Food Chains and Food Webs

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.Which of the following represents a simple Grazing Food Chain (GFC) in a terrestrial ecosystem?

   • A.Detritus -> Earthworm -> Sparrow -> Falcon
   • B.Grass -> Grasshopper -> Frog -> Snake -> Hawk✓ Correct Answer
   • C.Phytoplankton -> Zooplankton -> Fish -> Crane
   • D.Grass -> Wolf -> Deer -> Tiger

   Explanation: As per NCERT Class 12 Biology, a grazing food chain (GFC) starts with green plants (producers). A classic terrestrial example is Grass (T1) -> Grasshopper (T2) -> Frog (T3) -> Snake (T4) -> Hawk (T5).

2. Q2.Which of the following organisms can occupy more than one trophic level in the same ecosystem at the same time?

   • A.Rabbit
   • B.Phytoplankton
   • C.Sparrow✓ Correct Answer
   • D.Deer

   Explanation: NCERT Class 12 Biology Chapter 14 states that a sparrow is a primary consumer when it eats seeds, fruits, and peas (T2), but it becomes a secondary consumer when it eats insects and worms (T3).

3. Q3.A food web is more stable than a single food chain because in a food web:

   • A.If one prey species decreases, predators have alternative food sources.✓ Correct Answer
   • B.Energy flow becomes bidirectional.
   • C.Primary producers are not required.
   • D.Nutrients are not recycled.

   Explanation: Based on NCERT concepts, a food web consists of interconnected food chains. This provides alternative feeding pathways. If one species' population drops, the consumers can feed on alternative species, preventing the collapse of the ecosystem.

4. Q4.In which of the following food chains does the size of organisms generally decrease as we move to higher levels?

   • A.Grazing Food Chain
   • B.Parasitic Food Chain✓ Correct Answer
   • C.Detritus Food Chain
   • D.Predator Food Chain

   Explanation: In a parasitic food chain, the chain starts from larger organisms (like a tree or herbivore) and goes to smaller organisms (parasites like fleas, lice, and microbes). Thus, the size of organisms decreases.

5. Q5.What is the primary difference between how energy and nutrients move through a food chain?

   • A.Energy cycles, while nutrients flow unidirectionally.
   • B.Nutrients cycle, while energy flows unidirectionally.✓ Correct Answer
   • C.Both energy and nutrients cycle continuously.
   • D.Both energy and nutrients flow in one direction only.

   Explanation: NCERT Class 12 Biology and Class 7 Geography state that energy flow in an ecosystem is unidirectional and is eventually lost as heat, whereas nutrients (like carbon, nitrogen) cycle continuously between living organisms and the environment.

6. Q6.Which of the following acts as primary producers in a marine food chain?

   • A.Zooplankton
   • B.Phytoplankton✓ Correct Answer
   • C.Crustaceans
   • D.Small fish

   Explanation: NCERT Chapter 14 states that in aquatic/marine ecosystems, the primary producers are phytoplankton (microscopic photosynthetic organisms like diatoms and dinoflagellates).

7. Q7.Organisms like humans and crows, which feed on both plants and animals, are placed in which category?

   • A.Herbivores
   • B.Carnivores
   • C.Omnivores✓ Correct Answer
   • D.Detritivores

   Explanation: Omnivores are organisms that feed on both producers (plants) and other consumers (animals). Crows and humans are classic examples of omnivores and can occupy multiple trophic levels (T2, T3, etc.).

8. Q8.A detritus food chain (DFC) can be connected to a grazing food chain (GFC) because:

   • A.They both start with green plants.
   • B.Detritivores can be eaten by grazing predators.✓ Correct Answer
   • C.They share the same solar energy source directly.
   • D.Both chains occur only in water.

   Explanation: In an ecosystem, DFC and GFC are not isolated. Animals in the DFC (like earthworms or insects feeding on dead matter) are eaten by animals in the GFC (like birds, frogs, or lizards). This interlinks the two chains into a food web.

9. Q9.Which trophic level has the highest concentration of toxins (like DDT) due to biomagnification?

   • A.First trophic level (Producers)
   • B.Second trophic level (Herbivores)
   • C.Third trophic level (Primary Carnivores)
   • D.Top trophic level (Top Carnivores)✓ Correct Answer

   Explanation: NCERT Class 12 Biology, Chapter 16 (Environmental Issues) states that toxic substances like DDT or mercury, which cannot be metabolized or excreted, get accumulated at each successive trophic level. Hence, biomagnification results in the highest concentration at the top consumer level.

