1. Photosynthesis, Respiration, and the Global Carbon CycleWithout
the process of photosynthesis, Earth would have an entirely different
atmosphere—and would probably be without life as we know it. Through
photosynthesis, plants utilize light energy from the Sun to make food.
Because it requires sunlight, photosynthesis occurs only during the day.
It also requires chlorophyll, an organic substance found in green
plants and some single-celled organisms. Photosynthesis converts solar
energy, water, and carbon dioxide into simple carbohydrates. These can
then be converted to complex carbohydrates, starches, and proteins, all
of which supply plants with the material for their own growth. Plants in
turn provide the basic nutrients for grazing and browsing animals.In
addition to photosynthesis, an exchange of gases takes place through the
leaves of plants—respiration. Respiration provides the mechanism by
which plants obtain the oxygen they need to perform their metabolic
processes, (For animals, respiration is synonymous with breathing. After
a plant dies, however, it no longer takes in CO2 from the air. Instead,
its stored carbon is oxidized and released back to the atmosphere as
CO2 as the plant decomposes. If no major changes occur in the amount and
distribution of vegetation, CO2 intake (for photosynthesis) balances
CO2 output (from respiration and decay) over the course of a year, and
the total store of atmospheric CO2 is unaffected by plant growth.There
is, however, another factor governing the CO2 balance. Under some
circumstances, dead plant material is quickly buried beneath the
surface, does not decompose, and therefore does not release its stored
carbon back into the atmosphere. Instead, over millions of years the
material is transformed into fossil fuels, such as petroleum or coal,
which we extract from the ground and burn for heat and energy, yielding
CO2 as a combustion product. In doing so, we release carbon that
otherwise would have remained underground for eons. Although we speak of
“adding” to the atmosphere, it is probably more accurate to think of
“moving” carbon back to the atmosphere. Regardless, the result is
certainly an increase in atmospheric CO2, with potentially global
consequences.Figure 1-2-1 shows these exchanges and others comprising
the global carbon cycle. The values shown are billions of metric tons (a
metric ton is a little more than a U.S. ton). Although no carbon
disappears, some branches of the cycle are obviously very long lived,
such as the return of carbon buried in rocks. In addition, the figure is
accurate only for the present time. Most importantly, the fossil fuel
branch has been growing for the past 150 years and will continue to do
so in the coming century. We should mention that the transfers shown in
the figure are the best that science can produce, yet they do not
balance—they imply a loss of 2 to 3 billion metric tons per year from
the atmosphere that is not accounted for in transfers to other
reservoirs. Evidence increasingly suggests that the balance is taken up
by the biosphere, but it is not clear where or how. As will be seen
later, this uncertainty has implications for understanding both past and
future changes in CO2.FIGURE 1-2-1 The Global Carbon Cycle. Transfers
and stores of carbon are shown in billions of metric tons (about 1.1
billion U.S. tons)....What is the largest carbon reservoir on Earth? Get solution
2. Photosynthesis, Respiration, and the Global Carbon CycleWithout the process of photosynthesis, Earth would have an entirely different atmosphere—and would probably be without life as we know it. Through photosynthesis, plants utilize light energy from the Sun to make food. Because it requires sunlight, photosynthesis occurs only during the day. It also requires chlorophyll, an organic substance found in green plants and some single-celled organisms. Photosynthesis converts solar energy, water, and carbon dioxide into simple carbohydrates. These can then be converted to complex carbohydrates, starches, and proteins, all of which supply plants with the material for their own growth. Plants in turn provide the basic nutrients for grazing and browsing animals.In addition to photosynthesis, an exchange of gases takes place through the leaves of plants—respiration. Respiration provides the mechanism by which plants obtain the oxygen they need to perform their metabolic processes, (For animals, respiration is synonymous with breathing. After a plant dies, however, it no longer takes in CO2 from the air. Instead, its stored carbon is oxidized and released back to the atmosphere as CO2 as the plant decomposes. If no major changes occur in the amount and distribution of vegetation, CO2 intake (for photosynthesis) balances CO2 output (from respiration and decay) over the course of a year, and the total store of atmospheric CO2 is unaffected by plant growth.There is, however, another factor governing the CO2 balance. Under some circumstances, dead plant material is quickly buried beneath the surface, does not decompose, and therefore does not release its stored carbon back into the atmosphere. Instead, over millions of years the