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About This Drill
AP Biology — Unit 8 — Biogeochemical Cycles — Drill 35 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
Practice interpreting carbon and nitrogen flux data in this AP Biology drill on biogeochemical cycles. Analyze ecosystem nutrient movement before and after a disturbance, apply carbon cycle calculations, and evaluate claims about nitrogen cycling processes.
Passage
Researchers studying nutrient cycling in a temperate forest ecosystem measure carbon and nitrogen movement across ecosystem compartments over one year. The forest was undisturbed for the first six months, then subjected to a controlled burn in month seven. All values are in kilograms per hectare per year (kg/ha/yr).
| Flux Pathway | Carbon Before Burn (kg/ha/yr) | Carbon After Burn (kg/ha/yr) | Nitrogen Before Burn (kg/ha/yr) | Nitrogen After Burn (kg/ha/yr) |
|---|
| Photosynthesis (atmosphere to plant) | 4,200 | 1,100 | -- | -- |
| Plant respiration (plant to atmosphere) | 1,800 | 420 | -- | -- |
| Decomposer respiration (soil to atmosphere) | 940 | 210 | -- | -- |
| Nitrification (NH4+ to NO3-) | -- | -- | 180 | 44 |
| Denitrification (NO3- to N2) | -- | -- | 38 | 91 |
| Nitrogen fixation (N2 to NH4+) | -- | -- | 12 | 67 |
Questions in This Drill
- In the nitrogen cycle, which process converts atmospheric nitrogen (N2) into a form usable by plants?
- Before the burn, what is the net carbon flux between the forest ecosystem and the atmosphere, considering only photosynthesis and total respiration (plant plus decomposer)?
- After the burn, denitrification increases from 38 to 91 kg N/ha/yr while nitrogen fixation increases from 12 to 67 kg N/ha/yr. Which explanation best accounts for both changes occurring simultaneously?
- Carbon fixed by photosynthesis can reach the soil carbon pool through multiple pathways. Which sequence correctly traces one such pathway?
- A forest ecologist argues that the controlled burn converted this ecosystem from a long-term carbon sink to a carbon source. Which combination of data from the table most directly evaluates this argument?