Q.Name an organism found as secondary carnivore in an aquatic ecosystem.
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Ecological Pyramid
Picture a real pyramid -- wide at the base, narrowing all the way up to a single point at the top. Ecologists borrow exactly this shape to describe something that has nothing to do with stone: how numbers, weight (biomass), or energy are distributed across the feeding levels of a food chain. This visual model is called an ecological pyramid.
Every ecological pyramid works the same way. In your NCERT textbook (Class 12 Biology, Chapter 12, Ecosystem, section 12.5), the base always represents the producers -- the first trophic level -- and each successive tier above it represents the next trophic level up (herbivores, then primary carnivores, then secondary or top carnivores), with the apex representing the top-level consumer. Three distinct types are studied, because the same food-chain relationship can be measured in three different ways:
- Pyramid of numbers -- plots the count of individual organisms at each trophic level. NCERT's own grassland example is dramatic: nearly 6 million producer plants are needed to support just three top-carnivores at the apex.
- Pyramid of biomass -- plots the standing crop (usually expressed as dry weight, which is more accurate than fresh weight) of organisms at each level, rather than headcount.
- Pyramid of energy -- plots the amount of energy present at each trophic level, measured per unit area, usually annually.
In most ecosystems, all three pyramids come out upright -- producers are more numerous and have more biomass than herbivores, and herbivores more than carnivores -- because energy shrinks at every step up the food chain (the same 10 per cent law behind energy flow: only about 10 per cent of the energy at one trophic level is transferred to the next).
When a pyramid turns upside down -- numbers and biomass pyramids don't always come out upright, and NCERT points to genuine exceptions you're expected to reason through, not just memorise:
- A single large tree can support so many feeding insects that a pyramid of numbers built around it is inverted right at the base -- one producer, many primary consumers.
- The pyramid of biomass in the sea is commonly inverted: at any given moment the standing crop of tiny, fast-reproducing phytoplankton is small, yet it is turning over fast enough to support a much larger standing crop of the zooplankton feeding on it.
The pyramid of energy is the one type that is never inverted -- it is always upright, in every ecosystem, without exception. Energy is lost as heat at every transfer between trophic levels (unlike nutrients, it is never recycled back), so the level below always has to hold more usable energy than the level feeding on it. …
In an aquatic ecosystem, the trophic levels are arranged as follows: producers (phytoplankton), primary consumers (zooplankton), primary carnivores (small fish that eat zooplankton), and secondary carnivores (larger fish that birds or humans eat). The secondary carnivore occupies the topmost trophic level in such a food chain.
- A classic example from the NCERT textbook is the large fish that feeds on smaller fish.
- Other examples include fish-eating birds (like herons or kingfishers) or turtles that prey on small fish. …
In an aquatic ecosystem, a secondary carnivore is a fish that eats smaller fish, such as a large fish like a Rohu or a Catla.
The concept of an ecological pyramid helps us understand how energy flows through an ecosystem. In any ecosystem, organisms are arranged in trophic levels based on what they eat. The first level is always the producers (like phytoplankton in water), followed by primary consumers (herbivores), then secondary consumers (carnivores that eat herbivores), and finally tertiary consumers (carnivores that eat other carnivores). In an aquatic ecosystem, the pyramid often has a broad base of tiny producers and narrows as you go up.
Now, a secondary carnivore is an animal that eats other carnivores. In a pond or lake, the simplest food chain might look like this: phytoplankton → zooplankton → small fish → large fish. Here, the small fish are primary carnivores (they eat zooplankton, which are herbivores). The large fish that eats these small fish is a secondary carnivore.
This follows directly from the aquatic trophic sequence in this chapter's own Section 12.4 (Energy Flow): phytoplankton (producers) -> zooplankton (primary consumers) -> small fish (primary carnivores/secondary consumers) -> large fish (secondary carnivores/tertiary consumers). A large fish such as Rohu or Catla is a common real-world example of the top rung of this chain, though the exact species varies by water body. …
Build the aquatic chain rung by rung from the producer up (phytoplankton -> zooplankton -> small fish -> large fish) and read off whichever organism sits on the FOURT …
- KCET 2025Set C-41 markMCQQ.If 8 individuals in a laboratory population of 80 fruit flies died during a specified time interval, the death rate in the population during that period is (A) 0.001 individual/time interval (B) 0.1 individual/time interval (C) 1 individual/time interval (D) 0.01 individual/time interval
›Reveal solutionSolution
Death rate = (number of deaths)/(initial population size) per unit time =8/80=0.1.
- The concept. In population ecology, the death rate (mortality rate) is expressed on a per capita basis: it is the number of individuals that die per individual of the population, per unit time.
Death rate=initial population sizenumber of deaths during the interval
- Substitute the data. The laboratory population has N=80 fruit flies, and 8 individuals died in the specified time interval: Death rate=808=0.1 …
- KCET 2022Set A-11 markMCQQ.Cuscuta is an example of (A) Ectoparasitism (B) Broad Parasitism (C) Predation (D) Endoparasitism
›Reveal solutionSolution
Cuscuta grows on the outer surface of its host plant (twining stems + haustoria into the host phloem), which by definition makes it an ectoparasite.
