NTSE Biology – Food Chains
Subject: Biology
Topic: Food Chains
Target: Students preparing for the National Talent Search Examination (NTSE)
1. Simple Explanation
A food chain is a linear sequence that shows how energy and nutrients move from one organism to another in an ecosystem.
- Source of energy: Sunlight (photosynthesis) → Primary producers (plants, algae).
- Transfer of energy: Herbivores eat plants → Carnivores eat herbivores → Apex predators eat carnivores.
- Result: Each step removes most of the energy as heat or waste; only a small fraction (≈10 %) is passed on to the next level.
Key idea: The flow of energy is unidirectional; nutrients cycle, but energy does not.
2. Key Points
| Concept | Details |
|---|---|
| Trophic Levels | 1. Primary producers (plants, algae) 2. Primary consumers (herbivores) 3. Secondary consumers (carnivores that eat herbivores) 4. Tertiary consumers (carnivores that eat other carnivores) 5. Decomposers (bacteria, fungi) – recycle nutrients |
| Energy Transfer Efficiency | Roughly 10 % of energy is transferred from one trophic level to the next (the “10 % rule”). |
| Energy Losses | Heat (via metabolism), excretion, unconsumed food, and waste products. |
| Food Chain vs. Food Web | A food chain is a single, linear path; a food web is a network of many interlinked food chains in an ecosystem. |
| Factors Affecting Food Chains | Availability of food, population size, environmental conditions (temperature, water), human activities (deforestation, pollution). |
| Importance | • Maintains ecosystem balance • Regulates population sizes • Provides food for humans and animals • Supports nutrient cycling |
3. Worked Example
Example Food Chain
Grass → Grasshopper → Small Bird → Fox → Human
Energy Transfer (kJ per kg of organism)
| Trophic Level | Organism | Energy (kJ kg⁻¹) |
|---|---|---|
| 1 (Producer) | Grass | 1 000 |
| 2 (Primary) | Grasshopper | 100 |
| 3 (Secondary) | Small Bird | 10 |
| 4 (Tertiary) | Fox | 1 |
| 5 (Human) | Human | 0.1 |
Explanation of calculations
- Grass → Grasshopper
- 10 % of 1 000 kJ kg⁻¹ = 100 kJ kg⁻¹ (grasshopper).
- Grasshopper → Small Bird
- 10 % of 100 kJ kg⁻¹ = 10 kJ kg⁻¹ (bird).
- Small Bird → Fox
- 10 % of 10 kJ kg⁻¹ = 1 kJ kg⁻¹ (fox).
- Fox → Human
- 10 % of 1 kJ kg⁻¹ = 0.1 kJ kg⁻¹ (human).
Observation: The amount of energy available to each successive level decreases dramatically.
4. Quick Revision Summary
| Topic | Take‑Away |
|---|---|
| What is a food chain? | Linear path of energy transfer from producers to apex consumers. |
| Primary producers | Plants, algae – convert solar energy to chemical energy. |
| Trophic levels | 1 = producers, 2 = primary consumers, 3 = secondary, 4 = tertiary, 5 = decomposers. |
| Energy transfer rule | ~10 % efficiency; 90 % lost as heat or waste. |
| Food web vs. Food chain | Web = network of many chains; chain = single path. |
| Key factors | Food availability, population size, environment, human impact. |
| Why it matters? | Keeps ecosystems balanced, supports human food supply, recycles nutrients. |
Quick Mnemonics
- “The Sun Gives All” – Sun → Plants → Herbivores → Carnivores → Human
- “10 % Rule” – Remember the drop in energy at each step.
Tip for NTSE:
- When answering questions, identify the trophic level of each organism, apply the 10 % rule for energy calculations, and explain the implications of energy loss on population dynamics and ecosystem health.
Good luck with your preparation!