Nutrient cycles: carbon, nitrogen, and phosphorus

What you’ll practice

Move confidently between the carbon, nitrogen, and phosphorus cycles by identifying reservoirs, fluxes, and the organisms driving each step. You’ll also connect real-world issues - like eutrophication and climate change - to the underlying biogeochemistry.

Every question uses 4 options and there’s no timer, so you can slow down to reason through pathways, units, and cause-and-effect.

Common pitfalls to avoid

Many learners mix up where each cycle has a major atmospheric component (carbon and nitrogen) versus where it does not (phosphorus). Another frequent slip is confusing similar processes - like nitrification vs. denitrification - or treating decomposition as separate from nutrient cycling.

• Mixing nitrification (NH4+ → NO3−) with denitrification (NO3− → N2)
• Forgetting phosphorus lacks a significant gaseous phase in most models
• Confusing assimilation by plants with mineralization by decomposers
• Overlooking human inputs (fertilizer, fossil fuels) when explaining flux changes
• Treating “reservoir” and “flux” as interchangeable terms

Difficulty and question settings

Difficulty is balanced across the set: you’ll see straightforward definitions, then progressively more applied questions using scenarios (e.g., runoff, algal blooms, soil oxygen levels). Choose your preferred question count and difficulty before starting - short runs are great for quick review, while longer sessions build endurance across all subtopics.