Energy pyramids and the 10 percent rule Knowledge-Based Practice

Questions

1. 1.

   Which two factors primarily determine the total amount of energy available to apex consumers at the top of an ecological energy pyramid?

   • A) The rate of mineral weathering in bedrock and the total metabolic activity of soil decomposers
   • B) The total gross photosynthetic rate of producers and the atmospheric concentration of carbon dioxide
   • C) The physical body size of individual predators and their behavioral adaptations for capturing prey
   • D) The magnitude of net primary productivity at the base and the efficiency of energy transfer between intervening trophic levels
2. 2.

   Why can an ecological pyramid of energy never appear inverted in a natural ecosystem, unlike pyramids of biomass or numbers?

   • A) Net energy strictly decreases with each successive trophic step because roughly 90% is dissipated as non-reusable metabolic heat and waste.
   • B) The total number of individual primary producers must always exceed the number of primary consumers to maintain ecological balance.
   • C) Decomposers continuously return lost thermal energy to autotrophs, maintaining an absolute energy surplus at the base.
   • D) Apex predators require exponentially less total energy to survive than lower-level consumers due to higher physiological efficiency.
3. 3.

   Which ecological pattern is a direct consequence of the ten percent rule of energy transfer in an ecological pyramid?

   • A) The continuous recycling and reuse of energy by primary producers within the food web
   • B) The frequent inversion of energy pyramids in marine habitats during seasonal algal blooms
   • C) An exponential increase in the biomass of apex predators relative to primary consumers
   • D) The strict limitation of food chain length to rarely more than four or five trophic levels
4. 4.

   In an ecological energy pyramid, only about 10% of the energy available at one trophic level is typically incorporated into the biomass of the next trophic level. Which of the following best explains what happens to the remaining 90% of the energy?

   • A) It is recycled through biogeochemical cycles and absorbed by autotrophs to fuel further photosynthesis.
   • B) It is converted directly into potential chemical energy stored indefinitely in abiotic soil reservoirs.
   • C) It is completely destroyed during digestion, reducing the total amount of energy present in the biosphere.
   • D) It is released into the environment as metabolic heat during cellular respiration and lost in uneaten matter or waste.
5. 5.

   In a grassland ecosystem, the primary producers assimilate an estimated 40,000 kJ of net energy per unit area annually. According to the 10 percent rule of ecological efficiency, approximately how much energy is transferred to the secondary consumer trophic level?

   • A) 40,000 kJ
   • B) 4,000 kJ
   • C) 2,000 kJ
   • D) 400 kJ

Answers and step-by-step solutions appear after you finish the test.