis and respiration?
- How is this activity relevant to humans in space? What implications
does this study have for space travel and for living in a closed environment?
Part A-The Role of CO2 in Living Systems
- Have the students write descriptive sentences using each of these
words or phrases: carbon dioxide, plant, animal, waste elimination,
general health, behavior, photosynthesis, oxygen, respiration, and indicator.
- Laboratory activity-give the students the following directions:
a. Fill a 15 ml test tube with about 10 ml of clean aquarium water
and add about 3 drops of bromthymol blue solution. Using a soda straw,
gently blow into the bottom of the test tube. Is there a color change
in this solution? What may account for this color change? Use the
above measurements for all test tubes in this lab.
b. Observe the aquarium snails in their natural environment. Record
any observation that relates to their movement, feeding habits,
waste elimination, general health, and behavior.
c. Label your test tubes A through H.
d. Prepare the following test tubes in this manner.
A & E One stalk of Elodea
C & G One snail-one Elodea
B & F One water snail
D & H Nothing
e. To test tubes A, B, C, and D add water only.
f. To test tubes E, F, G, and H add bromthymol blue solution.
g. Place a stopper on each of the test tubes and place the tubes
in your test tube rack.
h. Place the racks near a light source. See Illustration 1
Illustration 1. Setting Up the Test Tubes
Part B-Effects of Excess Carbon Dioxide On Plants
- Tell the class that in understanding the role of CO2 in living systems,
it seems ideal that plants require the substance that is the waste product
of animal respiration. Place this in the context of the evolution of
ecosystems, including the Earth's. We might ask, "What are the effects
of excess amounts of CO2 for respiring animals versus the effects for
photosynthetic plants?" We are all familiar with the effects of excess
buildup of CO2 in our own bodies. Just remember the last time you were
in a stuffy room full of people without adequate ventilation. (Fell
asleep?) However, there is abundant evidence that plants do better and
grow faster in an environment rich in CO2. Likewise there is some evidence
that humans can perform and recover from certain work related tasks
when exposed to an environment rich in the waste product of plants.
The problems encountered by humans in space are numerous; getting rid
of CO2 is one of the most onerous.
- Tell the students they will be doing an experiment in an attempt to
answer the key question, "What happens to plants when they are placed
in an environment saturated with CO2 for a period of time?"
- Instruct the students to set up a new experiment as follows:
a. Wash and reuse the four test tubes that you have previously set
up (ABCD), replacing the Elodea and snails as appropriate.
See Illustration 2.
b. Relabel these test tubes IJKL.
c. Add three drops of bromthymol blue to each of these test tubes.
d. Saturate the air space in each test tube with CO2 from a liter
bottle of club soda and seal with a stopper.
- Have the students record observations on the "Excess Carbon Dioxide
Experiment Observations" sheet
Allow students to share their findings with others. Students may share information
with others in many ways, including:
- Poster sessions
- Video recordings of their investigations
- Electronic presentations of their work using computer software packages
such as PowerPoint, Astound, and More
- In-class paper presentations
- Journal entries
- Electronic logs - constructed with computer applications such as HyperStudio,
The Digital Chisel, and Gray Slate
- Construct a letter to a friend reporting on what you have learned
about closed environments
More Activity Ideas
The splint test is traditionally a test for the presence of oxygen. To do
this test, light a splint, and allow it to flame for a few moments. Then
blow out the flame, remove the stopper, and plunge the glowing ember of
the splint into the air space of the tube. If the splint rekindles this
is an indicator of the presence of oxygen. Choose one or two tubes to test.
Which did you choose? Why?
Another splint test can be for the presence of CO2. In this case you
will plunge lighted splint into the air space of the test tube. What should
happen? Choose one or two tubes to test. Which did you choose? Why?
Background for Teachers
As Earthlings, regardless of the efforts we take and the costs we assume,
it's impossible to replicate on Earth exactly the conditions found in space.
Students can simulate the kinds of problems living systems encounter in
the space environment and reproduce some aspects of that environment in
In this activity, we are attempting to replicate a closed system such
as that found in a spacecraft or habitat. For life in space, provisions
must be made for food supplies, oxygen, gravity, energy, and the disposal
(or reclamation) of CO2 and waste for both humans and plants. By placing
snails in a closed system with certain plants, we can take a look at the
reactions necessary for the survival of living things.
We can start this experiment with the study of photosynthesis and respiration-both
plants and animals are dependent upon this reaction. On current missions,
we do not grow plants in spacecraft in order that astronauts may breathe
the oxygen-O2 is supplied artificially. The same is true with all other
living system needs; such as waste and CO2 removal, and the provision
of O2 and energy (food and light)-all are artificially supplied. In the
future, we would like to create self-supporting systems so that astronauts
living in space will have a renewable source of oxygen gas-thus the emphasis
in growing plants in space.
As can be observed in the above diagram, photosynthesis and respiration
have the same overall equation, though they proceed in the opposite direction.
It is possible to measure several of these reactants and make observations
on this closed system.
Organisms interact with many substances in nature. One such substance,
carbon dioxide, is exchanged between organisms and their environments
during the process of photosynthesis and respiration. This investigation
uses an indicator, bromthymol blue, which turns yellow when carbon dioxide
is added to a solution. Carbon dioxide and water form a weak carbonic
acid solution that is indicated by color change in the 6.0 - 7.6 pH range.
- Respiration - the process in which living things use food and oxygen
to create energy, water and carbon dioxide
- Photosynthesis - the process in which plants combine carbon dioxide,
water and sunlight to produce food (sugars), oxygen, and water
- Oxygen - element 16 in the periodic table; essential for respiration
- Carbon dioxide - a compound that has molecules consisting of one atom
of carbon bound to two atoms of oxygen
- Carbon - element in the periodic table; essential for "carbon-based
lifeforms" like ourselves
- Interdependence - a state of depending on one another
- Reactants - the chemicals that combine together in a chemical reaction
- Indicator - a chemical which changes property (such as color) in the
presence of certain other chemicals
- Recording data
- Analyzing data
- Reporting findings
Keywords: Cardiovascular, Respiration, Photosynthesis