Q.In a grassland ecosystem, the producers fix 20,000 kcal/m^2/yr of energy. Assuming the 10 per cent law of energy transfer applies at every step, calculate the energy available to

Applying the 10% law twice (producers→herbivores→carnivores) from 5000 J gives 50 J reaching secondary consumers.

According to Lindeman's ten percent law, only about 10% of the energy present at one trophic level is transferred to and becomes incorporated as biomass at the next trophic level; the rest is lost mainly as heat through respiration and other metabolic processes. Starting with 5000 Joules of light energy captured by the producers: primary consumers (herbivores) would receive about 10% of this, i.e., 5000 × 10/100 = 500 Joules. Secondary consumers (carnivores, i.e., the level asked about) would then receive about 10% of the herbivores' energy, i.e., 500 × 10/100 = 50 Joules. So 50 Joules of energy would ultimately be available to/transferred to the carnivores (secondary consumers).

Applying the 10% law twice: 1000 J → 100 J → 10 J reaches the lion.

Energy flow through a food chain is unidirectional and follows Lindeman's 10% law: at each trophic transfer, only about 10% of the energy received is passed on to the next level, the rest being lost as heat during respiration, used in metabolism, or left undigested. Starting with 1000 J captured by the producers (plants), the herbivore (deer) receives about 10% of this, i.e. 100 J. The carnivore (lion), one level further, receives about 10% of 100 J, i.e. 10 J. This progressive energy loss is why food chains rarely extend beyond 4–5 trophic levels and why the energy pyramid is always upright.

Green plants photosynthetically use only about 2-10% of the total solar energy that falls on them.

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Sunlight reaching a plant canopy is far from fully converted into chemical energy through photosynthesis. Much of the incident solar radiation is: reflected off leaf surfaces, transmitted straight through the leaf without being absorbed, absorbed but outside the photosynthetically active radiation (PAR) waveband (400-700 nm), or absorbed as PAR but lost as heat rather than being fixed. As a result, in most natural ecosystems, only a small fraction of the total incoming solar energy -- about 2-10% -- is actually captured and fixed by green plants during photosynthesis and made available as chemical (food) energy to enter the food chain. This limited efficiency of primary production is one reason why energy transfer through trophic levels in an ecosystem is comparatively small and why food chains rarely extend beyond four or five trophic levels.

Green plants use only about 2-10% of incident solar energy for photosynthesis.

Only a portion of the sunlight that falls on a leaf is of a wavelength and intensity that chlorophyll a, chlorophyll b and the accessory pigments can actually absorb and channel into the light reactions of photosynthesis; much of the incident radiation is reflected off the leaf surface, transmitted straight through, or absorbed and simply dissipated as heat rather than being converted into chemical energy. Because of these physical and biochemical losses at every stage -- reflection, transmission, non-photosynthetic absorption and the inherent inefficiency of converting light energy into ATP and NADPH -- ecologists estimate that green plants effectively use only about 2 to 10% of the solar energy incident upon them for photosynthesis, and this modest efficiency is what ultimately caps the Gross Primary Productivity of an ecosystem and the amount of energy available to all subsequent trophic levels.

Green plants convert only about 2-10% of incident solar radiation into chemical energy via photosynthesis.

A leaf receives the full spectrum of incident sunlight, but only the visible, Photosynthetically Active Radiation (PAR) band can be absorbed by chlorophyll and accessory pigments, and even within PAR much of the energy is lost to reflection, transmission through the leaf, and non-photochemical heat dissipation. As a result, under natural field conditions the overall efficiency with which green plants convert incident solar energy into the chemical energy of photosynthate is only about 2-10%, and this trapped fraction is what constitutes the gross primary productivity (GPP) of an ecosystem, the base on which all subsequent trophic levels depend. This low first-step efficiency, compounded further by respiratory losses and the roughly 10% ecological efficiency of energy transfer between successive trophic levels, explains why food chains are typically short and why higher trophic levels support far less biomass than primary producers.