Name _________________________________
Self-sustaining Aquarium
Period _____ Date ____________ Seat ____
Randy and Rhonda have a large glass aquarium near a large window in their living room. Upon
closer inspection, a visiting friend noticed the aquarium is completely sealed off so that only
sun light can enter—it is a closed system. Ronda informed her friend that although the
aquarium has been sealed for over a year, it is self-sustaining. The aquarium’s ecosystem
consisted of small fairy shrimp, protozoa, bacteria, algae, and aquatic plants. The food web
below shows how energy flows in the closed aquarium ecosystem.
Euglena
(a protozoan)
Fairy shrimp
Algae
Aquatic plant
Paramecium
(a protozoan)
Organic
matter from
aquarium
organisms
Bacteria
Drawings are not to scale.
a) Describe how the organisms inside the sealed aquarium can survive when no outside
matter is able to enter or leave.
In your description, be sure to:


Describe how algae provide energy and recycle matter to the shrimp in the
closed system. Use the term photosynthesis in your description.
Describe how fairy shrimp recycle matter back to the plants in the closed system.
Use the term cellular respiration in your description.
You may use words, chemical formulas, and/or labeled diagrams in your answer.
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Self-sustaining Aquarium
How does algae provide energy and recycle matter to the shrimp?
How does shrimp recycle matter back to the algae?
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Self-sustaining Aquarium
Example Responses
How does algae provide energy and recycle matter to the shrimp?
Sunlight entering the aquarium penetrates the chloroplasts within the cytoplasm
of algae cells. Carbon dioxide and water also enter the algae cells. In the
chloroplast, the pigment chlorophyll absorbs this light energy (mainly the blue
and red spectrums) and converts it into chemical energy. Water molecules are
split and oxygen gas is produced during this process. Also inside the chloroplast,
carbon dioxide is used to make sugar molecules. The energy absorbed from
sunlight is stored in the bonds of the sugar molecules. This process that coverts
light energy into chemical energy is called photosynthesis. Excess sugars made
by algae are stored as the starch in starch granules. Excess oxygen is released
outside the cell and used by other organisms in the aquarium, such as shrimp.
The shrimp obtains energy by consuming algae. The starch stored in algae is
then used by the shrimp as a source of energy.
The photosynthetic reaction is 6CO2 + 6H2O
sunlight
6O2 + C6H12O6
How does shrimp recycle matter back to the algae?
When shrimp consume algae, starches stored in the algae, along with other large
molecules, like proteins, lipids, and nucleic acids, are then used by the shrimp as a
sources of energy. Enzymes in the digestive tract of the shrimp break down the
larger molecules into smaller molecules. These smaller molecules, like the glucose
that comes from starch, enter the body cells of the shrimp. Enzymes within the
cells then split the glucose molecule into two, 3-carbon molecules (pyruvates).
These 3-carbon molecules enter the mitochondria along with oxygen. Some of
this oxygen comes from the photosynthetic processes in algae. In the
mitochondria, the 3-carbon molecules are converted into high-energy molecules
called ATP. One glucose molecule will produce about 38 ATP. ATP is used to
power the activities within the cell. As ATP is made, carbon dioxide and water are
also produced. Carbon dioxide and water leave the shrimp, some of which will be
taken in by algae. This process of converting glucose into ATP is called cellular
respiration. The cellular respiration reaction is
C6H12O6 + 6O2
6CO2 + 6H2O + energy (38 ATP)
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