Explain it simply: Why does only 10% of energy pass between trophic levels?

Imagine you eat a big meal — say 2,000 kilocalories of rice. Your body uses most of that energy to:

• Keep your heart beating
• Maintain your body temperature at 37°C (warm-blooded!!)
• Move your muscles
• Run your brain

By the time you've done all that living, only about 200 kilocalories get "stored" in your body's actual flesh (fat, protein). That's 10%.

Now if a lion eats YOU (hypothetically), the lion only gets 10% of those 200 kilocalories = 20 kilocalories "stored" in lion flesh.

That is the 10% law.

The Math (simple version)

If grass fixes 10,000 kJ:

• Grasshopper eats grass → gets 1,000 kJ (10%)
• Frog eats grasshopper → gets 100 kJ (10% of 10%)
• Snake eats frog → gets 10 kJ (10% of 10% of 10%)
• Hawk eats snake → gets 1 kJ (10% of 10% of 10% of 10%)

The 10,000 kJ became 1 kJ at the hawk level — 99.99% lost as heat.

Why is the pyramid of energy ALWAYS upright?

Because you can never have MORE energy at a higher trophic level than at a lower one. Energy only flows down (in terms of quality and quantity). Heat is released at every step — it's thermodynamics. You can't recycle heat back into food.

NEET Exam application

If a question says "$T_{1}$ = 1,000,000 kJ, find $T_{4}$":

• Count the number of steps: $T_{1}$ → $T_{2}$ → $T_{3}$ → $T_{4}$ = 3 steps
• Multiply by (0.1)^{3}: 1,000,000 × 0.001 = 1,000 kJ