multiple choice 20 points
in the carbon cycle, which process takes carbon dioxide from the atmosphere and converts it into organic compounds?
respiration
decomposition
photosynthesis
combustion

multiple choice 20 points
forests are considered a carbon sink because trees store large amounts of carbon. if a large-scale event, such as a major wildfire, occurs, how does this specifically disrupt the steps of the carbon cycle and affect the atmosphere?
it accelerates decomposition, which removes carbon from the atmosphere, causing a cooling effect.
it increases photosynthesis, which adds more oxygen to the atmosphere, but has no effect on carbon.
it leads to increased respiration by animals, which speeds up the release of stored carbon from the forest floor.
it releases stored carbon into the atmosphere through combustion and reduces the rate of photosynthesis, leading to an overall increase in atmospheric co₂.

multiple choice 20 points
the phosphorus cycle is distinct from the nitrogen and carbon cycles. based on your understanding of the steps in these cycles, what is a key difference in how phosphorus moves through the ecosystem compared to nitrogen and carbon?
the phosphorus cycle requires a direct step called nitrogen fixation to make it available to plants.
the phosphorus cycle includes a significant atmospheric gas phase, unlike the nitrogen and carbon cycles.
the phosphorus cycle primarily moves from rock through the food web to sediment, lacking significant time in the atmosphere
the phosphorus cycle is a faster cycle because it relies on biological processes like photosynthesis and respiration.

multiple choice 20 points
the oxygen cycle is closely linked to the carbon cycle. based on the steps of these two cycles, what would be the most likely consequence of a massive decline in a planets producer population (e.g., plants and algae)?
atmospheric oxygen would decrease due to a reduction in photosynthesis, and atmospheric carbon dioxide would increase as respiration from other organisms continues.
the concentration of atmospheric oxygen would increase due to a decrease in respiration from the producer population.
both atmospheric carbon dioxide and oxygen levels would increase because there would be fewer organisms to consume them.
atmospheric oxygen would increase as animals no longer have a food source, and atmospheric carbon dioxide would decrease as a result.

multiple choice 20 points
a global climate model predicts that a significant increase in average temperatures will lead to more frequent and intense droughts. evaluate this prediction in the context of both the hydrologic (water) and carbon cycles and construct a logical argument for how a prolonged drought would create a positive feedback loop that intensifies climate change.
droughts kill animals, and the decomposition of their remains releases a significant amount of carbon dioxide into the atmosphere, which then causes temperatures to rise further
a prolonged drought decreases precipitation and runoff, causing less water to be available for plant growth. this reduces the rate of photosynthesis, which in turn reduces the amount of carbon dioxide removed from the atmosphere, further contributing to the warming that caused the drought in the first place.
the lack of water from a drought decreases the amount of nitrogen available in the soil, which leads to less primary productivity and a decrease in the atmospheric oxygen produced by plants.
drought conditions reduce evaporation, which leads to less cloud cover. this allows more solar radiation to reach the earths surface, causing temperatures to rise and intensifying the drought

Question

multiple choice 20 points
in the carbon cycle, which process takes carbon dioxide from the atmosphere and converts it into organic compounds?
respiration
decomposition
photosynthesis
combustion

multiple choice 20 points
forests are considered a carbon sink because trees store large amounts of carbon. if a large-scale event, such as a major wildfire, occurs, how does this specifically disrupt the steps of the carbon cycle and affect the atmosphere?
it accelerates decomposition, which removes carbon from the atmosphere, causing a cooling effect.
it increases photosynthesis, which adds more oxygen to the atmosphere, but has no effect on carbon.
it leads to increased respiration by animals, which speeds up the release of stored carbon from the forest floor.
it releases stored carbon into the atmosphere through combustion and reduces the rate of photosynthesis, leading to an overall increase in atmospheric co₂.

multiple choice 20 points
the phosphorus cycle is distinct from the nitrogen and carbon cycles. based on your understanding of the steps in these cycles, what is a key difference in how phosphorus moves through the ecosystem compared to nitrogen and carbon?
the phosphorus cycle requires a direct step called nitrogen fixation to make it available to plants.
the phosphorus cycle includes a significant atmospheric gas phase, unlike the nitrogen and carbon cycles.
the phosphorus cycle primarily moves from rock through the food web to sediment, lacking significant time in the atmosphere
the phosphorus cycle is a faster cycle because it relies on biological processes like photosynthesis and respiration.

