Lab 7 Identifying Limiting Nutrient - Sayre School

Lab 7: The Ecosystem Drawing
Carbon enters the living world through the action of autotrophs (plants and algae) that use
the sun’s energy to convert carbon dioxide (CO 2
) into organic sugar. Animals eat plants to
get the energy rich sugar, and perform cellular respiration to convert the sugar into usuable
energy. Carbon returns to the atmosphere by respiration, burning fossil fuels, and decay.
The uptake and return of CO 2
are not currently in balance. The carbon
dioxide content of the atmosphere is gradually and steadily increasing.
The graph shows the CO 2
concentration at a summit in Hawaii from 1958
through 1999. The seasonal fluctuation is caused by the increased uptake
of CO 2
by plants in the summer. Samples of air trapped over the centuries
in the glacial ice of Greenland show no change in CO 2
content until 300
years ago.
• Since 1958 concentrations have risen over 20%. This increase is caused by human activities:
burning fossil fuels (coal, oil, natural gas) which returns to the atmosphere carbon that has
been locked within the earth for millions of years.
• clearing and burning of forests, especially in the tropics. In recent decades, large areas of
the Amazon rain forest have been cleared for agriculture and cattle grazing.
Despite CO 2
sinks (ocean, desert sand, plants), the concentration of atmospheric CO 2
continues
to rise. Carbon dioxide is transparent to light but rather opaque to heat rays. Therefore, CO 2
in
the atmosphere retards the radiation of heat from the earth back into space - the “greenhouse
effect”. This greenhouse effect is causing a change in the world’s climate.
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glossary 7.4