Energy Flow and Food Chains Practice Questions
20 free Energy Flow and Food Chains practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
What percentage of the incident solar radiation is generally captured by plants to sustain the entire ecosystem?
- A Between 1 and 5 percent
- B 2-10 percent
- C More than 50 percent
- D Exactly 25 percent
Correct answer: 2-10 percent
Of the incident solar radiation, less than 50 percent is photosynthetically active radiation (PAR). Plants capture only 2-10 percent of this PAR, and this small amount of energy sustains the entire living world.
In a Grazing Food Chain (GFC), which of the following represents the correct sequence of energy flow?
- A Producers -> Primary Consumers -> Secondary Consumers
- B Detritus -> Herbivores -> Carnivores -> Top Predators
- C Producers -> Decomposers -> Herbivores -> Carnivores
- D Primary Consumers -> Producers -> Tertiary Consumers
Correct answer: Producers -> Primary Consumers -> Secondary Consumers
The GFC starts with producers (autotrophs) at the first trophic level. Energy then flows to primary consumers (herbivores) and then to secondary consumers (carnivores).
The Detritus Food Chain (DFC) begins with:
- A Green plants and producers
- B Dead organic matter
- C Freshwater phytoplankton
- D Incoming solar energy
Correct answer: Dead organic matter
Unlike the GFC, the DFC begins with dead organic matter (detritus). It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria.
In terrestrial ecosystems, a much larger fraction of energy flows through which of the following?
- A Grazing Food Chain
- B Detritus Food Chain
- C Parasitic Food Chain
- D Solar radiation chain
Correct answer: Detritus Food Chain
In terrestrial ecosystems, the DFC is the major conduit for energy flow because a significant amount of net primary production ends up as detritus rather than being consumed by herbivores.
Which of the following organisms can occupy more than one trophic level in the same ecosystem at the same time?
- A Goat, which eats only grass
- B Lion, which hunts only meat
- C Sparrow
- D Rabbit, which eats only plants
Correct answer: Sparrow
A sparrow is a primary consumer when it eats seeds or fruits, but becomes a secondary consumer when it eats insects or worms. This demonstrates that a species can belong to multiple trophic levels simultaneously.
Energy flow in an ecosystem is always:
- A Bidirectional
- B Unidirectional
- C Multidirectional
- D Cyclic
Correct answer: Unidirectional
Energy flow is unidirectional: from the sun to producers and then to consumers. Energy lost as heat at each step cannot be recycled back to the previous level or the sun.
According to the 10 percent law, if 10,000 J of energy is available at the producer level, how much energy will be available at the tertiary consumer level?
- A 1,000 J
- B 100 J
- C 10 J
- D 1 J only
Correct answer: 10 J
Only 10 percent of energy is transferred to the next level. Level 1 (Producers) = 10,000 J; Level 2 (Primary) = 1,000 J; Level 3 (Secondary) = 100 J; Level 4 (Tertiary) = 10 J.
What is a 'standing crop' in the context of trophic levels?
- A The total amount of inorganic nutrients stored in the soil at any time
- B The total living biomass present at a particular trophic level at a given time
- C The cumulative solar energy captured and stored by green plants
- D The rate at which consumers produce new biomass each season
Correct answer: The total living biomass present at a particular trophic level at a given time
Standing crop refers to the total biomass of living organisms present in a specific trophic level at a given time. It is usually expressed as fresh or dry weight per unit area.
The interconnected matrix of various food chains in an ecosystem is known as a:
- A Trophic level
- B Ecological pyramid
- C Food web network
- D Energy gradient
Correct answer: Food web network
In nature, food chains are rarely isolated; they are interconnected to form a food web. This provides alternative pathways for energy flow and increases ecosystem stability.
Which organisms are referred to as 'saprotrophs' in the energy flow model?
- A Herbivores that graze on live plant material in the ecosystem
- B Decomposers that break down detritus to meet their energy needs
- C Green plants that synthesise food from inorganic sources using sunlight
- D Top carnivores that actively hunt and consume other animals
Correct answer: Decomposers that break down detritus to meet their energy needs
Saprotrophs, such as fungi and bacteria, secrete digestive enzymes that break down dead and waste materials into simple, inorganic substances which they then absorb.