multiple choice 20 points
the oxygen cycle is closely linked to the carbon cycle. based on the steps of these two cycles, what would be the most likely consequence of a massive decline in a planets producer population (e.g., plants and algae)?
atmospheric oxygen would decrease due to a reduction in photosynthesis, and atmospheric carbon dioxide would increase as respiration from other organisms continues.
the concentration of atmospheric oxygen would increase due to a decrease in respiration from the producer population.
both atmospheric carbon dioxide and oxygen levels would increase because there would be fewer organisms to consume them.
atmospheric oxygen would increase as animals no longer have a food source, and atmospheric carbon dioxide would decrease as a result.

multiple choice 20 points
a global climate model predicts that a significant increase in average temperatures will lead to more frequent and intense droughts. evaluate this prediction in the context of both the hydrologic (water) and carbon cycles and construct a logical argument for how a prolonged drought would create a positive feedback loop that intensifies climate change.
droughts kill animals, and the decomposition of their remains releases a significant amount of carbon dioxide into the atmosphere, which then causes temperatures to rise further
a prolonged drought decreases precipitation and runoff, causing less water to be available for plant growth. this reduces the rate of photosynthesis, which in turn reduces the amount of carbon dioxide removed from the atmosphere, further contributing to the warming that caused the drought in the first place.
the lack of water from a drought decreases the amount of nitrogen available in the soil, which leads to less primary productivity and a decrease in the atmospheric oxygen produced by plants.
drought conditions reduce evaporation, which leads to less cloud cover. this allows more solar radiation to reach the earths surface, causing temperatures to rise and intensifying the drought

Accepted Answer

# Brief Explanations:
1. **Photosynthesis** is the process where plants take in $CO_2$ from the atmosphere and convert it into organic compounds (like glucose) using sunlight. Respiration releases $CO_2$, decomposition breaks down organic matter (releasing $CO_2$ in some cases), and combustion (burning) also releases $CO_2$.
2. Forests store carbon. A wildfire (combustion) releases stored carbon ($CO_2$) into the atmosphere. Also,  if trees (which carry out photosynthesis - a process that takes in $CO_2$) are burned, the rate of photosynthesis (which removes $CO_2$ from the atmosphere) is reduced. So, atmospheric $CO_2$ increases.
3. The phosphorus cycle mainly starts with rocks (phosphorus in rocks). Through weathering, it gets into the soil, then is taken up by plants, moves through the food web, and finally to sediments. Unlike nitrogen (which has nitrogen - fixation step and a large atmospheric gas phase as $N_2$) and carbon (which has a significant atmospheric gas phase as $CO_2$), phosphorus has little time in the atmosphere.
4. Producers (plants, algae) carry out photosynthesis. Photosynthesis produces $O_2$ (from $H_2O$) and takes in $CO_2$. If producer population declines,  less $O_2$ is produced (so atmospheric $O_2$ decreases) and less $CO_2$ is removed (while other organisms still respire - releasing $CO_2$, so atmospheric $CO_2$ increases).
5. In a drought, less water is available for plant growth. Plants carry out less photosynthesis (since water is a reactant in photosynthesis - $6CO_2 + 6H_2O
ightarrow C_6H_{12}O_6+6O_2$). Less photosynthesis means less $CO_2$ is removed from the atmosphere. The initial warming (which caused the drought) is further enhanced as $CO_2$ (a greenhouse gas) accumulates, creating a positive - feedback loop.

# Answer:
1. C. Photosynthesis
2. D. It releases stored carbon into the atmosphere through combustion and reduces the rate of photosynthesis, leading to an overall increase in atmospheric $CO_2$.
3. C. The phosphorus cycle primarily moves from rock through the food web to sediment, lacking significant time in the atmosphere
4. A. Atmospheric oxygen would decrease due to a reduction in photosynthesis, and atmospheric carbon dioxide would increase as respiration from other organisms continues.
5. B. A prolonged drought decreases precipitation and runoff, causing less water to be available for plant growth. This reduces the rate of photosynthesis, which in turn reduces the amount of carbon dioxide removed from the atmosphere, further contributing to the warming that caused the drought in the first place.

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