Which term describes the total energy expenditure of an organism over time?

• A. Littoral Zone
• B. Metabolic Rate
• C. Nitrifying Bacteria
• D. Nitrogen Cycle

Answer: (B)

The concept being tested is how energy use by an organism is quantified over time. Metabolic rate is the energy expenditure per unit time, so it describes how quickly an organism is using energy. If you want the total energy used over a period, you can multiply this rate by the time elapsed (and account for variations due to activity, digestion, and temperature). The other terms don’t pertain to energy use: the littoral zone is a coastal habitat, nitrifying bacteria are organisms involved in the nitrogen cycle, and the nitrogen cycle itself tracks nitrogen transformations in ecosystems.