Biology · Chapter 10

🌳 Ecosystems

Food chains, 10% energy rule, biodiversity.

💡 How Nature Connects

An ecosystem is a community of living organisms (biotic) + their physical environment (abiotic) interacting as a system. A pond, forest, desert, or even a fish tank is an ecosystem.

Components:

• Producers (autotrophs) — make their own food (plants, algae)
• Consumers (heterotrophs) — eat others
   – Primary consumers — herbivores (cow, deer, grasshopper)
   – Secondary consumers — eat herbivores (frog, snake)
   – Tertiary — top predators (eagle, tiger)
• Decomposers — break down dead matter (bacteria, fungi)

Food chain example: Grass → Grasshopper → Frog → Snake → Eagle

A food web is many food chains interconnected — closer to real life.

⚡ The 10% energy rule (NEET high-yield)

Only about 10% of energy transfers from one trophic level to the next. The rest is lost as heat, used for life processes, or remains in undigested parts.

Producers (1000 kcal) → Herbivores (100 kcal) → Primary carnivores (10 kcal) → Top predators (1 kcal)

This is why food chains rarely have more than 4-5 levels. Not enough energy for higher levels.

Tropical rainforest — highest biodiversity ecosystem
Tropical rainforest — highest biodiversity ecosystemWikimedia Commons / CC BY-SA 3.0
Coral reef ecosystem — ocean's most diverse habitat
Coral reef ecosystem — ocean's most diverse habitatWikimedia Commons / CC BY-SA 3.0
♻️ Nutrient cycles

Unlike energy (one-way flow), nutrients cycle through ecosystems:

• Carbon cycle — CO₂ ↔ glucose (photosynthesis/respiration) ↔ fossil fuels
• Water cycle — evaporation → clouds → rain → rivers → ocean → repeat
• Nitrogen cycle — atmospheric N₂ → soil (by bacteria) → plants → animals → back to atmosphere

🌍 Threats and balance

Ecosystems can collapse when:

• A key species is removed (e.g., wolves removed from forests → deer explode → trees stripped → habitat lost)
• Pollution disrupts balance (DDT killed eagles by thinning eggshells)
• Climate change shifts conditions faster than species can adapt

This is why biodiversity matters — more species = more resilience.

🎬

A Forest Food Chain

Animation
ENERGY FLOW IN A FOOD CHAIN (10% RULE) PRODUCER (Grass) 🌾 1000 kcal energy stored 100% PRIMARY CONSUMER (Grasshopper) 🦗 100 kcal — only 10% gained SECONDARY CONSUMER (Frog) 🐸 10 kcal TERTIARY CONSUMER (Snake) 🐍 1 kcal TOP PREDATOR (Eagle) 🦅 0.1 kcal — chain ends here ↓ ↓ ↓ WHY FOOD CHAINS ARE SHORT 90% energy is lost at each level (heat, life processes). After 4-5 levels, nothing left to sustain higher predators.

Bar widths show actual energy — see how rapidly energy diminishes. That's why apex predators are rare.

🔬

Build a Food Web

Interactive

Pick an organism — see what eats it and what it eats.

Trophic levelProducer (1st level)
EatsMakes own food via photosynthesis
Eaten byRabbits, mice, grasshoppers, deer
Grass is a producer — the foundation of most terrestrial food chains.
Practice (NCERT): In a food chain "grass → grasshopper → frog → snake → eagle", what happens if frogs are eliminated?
Removing frogs would cause a chain reaction:
1. Grasshoppers explode in number (no predator to control them)
2. Grass gets overgrazed → less grass → soil erosion
3. Snakes and eagles starve → their numbers drop drastically
4. Ecosystem collapses from imbalance
This shows why every species matters, no matter how small. Removing one link affects all others.
Practice (NEET): Why is the amount of energy decreasing at each successive trophic level?
According to the 10% rule (Lindeman's law of energy transfer), only ~10% of energy moves up to the next trophic level. The other 90% is lost because:
• Most energy is used for life processes (movement, growth, reproduction)
• Lost as heat during metabolism (respiration)
• Some parts of the prey are undigested (bones, hair)
• Some prey escape predators
• Decomposers consume the rest after death

That's why pyramids of energy are always upright (decreasing) and ecosystems can rarely support more than 4-5 trophic levels.
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