Which of the following limits the number of trophic levels in a food chain ?

The number of trophic levels in a food chain is primarily limited by the progressive decrease in available energy at higher levels. According to the 10% rule, only about 10% of the energy from one trophic level is transferred to the next, while the remaining 90% is lost as unusable heat during metabolism, respiration, and digestion [2]. As energy moves upward, the amount of usable energy diminishes significantly [4]. Consequently, after four or five trophic levels, the remaining energy is typically insufficient to support a viable population of organisms at a higher level [1]. This thermodynamic inefficiency explains why food chains are generally short and seldom exceed five or six steps [2]. While factors like food supply and environmental conditions play roles, the fundamental constraint is the energy pyramid's structure where the 'step' eventually becomes too small to sustain another level [2].

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > z.r.r. Trophic level interaction > p. 11
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 13: Our Environment > 13.1.1 Food Chains and Webs > p. 210
3. [4] https://education.nationalgeographic.org/resource/energy-flow-and-10-percent-rule/5th-grade/