Botany · Ch 7 — Ecosystem
Energy Flow
Energy Flow
Energy flow is the transfer of energy between trophic levels in an ecosystem, and it is the single most important function an ecosystem performs. Part of the solar energy a producer captures is passed on to consumers and then to decomposers, one trophic level at a time, while a portion is lost as heat at every single transfer — and crucially, this flow only ever moves in one direction, from producer toward the higher trophic levels, never in reverse. Two laws of thermodynamics govern how this storage and loss plays out. The first law states that energy can be transformed from one form into another but is never created or destroyed, so the total energy in the universe stays constant — photosynthesis is the textbook example, where light energy is simply converted into the chemical energy stored in starch, with nothing gained or lost overall. The second law states that every energy transformation reduces the free (usable) energy of the system and is never 100% efficient — as food energy passes from one organism to the next, only part of it is retained in living tissue, while a large share is dissipated as heat through respiration, and this loss is irreversible. This second law is captured quantitatively by the ten percent law, proposed by Lindeman in 1942: at every trophic transfer, only about 10% of the energy is stored by the receiving level, while the remaining 90% is lost to respiration, decomposition and heat. Concretely, of 1000 joules of solar energy trapped by producers, only about 100 joules is stored as chemical energy; herbivores feeding on t …
What this figure shows. A linear flow diagram running Sun → Plants → Herbivores → Carnivores → Decomposers, with a 'Heat' box branching off the main line after each of the three transfer arrows (Plants→Herbivores, Herbivores→Carnivores, Carnivores→Decomposers), visually showing that some energy escapes as heat at every single trophic transfer while the surviving energy keeps moving forward in one direction only, never l …
What this figure shows. A stepped energy-flow diagram starting at Sunlight (1000 Joules) entering Producers, which store 100 Joules (losing 900 Joules as heat); Producers pass energy to Primary consumers, which store only 10 Joules (losing 90 Joules); Primary consumers pass energy to Secondary consumers, which store only 1 Joule (losing 9 Joules); and Secondary consumers pass energy to Tertiary consumers, which store only 0.1 Joule (losing 0.9 Joule). Each transfer arrow is paired with its own 'Energy lost' label, visually demonstrating that only about one-tenth of the energy at any leve …