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Water Cycle
The
atoms and molecules on the Earth cycle among the living and
nonliving components of the
biosphere. Some of the water molecules which are used in
photosynthesis are returned to the environment.
The change of water from the liquid to the gas state is called
evaporation, while the water lost to the atmosphere by the
activities of plants is referred to as transpiration
water loss. This water vapor eventually condenses
to form clouds, and is returned to the earth as
precipitation. This process is called the water
cycle. The processes of cell respiration and
excretion also releases some water to the environment as well.
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The Water Cycle |
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Carbon-Oxygen Cycle
Carbon
dioxide molecules are used in the process of photosynthesis to
form energy-rich organic sugar compounds.
These carbon dioxide molecules are returned to the environment
by the process of cell respiration, when the energy from these
compounds is eventually released by cells. Some carbon is also
returned to the environment by the decomposition of dead
organisms.
Oxygen is required by
many living things to release the energy in their food in the
process of aerobic cellular respiration. Oxygen is
released to the environment as a waste product of the process
of photosynthesis.
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The Carbon-Oxygen
Cycle |
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Other compounds, such
as nitrogen, are cycled in the environment when organisms
synthesize proteins from simpler compounds and then return
these nitrogen compounds to the environment when they die and
decompose.
Role of
Decomposers
The
number of organisms any environment can support is the carrying
capacity of the environment. Carrying
capacity is limited by the available energy, water,
oxygen, and minerals, and by the ability of ecosystems
to recycle the remains of dead organisms through the
activities of decomposers such as bacteria and
fungi.
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