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Ecology looks like the easy part of the biology syllabus. The chapters are short and the ideas feel like common sense. Then the exam asks how much energy reaches a secondary carnivore, or which pyramid can be inverted, and the common sense gives the wrong answer. This post covers the rules those questions test, with worked examples, the usual mistakes and a weekly routine.
What does the NEET syllabus include in ecology?
The NEET (UG)-2026 syllabus from the National Medical Commission lists "Ecology and Environment" as Unit 10 of biology. It covers population interactions (mutualism, competition, predation, parasitism), population attributes (growth, birth rate, death rate, age distribution), the ecosystem (productivity, decomposition, energy flow, and pyramids of number, biomass and energy) and biodiversity and its conservation. These map onto chapters 11 to 13 of the Class 12 NCERT biology book, free on the NCERT textbooks page. NMC issues a syllabus for each exam year, so check the one for your year when it comes out.
How do you calculate energy at each trophic level?
NCERT's Ecosystem chapter gives two numbers you need. Plants capture only 2 to 10 per cent of the photosynthetically active radiation, and the transfer of energy between trophic levels follows the "10 per cent law": only about 10 per cent of the energy at one level reaches the next.
Worked example. Producers in a grassland have a net primary productivity of 20,000 kJ in a season. How much energy reaches the secondary carnivores?
Producers (first trophic level): 20,000 kJ.
Herbivores (second level): 10% of 20,000 = 2,000 kJ.
Primary carnivores (third level): 10% of 2,000 = 200 kJ.
Secondary carnivores (fourth level): 10% of 200 = 20 kJ.
Run it backwards for the reverse question. If a top carnivore at the fourth level receives 15 kJ, the producers must have held 15 × 10 × 10 × 10 = 15,000 kJ.
Two mistakes cost marks here. The first is counting levels wrongly: herbivores are the second trophic level, not the first, so the number of 10 per cent steps is one less than the level number. The second is applying the 10 per cent law to sunlight. The law starts from what producers have already fixed, not from the light falling on them.
Which ecological pyramids can be inverted?
NCERT gives the rule and its exceptions together. In most ecosystems all three pyramids are upright. But a single large tree supporting many insects, which support fewer birds, gives an inverted pyramid of numbers at its base. In the sea, the pyramid of biomass is generally inverted because a small standing crop of phytoplankton supports a larger standing crop of zooplankton and fish. The pyramid of energy is always upright, because some energy is lost as heat at every transfer.
NCERT also reminds you that a trophic level is a functional level, not a species. A sparrow eating seeds is a primary consumer; the same sparrow eating insects is a secondary consumer. Questions that ask "which trophic level does this animal occupy?" often hinge on this.
Why do food web questions trip students up?
In a study of 200 students, Griffiths and Grant (1985) proposed a ladder of food web skills and found the data fitted it closely. The top of the ladder was predicting how a change in one population affects another population in the same web but not on the same chain. That is exactly the kind of question exams like.
Try this. Grass is eaten by grasshoppers and rabbits. Frogs eat grasshoppers. If disease removes the frogs, grasshoppers increase, they eat more grass, and the rabbits, which share that grass, may decline. Rabbits and frogs never meet, but they are linked through two steps. Trace every arrow before you answer.
How do population growth questions work?
NCERT's Organisms and Populations chapter defines birth and death rates per individual. It gives the exponential model, dN/dt = rN, where r is the intrinsic rate of natural increase (birth rate minus death rate), and the Verhulst-Pearl logistic model, dN/dt = rN(K − N)/K, where K is the carrying capacity.
Worked example. A pond has 200 frogs. In a year there are 60 births and 20 deaths.
Birth rate b = 60/200 = 0.3 per frog per year. Death rate d = 20/200 = 0.1.
r = b − d = 0.2 per year.
Exponential growth rate now: dN/dt = 0.2 × 200 = 40 frogs per year.
If the pond's carrying capacity is K = 1,000, logistic growth gives dN/dt = 0.2 × 200 × (1,000 − 200)/1,000 = 32 frogs per year.
Logistic growth is fastest at N = K/2 = 500, where dN/dt = 0.2 × 500 × 0.5 = 50 frogs per year.
Common mistakes: using total births instead of births per individual, and forgetting that growth slows to zero as N approaches K. For interaction questions, learn NCERT's sign table: mutualism (+, +), competition (−, −), predation and parasitism (+, −), commensalism (+, 0), amensalism (−, 0).
A weekly routine for ecology
Two energy problems a day for a week. One forwards, one backwards. Write the trophic level number next to each value.
Draw every pyramid exception from memory. Tree and insects, sea biomass, and the energy pyramid. Label why each has its shape.
One food web question every other day. Draw the web, change one population, and trace the effect along every arrow before choosing an option.
Five population calculations. Vary N and K, and check that the logistic rate is largest at K/2.
Test yourself on the interaction table. Cover the names and fill them in from the signs.
If a term such as standing crop or net primary productivity keeps slipping, look it up properly rather than guessing. The Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, each with its own lesson. For how to read the NCERT chapters themselves, see our guide on studying NCERT textbooks actively.
Tonight, do the frog example again with K = 600 and check your answer before you look at any options.
