Transfer of Energy and Matter · Paper 2 — Free Biology HL Practice Questions

In a coastal salt marsh ecosystem, the water cycle and nitrogen cycle interact closely. During a spring tide, seawater floods the marsh, depositing dissolved inorganic nitrogen (mainly $\text{NO}_3^-$ and $\text{NH}_4^+$) at a concentration of $0.8\,\text{mg L}^{-1}$. The total volume of seawater flooding the marsh is $5000\,\text{m}^3$. The marsh plants, primarily Spartina alterniflora, take up this nitrogen for growth. After the tide recedes, evaporation and plant transpiration remove water from the marsh soil.

A coastal marine ecosystem contains the following organisms: - Phytoplankton (primary producers) - Zooplankton and mussels (primary consumers) - Small fish and crabs (secondary consumers; crabs eat mussels and zooplankton; small fish eat zooplankton) - Seabirds and large fish (tertiary consumers; both eat small fish and crabs) The total energy stored in phytoplankton biomass is $50{,}000\,\text{kJ m}^{-2}$. Ecological efficiencies are: phytoplankton → primary consumers $= 10\%$; primary consumers → secondary consumers $= 15\%$; secondary consumers → tertiary consumers $= 8\%$. Assume primary consumers collectively consume all available phytoplankton energy.