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Module: Cardiovascular
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| A & E | One stalk of Elodea |
| C & G | One snail-one Elodea |
| B & F | One water snail |
| D & H | Nothing |
1. 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.
2. 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?"
3. 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.
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.
See Illustration 2.
4. Have the students record observations on the "Excess Carbon Dioxide Experiment Observations" sheet
Illustration 2
Allow students to share their findings with others. Students may share
information with others in many ways, including:
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?
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 the classroom.
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.
Skills:
Concepts:
Keywords: Cardiovascular, Respiration, Photosynthesis
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