Step 1 — What Cuscuta is. Cuscuta (dodder, 'amarbel') is a total stem parasite: it has lost its chlorophyll and its leaves are reduced to scales, so it cannot photosynthesise. It commonly grows on hedge plants such as Duranta.
Step 2 — How it feeds. Its twining stems wrap around the host's shoot and send haustoria — modified absorptive roots — through the host's tissue into the phloem, drawing off water and ready-made food. Note the body of the parasite stays on the outside of the host.
Step 3 — Classify the parasitism.
- Ectoparasite — lives on the external surface of the host (e.g. lice, ticks, Cuscuta).
- Endoparasite — lives inside the host's body (e.g. Ascaris, liver fluke, Plasmodium). Since Cuscuta lives on the host's surface, it is an ectoparasite → ectoparasitism. …
- KCET 2021Set C-31 markMCQQ.Pneumonia is caused by (A) Streptococcus pneumonia (B) Haemophilus influenza (C) Both A and B (D) None
›Reveal solutionSolution
NCERT names two bacteria as the causative agents of pneumonia — Streptococcus pneumoniae and Haemophilus influenzae — so both options A and B are right.
Step 1 — The disease
Pneumonia is a bacterial disease of humans that affects the alveoli (air sacs) of the lungs.
Causative agents: Streptococcus pneumoniae and Haemophilus influenzae.
Step 2 — Pathology (why it is dangerous)
In an infected person, the alveoli become filled with fluid, which severely impairs gaseous exchange:
- Symptoms: fever, chills, cough and headache; in severe cases the lips and finger-nails turn grey to bluish — cyanosis, the visible sign of poor oxygenation of the blood.
- Transmission: by inhaling the droplets/aerosols released by an infected person, or even by sharing glasses and utensils with them.
Step 3 — Evaluate the options
- (A) Streptococcus pneumoniae — a genuine causative agent. ✓ …
- KCET 2020Set A-11 markMCQQ.Which one of the following is a wrong statement ? (A) Most of the forests have been lost in tropical areas. (B) Green house effect is a natural phenomenon. (C) Eutrophication is a natural phenomenon in fresh water lakes. (D) Ozone in upper part of the atmosphere is harmful to animals.
›Reveal solutionSolution
The question asks you to identify the incorrect statement among four environmental claims. The wrong one is (D) — ozone in the upper atmosphere (the stratosphere) is beneficial, not harmful, because it absorbs harmful UV radiation.
The key here is to know the role of ozone in different atmospheric layers. Many students confuse the "bad ozone" at ground level (a pollutant) with the "good ozone" high up that protects life. Let’s check each statement carefully.
-
Statement (A): "Most of the forests have been lost in tropical areas."
This is true. Tropical rainforests (like the Amazon, Congo Basin, and Southeast Asia) have experienced massive deforestation due to logging, agriculture, and urbanization. Over half of the world’s original tropical forests are already gone.
-
Statement (B): "Greenhouse effect is a natural phenomenon."
This is also true. Without the natural greenhouse effect (from water vapour, CO₂, methane, etc.), Earth’s average temperature would be about -18°C instead of the current 15°C. The problem today is the enhanced greenhouse effect from human emissions — but the phenomenon itself is natural.
-
Statement (C): "Eutrophication is a natural phenomenon in freshwater lakes."
This is true, but with a nuance. Eutrophication — the enrichment of water with nutrients (especially phosphorus and nitrogen) leading to algal blooms and oxygen depletion — can occur naturally over centuries as a lake ages. However, human activities (fertilizer runoff, sewage) greatly accelerate it. The statement says it is a natural phenomenon, which is correct; it does not claim it is only natural. …
-
- KCET 2019Set A-11 markMCQQ.Of the total incident solar radiation the percentage Photosynthetically Active Radiation (PAR) captured by the plants (A) 2−10% of PAR only (B) 30−40% of PAR only (C) 10−20% of PAR only (D) 0−10% of PAR only
›Reveal solutionSolution
The question asks what percentage of Photosynthetically Active Radiation (PAR) is actually captured by plants. The correct range is 2–10% of PAR, which corresponds to option (A).
The key here is to distinguish between two very different numbers that often get confused in ecology: the fraction of total solar radiation that is PAR, and the fraction of PAR that plants actually use.
Photosynthetically Active Radiation (PAR) is the portion of sunlight with wavelengths between 400 and 700 nm — the part that drives photosynthesis. About 50% of the total solar radiation reaching Earth's surface falls in this range. But that's not what the question is asking. The question asks: of the PAR that reaches the plant, how much is actually captured and used?
Plants do not absorb every photon that hits them. Leaves reflect some light (especially green), transmit some through the leaf, and only a fraction of the absorbed photons actually drives carbon fixation. The rest is lost as heat or fluorescence. On top of that, canopy structure, leaf angle, and non-photosynthetic tissues all reduce the effective capture.