10. Q10.In a forest ecosystem, which of the following acts as primary consumers?

    • A.Tigers and Leopards
    • B.Deer, Grasshoppers, and Elephants✓ Correct Answer
    • C.Trees and Shrubs
    • D.Fungi and Bacteria

    Explanation: Trees and shrubs are producers (T1). Deer, grasshoppers, and elephants directly feed on plants, making them primary consumers (T2). Tigers and leopards are carnivores (T3 or higher). Fungi and bacteria are decomposers.

11. Q11.Why do food chains in nature seldom consist of more than four or five trophic levels?

    • A.Top predators prevent more levels from forming.
    • B.Decomposers break down the upper levels.
    • C.The energy loss at each step is too high to sustain organisms at a fifth or sixth level.✓ Correct Answer
    • D.No organisms exist that can eat top predators.

    Explanation: According to NCERT Class 12 Biology, because of the 10% law of energy transfer, only a tiny fraction of the original solar energy reaches higher levels. By the 4th or 5th level, the remaining energy is insufficient to support another trophic level.

12. Q12.A caterpillar feeding on a leaf is a primary consumer. A frog eating the caterpillar is a secondary consumer. A snake eating the frog is a:

    • A.Primary producer
    • B.Tertiary consumer✓ Correct Answer
    • C.Quaternary consumer
    • D.Decomposer

    Explanation: Leaf = Producer (T1). Caterpillar = Primary Consumer (T2). Frog = Secondary Consumer (T3). Snake = Tertiary Consumer (T4).

13. Q13.In a pond ecosystem, small free-floating animals that feed on phytoplankton belong to which category?

    • A.Primary producers
    • B.Zooplankton (Primary consumers)✓ Correct Answer
    • C.Benthos
    • D.Decomposers

    Explanation: NCERT Class 12 Biology pond ecosystem diagram identifies phytoplankton as producers and zooplankton (microscopic animals) as primary consumers that feed on phytoplankton.

14. Q14.Which of the following is NOT a characteristic of a food web?

    • A.It is a network of interconnected food chains.
    • B.An animal can have more than one source of food.
    • C.Energy flows in multiple directions including back to the sun.✓ Correct Answer
    • D.It helps in maintaining ecological balance.

    Explanation: Even in a food web, energy flow remains strictly unidirectional (never goes back to the sun or lower levels). Options 1, 2, and 4 are correct characteristics of a food web.

15. Q15.The role of vultures and jackals in an ecosystem is primarily that of:

    • A.Primary producers
    • B.Scavengers✓ Correct Answer
    • C.Primary consumers
    • D.Parasites

    Explanation: Vultures and jackals feed on dead animals killed by other predators or by natural causes. They are called scavengers. They help clean the environment and recycle organic matter into the detritus food chain.

16. Q16.In a parasitic food chain, which of the following occupies the terminal (topmost) position?

    • A.A large green tree
    • B.Herbivorous birds
    • C.Hyperparasites (like bacteria and fungi on parasites)✓ Correct Answer
    • D.Apex carnivores

    Explanation: In a parasitic food chain, the energy flows from large host organisms to smaller parasites, and further to even smaller hyperparasites (parasites on parasites), which occupy the topmost level.

17. Q17.Which of the following is a biotic component that initiates a Detritus Food Chain?

    • A.Fallen leaves and dead wood
    • B.Fungi and bacteria (decomposers)✓ Correct Answer
    • C.Herbivorous insects
    • D.Green algae

    Explanation: While DFC starts with dead organic matter (leaves/wood, which are abiotic/dead), the primary *biotic* components that act upon it and initiate the active transfer of energy within this chain are decomposers (fungi and bacteria).

18. Q18.If all herbivores are removed from a forest ecosystem, what will happen to the food chain?

    • A.Producers will decrease in number.
    • B.Carnivores will die out due to lack of food.✓ Correct Answer
    • C.Decomposers will stop working.
    • D.Energy flow will reverse.

    Explanation: Carnivores (secondary consumers) depend directly on herbivores (primary consumers) for food. If herbivores are removed, carnivores will face starvation and die out.

19. Q19.Which of the following describes the trophic cascade concept in a food web?

    • A.Energy flow strictly within a single trophic level.
    • B.The removal of a top predator affecting multiple lower trophic levels in a chain reaction.✓ Correct Answer
    • C.The accumulation of nutrients in the standing state.
    • D.The decomposition of litter by fungi.

    Explanation: A trophic cascade occurs when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation (affecting multiple lower levels in a chain reaction).

20. Q20.The terminal or apex carnivores in a food chain are generally:

    • A.Eaten by herbivores
    • B.Not preyed upon by any other organisms✓ Correct Answer
    • C.Primary consumers
    • D.Saprotrophs

    Explanation: Apex or terminal carnivores (like tigers, lions, or eagles) occupy the highest trophic level in a food chain and have no natural predators in their ecosystem.