Pre AP Biology -CELLS 6.1 Photosynthesis- FRQ Exam Style Questions -New Syllabus

(a)
The biological process is cellular respiration. In this process, organisms (including plants, animals, and fungi) break down glucose and other organic molecules in the presence of oxygen to release energy (ATP). A byproduct of this reaction is carbon dioxide ($CO_2$), which is released back into the atmosphere.
The general equation for cellular respiration is:$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}$$

(b)
The lowest carbon dioxide concentrations are found closest to the forest because the trees are actively performing photosynthesis. During the middle of the day, plants absorb atmospheric carbon dioxide through their stomata to synthesize glucose. This high rate of uptake creates a localized reduction in $CO_2$ levels near the dense vegetation.
The equation for photosynthesis is:$$6CO_2 + 6H_2O + \text{Light Energy} \rightarrow C_6H_{12}O_6 + 6O_2$$Here, carbon dioxide ($CO_2$) and water ($H_2O$) are the reactants that are consumed to produce glucose ($C_6H_{12}O_6$) and oxygen ($O_2$).

(c)
Nighttime carbon dioxide concentrations near the forest should be higher compared to midday concentrations. This difference is due to the interaction of two biological processes:

• Photosynthesis: This process requires light energy. Therefore, at night, photosynthesis stops, meaning the trees stop absorbing $CO_2$ from the atmosphere.
• Cellular Respiration: This process occurs continuously, day and night. The trees, animals, and soil organisms continue to break down glucose and release $CO_2$ into the air.

Since $CO_2$ is being added (via respiration) but not removed (via photosynthesis) during the night, the overall concentration accumulates and rises.