Energy pyramids and the 10 percent rule Knowledge-Based Download PDF

Questions

1. 1.

   In ecology, the 10 percent rule characterizes trophic efficiency across an ecological pyramid of energy. Which statement correctly describes what this efficiency measures?

   • A) The proportion of incident solar energy that primary producers convert into organic chemical bonds
   • B) The fraction of ingested food that an individual animal absorbs across its gut rather than eliminating as feces
   • C) The proportion of energy stored as biomass at one trophic level that is incorporated into biomass at the next trophic level
   • D) The ratio of energy released as metabolic heat compared to the total gross energy taken in by an organism
2. 2.

   Unlike pyramids of numbers or biomass, which can occasionally appear inverted in certain ecosystems, an ecological pyramid of energy is always upright. Which statement best explains why an energy pyramid can never be inverted?

   • A) Primary consumers reproduce at much faster rates than tertiary consumers, which balances their total caloric expenditure over time.
   • B) Each successive trophic level inevitably receives only a fraction of the energy from the level below it due to continuous energetic losses.
   • C) Decomposers immediately cycle all non-transferred energy back into the primary producers to maintain energetic equilibrium.
   • D) Top carnivores possess a significantly lower metabolic rate per unit mass than autotrophic organisms, conserving overall energy.
3. 3.

   In an ecological energy pyramid, approximately 90 percent of the energy entering any trophic level fails to pass to the subsequent level. Which statement correctly identifies the major fate of this non-transferred energy?

   • A) It is absorbed by primary producers directly from the atmosphere to drive photosynthesis.
   • B) It is converted into physical matter and stored indefinitely within non-living geological formations.
   • C) It accumulates permanently in the tissues of top predators via biomagnification.
   • D) It is dissipated into the environment as metabolic heat generated through cellular respiration.
4. 4.

   Which statement best explains why natural food chains rarely contain more than four or five trophic levels according to the principles of ecological energy pyramids?

   • A) Organisms at higher trophic levels face increased direct competition for abiotic resources such as sunlight and carbon dioxide.
   • B) The substantial loss of usable energy at each transfer leaves insufficient energy to sustain viable populations at higher trophic levels.
   • C) Top predators reproduce significantly faster than primary consumers, rapidly exhausting their prey base.
   • D) Decomposers selectively consume the majority of top predators, preventing the formation of additional feeding tiers.
5. 5.

   In a grassland ecosystem, primary producers store approximately 50,000 kJ of energy in their biomass. According to the 10 percent rule of ecological energy transfer, how much of this energy is expected to be incorporated into the biomass of secondary consumers?

   • A) 500 kJ
   • B) 5,000 kJ
   • C) 50 kJ
   • D) 45,000 kJ