Biodiversity, Food Chains and Pyramids

Overview

Biodiversity, food chains and ecological pyramids form the foundation of understanding how living organisms interact with each other and their environment. For KAR TET Environmental Studies, this topic connects directly to the syllabus focus on ecosystem components and helps explain energy flow and nutrient cycling in nature.

This topic appears frequently in TET exams because it tests both factual recall and conceptual understanding. Students must know definitions, be able to trace energy flow through ecosystems, and interpret pyramid diagrams. The content also links to Karnataka-specific biodiversity, making it relevant for questions about the Western Ghats and local ecosystems.

Mastering this topic requires understanding three interconnected ideas: what biodiversity means and why it matters, how energy moves through food chains and webs, and how ecological pyramids represent different aspects of ecosystems.

Key Concepts

• **Biodiversity** refers to the variety of life forms at three levels: genetic diversity (variation within species), species diversity (number of different species), and ecosystem diversity (variety of habitats).

• **Food chain** is a linear sequence showing how energy transfers from one organism to another — always starting with producers and moving through consumers to decomposers.

• **Food web** represents the realistic interconnection of multiple food chains in an ecosystem, showing that most organisms have multiple food sources and predators.

• **Trophic levels** are the feeding positions in a food chain: producers (first level), primary consumers (second), secondary consumers (third), and tertiary consumers (fourth).

• **10% rule of energy transfer** states that only about 10% of energy passes from one trophic level to the next; the rest is lost as heat through respiration.

• **Ecological pyramids** are graphical representations of trophic structure — they can show numbers, biomass, or energy at each level.

• **Decomposers** (bacteria, fungi) break down dead organic matter and return nutrients to the soil, completing the nutrient cycle.

• **Western Ghats** is a biodiversity hotspot in Karnataka with high species richness and endemism, often tested in state-level exams.

Key Facts

| Concept | Essential Information | |---------|----------------------| | Biodiversity hotspots in India | 4 — Western Ghats, Himalayas, Indo-Burma, Sundaland | | Western Ghats endemic species | Over 5,000 flowering plants, 139 mammal species, 508 bird species | | Energy transfer efficiency | Approximately 10% per trophic level | | Maximum trophic levels | Usually 4–5 (limited by energy loss) | | Types of ecological pyramids | Number, Biomass, Energy | | Pyramid of energy | Always upright (energy decreases at each level) | | Pyramid of numbers (inverted example) | Tree ecosystem — one tree supports many insects | | Pyramid of biomass (inverted example) | Aquatic ecosystems — phytoplankton biomass less than zooplankton at a given moment | | Autotrophs | Producers — make their own food (plants, algae) | | Heterotrophs | Consumers — depend on others for food |

Worked Examples

**Example 1: Constructing a Food Chain**

*Question: Arrange the following organisms into a food chain: Frog, Grasshopper, Snake, Grass, Hawk*

**Step 1:** Identify the producer — Grass (makes its own food through photosynthesis)

**Step 2:** Identify primary consumer (herbivore) — Grasshopper (eats grass)

**Step 3:** Identify secondary consumer — Frog (eats grasshopper)

**Step 4:** Identify tertiary consumer — Snake (eats frog)

**Step 5:** Identify top predator — Hawk (eats snake)

**Answer:** Grass → Grasshopper → Frog → Snake → Hawk

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**Example 2: Energy Calculation Using 10% Rule**

*Question: If producers in an ecosystem have 10,000 joules of energy, how much energy is available to secondary consumers?*

**Step 1:** Energy at producer level = 10,000 J

**Step 2:** Energy at primary consumer level = 10% of 10,000 = 1,000 J

**Step 3:** Energy at secondary consumer level = 10% of 1,000 = 100 J

**Answer:** 100 joules

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**Example 3: Identifying Pyramid Type**

*Question: In a grassland ecosystem, there are 1000 grass plants, 100 rabbits, 10 foxes, and 2 eagles. What type of pyramid does this represent, and what is its shape?*

**Solution:** This shows the number of organisms at each trophic level.

• Producers: 1000 (grass)
• Primary consumers: 100 (rabbits)
• Secondary consumers: 10 (foxes)
• Tertiary consumers: 2 (eagles)

**Answer:** Pyramid of Numbers; Upright shape (numbers decrease at higher levels)

Common Mistakes

• **Confusing food chain with food web** → A food chain is a single linear pathway; a food web shows multiple interconnected chains. When asked about "realistic feeding relationships," the answer is food web, not food chain.

• **Thinking all pyramids are upright** → Only pyramid of energy is always upright. Pyramid of numbers can be inverted (tree ecosystem) and pyramid of biomass can be inverted (aquatic ecosystems). Check the ecosystem context before answering.

• **Forgetting decomposers in the cycle** → Students often end food chains at top predators. Remember that decomposers act on dead matter at ALL trophic levels and return nutrients to producers.

• **Placing organisms at wrong trophic levels** → An organism's trophic level depends on what it eats in that specific chain. A human eating vegetables is a primary consumer; the same human eating chicken is a secondary consumer.

• **Confusing biodiversity with just species count** → Biodiversity includes genetic, species AND ecosystem diversity. A question asking about "levels of biodiversity" requires all three.

Quick Reference

• **Biodiversity = Genetic + Species + Ecosystem diversity**

• **Food chain direction: Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer**

• **10% energy transfers to next level; 90% lost as heat**

• **Pyramid of Energy = ALWAYS upright**

• **Western Ghats = Karnataka's biodiversity hotspot**

• **Decomposers recycle nutrients at ALL levels**