In relation to energy transfer in ecosystem, explain the statement "10kg of deer's meat is equivalent to 1 kg

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Q. In relation to energy transfer in ecosystem, explain the statement "10kg of deer's meat is equivalent to 1 kg of lion's flesh".

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Concept understanding — Energy Flow Ecology

Imagine you are looking at a simple meal: a plate of rice and vegetables. Where did the energy in that food come from? The rice grew in a paddy field, using sunlight. The vegetables grew in the soil, also using sunlight. That sunlight is the original source of nearly all energy on Earth. Now think of a tiger eating a deer, or a cow eating grass. In every case, energy is being passed from one living thing to another. This passing of energy from the sun through plants, then to animals, and eventually back to the environment, is what ecologists call energy flow.

The key idea is that energy does not cycle. Unlike water or carbon, which get reused, energy enters an ecosystem, is used, and then leaves as heat. It is a one-way street. The sun provides a constant supply, but at every step, some energy is lost — mostly as heat from the organism’s own life processes like breathing, moving, and growing. This is why there are fewer tigers than deer, and fewer deer than grass plants. Each level can support only a fraction of the energy that came from the level below.

In your NCERT textbook (Class 12 Biology, Chapter 14), this is explained through the concept of trophic levels — the feeding steps in a food chain. The first trophic level is always the producers (green plants). The second is herbivores (plant-eaters). The third is carnivores (meat-eaters). And so on. The flow of energy from one trophic level to the next is called energy transfer, and it is never 100% efficient. Most of the energy is used for the organism’s own survival and is lost as heat.

Important

Energy flow is unidirectional — it moves from the sun to producers to consumers and finally to decomposers, and then dissipates as heat. It never flows backward. This is a fundamental law of ecology, rooted in the second law of thermodynamics.

Why does this matter for you, even as a humanities or commerce student? Because it explains why food chains are short — usually only 4 or 5 steps. Beyond that, there simply isn’t enough energy left to support another level. It also explains why the number of organisms at each level decreases as you go up. This is often shown as a pyramid of energy, where the base (producers) has the most energy, and the top (apex predators) has the least.

Here are the key points to remember:

Source: The sun is the primary energy source for almost all ecosystems.
Direction: Energy flows in one direction — from sun → producers → consumers → decomposers → lost as heat. …

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The statement illustrates the 10% law of energy transfer: only about 10% of energy from one trophic level passes to the next, so a lion must consume roughly 10 kg of deer to build 1 kg of its own body mass.

When we think about how energy moves through an ecosystem, we're really tracking a story of loss and inefficiency. Energy enters through producers—plants capturing sunlight—and then flows upward through herbivores, carnivores, and top predators. But at every step, most of that energy vanishes, spent on life's daily operations rather than building new tissue.

The deer, a herbivore, eats plants. It uses the chemical energy stored in grass, leaves, and shoots to power its muscles, maintain body temperature, digest food, escape predators, and carry out countless metabolic processes. Only a small fraction—roughly 10%—of the energy the deer extracts from plants actually gets converted into deer biomass: muscle, bone, organs, fat. The rest is lost as heat during respiration, excreted as waste, or used up in movement and maintenance.

Now the lion enters the picture. When it hunts and consumes that deer, it faces the same constraint. The lion's body must digest the meat, fuel its own metabolism, maintain its body temperature, power its hunts, and sustain all cellular functions. Again, only about 10% of the energy contained in the deer's flesh becomes lion flesh. The remaining 90% dissipates as heat, gets excreted, or fuels the lion's activities.

Important

This pattern—where each trophic level captures only about 10% of the energy from the level below—is known as the 10% law or Lindeman's law, after ecologist Raymond Lindeman who formalized it in the 1940s.

