Test: Energy Flow (NCERT) - NEET MCQ

• In a grazing food chain, the first trophic level consists of primary producers, which are green plants (like the living oak leaf in this case).
• In a detritus food chain, the first trophic level consists of detritus or dead organic matter (like the dead oak leaf in this case).

Thus, the first trophic levels for the grazing food chain and detritus food chain are living oak leaf and dead oak leaf, respectively.

Topic in NCERT: Trophic Levels in an Ecosystem

Line in NCERT: "Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third."

In the given food web, organisms I (phytoplanktons) act as producers, organisms II, V and VII act as primary consumers as they feed on producers, organisms III and VI act as secondary consumers as they upon primary consumers, and organism IV acts as a tertiary consumer.

Topic in NCERT: Trophic Levels in an Ecosystem

Line in NCERT: "Those animals that depend on the primary carnivores for food are labelled secondary carnivores."

Less that 50% of the solar energy incident over earth is PAR (photosynthetically active radiation).

Topic in NCERT: ENERGY FLOW

Line in NCERT: "Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR)."

About 1−5% of incident solar energy or 2−10% of PAR is captured by the photosynthetic organisms for the synthesis of organic matter(Gross primary productivity). Roughly 20% of it is consumed in respiration so that net capture of energy(net primary productivity) is 0.8−4% of incident radiation or 1.6−8% of PAR.

Topic in NCERT: ENERGY FLOW

Line in NCERT: "Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world."

Decomposers and detritivores constitute the first trophic level of a detritus food chain.

Topic in NCERT: Trophic Levels in Ecosystems

Line in NCERT: Death of organism is the beginning of the detritus food chain/web. The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria

Only 10 % of energy is transferred from one trophic level to the next trophic level of a food chain (ten percent law, given by Linderman). In present case, energy available at producer level is 10 J. Hence energy at primary consumer level would be 1 H (10% of 10 J). Similarly, at secondary consumer level, energy present will be 0.1 J (100 % of 1 J).

Topic in NCERT: Trophic Levels in Food Chains

Line in NCERT: "The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law - only 10 per cent of the energy is transferred to each trophic level from the lower trophic level."

Trophic level is a functional level. A single species may occupy more than one trophic level. Insectivorous plants are producers, occupying first trophic level. They also eat insects and thus, occupy third trophic level also.

If population of hawks would increase, they would feed on more grasshoppers which will result in decrease of grasshoppers population, so option C is wrong

In a grassland ecosystem, the pyramid of numbers is upright. If primary producers are approximately 6 million plants, then number of top carnivores must be less than 6 milliion. Hecne, according to the option given, there would be 3 million top carnivores.

Pyramid of numbers in a grassland ecosystem. Only three top-carnivores are supported in an ecosystem based on production of nearly 6 millions plants

A single species may occupy more than one trophic level. Sparrow being omnivorous can be a primary consumer if it feeds on seeds, fruits and peas or a secondary consumer if it feeds on insects and worms.

Topic in NCERT: Trophic Levels in Ecosystems

Line in NCERT: "A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms."

A lion feeds on a deer.
Deer are the primary consumer.
Fox acts a secondary consumer and feeds on a primary consumer such as Rabbit.
Frog feeds on a grasshopper and acts as a primary consumer.
Rat acts as prey for both Snake and a hawk.

To match column I with column II correctly:

- Gross primary productivity: Total organic matter produced from solar energy (iii)
- Secondary productivity: Rate of synthesis of organic matter by consumers (ii)
- Transducers: Green plants (i)
- Food web: Interconnection of food chains (iv)

Therefore, the correct match is:
B: A - (iii), B - (ii), C - (i), D - (iv).

This arrangement aligns with the definitions and roles of each concept in ecological systems, ensuring efficient energy flow and understanding of ecosystem dynamics.

In an aquatic ecosystem, the important herbivores are zooplankton, larvae, tadpoles, etc. Cows in grasslands also act as herbivores as these feed on producers. Thus, both cows and zooplankton occupy second trophic level in terrestrial and aquatic ecosystem respectively.
Line in ncert: The consumers are represented by the zooplankton, the free swimming and bottom dwelling forms

First-order consumers are animals that eat plants called herbivores. They are the first step in the food chain.

Topic in NCERT: Trophic Levels in an Ecosystem

Line in NCERT: "Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third."