Energy flow and the 10% law: Class 10 practice
Only about 10% of energy at one trophic level passes to the next; the rest is used in life processes or lost as heat. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Food chains
The idea behind energy flow and the 10% law
Only about 10% of energy at one trophic level passes to the next; the rest is used in life processes or lost as heat. So energy falls tenfold at each step of a food chain.
Step-by-step method
- Identify the trophic levels between the two organisms.
- Multiply by 0.1 for each step up (or 10 for each step down).
- Give the answer in the same unit.
Worked example 1 (Basic)
Producers trap 50,000 J. How much energy reaches the primary consumers?
- 1 step(s): × 0.1^1
- Answer: 5,000 J
Worked example 2 (Standard)
Producers trap 50,000 J. How much energy reaches the secondary consumers?
- 2 step(s): × 0.1^2
- Answer: 500 J
Worked example 3 (Challenge)
Tertiary consumers receive 70 J. How much energy did the producers trap?
- 3 steps down: × 10³
- Answer: 70,000 J
Common mistakes and misconceptions
- Multiplying by 0.1 once for several steps
- Going the wrong direction
Practice questions
- (Basic) Producers trap 50,00,000 J. How much energy reaches the primary consumers?
- (Basic) Producers trap 5,00,000 J. How much energy reaches the primary consumers?
- (Standard) Producers trap 2,00,000 J. How much energy reaches the secondary consumers?
- (Standard) Producers trap 10,000 J. How much energy reaches the secondary consumers?
- (Challenge) Tertiary consumers receive 80 J. How much energy did the producers trap?
- (Challenge) Tertiary consumers receive 20 J. How much energy did the producers trap?
Answer key with full working
- Q1: 1 step(s): × 0.1^1 → Answer: 5,00,000 J
- Q2: 1 step(s): × 0.1^1 → Answer: 50,000 J
- Q3: 2 step(s): × 0.1^2 → Answer: 2,000 J
- Q4: 2 step(s): × 0.1^2 → Answer: 100 J
- Q5: 3 steps down: × 10³ → Answer: 80,000 J
- Q6: 3 steps down: × 10³ → Answer: 20,000 J
Syllabus note
This skill is listed under "Our Environment" for Class 10 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is energy flow and the 10% law in?
"Our Environment", Class 10 Biology (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.