Consider the following jumbled food chain If the energy content of the frog is x kJ, the energy available to the primary consumer…

Question

Consider the following jumbled food chain:

Grasshopper, Grass, Hawk, Frog, Snake

If the energy content of the frog is x kJ, the energy available to the primary consumer is

1. A. 10x kJ (Correct answer)
2. B. x kJ
3. C. x/10 kJ
4. D. x/100 kJ

Correct Answer

Option A — 10x kJ

Detailed Solution & Explanation

The correct answer is 10x kJ.

Key Points

• Step 1 — arrange the food chain correctly. The jumbled organisms form:
  • $\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \rightarrow \text{Hawk}$
• Step 2 — identify the trophic levels.
  • Grass — producer (1st trophic level)
  • Grasshopper — primary consumer (2nd trophic level)
  • Frog — secondary consumer (3rd trophic level)
  • Snake — tertiary consumer (4th trophic level)
  • Hawk — quaternary consumer (5th trophic level)
• Step 3 — apply Lindeman's 10% law. Only about 10% of energy passes from one trophic level to the next, so moving down a level multiplies the energy by 10.
• The frog (3rd level) holds $x$ kJ, and the grasshopper sits one level below it, so:
  • $\text{Energy at grasshopper} = 10 \times x = \mathbf{10x \text{ kJ}}$

Additional Information

• Lindeman's 10% law (1942): at each transfer, roughly 90% of energy is lost as heat during respiration, in undigested matter, and through excretion. Only about a tenth is stored as biomass available to the next level.
• Consequences of the law:
  • Food chains rarely exceed four or five trophic levels — too little energy remains beyond that.
  • The pyramid of energy is always upright, in every ecosystem without exception.
  • Eating at a lower trophic level supports far more people from the same land, which is the ecological argument behind vegetarian diets.
• Pyramids that can be inverted: the pyramid of numbers (a single tree supporting many insects) and the pyramid of biomass in aquatic ecosystems (small phytoplankton biomass supporting larger zooplankton biomass at any instant). The pyramid of energy never inverts.
• Common error: reading "primary consumer" as the frog. The primary consumer is always the herbivore — here the grasshopper, which eats the grass.