In an aquatic ecosystem, the major conduit for energy flow is the:
- A Detritus Food Chain (DFC)
- B Grazing Food Chain (GFC)
- C Parasitic Food Chain
- D Decomposition chain
Correct answer: Grazing Food Chain (GFC)
In aquatic environments, the GFC is the primary pathway for energy flow because phytoplankton are rapidly consumed by zooplankton and fish, leaving less organic matter to enter the DFC compared to land.
Why is the number of trophic levels in a food chain generally limited to 4 or 5?
- A Because predators at higher levels become physically too large to be preyed upon
- B Because the steep energy loss at each transfer leaves too little for higher levels
- C Because there is insufficient habitat space for organisms beyond the fifth level
- D Because decomposers consume and dismantle the chain once it exceeds five links
Correct answer: Because the steep energy loss at each transfer leaves too little for higher levels
Due to the 10 percent law, energy decreases exponentially at each level. By the 4th or 5th level, the remaining energy is usually too low to support a viable population of a higher trophic level.
Which of the following is a primary consumer in a pond ecosystem?
- A Phytoplankton
- B Zooplankton
- C Small fish
- D Bacteria
Correct answer: Zooplankton
Phytoplankton are the producers. Zooplankton feed directly on phytoplankton, making them the primary consumers (herbivores) of the pond ecosystem.
If we consider a simple food chain: Grass -> Goat -> Man, the 'Man' occupies which trophic level?
- A First
- B Second
- C Third
- D Fourth
Correct answer: Third
Grass is at the first trophic level (Producer), Goat is at the second (Primary Consumer), and Man is at the third (Secondary Consumer).
Based on the source of their nutrition or food, organisms occupy a specific place in the food chain known as their:
- A Standing state
- B Niche
- C Trophic level
- D Stratum
Correct answer: Trophic level
A trophic level represents a functional level in the ecosystem based on the organism's feeding relationship with other organisms in the community.
Which of the following is NOT a characteristic of the Detritus Food Chain?
- A It begins with dead organic matter
- B It is never connected to the Grazing Food Chain
- C It involves saprotrophs
- D Energy flow depends on the availability of detritus
Correct answer: It is never connected to the Grazing Food Chain
Some organisms of the DFC are prey to GFC animals (e.g., earthworms being eaten by birds). Thus, the two chains are often interconnected at various levels.
The measurement of biomass in terms of dry weight is more accurate than fresh weight because:
- A Dry weight is simpler and faster to measure under field conditions
- B Fresh weight varies significantly with the organism's water content
- C Dry weight accounts for the mass of metabolic gases trapped internally
- D Fresh weight omits the contribution of structural proteins to total mass
Correct answer: Fresh weight varies significantly with the organism's water content
Water content in organisms can fluctuate rapidly based on environmental conditions and physiological state. Dry weight provides a consistent measure of the actual organic matter.
In a food chain consisting of Grass -> Grasshopper -> Frog -> Snake -> Eagle, which organism is the 'Tertiary Consumer'?
- A Frog
- B Snake
- C Eagle
- D Grasshopper
Correct answer: Snake
Grass (Producer), Grasshopper (Primary Consumer), Frog (Secondary Consumer), Snake (Tertiary Consumer), and Eagle (Quaternary Consumer/Top Carnivore).
The second law of thermodynamics is relevant to ecosystems because:
- A Energy is conserved and can never be created or destroyed in any system
- B Ecosystems need a constant energy input to counteract the increase in entropy
- C All energy in an ecosystem is eventually converted back into usable matter
- D Biological energy transfers are highly efficient, approaching 100 percent
Correct answer: Ecosystems need a constant energy input to counteract the increase in entropy
The second law states that every energy transfer involves a loss of usable energy (as heat). Ecosystems must constantly receive solar energy to maintain order and offset this natural tendency toward disorder (entropy).
Which of the following groups of organisms constitute the second trophic level in a forest ecosystem?
- A Tiger and Lion
- B Deer and Rabbit
- C Fungi and Bacteria
- D Trees and Ferns
Correct answer: Deer and Rabbit
The second trophic level consists of primary consumers or herbivores. In a forest, animals like deer and rabbits feed on the producers (first trophic level) and thus occupy the second level.