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Difficulty: MediumEnergy Flow, Food Chains, and Ecological Pyramids

In a tropical savanna ecosystem, energy fixed by photosynthetic plants is transferred through a sequential feeding hierarchy. Based on the thermodynamic principles governing energy loss across trophic levels, arrange the following organisms in sequence from HIGHEST available energy per unit area to LOWEST available energy per unit area.

  1. 1Elephant grass (*Pennisetum purpureum*)
  2. 2African grasshopper (*Zonocerus elegans*)
  3. 3Agama lizard (*Agama agama*)
  4. 4Martial eagle (*Polemaetus bellicosus*)

Answer

The correct order from highest to lowest available energy per unit area is: Elephant grass (*Pennisetum purpureum*) → African grasshopper (*Zonocerus elegans*) → Agama lizard (*Agama agama*) → Martial eagle (*Polemaetus bellicosus*).
According to ecological energy dynamics, available energy decreases exponentially from lower to higher trophic levels. Primary producers (Elephant grass) capture sunlight and hold the highest energy pool. Primary consumers (grasshoppers) access ~10% of this energy, secondary consumers (Agama lizards) access ~1%, and tertiary consumers (Martial eagles) retain the smallest proportion (~0.1%). Arranging from highest to lowest energy yields: Elephant grass → African grasshopper → Agama lizard → Martial eagle.

Step-by-Step Solution

1
Assign each organism to its corresponding trophic level within the savanna food chain.
Elephant grass is a primary producer (Trophic Level 1), the African grasshopper is a primary consumer (Trophic Level 2), the Agama lizard is a secondary consumer (Trophic Level 3), and the Martial eagle is a tertiary consumer (Trophic Level 4).
Energy flows unidirectional from producers through herbivores to successive carnivorous consumers.
2
Apply the 10% law of energy transfer across trophic levels.
Only about 10% of energy is passed to the next level, while roughly 90% is dissipated as metabolic heat, respiration, and unconsumed organic matter.
The Second Law of Thermodynamics dictates that energy transformations are inefficient, causing progressive reduction in stored energy at higher trophic levels.
3
Rank the organisms in order of decreasing available energy.
Trophic Level 1 (Elephant grass) > Trophic Level 2 (Grasshopper) > Trophic Level 3 (Agama lizard) > Trophic Level 4 (Martial eagle).
The lowest trophic level holds the greatest energy content, whereas apex predators at the top of the pyramid possess the least energy per unit area.

Key Concept

Trophic Level Energy Transfer and Progressive Energy Loss
Estimated Time:1m 0s
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Topics

Energy Flow, Food Chains, and Ecological Pyramids

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