So if we do the arithmetic: to produce 1 kg of lion tissue, the lion needs roughly 10 kg of deer. But those 10 kg of deer required about 100 kg of plant material to build. And those plants needed a certain amount of solar energy captured through photosynthesis. The energy pyramid grows rapidly wider as you move down, which is why ecosystems can support far fewer top predators than herbivores, and far fewer herbivores than the plant mass that feeds them. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

AHSEC Higher Secondary (HS) Final Examination 2025Set ANNUAL5 marks
$Q. What is Food Chain? Write about the trophic level of food chain. OR Describe the chromosomal theory of inheritance.$
›Reveal solutionSolution
A food chain is the linear transfer sequence of food/energy from producers through successive consumers, and each feeding step in it is a trophic level. (OR: The chromosomal theory of inheritance states genes are located on chromosomes, whose meiotic behaviour parallels and explains Mendel's laws.)

Food chain and trophic levels:

A food chain is the sequence of organisms in an ecosystem through which food energy (originally fixed by photosynthetic producers) is transferred, each organism feeding on (and being eaten by) the next, e.g.:

Grass (producer) → Grasshopper (primary consumer) → Frog (secondary consumer) → Snake (tertiary consumer) → Hawk (top predator)

Each step is a trophic level:

First trophic level — Producers (autotrophs, mainly green plants/algae, fixing solar energy via photosynthesis).

Second trophic level — Primary consumers (herbivores feeding on producers).

Third trophic level — Secondary consumers (carnivores eating herbivores).

Fourth trophic level — Tertiary consumers (carnivores eating secondary consumers), and so on to apex consumers.

At each trophic level only about 10% of the energy received from the previous level is transferred onward (the rest lost mainly as heat during respiration) — the 10% law — which explains why food chains are usually limited to 4-5 trophic levels and why biomass/numbers generally decrease at each successive level (forming an ecological pyramid). Two basic types exist: the grazing food chain (starting from living green plants) and the detritus food chain (starting from dead organic matter, broken down by decomposers).

OR: Chromosomal theory of inheritance:

Proposed by Walter Sutton and Theodor Boveri (1902): genes (Mendelian 'factors') are located on chromosomes, based on the parallel behaviour of chromosomes and genes during meiosis:

Chromosomes, like genes, occur in homologous pairs in a diploid cell, one from each parent — paralleling Mendel's factors existing in pairs.

During meiosis, homologous chromosomes segregate so each gamete receives one of each pair — paralleling Mendel's Law of Segregation. …
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AHSEC Higher Secondary (HS) Final Examination 2019Set ANNUAL5 marks
$Q. Describe the process of the flow of energy in different trophic level of an ecosystem. OR What is ecological pyramid? Explain different types of ecological pyramid with diagram.$
›Reveal solutionSolution
Energy enters an ecosystem as sunlight fixed by producers and flows unidirectionally through the food chain's trophic levels, with only about 10% transferred at each step (the rest lost as respiratory heat) — described by Lindeman's 10% law.

Unlike nutrients, which cycle repeatedly through an ecosystem (biogeochemical cycles), energy flows only in one direction — from the sun, through producers, and then through successive consumers — and is progressively lost as heat at each step; it is never recycled back to the sun.

Steps in the flow of energy:

Producers (1st trophic level): Green plants and other autotrophs capture only a small fraction (about 2-10%) of the incident solar radiation through photosynthesis, converting light energy into chemical energy stored in organic compounds. This is called Gross Primary Productivity (GPP); after subtracting respiratory losses (R), the Net Primary Productivity (NPP) is what is actually available to the next trophic level.

Primary consumers/herbivores (2nd trophic level): These organisms feed on producers, acquiring the chemical energy stored in plant tissue.

Secondary consumers/primary carnivores (3rd trophic level): These feed on herbivores, in turn obtaining the energy.

Tertiary consumers/secondary carnivores (4th trophic level) and beyond: Energy continues to pass along the chain (e.g., grass -> deer -> tiger). …
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Q.In relation to energy transfer in ecosystem, explain the statement "10kg of deer's meat is equivalent to 1 kg of lion's flesh".

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