Francine is developing a model of the carbon cycle, which involves the movement of carbon among various Earth systems. She begins by drawing the diagram shown below. Her friend Byron evaluates the model, and suggests that she thicken the arrow leading from fossil fuels to the atmosphere. His reasoning is that fossil fuels are being burned at a much faster rate than natural processes are restoring them. A. The model shows that their combined effects determine the amount of solid carbon compounds in the geosphere. B. The model shows that their combined effects determine the level of carbon dioxide that dissolves in the hydrosphere.
C. The model shows that they have identical effects on carbon dioxide levels in the atmosphere.
D. The model shows that they have opposite effects on carbon dioxide levels in the atmosphere.

The missing part of this incomplete question is :

How does Francine's model show the effect of photosynthesis and cellular respiration on Earth systems?

The correct answer is - option D. The model shows that they have opposite effects on carbon dioxide levels in the atmosphere.

Explanation:

Cellular respiration and photosynthesis are two major processes are involved in the carbon cycle and both have the opposite effect on carbon dioxide levels in the atmosphere.

Photosynthesis uses carbon dioxide from the atmosphere to produce glucose with the reaction with the water whereas cellular respiration produces energy and carbon dioxide that is restored in the atmosphere.

Thus, both the processes have the opposite effect on the carbon dioxide levels in the atmosphere as photosynthesis decreases and cellular respiration increases in the atmosphere.