Chapter 13 · Question 3

What is a food chain? Explain the concept of trophic levels. Give an example of a food chain found in a grassland ecosystem and state the trophic levels of each organism in it.

Answer Revealed

Direct Answer:

A food chain is a series of organisms feeding on one another at various biotic levels, representing the transfer of food energy from producers through a sequence of consumers. Each step or level of the food chain is called a trophic level. Trophic levels from base to top: first (producers/autotrophs), second (primary consumers/herbivores), third (secondary consumers/small carnivores), fourth (tertiary consumers/larger carnivores). A grassland food chain:

\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \rightarrow \text{Eagle}

. Here, grass is the producer (1st trophic), grasshopper is primary consumer (2nd), frog is secondary consumer (3rd), snake is tertiary consumer (4th), and eagle is the top carnivore.

Simple Explanation

A food chain shows 'who eats whom' in nature, like a chain of feeding links. Each step in this chain is called a trophic level. In a grassland: grass grows using sunlight, a grasshopper eats the grass, a frog eats the grasshopper, a snake eats the frog, and an eagle eats the snake. Each of them sits on a different trophic level — grass at the bottom, eagle at the top. The population is typically largest at the bottom and smallest at the top.

Exam-Ready Structure

A food chain is the sequential representation of feeding relationships in an ecosystem, showing the unidirectional flow of energy from one organism to another. 1. Definition: A food chain is a series of organisms related to each other through feeding, where one organism is eaten by the next. Each food chain represents a single pathway of energy transfer through the ecosystem. 2. Trophic levels: Each step or level of the food chain forms a trophic level (from the Greek 'trophe' meaning nourishment). NCERT Figure 13.2 illustrates trophic levels as a pyramid: (a) First trophic level: Producers / Autotrophs (green plants, certain bacteria) — they capture solar energy and convert it into chemical energy through photosynthesis. (b) Second trophic level: Primary consumers / Herbivores (grasshopper, deer, rabbit) — organisms that feed directly on producers. (c) Third trophic level: Secondary consumers / Small carnivores (frog, small fish, birds) — feed on primary consumers. (d) Fourth trophic level: Tertiary consumers / Larger carnivores (snake, tiger, eagle) — feed on secondary consumers. Some food chains may have a fifth level of top carnivores. 3. Examples from NCERT Figure 13.1: (a) Forest:

\text{Trees (Producers)} \rightarrow \text{Deer (Herbivore)} \rightarrow \text{Tiger (Carnivore)}

. (b) Grassland:

\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \rightarrow \text{Eagle}

. (c) Pond:

\text{Aquatic Plants} \rightarrow \text{Aquatic Crustacean/Insect} \rightarrow \text{Fish} \rightarrow \text{Water Bird (Heron/Crane)}

. 4. Key characteristics: (a) The population (number of organisms) is largest at the lowest trophic level and decreases at successive levels — there are far more grass plants than grasshoppers, more grasshoppers than frogs, and so on. (b) This population gradient is because energy diminishes at each transfer, supporting fewer organisms at higher levels.

Key Points

Food chain: series of organisms showing who eats whom, representing a single energy transfer pathway
Trophic level: each step in a food chain — named after the feeding position of the organism
1st trophic level: Producers (green plants); 2nd: Primary consumers (herbivores); 3rd: Secondary consumers (small carnivores); 4th: Tertiary consumers (larger carnivores)
Grassland food chain: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Eagle
Population size is largest at the lowest trophic level and smallest at the highest

Common Mistakes

Confusing secondary consumers (3rd level) with tertiary consumers (4th level) — count from producers as level 1
Thinking all food chains must have exactly four levels — the number of trophic levels depends on the specific ecosystem

What is a food chain? Explain the concept of trophic levels. Give an example of a food chain found in a grassland ecosystem and state the trophic levels of each organism in it.