material is transformed into fossil fuels, such as petroleum or coal, which we extract from the ground and burn for heat and energy, yielding CO2 as a combustion product. In doing so, we release carbon that otherwise would have remained underground for eons Although we speak of “adding” to the atmosphere, it is probably more accurate to think of “moving” carbon back to the atmosphere. Regardless, the result is certainly an increase in atmospheric CO2, with potentially global consequences.Figure 1-2-1 shows these exchanges and others comprising the global carbon cycle. The values shown are billions of metric tons (a metric ton is a little more than a U.S. ton). Although no carbon disappears, some branches of the cycle are obviously very long lived, such as the return of carbon buried in rocks. In addition, the figure is accurate only for the present time. Most importantly, the fossil fuel branch has been growing for the past 150 years and will continue to do so in the coming century. We should mention that the transfers shown in the figure are the best that science can produce, yet they do not balance—they imply a loss of 2 to 3 billion metric tons per year from the atmosphere that is not accounted for in transfers to other reservoirs. Evidence increasingly suggests that the balance is taken up by the biosphere, but it is not clear where or how. As will be seen later, this uncertainty has implications for understanding both past and future changes in CO2.FIGURE 1-2-1 The Global Carbon Cycle. Transfers and stores of carbon are shown in billions of metric tons (about 1.1 billion U.S. tons)....What process is most important in moving carbon from the surface to the atmosphere? Get solution
2. Photosynthesis, Respiration, and the Global Carbon CycleWithout the process of photosynthesis, Earth would have an entirely different atmosphere—and would probably be without life as we know it. Through photosynthesis, plants utilize light energy from the Sun to make food. Because it requires sunlight, photosynthesis occurs only during the day. It also requires chlorophyll, an organic substance found in green plants and some single-celled organisms. Photosynthesis converts solar energy, water, and carbon dioxide into simple carbohydrates. These can then be converted to complex carbohydrates, starches, and proteins, all of which supply plants with the material for their own growth. Plants in turn provide the basic nutrients for grazing and browsing animals.In addition to photosynthesis, an exchange of gases takes place through the leaves of plants—respiration. Respiration provides the mechanism by which plants obtain the oxygen they need to perform their metabolic processes, (For animals, respiration is synonymous with breathing. After a plant dies, however, it no longer takes in CO2 from the air. Instead, its stored carbon is oxidized and released back to the atmosphere as CO2 as the plant decomposes. If no major changes occur in the amount and distribution of vegetation, CO2 intake (for photosynthesis) balances CO2 output (from respiration and decay) over the course of a year, and the total store of atmospheric CO2 is unaffected by plant growth.There is, however, another factor governing the CO2 balance. Under some circumstances, dead plant material is quickly buried beneath the surface, does not decompose, and therefore does not release its stored carbon back into the atmosphere. Instead, over millions of years the material is transformed into fossil fuels, such as petroleum or coal, which we extract from the ground and burn for heat and energy, yielding CO2 as a combustion product. In doing so, we release carbon that otherwise would have remained underground for eons Although we speak of “adding” to the atmosphere, it is probably more accurate to think of “moving” carbon back to the atmosphere. Regardless, the result is certainly an increase in atmospheric CO2, with potentially global consequences.Figure 1-2-1 shows these exchanges and others comprising the global carbon cycle. The values shown are billions of metric tons (a metric ton is a little more than a U.S. ton). Although no carbon disappears, some branches of the cycle are obviously very long lived, such as the return of carbon buried in rocks. In addition, the figure is accurate only for the present time. Most importantly, the fossil fuel branch has been growing for the past 150 years and will continue to do so in the coming century. We should mention that the transfers shown in the figure are the best that science can produce, yet they do not balance—they imply a loss of 2 to 3 billion metric tons per year from the atmosphere that is not accounted for in transfers to other reservoirs. Evidence increasingly suggests that the balance is taken up by the biosphere, but it is not clear where or how. As will be seen later, this uncertainty has implications for understanding both past and future changes in CO2.FIGURE 1-2-1 The Global Carbon Cycle. Transfers and stores of carbon are shown in billions of metric tons (about 1.1 billion U.S. tons)....What process is most important in moving carbon from the surface to the atmosphere? Get solution