The well-established ecological figure is that plants capture only about 2–10% of the incident PAR. This is the net primary productivity efficiency relative to the PAR input. The other options — 30–40% or 10–20% — are far too high; those numbers might correspond to the absorption efficiency of a single leaf in a lab, not a whole plant or canopy in the field.
-
Identify what the question is actually measuring.
The phrase "captured by the plants" means the energy that ends up stored as biomass (gross primary productivity minus respiration losses) relative to the PAR that falls on the plant. This is the ecological efficiency of photosynthesis in natural conditions.
-
Recall the known range from ecology.
In most terrestrial ecosystems, the efficiency of converting PAR into plant biomass is low — typically between 2% and 10%. Even the most productive crops (like sugarcane or maize) rarely exceed 6–8% over a growing season. Natural forests and grasslands are often at the lower end, around 2–4%.
-
Eliminate the wrong options.
- Option (B) 30–40%: This is roughly the fraction of total solar radiation that is PAR, not the fraction captured. A common confusion. …
-
- KCET 2019Set A-11 markMCQQ.In an area where DDT has been used extensively, the population of birds declined significantly because – (A) Birds stopped laying eggs. (B) Earthworms in the area got eradicated. (C) Birds became vulnerable to predators. (D) Many of the eggs laid by birds showed pre-matured breaking.
›Reveal solutionSolution
DDT is a fat-soluble, non-biodegradable pesticide that undergoes biological magnification through the food chain. In birds, it interferes with calcium metabolism, causing eggshell thinning — the eggs break prematurely under the parent's weight, leading to population decline. The correct answer is (D).
The concept: Biological magnification and eggshell thinning
DDT (dichlorodiphenyltrichloroethane) is a persistent organic pollutant. It does not break down easily in the environment and is fat-soluble, meaning it accumulates in the fatty tissues of organisms. When a predator eats prey contaminated with DDT, the chemical gets concentrated further up the food chain — this is called biological magnification (or biomagnification).
In birds of prey (like falcons, eagles, and pelicans), DDT at the top of the food chain reaches very high concentrations. The key effect is not direct poisoning of adult birds, but a subtle disruption of their calcium metabolism. DDT interferes with the enzyme carbonic anhydrase, which is needed to deposit calcium carbonate into eggshells. The result: eggs with abnormally thin, fragile shells.
Watch outA common mistake is to think DDT kills birds directly or makes them stop laying eggs. Neither is true — the birds lay eggs, but the shells are so weak that they crack under the weight of the incubating parent. The population crashes because very few chicks survive to hatching.
Step-by-step reasoning
-
DDT enters the food chain
DDT sprayed on crops is washed into soil and water. It is absorbed by small organisms like plankton and insects. These are eaten by fish and earthworms, which are in turn eaten by birds. Because DDT is stored in fat and not excreted, its concentration increases at each trophic level.
-
Top predators accumulate the highest doses
Birds that feed on fish or earthworms in DDT-treated areas accumulate the chemical in their bodies. The concentration can be millions of times higher than in the surrounding environment.
-
DDT disrupts eggshell formation
In female birds, DDT (and its metabolite DDE) inhibits the action of carbonic anhydrase in the shell gland. This enzyme normally helps deposit calcium carbonate to form a strong shell. Without it, the shell is deposited too thinly.
-
Eggs break before hatching
When the parent bird sits on the nest to incubate the eggs, the thin shells crack under the pressure. The eggs break prematurely, killing the embryos. Very few chicks survive, so the bird population declines over time. …
-
- KCET 2018Set A-11 markMCQQ.The microorganisms involved in floc formation during sewage treatment are (A) Anaerobic bacteria and fungus (B) Aerobic bacteria and fungus (C) Autotrophic bacteria and yeast (D) Fungus and algae
›Reveal solutionSolution
Floc formation in secondary sewage treatment is driven by aerobic bacteria and fungi that decompose organic matter while clumping together into settleable masses. The correct option is (B).
The key to this question lies in understanding what "floc" actually is and the environment in which it forms. Sewage treatment has two main stages: primary (physical settling) and secondary (biological treatment). Floc formation is the hallmark of the secondary stage.
In secondary treatment, the sewage is constantly aerated — air is pumped in. This creates an aerobic (oxygen-rich) environment. The microorganisms that thrive here are primarily aerobic bacteria and fungi. They feed on the dissolved organic matter in the sewage, breaking it down into simpler substances. As they grow and metabolize, they secrete sticky, gelatinous substances (polysaccharides and proteins) that cause them to clump together. These clumps, called flocs, also trap suspended particles and other microbes.
The floc itself is a complex community, but the dominant, active decomposers are aerobic bacteria and fungi. The flocs eventually settle out in a sedimentation tank, leaving clarified water.
Watch outA common mistake is to think of anaerobic bacteria here. Anaerobic bacteria are indeed used in sewage treatment, but in a different stage — the sludge digester, where settled sludge is broken down in the absence of oxygen. Floc formation happens in the aeration tank, which is aerobic.
Let's eliminate the other options:
- Option (A) — Anaerobic bacteria and fungus: Incorrect. The aeration tank is aerobic, not anaerobic. Anaerobic bacteria would not be the primary floc-formers here. …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.