Question

During energy transfer between trophic levels, what percentage of potential energy is dissipated as heat?

• A. A) 10-20%
• B. B) 20-30%
• C. C) 50-70%
• D. D) 80-90%

Answer 1

Answer:

D. D) 80-90%

Energy Transfer Between Trophic Levels

• Energy flows through an ecosystem from lower to higher trophic levels, beginning with producers.
• This energy transfer is not 100% efficient due to the Second Law of Thermodynamics, which states that during energy transformation, some energy is always lost as heat.

The 10% Law (Lindeman's Law)

• According to the 10% Law of Energy Transfer, only approximately 10% of the energy from one trophic level is assimilated and transferred to the next higher trophic level.
• The vast majority, about 80-90% of the potential energy, is lost or dissipated as heat during this transfer.
• This fundamental ecological principle was proposed by Raymond Lindeman in 1942, based on studies of aquatic ecosystems.

Reasons for 80-90% Energy Dissipation as Heat

• Metabolic Processes: A significant portion of the energy consumed by an organism is used for its own life-sustaining activities such as respiration, digestion, movement, growth, and reproduction. All these metabolic activities generate and release heat into the environment.
• Respiration: Cellular respiration, the process by which organisms convert organic molecules into ATP (usable energy), is a major contributor to heat loss. A large fraction of the chemical energy stored in food is released as heat during respiration.
• Incomplete Consumption: Not all parts of an organism at one trophic level are consumed by the next. For example, bones, fur, wood, or roots might not be eaten, or are not digestible, meaning the energy contained within them is not transferred.
• Waste Products: Energy is also lost through unassimilated food material and excretory waste products (e.g., feces, urine) that are egested from the organism's body.

Implications for Ecosystems and Competitive Exams

• Due to this substantial energy loss at each step, food chains are generally limited to 3 to 5 trophic levels. Longer food chains are unsustainable as there wouldn't be enough energy to support the higher levels.
• This energy loss explains why the biomass and number of individuals generally decrease at successively higher trophic levels, leading to the characteristic pyramid shape of ecological energy pyramids.
• The pyramid of energy is always upright in a healthy ecosystem, as energy always decreases at each successive trophic level.
• Producers (e.g., plants) form the base with the largest energy content, while apex predators occupy the top with the least energy.